25F with headache • Xray of the Week
Figure 1. What is the diagnosis?
Figure 2. MRI Brain without contrast. Nodule of intermediate signal intensity in the anterior third ventricle (red arrow). Subtle on MRI due to intermediate signal intensity on all sequences, but definite contour abnormality in anterior third ventricle. There is no hydrocephalus.
A. Sagittal T1-weighted image. Isointense nodule in the anterior third ventricle (red arrow).
B. Axial FLAIR image. Isointense nodule in the anterior third ventricle (red arrow).
C. Coronal T2* image. Nodule in the anterior third ventricle (red arrow) with low to intermediate signal intensity.
Figure 3. CT Brain without contrast. Nodule in the anterior third ventricle is well seen on CT due to high protein content of cyst.
A. Sagittal CT brain. B. Axial CT brain. C. Coronal CT brain.
Colloid cysts are epithelial-lined cysts containing gelatinous material such as mucin, old blood, cholesterol, and ions (1). They are typically located in the rostral third ventricle near the foramen of Monroe (1). The etiology is unclear but the cyst is thought to be a remnant of the paraphysis element, respiratory epithelium, ependymal cyst from the diencephalon, or invagination of the neuroepithelium of the lateral ventricle (1). Colloid cysts are benign growths but they can cause symptoms such as headaches, diplopia, memory issues, and vertigo due to obstructive hydrocephalus when they block the the flow of cerebrospinal fluid from the lateral ventricles at the foramen of Monroe (1). This can occur via a ball-valve mechanism, in which mobile colloid cysts attached to the ceiling of the third ventricle via a thin peduncle can block CSF flow causing intermittent obstructive hydrocephalus and positional headache (1).
On CT, colloid cysts appear as a round mass with a hyperdense appearance, especially when the cyst contains protein or cholesterol or is highly viscous (Fig. 3) (2,3). They can appear as hypodense or isodense in rare cases (2). In isodense cysts, it may be possible to visualize hyperdense areas in the lesion which represent acute hemorrhage on CT (4). Increased intraventricular pressure and transependymal cerebrospinal fluid leak can lead to periventricular hypodensity or enlarged temporal horns on CT, and calcification and hemorrhage may be seen as well (2).
Colloid cysts have variable appearance on MRI depending on the material in the cyst. Protein and cholesterol cysts shorten the T1 relaxation time and tend to be hyperintense on T1-weighted images and hypointense on T2-weighted images (2). Cysts that are hypointense on T2-weighted images may be more difficult to view on FLAIR (5). As seen in this case, isointense cysts can be seen on CT scan but may be difficult to see on MRI (5). A rim of peripheral enhancement representing the cyst capsule may be seen, but this may represent enhancement of stretched septal veins that are adjacent to the cyst (1). MRI may show intracystic fluid levels or homogeneous appearance (5).
Treatment options are craniotomy, endoscopic aspiration or resection, stereotactic aspiration, and permanent CSF diversion via shunt (6). Stereotaxic aspiration can be used for cysts that show hypodensity on CT and hyperintensity on T2-weighted sequences (7). Cysts with a hypointense appearance on T2-weighted images are less likely to be suitable for aspiration and may require alternate surgical intervention (5).
Tenny, Steven, and William Thorell. Colloid Brain Cyst. StatPearls, StatPearls Publishing, 2020. PubMed, http://www.ncbi.nlm.nih.gov/books/NBK470314/
Algin O, Ozmen E, Arslan H. Radiologic manifestations of colloid cysts: a pictorial essay. Can Assoc Radiol J. 2013;64(1):56-60. doi:10.1016/j.carj.2011.12.011
Mamourian, A. C., et al. Colloid cyst of the third ventricle: sometimes more conspicuous on CT than MR. AJNR. American Journal of Neuroradiology, vol. 19, no. 5, May 1998, pp. 875–78. http://www.ajnr.org/content/19/5/875
Hamidi H, Faizi FR, Rasouly N, Hoshang MM. CT and MRI Features of Pediatric-Aged Colloid Cysts: Report of Two Cases. Case Rep Radiol. 2017;2017:2467085. doi:10.1155/2017/2467085
Armao D, Castillo M, Chen H, Kwock L. Colloid cyst of the third ventricle: imaging-pathologic correlation. AJNR Am J Neuroradiol. 2000;21(8):1470-1477. http://www.ajnr.org/content/21/8/1470.long
Morgan JP, McGraw SC, Asfora WT. Treatment of colloid cyst of the third ventricle by stereotactic aspiration followed by radiosurgery: Report of four cases. Surg Neurol Int. 2018;9:3. Published 2018 Jan 10. doi:10.4103/sni.sni_180_17
Noukoua C. Obstructive Colloid Cyst of the Third Ventricle. J Belg Soc Radiol. 2017;101(1):20. Published 2017 Apr 25. doi:10.5334/jbr-btr.1306
Amara Ahmed is a medical student at the Florida State University College of Medicine. She serves on the executive board of the American Medical Women’s Association and Humanities and Medicine. She is also an editor of HEAL: Humanism Evolving through Arts and Literature, a creative arts journal at the medical school. Prior to attending medical school, she graduated summa cum laude from the Honors Medical Scholars program at Florida State University where she completed her undergraduate studies in exercise physiology, biology, and chemistry. In her free time, she enjoys reading, writing, and spending time with family and friends.
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Kevin M. Rice, MD is the president of Global Radiology CME
Dr. Rice is a radiologist with Renaissance Imaging Medical Associates and is currently the Vice 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.
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