Amelanotic Melanoma

Findings:
Multiple MR images show an extraconal mass in the right orbit which has intermediate signal intensity on T2 and is isointense to gray matter on unenhanced T1. The axial contrast enhanced T1 weighted image shows mild homogenous enhancement of this lesion.

Differential Diagnosis:
This tumor has a nonspecific imaging appearance. Intermediate signal on T2 suggests that this is a cellular lesion, and tumors such as lymphoma could be considered. Other lesions to consider include metastasis and amelanotic melanoma.

Discussion:
Melanin producing melanomas show hyperintensity on T1 and hypointensity on T2. Amelanotic lesions have a nonspecific appearance, generally  hypo/hyper T1/T2. Melanoma is the most common intraocular malignancy in adults, but extraconal lesions are uncommon.

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