Intracranial Metastatic Melanoma
Updated: Apr 15, 2021
76 yo M acute right side weakness • Xray of the Week
Figure 1. What is the diagnosis?
A. T1 weighted image. Note the hyperintense nodules and masses with surrounding edema (red arrows). There is mass effect with narrowing of the left lateral ventricle and third ventricle, as well as rightward midline shift. B. T1 weighted image with contrast. Hyperintense nodules and masses with surrounding edema which also demonstrate contrast enhancement (yellow arrows) and large hemorrhagic lesion in left frontal lobe (green arrow) with hematocrit level compatible with hemorrhage. C. FLAIR image showing large hemorrhagic lesion in left frontal lobe with hematocrit level (green arrow).
Melanomas are skin cancers that develop in melanocytes, which are derived from the neural crest and produce melanin (1). If sufficient melanin is present in a melanoma, it can appear on T1-weighted magnetic resonance imaging as high signal intensity (1). Melanomas can metastasize to the regional lymph nodes, but hematogenous spread to other organs is most common in advanced stages (1). Advanced melanoma is commonly associated with brain metastases. Nearly 20% of patients have brain metastasis at time of diagnosis of metastatic melanoma while over 50% of patients develop brain metastasis after diagnosis (2). Intracranial melanoma metastases (IMM) can be classified as melanotic with more than 10% melanotic cells or amelanotic with less than 10% melanotic cells (3). They also commonly present with large hemorrhagic lesions as seen in this case.
Most intracranial lesions are hypointense on T1-weighted images, but high signal intensity can occur with various substances including gadolinium contrast, intra- and extra-cellular methemoglobin, fat, proteins, minerals such as manganese copper and calcium, and melanin (4,5). The unique T-1 hyperintensity on MR can help in narrowing the differential diagnosis. Melanin pigment has stable free radicals which are paramagnetic and cause shortening of T1 and T2 relaxation times (3,6). Chelated metal ions in melanin and unpaired electrons in free radicals can also cause dipole-dipole interactions and proton relaxation enhancement (3,6).
On MRI, melanotic IMM appears as hyperintense relative to the cortex in T1-weighted images due to melanin pigment and hemorrhage, as in this case. Contrast enhancement demonstrates a peripheral rim or diffusely heterogeneous pattern (3). Hypointensity can be seen on T2-weighted images and isointensity or hyperintensity can be seen on proton density-weighted images (3). Amelanotic melanomas show hypointensity or isointensity relative to the cortex on T1 and hyperintensity or isointensity on T2 (3). On CT, IMM can present as single or multiple nodules with increased attenuation and frequent ring-enhancement (5,7). Optical Coherence Tomography (OCT) can also be used to identify intracortical melanomas intraoperatively. This technique is similar to ultrasound B-imaging but it uses reflections of infrared light instead of sound (7). Increased optical backscatter suggests the presence of the tumor in this method (7).
Prognosis of IMM is poor, and treatment is controversial (7-9). Current options include surgical resection, stereotactic radiosurgery, whole brain radiation therapy, and immune checkpoint inhibitors, but varying combinations of these methods are typically used (8,9).
1. Patnana M, et al. Multimethod Imaging, Staging, and Spectrum of Manifestations of Metastatic Melanoma. Clinical Radiology, vol. 66, no. 3, Mar. 2011, pp. 224–36. doi:10.1016/j.crad.2010.10.014 2. Vosoughi Elham, et al. Survival and Clinical Outcomes of Patients with Melanoma Brain Metastasis in the Era of Checkpoint Inhibitors and Targeted Therapies. BMC Cancer, vol. 18, no. 1, Apr. 2018, p. 490. BioMed Central, doi:10.1186/s12885-018-4374-x 3. Isiklar I, et al. Intracranial Metastatic Melanoma: Correlation between MR Imaging Characteristics and Melanin Content. American Journal of Roentgenology, vol. 165, no. 6, Dec. 1995, pp. 1503–12. doi:10.2214/ajr.165.6.7484597 4. Cakirer S, et al. Spontaneously T1-Hyperintense Lesions of the Brain on MRI: A Pictorial Review. Current Problems in Diagnostic Radiology, vol. 32, no. 5, Oct. 2003, pp. 194–217. PubMed, doi:10.1016/s0363-0188(03)00026-4
5. Zimny A, et al. Intracranial Lesions with High Signal Intensity on T1-Weighted MR Images – Review of Pathologies. Polish Journal of Radiology, vol. 78, no. 4, 2013, pp. 36–46. PubMed: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3908506/
6. Ma, Mian, et al. Neurocutaneous Melanosis in an Adult Patient with Intracranial Primary Malignant Melanoma: Case Report and Review of the Literature. World Neurosurgery, vol. 114, June 2018, pp. 76–83. ScienceDirect. doi:10.1016/j.wneu.2018.02.007 7. Goulart CR, et al. Cerebral Melanoma Metastases: A Critical Review on Diagnostic Methods and Therapeutic Options. ISRN Surgery, vol. 2011, 2011. doi:10.5402/2011/276908 8. Ma YF, et al. Intracranial Malignant Melanoma: A Report of 7 Cases. Oncology Letters, vol. 10, no. 4, Oct. 2015, pp. 2171–75. PubMed Central, doi:10.3892/ol.2015.3537 9. Goyal S, et al. The Clinical Management of Multiple Melanoma Brain Metastases: A Systematic Review. JAMA Oncology, vol. 1, no. 5, Aug. 2015, pp. 668–76. doi:10.1001/jamaoncol.2015.1206
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.
Follow Amara Ahmed on Twitter @Amara_S98
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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