A 5-year-old male with medial foot pain. Diagnosis? Eponym? • Radiology Case of the Week Figure 1. 5-year-old male with medial foot pain. Diagnosis? Eponym? Figure 2. Radiographs of the foot (A–C) show thinning and mild fragmentation of the navicular (red arrows) with extensive sclerosis throughout and mild overlying soft tissue swelling. Diagnosis: Köhler disease. Epidemiology Köhler disease is a rare, self-limiting osteonecrosis of the tarsal navicular in children. It typically presents between 4 and 7 years of age, although onset as early as 2 years has been described [1,2]. Boys are affected more often than girls, with StatPearls citing a roughly five-fold male predominance [1]. The disease is usually unilateral, and about 25% of cases are reported to be bilateral [1]. Clinical Findings Children present with pain and swelling of the dorsomedial midfoot [3]. Examination may show point tenderness over the navicular, with or without redness, warmth, or swelling. Affected children often have an antalgic limp, bearing weight along the lateral foot [4]. A blood count and inflammatory markers are obtained when infection is suspected. Pathology The cause remains uncertain. The navicular is the last tarsal bone to ossify. As the child grows heavier, it may be compressed between the talus and cuneiforms, compromising its blood supply and causing central ischemia. Delayed ossification may contribute, and the central third of the navicular is a watershed area prone to avascular necrosis. Radiographic Features Plain radiographs are the imaging modality of choice. The navicular may appear thinned (wafer-like), flattened or collapsed, and fragmented, with patchy sclerosis, loss of the normal trabecular pattern, and overlying soft tissue swelling. Fragmentation should not be mistaken for a fracture. CT and MRI are usually unnecessary but may be considered if pain persists or the diagnosis is unclear. If symptoms persist, tarsal coalition should be considered [5,6]. In this patient, the navicular is thinned and mildly fragmented with extensive sclerosis and mild soft tissue swelling, consistent with Köhler disease. Treatment and Prognosis Management is conservative, and surgery is not indicated. A short leg walking cast for 4 to 6 weeks may shorten symptom duration. In one series, symptoms lasted an average of 15 months without casting and less than 3 months with a short leg cast [5]. At an average follow-up of 31.5 years, treatment did not affect the final outcome [6]; in another series, all 12 patients were asymptomatic at an average of 33 years [7]. Radiographic improvement typically occurs 6 to 48 months after symptom onset. Conclusion Köhler disease is a self-limiting osteonecrosis of the tarsal navicular in young children, most often boys, who present with medial midfoot pain, that worsens with weight bearing. Radiographs showing a thin, fragmented, sclerotic navicular establish the diagnosis. Management is conservative, and the prognosis is usually excellent. References: Trammell AP, Davis DD, Scott A. Kohler Disease. In: StatPearls. Treasure Island (FL): StatPearls Publishing; August 7, 2023. https://pubmed.ncbi.nlm.nih.gov/29939608/ Shastri N, Olson L, Fowler M. Kohler's Disease. West J Emerg Med. 2012;13(1):119 120. DOI: 10.5811/westjem.2011.1.6691 Holley KW, Price BJ, McCormick WF Jr, Littlefield ZL, Green BM. Kohler Disease With Concurrent Avascular Necrosis of the Medial Cuneiform: A Report of Two Cases. Cureus. 2025;17(8):e89411. Published 2025 Aug 5. DOI: 10.7759/cureus.89411 Achar S, Yamanaka J. Apophysitis and Osteochondrosis: Common Causes of Pain in Growing Bones. Am Fam Physician. 2019;99(10):610-618. https://pubmed.ncbi.nlm.nih.gov/31083875/ Williams GA, Cowell HR. Köhler's disease of the tarsal navicular. Clin Orthop Relat Res. 1981;(158):53-58. https://pubmed.ncbi.nlm.nih.gov/7273526/ Borges JL, Guille JT, Bowen JR. Köhler's bone disease of the tarsal navicular. J Pediatr Orthop. 1995;15(5):596-598. DOI: 10.1097/01241398-199509000-00009 Shastri N, Olson L, Fowler M. Kohler's Disease. West J Emerg Med. 2012;13(1):119 120. DOI: 10.5811/westjem.2011.1.6691 Umaiza Ihsan, MD is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

An 86-year-old female with chronic back pain and lower extremity pain. Diagnosis? Eponym?• Radiology Case of the Week Figure 1. An 86-year-old female with chronic back pain and lower extremity pain. Diagnosis? Eponym? Figure 2. Sagittal (A) and coronal (B) CT angiography reformats. Patent proximal abdominal aorta (yellow arrows) and the occluded distal aorta (red arrows). Extensive calcification of the plaque indicates that the occlusion is chronic. Note the dilated inferior mesenteric artery with reverse flow (green arrows). Diagnosis: Chronic Leriche syndrome. Figure 3. Axial CT angiography. A. Complete occlusion of the abdominal aorta below the level of the renal arteries (red arrow). B. Distal abdominal aorta is patent (yellow arrow) due to extensive collateral flow from superior mesenteric artery branches and reversed flow in a markedly dilated inferior mesenteric artery (green arrow). Figure 4. Doppler ultrasound of the common femoral arteries. A. Right (RT CFA). B. Left (LT CFA). Note the monophasic waveforms bilaterally indicating aortoiliac atherosclerotic stenotic disease or occlusion. Epidemiology The exact prevalence and incidence of Leriche syndrome are unknown. Leriche and Morel originally described it in young men, but older patients and women have since been reported [1,2]. It results from chronic aortoiliac atherosclerotic disease, so risk factors include age, smoking, hypertension, diabetes, and hyperlipidemia [3]. Clinical Findings The classic triad is claudication, impotence in men, and absent or diminished femoral pulses [3]. Claudication is cramping pain in the buttocks, hips, and thighs that is reproduced by exercise. Reduced or absent femoral pulses are the hallmark finding. Limb-threatening ischemia is not universal, because collateral circulation develops as the disease progresses slowly [3]. An ankle-brachial index below 0.9 is abnormal and is usually the first test. Pathology Leriche syndrome is caused by atherosclerotic plaque within the lumen. Stenosis greater than 50% produces claudication, because oxygen demand during exercise exceeds supply. The plaque can progress to complete occlusion of the distal aorta, and extensive calcification indicates a chronic process. Classification Leriche syndrome is classified by the extent of disease [3]. Type I is confined to the distal abdominal aorta and common iliac arteries. Type II involves mainly the distal abdominal aorta and extends into the common and external iliac arteries. Type III involves the aortoiliac segment and the femoropopliteal vessels. Radiographic Features Duplex ultrasound and CT angiography define the location and degree of disease. Duplex ultrasound is noninvasive and is typically the first imaging test, often after the ankle-brachial index. CT angiography is the imaging modality of choice: it confirms the occlusion, shows plaque calcification, and maps the collateral pathways before treatment [4,5]. MR angiography is an alternative when iodinated contrast is a concern. In this 86-year-old woman with chronic back and lower extremity pain, ultrasound and CT angiography together showed a chronic aortic occlusion with the distal aorta reconstituted by collateral flow (Figs. 1-4). Treatment and Prognosis Management combines risk-factor control with revascularization when needed. Therapy includes supervised walking, smoking cessation, diabetes control, antiplatelet, statin and antihypertensive therapy. Revascularization options are aortobifemoral bypass, thromboendarterectomy, and angioplasty with or without stenting [6]. In fit patients, aortobifemoral bypass has the best long-term patency, about 85% to 90% at five years; endovascular treatment suits patients with multiple comorbidities. Prognosis is poor without treatment but good with modern therapy. Complications include limb ischemia, gangrene, myocardial infarction, and death. Conclusion Leriche syndrome is chronic atherosclerotic occlusion of the distal aorta and may present with nonspecific back and leg pain. Monophasic lower extremity waveforms on Doppler ultrasound should prompt CT angiography, which confirms the occlusion and its collateral pathways and guides treatment. References: Leriche R, Morel A. The Syndrome of Thrombotic Obliteration of the Aortic Bifurcation. Ann Surg. 1948;127(2):193-206. DOI: 10.1097/00000658-194802000-00001 Kita K. Leriche syndrome (Aortoiliac occlusive disease). J Gen Fam Med. 2017;18(5):297-298. Published 2017 Apr 21. DOI: 10.1002/jgf2.63 Brown KN, Gonzalez L. Leriche Syndrome (Archived). In: StatPearls. Treasure Island (FL): StatPearls Publishing; February 13, 2023. https://pubmed.ncbi.nlm.nih.gov/30855836/ Frederick M, Newman J, Kohlwes J. Leriche syndrome. J Gen Intern Med. 2010;25(10):1102-1104. DOI: 10.1007/s11606-010-1412-z Ahmed S, Raman SP, Fishman EK. CT angiography and 3D imaging in aortoiliac occlusive disease: collateral pathways in Leriche syndrome. Abdom Radiol (NY). 2017;42(9):2346-2357. DOI: 10.1007/s00261-017-1137-0 Krankenberg H, Schlüter M, Schwencke C, et al. Endovascular reconstruction of the aortic bifurcation in patients with Leriche syndrome. Clin Res Cardiol. 2009;98(10):657 664. DOI: 10.1007/s00392-009-0052-y Umaiza Ihsan, MD is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

A 58-year-old male, asymptomatic. Identify the indicated structures and state the potential life-threatening complication. • Radiology Case of the Week Figure 1. Name the anatomy and potential life-threatening complication. Figure 2. A. Axial CT of the chest. The right-sided aortic arch lies to the right of the air-filled trachea (orange arrow), with the esophagus (blue arrow) situated immediately posterior to the trachea. An aberrant left subclavian artery (red arrow) arises from a focal, aneurysmal outpouching of the proximal descending aorta, the Kommerell diverticulum (yellow arrow). B. Sagittal CT of the chest. The Kommerell diverticulum (yellow arrow) is seen posterior to the esophagus (blue arrow). The air-filled trachea (orange arrow) is marked. Figure 3. A. Coronal CT of the chest, posterior projection. The right-sided aortic arch gives origin to an aberrant left subclavian artery (red arrow) that arises from the Kommerell diverticulum (yellow arrow). B. Coronal CT of the chest, anterior projection. The right-sided ascending aorta (green arrow) is seen on the right side of the air-filled trachea (orange arrow). The main pulmonary artery (purple arrow) is also well seen. Figure 4. A. Volume-rendered CT, anterior view. The ascending aorta (green arrow) gives rise to the right subclavian artery (white arrow) as its first branch; the right-sided aortic arch continues to the origin of the aberrant left subclavian artery (red arrow) arising from the Kommerell diverticulum (yellow arrow), with the main pulmonary artery (purple arrow) seen anteriorly. B. Volume-rendered CT, posterior view. The Kommerell diverticulum (yellow arrow) is again seen giving rise to the aberrant left subclavian artery (red arrow) from the right-sided aortic arch, which also gives rise to the right subclavian artery (white arrow). Epidemiology Kommerell diverticulum is a rare congenital anomaly of the aortic arch that is associated with an aberrant subclavian artery in the majority of reported cases, with most series describing an association in roughly 60–80% of patients [1]. Because an aberrant right subclavian artery is itself uncommon, occurring in approximately 0.5–2% of the general population, and an aberrant left subclavian artery is markedly rarer still, occurring in only about 0.04–0.4% of the population, Kommerell diverticulum with a right-sided aortic arch and aberrant left subclavian artery, as in the present case, represents one of the least frequently encountered configurations of this anomaly [1]. Clinical Findings Kommerell diverticulum is frequently discovered incidentally when cross-sectional imaging is performed for an unrelated indication, as illustrated by the asymptomatic 58-year-old man described [2]. When symptoms do occur, they most often relate to mechanical compression of the adjacent trachea and esophagus by the diverticulum and its associated vascular ring, presenting as dysphagia and dyspnea [3]. Less commonly, patients may present with chest pain or with embolic phenomena arising from mural thrombus within the diverticulum. The most feared complications, though uncommon, are aortic dissection and frank rupture of the diverticulum. Pathology Embryologically, the Kommerell diverticulum represents the persistent remnant of the dorsal portion of the fourth aortic arch [4]. In the setting of a right-sided arch specifically, it reflects persistence of the right fourth aortic arch together with involution of the left fourth arch, which normally forms the definitive arch in the more common left-arch configuration [5,6]. Histologic examination of resected diverticular tissue has demonstrated cystic medial necrosis within the wall of the diverticulum in a substantial proportion of cases, a finding that likely explains the propensity of this lesion toward dissection and rupture [7] which can be life-threatening. Classification Three principal patterns of aortic arch diverticulum have traditionally been described in the literature: a left-sided aortic arch with an aberrant right subclavian artery, which is the most common configuration; a right-sided aortic arch with an aberrant left subclavian artery, the pattern demonstrated in the present case; and, less commonly, a diverticulum situated at the aortoductal junction. When a right-sided aortic arch is present, further sub-classification follows the Edwards system, in which type I demonstrates mirror-image branching without a retroesophageal component, type II, the pattern seen here, consists of an aberrant left subclavian artery arising from a Kommerell diverticulum, and type III, the rarest variant, consists of an isolated left subclavian artery that communicates instead with the pulmonary artery via a ductal remnant [4]. Radiographic Features The aberrant subclavian artery can be seen to arise from a focal, saccular dilatation of the proximal descending thoracic aorta (Figs. 1-4). The diverticulum itself is conventionally measured in cross-section at the level of the origin of the aberrant subclavian artery, and in a right-sided arch such as this one, the arch and its proximal descending continuation characteristically lie to the right of the trachea rather than to the left (Fig. 1). Careful attention should also be paid to the caliber of the adjacent trachea and esophagus, since both structures may be compressed by the diverticulum and its associated ligamentous or ductal remnants. Treatment and Prognosis Small, asymptomatic diverticula can generally be managed with periodic imaging surveillance alone, since growth tends to be slow, on the order of roughly 1.5 mm per year in reported series. Most studies favor surgical or endovascular repair once the diverticulum orifice exceeds approximately 30 mm, once the adjacent descending aorta exceeds approximately 50 mm, or once the patient becomes symptomatic from airway or esophageal compression [7,8]. In one large surgical series, at least one death from aortic rupture has been reported in a nonoperatively managed patient whose diverticulum measured only 3.4 cm, a reminder that even moderately sized lesions warrant close follow-up. Conclusion Kommerell diverticulum is an uncommon congenital anomaly of the aortic arch that is most often identified incidentally in asymptomatic adults. Because the lesion is closely associated with an aberrant subclavian artery and carries a recognized risk of dissection and rupture, accurate characterization is essential once it is discovered. The three-dimensional reconstructions such as shown in Fig.4 are particularly valuable for delineating the overall arch anatomy and for planning any subsequent operative or endovascular approach [9]. References: Irshad S, Adrejiya P, Abubaker M, Whitaker J. Kommerell's Diverticulum Masquerading in a Right Aortic Arch: A Vascular Surprise. Methodist Debakey Cardiovasc J. 2025;21(1):81-83. Published 2025 Aug 20. DOI: 10.14797/mdcvj.1641 Erben Y, Brownstein AJ, Velasquez CA, Li Y, Rizzo JA, Mojibian H, Tanweer M, Zafar MA, Ziganshin BA, Elefteriades JA. Natural history and management of Kommerell's diverticulum in a single tertiary referral center. J Vasc Surg. 2020;71(6):2004-2011. DOI: 10.1016/j.jvs.2019.08.260. Vinnakota A, Idrees JJ, Rosinski BF, et al. Outcomes of Repair of Kommerell Diverticulum. Ann Thorac Surg. 2019;108(6):1745-1750. DOI: 10.1016/j.athoracsur.2019.04.122 Kanwal D, Khalil S, Attia K, Fam M, Arakkal M. Kommerell's diverticulum with right-sided aortic arch and anomalous origin of neck vessels: Uncommon imaging finding in neonate with cyanosis. BJR Case Rep. 2021;7(4):20200173. Published 2021 Apr 30. DOI: 10.1259/bjrcr.20200173 Summa CH, DeMaioribus CA, Swink D, et al. Hybrid repair of Kommerell's diverticulum with aberrant subclavian artery. J Vasc Surg Cases Innov Tech. 2026;12(2):102129. Published 2026 Jan 5. DOI: 10.1016/j.jvscit.2026.102129 Mubarak MY, Kamarul AT, Noordini MD. Right-sided Aortic Arch with Aberrant Left Subclavian Artery from Kommerell's Diverticulum. Iran J Radiol. 2011;8(2):103-106. https://pmc.ncbi.nlm.nih.gov/articles/PMC3522316/ Tanaka A, Milner R, Ota T. Kommerell's diverticulum in the current era: a comprehensive review. Gen Thorac Cardiovasc Surg. 2015;63(5):245-259. DOI: 10.1007/s11748-015-0521-3 Silva AF, Dos Santos JA. Aortic arch anomaly in an adult patient: a case of right aortic arch with aberrant left subclavian artery and Kommerell's diverticulum. Radiol Bras. 2016;49(4):274-275. DOI: 10.1590/0100-3984.2015.0087 Osawa H, Shinohara D, Orii K, et al. Right Aortic Arch and Kommerell's Diverticulum Repaired without Reconstruction of Aberrant Left Subclavian Artery. Case Rep Vasc Med. 2013;2013:840804. DOI: 10.1155/2013/840804 Umaiza Ihsan, MD is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

A 23-Year-Old female at First-Trimester Ultrasound. Diagnosis? • Radiology Case of the Week Figure 1. Transabdominal first-trimester pelvic ultrasound. 23-year-old patient presenting with vaginal bleeding: Diagnosis? Figure 2. A. Magnified sagittal ultrasound of the cystic structure shows a thin, complete outer wall (red arrow) and an internal septation (yellow arrow) crossing the cyst; ultrasound calipers measure 1.6 x 1.2 cm. Fetal pole (green arrow) is seen with the cystic structure (red arrows) immediately dorsal to it, at the craniocervical junction (blue arrow). B. Calipers placed across the dorsal nuchal region measure an additional, smaller 0.5 cm focus, in keeping with a markedly thickened/septated nuchal translucency. Note the midline septum representing the nuchal ligament (white arrow). Epidemiology Fetal cystic hygroma is identified in approximately 1 in 285 pregnancies undergoing first trimester nuchal translucency screening, with an estimated overall prenatal prevalence of 0.2-3%. It is far less common as a postnatal diagnosis, with an incidence at birth of only about 1 in 6000, since most affected pregnancies end in miscarriage, intrauterine fetal death, or elective termination (1). A chromosomal abnormality is identified in roughly half of prenatally detected cases overall, most commonly monosomy X (Turner syndrome), trisomy 21, trisomy 18, and triploidy (2,3). Clinical Manifestations Cystic hygroma is usually an incidental finding on first- or early second-trimester sonography, typically identified as a markedly increased and septated nuchal translucency. Severe lymphatic obstruction may progress to nonimmune hydrops fetalis, with generalized skin edema, pleural or pericardial effusion, and ascites, a combination associated with a markedly worse outcome. If it persists after birth, it can present as a soft, compressible, transilluminant neck mass (1). Pathology Cystic hygroma is a macrocystic lymphatic malformation resulting from failure of the paired jugular lymphatic sacs to establish normal communication with the internal jugular veins and the remainder of the venous system during the fifth to ninth week of gestation. The resulting obstruction causes progressive dilation of the sequestered sacs, producing thin-walled, multiloculated cystic spaces filled with proteinaceous lymphatic fluid within the posterior soft tissues of the fetal neck. Histologically, the cyst walls are lined by a single layer of flattened endothelium with scant surrounding stroma (1). Classification Cystic hygromas are classified sonographically as septated or nonseptated, a distinction with direct prognostic importance. The nonseptated form is a simple, markedly thickened nuchal translucency without an internal dividing line. The septated form, as in this case, shows a midline septum representing the nuchal ligament, flanked by paired symmetric cystic spaces. This distinction carries prognostic weight: in one comparative series, septated lesions had a 72% aneuploidy rate, a 40% rate of hydrops, and only a 12% livebirth rate, compared with 5.7%, under 2%, and 94%, respectively, for nonseptated lesions (3). Pathologically, lymphatic malformations are further categorized by cyst size as macrocystic (individual cysts greater than 2 cm), microcystic (less than 2 cm), or mixed. Radiographic Features On prenatal ultrasound, cystic hygroma appears as a thin-walled, anechoic to hypoechoic cystic structure in the soft tissues dorsal to the fetal craniocervical junction, frequently traversed by one or more internal septa (Figures 1-2) (4). Caliper measurements are used to document lesion size and to distinguish it from a simple increased nuchal translucency. Color Doppler characteristically shows no internal flow. Postnatally, MRI is the modality of choice for defining the full extent and its relationship to adjacent neurovascular structures before surgical planning. Treatment and Prognosis Once identified, cystic hygroma warrants karyotype, microarray testing (chorionic villus sampling or amniocentesis), a detailed fetal anatomic and cardiac survey, and serial sonographic surveillance for hydrops. Prognosis is governed chiefly by septation status, karyotype, and the presence of hydrops (5,6); pregnancies reaching the second trimester without these adverse features generally do well. Postnatally, a persistent or isolated lymphatic malformation is managed with intralesional sclerotherapy as first-line treatment, with surgery reserved for lesions that fail sclerotherapy, recur, or threaten the airway; an ex utero intrapartum treatment (EXIT) procedure may be needed when a large lesion is expected to obstruct the airway at delivery (7). Conclusion Fetal cystic hygroma is an important early sonographic marker of aneuploidy and adverse pregnancy outcome. Its recognition should prompt genetic counseling, karyotype testing, and close sonographic follow-up. References: Rangel V, Having K. Cystic Hygroma. J Diagn Med Sonogr. 2008;24(4):218-222. DOI: https://doi.org/10.1177/8756479308319969 Malone FD, Ball RH, Nyberg DA, et al. First-trimester septated cystic hygroma: prevalence, natural history, and pediatric outcome. Obstet Gynecol. 2005;106(2):288-294. DOI: 10.1097/01.AOG.0000173318.54978.1f Bronshtein M, Bar-Hava I, Blumenfeld I, Bejar J, Toder V, Blumenfeld Z. The difference between septated and nonseptated nuchal cystic hygroma in the early second trimester. Obstet Gynecol. 1993;81(5 ( Pt 1)):683-687. https://pubmed.ncbi.nlm.nih.gov/8469454/ Sepúlveda WH, Ciuffardi I. Early sonographic diagnosis of fetal cystic hygroma colli. J Perinat Med. 1992;20(2):149-152. DOI: 10.1515/jpme.1992.20.2.149 Chen HY, Zheng JQ, Zhang HP. A case report of Turner syndrome associated with fetal nuchal cystic hygroma and bilateral syndactyly of the hands and feet. Ital J Pediatr. 2019;45(1):85. Published 2019 Jul 18. DOI: 10.1186/s13052-019-0680-4 Rosati P, Guariglia L. Transvaginal ultrasound detection of septated and non-septated cystic hygroma in early pregnancy. Fetal Diagn Ther. 1997;12(3):132-135. DOI: 10.1159/000264452 Gowda M, Godipelli L, Gangadhar L, Jindal B, Deodar K, Yadav M. Management of isolated fetal lymphangiomas following prenatal diagnosis: case series. J Fetal Med. 2021;8(1):39-43. DOI: https://doi.org/10.1007/s40556-021-00288-5 Umaiza Ihsan, MD is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three- month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

Adolescent with Chronic Neck Pain and Suboccipital Discomfort: Diagnosis? • Xray of the Week Figure 1. CT images of the cervical spine (A) sagittal view and (B) coronal view. What is the important finding on this CT scan? Figure 2. A. Sagittal CT shows a small, round, well-corticated ossicle (yellow arrow) representing the os odontoideum separated from the underlying body of C2 (green arrow). Note the smooth, radiolucent gap between the body of C2 and the os odontoideum (red arrow). Also note the thickening and abnormal rounding of the anterior arch of C1 (blue arrow). B. Coronal CT section again demonstrates the well-corticated ossicle representing the os odontoideum (yellow arrow) positioned symmetrically between the lateral masses of C1 (blue arrows) and separated from the underlying body of C2 (green arrow). C. Axial CT through the ring of C1 shows the os odontoideum (yellow arrow) situated just posterior to the anterior arch of C1 (blue arrow). Note the thickening and abnormal rounding of the anterior arch of C1 (blue arrow). Feature Os Odontoideum Chronic Fracture Dens (Nonunion) Ossicle Margins Smooth, distinct, and completely well-corticated. Often irregular, sclerotic, but lack a uniform smooth outer cortex of an independent ossicle. Gap / Interface Wide, smooth, radiolucent gap with corticated margins on both opposing surfaces. Jagged or sharply angulated lucent cleft matching the original fracture line (typically Type II base). Morphology of Dens Hypoplastic, foreshortened, or round/oval ossicle located superiorly. Normal height/shape of the residual dens base, matching the displaced fragment size. C1 (Atlas) Remodeling Frequently shows hypertrophy and rounding of the anterior arch. Anterior arch of C1 is usually normal in morphology unless secondary degenerative changes exist. Location of Gap Typically well above the superior articulating facets of C2. Typically at the base of the dens (classic Type II location). Clinical Context May be an unrecognized childhood injury or congenital variant; highly prone to atlantoaxial instability. Known prior acute trauma history with documented failure of bony union. Table 1. Differentiating Os odontoideum from a chronic nonunited Type 2 dens fracture on a CT scan relies on margin characteristics, gap appearance, and associated bony remodeling as summarized here. Epidemiology Os odontoideum is a rare anomaly of the craniocervical junction. Its true prevalence and incidence are unknown, since most cases are discovered incidentally or only after symptoms develop; reported prevalence on adult imaging series is well under 1%. Diagnosis spans a wide age range, from early childhood through late adulthood, although many patients present within the first three decades of life. An increased frequency has been reported in patients with Down syndrome, spondyloepiphyseal dysplasia, Morquio syndrome, and other skeletal dysplasias, supporting a multifactorial rather than a single unifying etiology (1,2). Clinical Findings Many cases are asymptomatic and are identified incidentally on imaging obtained for unrelated indications. When symptomatic, neck pain is the most common complaint, followed by mechanical or intermittent neurologic symptoms related to atlantoaxial instability, including myelopathy, transient quadriparesis after minor trauma, and vertebrobasilar symptoms such as vertigo or syncope from vertebral artery compromise. Because an unstable ossicle may be tolerated for years before a seemingly trivial injury precipitates catastrophic cord compression, even an incidentally detected os odontoideum warrants further clinical and radiographic evaluation (3,4). Pathology The etiology of os odontoideum remains debated. The congenital theory attributes the anomaly to failure of fusion between the odontoid process and the body of the axis at the subdental synchondrosis. Growing evidence instead favors an acquired origin: an unrecognized fracture through the odontoid synchondrosis before ossification is complete (roughly before 5-6 years of age), with subsequent avascular remodeling of the separated fragment into a smooth, independently corticated ossicle (5). Both mechanisms likely contribute in different patients. Because the transverse atlantal ligament inserts on the mobile ossicle rather than on a fixed dens, it is rendered ineffective at restraining atlantoaxial translation. Classification Os odontoideum is divided into two types based on the position of the ossicle relative to the atlas and clivus. In the orthotopic type, the more common pattern, the ossicle lies in the normal anatomic position of the odontoid tip and moves together with the anterior arch of C1. In the dystopic type, the ossicle is displaced, most often superiorly, and may fuse to the basion/clivus, moving with the occiput rather than the atlas; this pattern is more frequently associated with instability and neurologic injury (6). Radiographic Features CT best depicts the bony morphology of os odontoideum and is the modality of choice for surgical planning. The ossicle appears round-to-oval, roughly half the size of a normal dens, with a smooth and completely corticated margin. It is separated from the hypoplastic dens/axis body by a wide, smooth, radiolucent gap located above the level of the superior articular facets of C2 (Figures 1-2). Compensatory hypertrophy and rounding of the anterior arch of C1 is a recognized associated finding. Dynamic flexion-extension radiographs or CT, together with MRI, are used to quantify atlantoaxial instability and to assess for cord compression or signal change (6,7). Differentiating os odontoideum from a chronic nonunited (Type II) dens fracture on CT relies on margin characteristics, gap appearance, and associated bony remodeling (Table 1). Treatment and Prognosis Management depends on symptoms and the degree of instability rather than on the mere presence of the ossicle. Asymptomatic patients without instability on flexion-extension imaging can be managed with observation and serial radiographic surveillance. Operative posterior C1-C2 fusion is favored for patients with neurologic deficits, myelopathy, or significant instability, given the risk of delayed neurologic deterioration, which has been documented even after a period of apparent clinical stability (7). Fusion rates and symptomatic improvement after surgery are high, although the timing of surgery in asymptomatic patients remains controversial. Conclusion Os odontoideum is an important, often incidental, cause of atlantoaxial instability that must be reliably distinguished from a chronic ununited dens fracture, as the two entities carry different implications for surveillance and treatment. Recognizing the smooth, corticated ossicle, the wide suprafacetal gap, and the hypertrophied anterior arch of C1 on CT allows a confident diagnosis and appropriate management, helping to avert neurologic catastrophe. References: Fielding JW, Hensinger RN, Hawkins RJ. Os Odontoideum. J Bone Joint Surg Am. 1980;62(3):376-383. https://pubmed.ncbi.nlm.nih.gov/7364809/ Sankar WN, Wills BP, Dormans JP, Drummond DS. Os odontoideum revisited: the case for a multifactorial etiology. Spine (Phila Pa 1976). 2006;31(9):979-984. DOI: 10.1097/01.brs.0000214935.70868.1c Fagan AB, Askin GN, Earwaker JW. The jigsaw sign. A reliable indicator of congenital aetiology in os odontoideum. Eur Spine J. 2004;13(4):295-300. DOI: 10.1007/s00586-004-0732-2 Klimo P Jr, Kan P, Rao G, Apfelbaum R, Brockmeyer D. Os odontoideum: presentation, diagnosis, and treatment in a series of 78 patients. J Neurosurg Spine. 2008;9(4):332-342. DOI: 10.3171/SPI.2008.9.10.332 Cho S, Shlobin NA, Dahdaleh NS. Os odontoideum: A comprehensive review. J Craniovertebr Junction Spine. 2022;13(3):256-264.DOI: 10.4103/jcvjs.jcvjs_71_22 Nelson C, Mujahed T, Tedford NJ. Adolescent male with neck pain. J Am Coll Emerg Physicians Open. 2024;5(3):e13222. Published 2024 Jun 16.DOI: 10.1002/emp2.13222 Menezes AH. Os odontoideum: database analysis of 260 patients regarding etiology, associated abnormalities, and literature review. Front Surg. 2023;10:1291056. Published 2023 Dec 5. DOI: 10.3389/fsurg.2023.12910561 Umaiza Ihsan, MD is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

Trauma due to motor vehicle collision. Diagnosis? • Xray of the Week Figure 1. CT images of the cervical spine (A) sagittal view and (B) coronal view. What is the important finding on this CT scan? Figure 2. CT scan of a Type I dens fracture. Red arrows point to the fracture line at the tip of the dens. Figure 3. Anderson and D’Alonzo dens fracture classification system. Diagram by Neal Joshi. Type I is an oblique avulsion fracture involving the upper tip of the dens, usually at the alar ligament insertion, and is generally considered stable when isolated. Type II occurs at the junction of the dens and the body of C2 and has a greater risk of displacement and nonunion. Type III extends from the base of the dens into the body of C2 and generally has better healing potential because the fracture extends into cancellous bone. Introduction: The odontoid process, or dens, is a superior projection of C2 that articulates with the anterior arch of C1 and functions as the pivot for atlantoaxial rotation. The alar ligaments arise from the upper dens and attach to the medial aspects of the occipital condyles, contributing to stability of the craniocervical junction (1,2). The Anderson and D'Alonzo classification is the most widely used system for classifying odontoid fractures according to the location of the fracture (3,4) (Fig. 3). Type I fracture is usually stable, however, an apparent Type I avulsion fracture may be associated with injury to the alar or other craniocervical ligaments; therefore, the surrounding ligamentous structures and craniocervical alignment should be assessed (5). Epidemiology Odontoid fractures are among the most common fractures of the upper cervical spine, particularly in older adults. Type I odontoid fractures are rare, representing approximately 2–3% of odontoid fractures. In a prospective study from the Swedish Fracture Register, 30 of 1,154 odontoid fractures were classified as Type I, compared with 583 Type II and 541 Type III fractures. Odontoid fractures in older adults are commonly associated with low-energy falls, whereas higher-energy mechanisms such as motor vehicle collisions are more frequent in younger patients (6,7). Clinical Manifestation Patients with Type I dens fractures typically present with upper cervical or posterior neck pain and tenderness following trauma. Pain may be aggravated by cervical movement and may be associated with restricted range of motion. Neurological deficits are uncommon but may occur in the presence of associated cervical or craniocervical injuries. Because Type I fractures are uncommon and may be associated with ligamentous injury, careful clinical and radiologic assessment for craniocervical instability is important (3). Radiographic Features Plain radiographs, including lateral and open-mouth odontoid views, may demonstrate a small avulsion fragment at the tip of the dens; however, a negative examination does not exclude fracture. When clinical suspicion persists, thin-section CT with sagittal and coronal reformations is the preferred imaging modality, allowing accurate assessment of fracture location, displacement, and atlantoaxial and craniocervical alignment (Fig. 1). In this patient, CT performed following a motor vehicle collision demonstrated a type I dens fracture (Fig. 2). Associated fractures of C1 and C2 should also be carefully evaluated (5). CT is also useful in distinguishing a type I odontoid fracture from os odontoideum. MRI may be useful when there is concern for associated ligamentous injury or craniocervical instability and can provide additional evaluation of the spinal cord. Treatment and Prognosis Isolated, nondisplaced Type I dens fractures are generally considered stable and are treated conservatively with external immobilization, most commonly with a rigid cervical collar. Current recommendations support immobilization with a hard collar for approximately 6–8 weeks, with clinical and radiographic follow-up to confirm stability and healing; duration may be extended based on follow-up imaging (8). Surgical treatment is rarely required for an isolated Type I fracture. However, operative stabilization may be considered when there is significant displacement, craniocervical instability, or associated ligamentous injury. The prognosis of an isolated Type I fracture is generally favorable with appropriate immobilization. In elderly patients specifically, rigid immobilization methods such as halo-vest bracing carry an increased mortality risk and should be weighed carefully against a rigid collar alternative when isolated Type I injuries are stable (9). Conclusion Type I dens fractures are rare avulsion injuries involving the superior tip of the odontoid process, usually at the site of alar ligament attachment. Although generally stable when isolated, they require careful evaluation for associated ligamentous injury and craniocervical instability. CT is the imaging modality of choice for defining the fracture and assessing alignment, while MRI may provide additional evaluation of ligamentous and neural structures. Recognition of this uncommon fracture pattern is important for appropriate management and favorable outcome. References: Clark CR, White AA 3rd. Fractures of the dens. A multicenter study. J Bone Joint Surg Am. 1985;67(9):1340-1348. https://pubmed.ncbi.nlm.nih.gov/4077905/ O'Brien WT Sr, Shen P, Lee P. The Dens: Normal Development, Developmental Variants and Anomalies, and Traumatic Injuries. J Clin Imaging Sci. 2015;5:38. Published 2015 Jun 30. DOI: 10.4103/2156-7514.159565 Anderson LD, D'Alonzo RT. Fractures of the odontoid process of the axis. J Bone Joint Surg Am. 1974;56(8):1663-1674. https://pubmed.ncbi.nlm.nih.gov/4434035/ Nouri A, Da Broi M, May A, et al. Odontoid Fractures: A Review of the Current State of the Art. J Clin Med. 2024;13(20):6270. Published 2024 Oct 21. DOI: 10.3390/jcm13206270 Jain N, Verma R, Garga UC, Baruah BP, Jain SK, Bhaskar SN. CT and MR imaging of odontoid abnormalities: A pictorial review. Indian J Radiol Imaging. 2016;26(1):108-119. DOI: 10.4103/0971-3026.178358 Baranto D, Steinke J, Blixt S, et al. The epidemiology of odontoid fractures: a study from the Swedish fracture register. Eur Spine J. 2024;33(8):3034-3042. DOI: 10.1007/s00586-024-08406-3 Hashem M, Surur S, Hamad AS. Clinical and Radiological Outcomes of Halo Vest Application for Type II and III Odontoid Fractures. Int J Gen Med. 2024;17:457-469. Published 2024 Feb 5. DOI: 10.2147/IJGM.S440126 Gonschorek O, Vordemvenne T, Blattert T, Katscher S, Schnake KJ; Spine Section of the German Society for Orthopaedics and Trauma. Treatment of Odontoid Fractures: Recommendations of the Spine Section of the German Society for Orthopaedics and Trauma (DGOU). Global Spine J. 2018;8(2 Suppl):12S-17S. DOI: 10.1177/2192568218768227 Tashjian RZ, Majercik S, Biffl WL, Palumbo MA, Cioffi WG. Halo-vest immobilization increases early morbidity and mortality in elderly odontoid fractures. J Trauma. 2006;60(1):199-203. DOI: 10.1097/01.ta.0000197426.72261.17 Umaiza Ihsan, MD is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three- month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

A 30-year-old female, after a motor vehicle collision, presented with chest pain, abdominal pain, shortness of breath, and rib fractures. Diagnosis? • Xray of the Week Figure 1. Coronal and axial CT Scan. Diagnosis? Figure 2. CT scan of traumatic left hemi-diaphragmatic rupture. (A) Coronal CT images demonstrate abdominal viscera herniating into the left hemithorax (yellow arrow pointing to colon), consistent with traumatic disruption of the left hemidiaphragm. (B) Axial CT image also demonstrates abdominal organs including spleen (red arrow) in the chest. Figure 3. Prior CT examination. Coronal CT image obtained one year earlier demonstrates the pre-trauma thoracoabdominal anatomy in the same patient without the left-sided intrathoracic visceral herniation seen on the current examination. Normal left hemidiaphragm (yellow arrow). Epidemiology Traumatic diaphragmatic rupture is uncommon, occurring in approximately 0.5% of all trauma patients and around 1–2% of patients with blunt trauma [1]. Motor vehicle collisions are a major cause of blunt diaphragmatic rupture. Left-sided injuries predominate, accounting for approximately 65–80% of cases, while right-sided and bilateral ruptures are less frequent. Diaphragmatic rupture commonly occurs in the setting of high-energy thoracoabdominal trauma and is frequently accompanied by other traumatic injuries [1,2]. Clinical Findings Clinical presentation of traumatic diaphragmatic rupture is variable and may be obscured by associated thoracic or abdominal injuries. Patients may present with chest or abdominal pain, dyspnea, tachypnea, or respiratory distress. Physical examination may demonstrate decreased breath sounds or, when abdominal viscera have herniated into the thorax, bowel sounds within the chest. Some injuries may initially be clinically occult, contributing to delayed diagnosis [1,2]. In this case, the 30-year-old woman presented following a motor vehicle collision with chest pain, abdominal pain, and shortness of breath; associated rib fractures were also documented. Pathology Traumatic diaphragmatic rupture results from disruption of the musculotendinous diaphragm following blunt or penetrating thoracoabdominal trauma. In blunt trauma, sudden elevation of intra-abdominal pressure and shearing forces can produce diaphragmatic tears, which commonly involve the posterolateral diaphragm [2]. The resulting defect may permit abdominal viscera to herniate into the thoracic cavity because of the pressure gradient between the abdomen and chest. If unrecognized, progressive herniation may lead to incarceration or strangulation of herniated viscera. Classification Traumatic diaphragmatic injuries are graded according to the American Association for the Surgery of Trauma (AAST) Organ Injury Scale. Grade I represents diaphragmatic contusion; Grade II, a laceration <2 cm; Grade III, a laceration 2–10 cm; Grade IV, a laceration >10 cm with tissue loss <25 cm²; and Grade V, a laceration with tissue loss >25 cm². Bilateral injuries are advanced by one grade up to Grade III [3]. This classification describes the anatomical severity of diaphragmatic injury. Radiographic Features Chest radiography may demonstrate an elevated or irregular hemidiaphragm, intrathoracic abdominal viscera, abnormal diaphragmatic contour, or associated pleural and pulmonary abnormalities; however, findings may be subtle or nonspecific [4]. Multidetector CT is the principal imaging modality for evaluating suspected traumatic diaphragmatic injury [5]. Direct CT findings include focal diaphragmatic discontinuity and the dangling diaphragm sign, representing inward curling of the torn diaphragmatic edge [6]. Indirect findings include intrathoracic herniation of abdominal viscera, the collar sign from waist-like constriction of herniated viscera at the defect, and the dependent viscera sign, in which herniated abdominal organs lie against the posterior thoracic wall [7]. Coronal and sagittal multiplanar reformations may facilitate identification of diaphragmatic defects and visceral herniation. Associated thoracoabdominal injuries, including rib fractures, may also be identified. Treatment and Prognosis Traumatic diaphragmatic rupture requires surgical repair once the patient's condition permits. Herniated abdominal viscera are reduced and the diaphragmatic defect is usually closed primarily with sutures; mesh may be required for larger defects that cannot be closed without tension [8]. The operative approach may be abdominal, thoracic, or minimally invasive depending on clinical stability, associated injuries, and timing of presentation [1,8]. Prognosis is largely determined by the severity of associated traumatic injuries rather than the diaphragmatic defect itself. Delayed or missed diagnosis may result in visceral incarceration, strangulation, or respiratory compromise [8]. Conclusion Traumatic diaphragmatic rupture is an uncommon but important complication of thoracoabdominal trauma that may be difficult to recognize clinically. Awareness of characteristic imaging findings, particularly on multidetector CT, is essential for prompt diagnosis and appropriate management, helping to reduce complications associated with delayed or missed injury. References Furák J, Athanassiadi K. Diaphragm and transdiaphragmatic injuries. J Thorac Dis. 2019;11(Suppl 2):S152-S157. doi:https://doi.org/10.21037/jtd.2018.10.76 Petrone P, Asensio JA, Marini CP. Diaphragmatic injuries and post-traumatic diaphragmatic hernias. Curr Probl Surg. 2017;54(1):11-32. doi:https://doi.org/10.1067/j.cpsurg.2016.11.001 Moore EE, Malangoni MA, Cogbill TH, et al. Organ injury scaling IV: thoracic vascular, lung, cardiac, and diaphragm. J Trauma. 1994;36(3):299-300. doi:https://doi.org/10.1097/00005373-199403000-00002 Desir A, Ghaye B. CT of blunt diaphragmatic rupture. Radiographics. 2012;32(2):477-498. doi:https://doi.org/10.1148/rg.322115082 Nchimi A, Szapiro D, Ghaye B, et al. Helical CT of blunt diaphragmatic rupture. AJR Am J Roentgenol. 2005;184(1):24-30. doi:https://doi.org/10.2214/ajr.184.1.01840024 Desser TS, Edwards B, Hunt S, Rosenberg J, Purtill MA, Jeffrey RB. The dangling diaphragm sign: sensitivity and comparison with existing CT signs of blunt traumatic diaphragmatic rupture. Emerg Radiol. 2010;17(1):37-44. doi:https://doi.org/10.1007/s10140-009-0819-5 Bergin D, Ennis R, Keogh C, Fenlon HM, Murray JG. The “dependent viscera” sign in CT diagnosis of blunt traumatic diaphragmatic rupture. AJR Am J Roentgenol. 2001;177(5):1137-1140. doi:https://doi.org/10.2214/ajr.177.5.1771137 Giuffrida M, Perrone G, Abu-Zidan F, et al. Management of complicated diaphragmatic hernia in the acute setting: a WSES position paper. World J Emerg Surg. 2023;18(1):43. doi:https://doi.org/10.1186/s13017-023-00510-x Umaiza Ihsan, MD, is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three- month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision-making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

24-year-old male with leg pain. Diagnosis? • Xray of the Week Figure 1. Radiographs of the left knee. (A) Frontal radiograph demonstrates an aggressive lesion centered in the distal left femur with a large mineralized soft-tissue component (yellow arrows). (B) Lateral radiograph further demonstrates the densely mineralized lesion and associated soft-tissue mass arising from the distal femur (yellow arrows). Figure 2. Postoperative CT Scan of the left femur. (A) Frontal CT Scout image demonstrates postoperative changes with metallic endoprosthetic reconstruction of the distal femur extending across the knee (yellow arrow). (B) Coronal CT image demonstrates the postoperative femoral reconstruction and prosthetic components (yellow arrow). Figure 3. Pulmonary metastatic disease in osteosarcoma. Axial CT image of the chest demonstrates peripheral pulmonary nodules (red arrows), consistent with pulmonary metastatic disease in this patient. Figure 4. Recurrent osteosarcoma with calcified pulmonary metastases in a different patient. (A) Coronal CT image demonstrates densely calcified pulmonary metastatic nodules (yellow arrows). (B) Postoperative radiograph demonstrates mineralized recurrent soft-tissue disease adjacent to the distal femoral endoprosthesis (red arrow). (C) Magnified radiograph further demonstrates the mineralized recurrent tumor adjacent to the prosthesis (black arrow). Epidemiology Osteosarcoma is the most common primary malignant bone tumor in children and adolescents, with an incidence of approximately 3–5 cases per million persons per year in younger populations [1,2]. Incidence peaks during adolescence and is slightly higher in males [1]. Osteosarcoma most commonly arises in the metaphyses of long bones, particularly around the knee. The distal femur is the most frequent site, followed by the proximal tibia and proximal humerus [1]. Clinical Findings Pain is the most common presenting symptom of osteosarcoma and may initially be intermittent before becoming persistent. Local swelling, a palpable mass, restricted joint movement, and limp may occur as the tumor enlarges. Pathological fracture is an uncommon presentation, while systemic symptoms are generally unusual [2,3]. In the primary case, the 24-year-old male presented with left leg pain. Pathology Osteosarcoma is a malignant mesenchymal neoplasm characterized by production of osteoid or immature bone directly by malignant tumor cells [2,3]. Conventional osteosarcoma is typically a high-grade intramedullary tumor composed of malignant pleomorphic cells with variable production of osteoid and other extracellular matrix. Tumor osteoid is often irregular and disorganized and may undergo mineralization. Histological response following neoadjuvant chemotherapy, particularly the degree of tumor necrosis, has important prognostic significance [2]. Classification Osteosarcoma comprises seven recognized primary subtypes: conventional, telangiectatic, low-grade central, small cell, parosteal, periosteal, and high-grade surface osteosarcoma [3,4]. Conventional osteosarcoma is the most common subtype, accounting for approximately 75–80% of cases, and may demonstrate osteoblastic, chondroblastic, or fibroblastic differentiation according to the predominant matrix [3,4]. Surface osteosarcomas include parosteal, periosteal, and high-grade surface variants, which differ in histologic grade, imaging appearance, treatment, and prognosis [4]. Radiographic Features Plain radiography is usually the initial imaging modality. Conventional osteosarcoma typically appears as an aggressive metaphyseal lesion with mixed lytic and sclerotic components, cortical destruction, an ill-defined zone of transition, mineralized osteoid matrix, and an associated soft-tissue mass (Fig. 1) . Aggressive periosteal reactions, including sunburst-type spiculation and a Codman triangle, may occur [2,4,5]. CT better depicts cortical destruction and mineralized tumor matrix and is important for assessment of pulmonary metastatic disease [4,5]. MRI is the preferred modality for local staging, defining intramedullary and soft-tissue extent, relationship to neurovascular structures and joints, and the presence of skip lesions [2,4]. Pulmonary metastases usually appear as solid pulmonary nodules on chest CT and may be multiple and bilateral. Calcification or ossification can occur (Figs. 3,4) and represents a recognized atypical appearance of osteosarcoma lung metastases [6]. Postoperative imaging provides a baseline for assessment of the reconstruction and subsequent surveillance. Comparison with prior examinations is important when evaluating for suspected local recurrence, with MRI particularly useful for assessing recurrent soft-tissue disease [7]. Treatment and Prognosis Treatment of high-grade osteosarcoma generally combines systemic chemotherapy with complete surgical resection of the primary tumor. Limb-salvage surgery (Fig. 2) is feasible in many patients when adequate oncologic margins and a functional extremity can be achieved; amputation remains necessary in selected cases [8-10]. Histologic response to chemotherapy and the presence of metastatic disease are important prognostic factors [9]. Contemporary series report 5-year survival of approximately 70–75% for patients with localized extremity osteosarcoma, whereas outcomes are substantially poorer in patients with metastatic or recurrent disease. The lungs are the predominant site of distant metastasis. In patients with resectable pulmonary metastatic disease, complete surgical removal of metastases is an important component of management and is associated with better outcomes in selected patients [7]. Conclusion Osteosarcoma is an aggressive primary bone malignancy that predominantly affects adolescents and young adults. Imaging plays a central role in diagnosis, local staging, treatment planning, and surveillance. Recognition of characteristic aggressive osseous features and careful assessment for pulmonary metastatic and recurrent disease are essential because disease stage and treatment response strongly influence prognosis. References Ottaviani G, Jaffe N. The epidemiology of osteosarcoma. Cancer Treat Res. 2009;152:313. https://doi.org/10.1007/978-1-4419-0284-9_1 Durfee RA, Mohammed M, Luu HH. Review of osteosarcoma and current management. Rheumatol Ther. 2016;3(2):221-243. https://doi.org/10.1007/s40744-016-0046-y Fox MG, Trotta BM. Osteosarcoma: review of the various types with emphasis on recent advancements in imaging. Semin Musculoskelet Radiol. 2013;17(2):123-136. https://doi.org/10.1055/s-0033-1342969 Yarmish G, Klein MJ, Landa J, Lefkowitz RA, Hwang S. Imaging characteristics of primary osteosarcoma: nonconventional subtypes. Radiographics. 2010;30(6):1653- 1672. https://doi.org/10.1148/rg.306105524 Crombé A, et al. Imaging of osteosarcoma: presenting findings, metastatic patterns, and features related to prognosis. J Clin Med. 2024;13(19):5710. https://doi.org/10.3390/jcm13195710 Silva JAM, Marchiori E, Amorim VB, Barreto MM, et al. CT features of osteosarcoma lung metastasis: a retrospective study of 127 patients. J Bras Pneumol. 2023;49(2):e20220433. https://doi.org/10.36416/1806-3756/e20220433 Garner HW, Kransdorf MJ, Peterson JJ. Posttherapy imaging of musculoskeletal neoplasms. Radiol Clin North Am. 2011;49(6):1307-1323. https://doi.org/10.1016/j.rcl.2011.07.011 Bielack SS, Kempf-Bielack B, Delling G, et al. Prognostic factors in high-grade osteosarcoma of the extremities or trunk: an analysis of 1,702 patients treated on neoadjuvant Cooperative Osteosarcoma Study Group protocols. J Clin Oncol. 2002;20(3):776-790. https://doi.org/10.1200/JCO.2002.20.3.776 Luetke A, Meyers PA, Lewis I, Juergens H. Osteosarcoma treatment—where do we stand? A state of the art review. Cancer Treat Rev. 2014;40(4):523-532. https://doi.org/10.1016/j.ctrv.2013.11.006 Briccoli A, Rocca M, Salone M, Guzzardella GA, Balladelli A, Bacci G. High grade osteosarcoma of the extremities metastatic to the lung: long-term results in 323 patients treated combining surgery and chemotherapy, 1985-2005. Surg Oncol. 2010;19(4):193-199. https://doi.org/10.1016/j.suronc.2009.05.002 Umaiza Ihsan, MD, is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision-making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

Dizziness and syncope. Diagnosis? • Xray of the Week Figure 1. What is this foreign body in the chest? Figure 2. Dislodged leadless pacemaker within the left pulmonary arterial circulation. (A) Frontal chest radiograph demonstrates the radiopaque leadless pacemaker projecting over the left hilar region (red arrow), rather than its expected position within the right ventricle. (B) Axial CT image confirms the leadless pacemaker within the left pulmonary arterial circulation (red arrow). Figure 3. Frontal and lateral CXR. Normal position of leadless pacemaker in a different patient (A) in the right ventricle. Incidental cardiac loop recorder (B). Epidemiology Leadless pacemaker dislodgement is an uncommon complication of implantation. In the Micra Post-Approval Registry, device dislodgement occurred in 0.13% of patients within 30 days [1]. More recent post-market data reported dislodgement and/or embolization in 0.29% of 72,237 Micra VR implants and 0.88% of 5,990 AVEIR VR implants [2]. Migration into the pulmonary arterial circulation is particularly rare and has predominantly been described in case reports [3-5]. Clinical Findings Leadless pacemaker dislodgement may be clinically silent or associated with pacemaker malfunction [3-5]. Device displacement may result in abnormal pacing parameters or loss of capture [3-6]. In this case, the patient presented with dizziness and syncope. Pulmonary artery embolization itself may remain asymptomatic, although serious vascular complications can rarely occur [5-7]. Pathology Leadless pacemakers are implanted directly into the right ventricular endocardium and use dedicated fixation mechanisms to maintain device stability [8]. Inadequate fixation or device release problems may result in dislodgement and subsequent embolization into the pulmonary arterial circulation [2,5]. Once dislodged from the right ventricle, the device may pass through the right ventricular outflow tract and pulmonary valve and lodge within a pulmonary arterial branch [3-5]. Radiographic Features On chest radiography, a normally positioned leadless pacemaker appears as a radiopaque device implanted within the right ventricular wall [9,10]. Device dislodgement should be suspected when the pacemaker is no longer seen in its expected intracardiac position and instead projects over the pulmonary arterial circulation (Figure 1A). Serial radiographs, when available, may demonstrate interval migration [5]. CT provides cross-sectional anatomic localization of an embolized device within the pulmonary vasculature and can delineate its relationship to adjacent pulmonary arterial branches (Figure 1B) [10]. Published cases demonstrate embolization into both central and more peripheral pulmonary arterial branches [3-5]. Treatment and Prognosis Management of an embolized leadless pacemaker depends on device location, clinical status, duration since implantation, and feasibility of retrieval [3,11]. Percutaneous retrieval may be performed using snare-based techniques introduced through a large-bore delivery catheter or steerable sheath [3,4,7,11]. When complete endovascular removal is not technically feasible, a surgical component may occasionally be required [4]. Following successful retrieval, further pacing therapy can be provided when clinically indicated [3,11]. Conclusion Leadless pacemaker dislodgement with pulmonary arterial embolization is a rare complication that may be clinically silent or result in pacemaker dysfunction and potentially serious vascular complications. Chest radiography can identify abnormal device position, while CT provides more precise anatomic localization within the pulmonary arterial circulation. Prompt recognition of device migration is important for guiding subsequent management. References 1. Roberts PR, Clementy N, Al Samadi F, et al. A leadless pacemaker in the real-world setting: the Micra Transcatheter Pacing System Post-Approval Registry. Heart Rhythm. 2017;14(9):1375-1379. https://doi.org/10.1016/j.hrthm.2017.05.017 2. Bahbah A, Sengupta J, Witt D, et al. Device dislodgement and embolization associated with a new leadless pacemaker. J Cardiovasc Electrophysiol. 2024;35(12):2483 2486. https://doi.org/10.1111/jce.16485 3. Terricabras M, Khaykin Y. Successful leadless pacemaker retrieval from the left pulmonary artery: a case report. HeartRhythm Case Rep. 2020;6(10):798-799. https://doi.org/10.1016/j.hrcr.2020.08.004 4. Barbieri F, Kranewitter C, Frech A, Hintringer F, Stühlinger M. Lost but not lost—embolization of a leadless pacemaker to the pulmonary artery with consecutive endovascular recovery. J Cardiovasc Dev Dis. 2021;8(4):37. https://doi.org/10.3390/jcdd8040037 5. Sugiura K, Baba Y, Hirota T, Kubo T, Kitaoka H. A drifting dislodged leadless pacemaker in the bilateral pulmonary arteries. JACC Case Rep. 2022;4(14):844-846. https://doi.org/10.1016/j.jaccas.2022.03.034 6. Amin MI, Saif S, Shivappa S, Noor H. Leadless pacemaker dislodgment: difficulty in release as a predictor for dislodgment and tools for successful retrieval. Heart Rhythm O2. 2024;5(10):739-740. https://doi.org/10.1016/j.hroo.2024.08.010 7. Abraham H, Assar MD, Chugh Y. A novel technique for percutaneous retrieval of an embolized atrial leadless pacemaker from the pulmonary artery. JACC Cardiovasc Interv. 2026;19(10):1333-1335. https://doi.org/10.1016/j.jcin.2026.02.025 8. El-Chami MF, Roberts PR, Kypta A, Omdahl P, Bonner MD, Kowal RC, Duray GZ. How to implant a leadless pacemaker with a tine-based fixation. J Cardiovasc Electrophysiol. 2016;27(12):1495-1501. https://doi.org/10.1111/jce.13092 9. Mathew RP, Alexander T, Patel V, Low G. Chest radiographs of cardiac devices (Part 1): cardiovascular implantable electronic devices, cardiac valve prostheses and Amplatzer occluder devices. S Afr J Radiol. 2019;23(1):1730. https://doi.org/10.4102/sajr.v23i1.1730 10. Conyers JM, Rajiah P, Ahn R, Abbara S, Saboo SS. Imaging features of leadless cardiovascular devices. Diagn Interv Radiol. 2018;24(4):203-208. https://doi.org/10.5152/dir.2018.17462 11. Afzal MR, Daoud EG, Cunnane R, et al. Techniques for successful early retrieval of the Micra transcatheter pacing system: a worldwide experience. Heart Rhythm. 2018;15(6):841-846. https://doi.org/10.1016/j.hrthm.2018.02.008 Umaiza Ihsan, MD, is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision-making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

A 15-year-old female Gymnastics injury. Diagnosis? • Radiology Case of the Week Figure 1. A 15-year-old female Gymnastics injury. Diagnosis? Figure 2. A. Cross-table lateral radiograph of the left knee. The patella (red arrows) is projected over the anterior femoral condyles (yellow arrow). B. Anteroposterior radiograph of the left knee. The patella (red arrows) is displaced laterally and lies beside the lateral femoral condyle (yellow arrow). C. Axial patellofemoral view of the left knee. The patella (red arrow) lies lateral to the lateral femoral condyle (yellow arrow), outside the trochlear groove (green arrow).. Epidemiology Lateral patellar dislocation is a common knee injury, particularly in children and adolescents. Acute patellar dislocation affects approximately 1 in 1000 healthy children aged 9–15 years, with the highest incidence occurring during adolescence. The injury is frequently associated with acute trauma or sporting activity [1,2]. Clinical Findings Patients typically present with acute knee pain, swelling, and limited range of motion following trauma. The patella frequently reduces spontaneously during knee extension. When persistent, the patella remains displaced laterally. Joint effusion and tenderness along the medial retinaculum are common, and the patellar apprehension test may be positive [2]. In the present case, the patient is a 15-year-old female and presents with lateral patellar dislocation following trauma. Pathology Lateral patellar dislocation results from displacement of the patella from the trochlear groove, with injury to the medial patellar stabilizers, particularly the medial patellofemoral ligament (MPFL) [3,5]. The patella may impact the lateral femoral condyle during dislocation, resulting in chondral or osteochondral injury. Predisposing anatomic factors include trochlear dysplasia, patella alta, lateral patellar tilt or subluxation, increased Q angle, femoral anteversion, and lateralization of the patellar tendon insertion [3,5]. Classification Patellar dislocations are classified according to the direction of displacement as lateral, medial, superior, or inferior. Lateral dislocation is the most common and typically occurs when the patella is displaced laterally from the trochlear groove. They may also be categorized as acute, recurrent, or chronic based on the clinical course [4]. Radiographic Features The standard radiographic series includes anteroposterior (AP), true lateral, and axial (sunrise) views. In this case, the patella is laterally displaced on the AP view and lies outside the trochlear groove on the axial view, consistent with lateral patellar dislocation (Fig. 2 C). Radiographs may also demonstrate joint effusion, lipohemarthrosis, osteochondral fracture of the medial patella, lateral patellar tilt or subluxation, and a deep lateral sulcus sign resulting from impaction of the lateral femoral condyle [5]. MRI is useful for further evaluation of associated soft-tissue and osteochondral injuries. Typical MRI findings include injury or disruption of the medial patellofemoral ligament (MPFL), bone marrow edema or contusions involving the medial patella and lateral femoral condyle, and predisposing anatomic abnormalities such as trochlear dysplasia and patella alta [3,5]. Treatment and Prognosis Initial management of a first-time lateral patellar dislocation generally involves reduction when necessary, followed by nonoperative treatment with bracing and rehabilitation focused on restoring range of motion and strengthening the quadriceps and medial stabilizers [6,7]. Surgical treatment may be considered in the presence of an associated osteochondral fracture, recurrent instability, or significant predisposing anatomic abnormalities [6,7]. Although many patients recover with conservative treatment, recurrent instability remains an important complication. Conclusion Lateral patellar dislocation is a common injury in adolescents and should be recognized promptly on radiographs. Assessment of patellar alignment, associated osteochondral injury, and underlying anatomic risk factors is important for appropriate management and prediction of recurrence. References: Sanders TL, Pareek A, Hewett TE, Stuart MJ, Dahm DL, Krych AJ. Incidence of First-Time Lateral Patellar Dislocation: A 21-Year Population-Based Study. Sports Health. 2018;10(2):146-151. DOI: 10.1177/1941738117725055 Gao B, Shi Y, Zhang F. Pediatric patellar dislocation. Minerva Pediatr. 2020;72(1):65-71. DOI: 10.23736/S0026-4946.17.04882-4 Earhart C, Patel DB, White EA, Gottsegen CJ, Forrester DM, Matcuk GR Jr. Transient lateral patellar dislocation: review of imaging findings, patellofemoral anatomy, and treatment options. Emerg Radiol. 2013;20(1):11-23. DOI: 10.1007/s10140-012-1073-9 Parikh SN, Lykissas MG. Classification of Lateral Patellar Instability in Children and Adolescents. Orthop Clin North Am. 2016;47(1):145-152. DOI: 10.1016/j.ocl.2015.08.016 5.Kim HK, Parikh S. Patellofemoral Instability in Children: Imaging Findings and Therapeutic Approaches. Korean J Radiol. 2022;23(6):674-687. DOI: 10.3348/kjr.2021.0577 Smith TO, Song F, Donell ST, Hing CB. Operative versus non-operative management of patellar dislocation. A meta-analysis. Knee Surg Sports Traumatol Arthrosc. 2011;19(6):988-998. DOI: 10.1007/s00167-010-1355-2 Parikh SN, Schlechter JA, Veerkamp MW, et al. Consensus-Based Guidelines for Management of First-Time Patellar Dislocation in Adolescents. J Pediatr Orthop. 2024;44(4):e369-e374. DOI: 10.1097/BPO.0000000000002616 Umaiza Ihsan, MD is a medical graduate of King Edward Medical University, Pakistan. She completed her internship at Mayo Hospital, Lahore, including a three month rotation in Radiology, which further strengthened her interest in diagnostic imaging. She has gained additional clinical exposure in Radiology through observerships at Mon Health Morgantown and the University of Maryland, Baltimore. She has a strong interest in Radiology, particularly diagnostic imaging and its role in clinical decision making, and is actively interested in clinical research, with experience in systematic reviews and medical research. All posts by Umaiza Ihsan, MD Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

A 70-year-old female fell off her bed while changing a light bulb and complains of left shoulder pain. What is the diagnosis? • Xray of the Week Figure 1. Non-contrast CT of the cervical spine. What is the diagnosis? Figure 2. Non-contrast CT of the cervical spine (sagittal reconstructions): Bilateral facet dislocation at C7-T1 with anterior subluxation of C7 on T1. The inferior facets of C7 are locked anterior to the superior facets of T1 (yellow and green arrows), with anterior vertebral body translation present. There are associated fractures of C7 and T1 (red arrows). Figure 2. Non-contrast axial CT of the cervical spine: Bilateral facet dislocation at C7-T1 with naked facet sign (green arrow) and reverse hamburger bun sign (red arrow). Discussion The cervicothoracic junction (C7–T1) represents a biomechanical transition between the mobile cervical spine and the rigid thoracic spine, making it particularly vulnerable to traumatic instability. Bilateral facet dislocation at this level is a highly unstable injury most commonly associated with high-energy trauma but may also occur after low-energy falls in elderly patients due to osteopenia and degenerative stiffness. [1] The injury involves both facets "jumping" anteriorly, disrupting ligamentous stability and risking cord compression.[2] Delayed diagnosis can occur due to poor visualization of C7-T1 on plain films, emphasizing the need for CT in suspected cases.[3] As seen in this case, "teardrop" fragment on C7 or T1 represents a highly unstable flexion-compression or flexion-distraction injury; it is not a minor avulsion and signifies severe ligamentous damage.[5] Imaging Findings CT is the imaging modality of choice for evaluating suspected cervicothoracic junction trauma, as plain radiographs frequently fail to visualize C7–T1 due to shoulder overlap. Multiplanar CT reformations are essential for assessing alignment, facet integrity, and associated fractures. [1] Key CT findings include: High-grade anterior translation of C7 relative to T1 Bilateral jumped or locked facets with loss of normal facet articulation Widening of the interspinous distance indicating posterior ligamentous complex disruption Small anterior vertebral body fracture fragments at C7 and T1 consistent with flexion teardrop fractures Marked narrowing of the spinal canal at the C7–T1 level Axial CT images demonstrate bilateral reverse hamburger bun and naked facet signs, which are pathognomonic for facet dislocation. [2,3] Differential Diagnosis Traumatic bilateral facet dislocation must be distinguished from degenerative spondylolisthesis, which is common in geriatric patients but lacks joint capsule disruption and typically involves less than 4 mm of translation. Unilateral facet dislocation involves a rotational component and manifests as a "bow-tie" sign on lateral radiographs with less than 25% anterior translation. Isolated flexion teardrop fractures involve significant three-column injury but lack the mechanical "locking" of the facet joints seen in dislocations. Traumatic dislocation is favored when there is facet joint disruption, significant translation, and associated ligamentous injury. [1] Management and Prognosis Bilateral facet dislocation at C7–T1 represents a surgical emergency due to profound instability and high risk of neurologic deterioration. Initial management includes cervical immobilization and urgent neurosurgical consultation. Most cases require operative fixation, often via posterior or combined anterior-posterior approaches. Prognosis depends largely on neurologic status at presentation. [1] Key Learning Points C7–T1 injuries are frequently missed on plain radiographs Low-energy falls can cause severe cervical instability in elderly patients Reverse hamburger bun and naked facet signs are key CT indicators Anterior teardrop fractures signify severe ligamentous injury Early recognition and surgical management are critical Correlate with MRI for soft tissue/cord assessment. References Raniga SB, Menon V, Al Muzahmi KS, Butt S. MDCT of acute subaxial cervical spine trauma: a mechanism-based approach. Insights Imaging. 2014;5(3):321–338. doi: 10.1007/s13244-014-0311-y Daffner SD, Daffner RH. Computed tomography diagnosis of facet dislocations: the hamburger bun and reverse hamburger bun signs. J Emerg Med. 2002;23(4):387–394. DOI: 10.1016/s0736-4679(02)00577-2 Lingawi SS. The naked facet sign. Radiology. 2001;219(2):366–367. DOI: 10.1148/radiology.219.2.r01ma06366 Kim KS, Chen HH, Russell EJ, Rogers LF. Flexion teardrop fracture of the cervical spine: radiographic characteristics. AJR Am J Roentgenol. 1989;152(2):319–326. DOI: 10.2214/ajr.152.2.319 Kim KS, Chen HH, Russell EJ, Rogers LF. Flexion teardrop fracture of the cervical spine: radiographic characteristics. AJR Am J Roentgenol. 1989;152(2):319-326. DOI: 10.2214/ajr.152.2.319 Nishad Kosaraju is a second-year osteopathic medical student (OMS-II) at the Edward Via College of Osteopathic Medicine–Carolinas Campus (VCOM Carolinas). He has a strong interest in diagnostic imaging and interventional radiology, with particular enthusiasm for case-based learning and understanding how imaging directly informs clinical decision-making. Nishad did his undergraduate education at UNC Chapel Hill, where he studied Exercise and Sports Science. Nishad enjoys contributing educational radiology cases that highlight classic imaging findings, uncommon presentations of common conditions, and high-yield diagnostic pearls for trainees. Outside of medicine, he enjoys golf, classical music, and technological advances in medicine. Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state-of-the-art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone he has mentored has been accepted into top programs across the country, including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD

Lung mass. Diagnosis? • Xray of the Week Figure 1. What is the lung mass? Figure 2. Pulmonary hamartoma Figures 2A and 2B: Axial CT chest demonstrating well-demarcated, solitary peripheral, and inhomogeneous pulmonary mass arising from right lower lung lobe (yellow arrows). Note the low attenuation fat in the mass which is diagnostic of hamartoma. Small calcifications are also present. Figure 2C: Sagittal CT chest demonstrates posteriorly located well-demarcated solitary peripheral pulmonary mass. The mass is above the intact diaphragm (red arrow). Figure 2D: Coronal CT chest and abdomen demonstrates solitary lung mass arising from the right lung superior to the diaphragm with evidence of calcification. The mass is above the intact diaphragm (red arrow). Discussion: A hamartoma is a noncancerous focal proliferation of cells that is typically found in the organ or surrounding structures from which it arises (1). Hamartomas are commonly composed of mesenchymal tissue such as adipose tissue, epithelium, fibrous tissue, and cartilaginous tissue (2,3). Pulmonary hamartomas, dominantly composed of cartilaginous and adipose tissue, are the most common benign lung neoplasm, accounting for approximately 6% of solitary pulmonary nodules (3). They are commonly incidental findings found in the fourth to sixth decades of life with a male predilection and no current identifiable risk factors (3,9). Though often incidentally diagnosed as most patients are asymptomatic, symptoms can present depending on the location of the hamartoma (5). If located within the endobronchial structures, patients can present with cough, hemoptysis, or endobronchial obstruction with associated fever and dyspnea (5). Pulmonary hamartomas are found on diagnostic imaging; however, some cases may require definitive diagnosis with cytological evaluation after biopsy. On imaging, computed tomography (CT) is more sensitive to detecting pulmonary hamartomas compared to chest radiographs (4). Findings on CT demonstrate solitary, well-defined, round or lobulated masses or lobules that are predominantly peripherally located in the lungs (3,4). The size of the mass or nodule can be variable, typically around 2 to 5 cm. However, pulmonary hamartomas can also be larger than 10 cm, as seen in Figure 1 and 2 (8). Approximately 60% of the masses or nodules contain adipose tissue and 30% contain popcorn-like calcifications (6,7). A well-circumscribed solitary pulmonary nodule which contains fat and remains stable in size is virtually pathognomonic of a pulmonary hamartoma (7). If asymptomatic, patients with pulmonary hamartomas do not require treatment. Surgical resection is reserved for rapidly proliferating or symptomatic masses for which malignancy cannot be ruled out (9). Prognosis is typically excellent as hamartomas are commonly slow growing with rare malignant transformation (9). ​​​​ References: Batsakis JG. Pathology consultation. Nomenclature of developmental tumors. Ann Otol Rhinol Laryngol. 1984 Jan-Feb;93(1 Pt 1):98-9. doi: 10.1177/000348948409300122. PMID: 6703601 Leiter Herrán F, Restrepo CS, Alvarez Gómez DI, Suby-Long T, Ocazionez D, Vargas D. Hamartomas from head to toe: an imaging overview. Br J Radiol. 2017;90(1071):20160607. doi:10.1259/bjr.20160607 Singh H, Khanna SK, Chandran V, Jetley RK. PULMONARY HAMARTOMA. Med J Armed Forces India. 1999;55(1):79-80. doi:10.1016/S0377-1237(17)30328-3 Radosavljevic V, Gardijan V, Brajkovic M, Andric Z. Lung hamartoma--diagnosis and treatment. Med Arch. 2012;66(4):281-2. doi: 10.5455/medarh.2012.66.281-282. PMID: 22919888 Thomas JW, Staerkel GA, Whitman GJ. Pulmonary hamartoma. AJR Am J Roentgenol. 1999 Jun;172(6):1643. doi: 10.2214/ajr.172.6.10350308. PMID: 10350308 Chai JL, Patz EF. CT of the lung: patterns of calcification and other high-attenuation abnormalities. AJR Am J Roentgenol. 1994;162 (5): 1063-6 doi:10.2214/ajr.162.5.8165982 Klein JS, Braff S. Imaging evaluation of the solitary pulmonary nodule. Clin. Chest Med. 2008;29 (1): 15-38, v. doi:10.1016/j.ccm.2007.11.007 Siegelman SS, Khouri NF, Scott WW Jr, Leo FP, Hamper UM, Fishman EK, Zerhouni EA. Pulmonary hamartoma: CT findings. Radiology. 1986 Aug;160(2):313-7. doi: 10.1148/radiology.160.2.3726106. PMID: 3726106 Lundeen KS, Raj MS, Rajasurya V, et al. Pulmonary Hamartoma. [Updated 2020 Jul 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan. https://www.ncbi.nlm.nih.gov/books/NBK539806/ UPDATE: 2022 - Dr. Zidi is a Radiology Resident at Northwestern University, in Chicago, Illinois. Rabab Zaidi is an aspiring radiologist and fourth year medical student at the Loyola University Chicago Stritch School of Medicine (SSOM). She currently serves as the Community Support Co-Lead for the Loyola University COVID-19 Response Team and Co-President of the Radiology Interest Group at SSOM. At the Stritch School of Medicine, she has also worked with the Department of Radiation Oncology to study prostate cancer imaging and adaptive radiotherapy techniques, where she learned about the intersection of patient care and radiology. Rabab graduated magna cum laude with a degree in Economics from Loyola University Chicago in 2016. She is further passionate about mentorship, advocacy, and photography. Follow Rabab Zaidi on Twitter @ZaidiRabab All posts by Rabab Zaidi Kevin M. Rice, MD is the president of Global Radiology CME and is a radiologist with Cape Radiology Group. He has held several leadership positions including Board Member and Chief of Staff at Valley Presbyterian Hospital in Los Angeles, California. Dr. Rice has made several media appearances as part of his ongoing commitment to public education. Dr. Rice's passion for state of the art radiology and teaching includes acting as a guest lecturer at UCLA. In 2015, Dr. Rice and Natalie Rice founded Global Radiology CME to provide innovative radiology education at exciting international destinations, with the world's foremost authorities in their field. In 2016, Dr. Rice was nominated and became a semifinalist for a "Minnie" Award for the Most Effective Radiology Educator. He was once again a semifinalist for a "Minnie" for 2021's Most Effective Radiology Educator by AuntMinnie.com. He has continued to teach by mentoring medical students interested in radiology. Everyone who he has mentored has been accepted into top programs across the country including Harvard, UC San Diego, Northwestern, Vanderbilt, and Thomas Jefferson. Follow Dr. Rice on Twitter @KevinRiceMD All posts by Kevin M. Rice, MD