Amelanotic Meningeal Melanoma with Leptomeningeal Dissemination: A Case Report and Systematic Literature Review.

Abstract

Meningeal melanoma is a rare tumor of the central nervous system, whose amelanotic variant is called "amelanotic meningeal melanoma" (AMM). AMM does not produce melanin and therefore does not exhibit typical short T1 and short T2 signal on magnetic resonance imaging and thus can be easily misdiagnosed and be inappropriately managed. To date, only 4 AMM cases have been reported in the English literature. Here, we report the fifth case. A 26-year-old female patient presented with a 4-month history of progressive headache and nausea, the conventional magnetic resonance imaging demonstrated a posterior fossa mass accompanied by diffuse leptomeningeal dissemination. Repeated cerebrospinal fluid cytology screening showed negative results. The functional magnetic resonance examinations, including diffusion-weighted imaging, proton magnetic resonance spectroscopy, and dynamic susceptibility contrast perfusion-weighted imaging, provided complementary information. The final diagnosis of AMM was made by immunohistochemistry. Despite gross total excision of the tumor, the disease progressed, and the patient died 10 months after diagnosis. Our experience with this case demonstrated that meningeal melanoma should be included in the differential diagnosis when an intracranial mass is accompanied by leptomeningeal dissemination, and especially when proton magnetic resonance spectroscopy and dynamic susceptibility contrast perfusion-weighted imaging indicate a malignant tumor whereas diffusion-weighted imaging does not. And the loss of a typical melanin signal should not server as an excluding criterion for meningeal melanoma.