LAUSR

Primary leptomeningeal melanomatosis (PLM) is an extremely rare diffuse malignant melanocytic neoplasm infiltrating into the subarachnoidal space and superficial brain without a localised mass. It may be found in isolation or in the context of neurocutaneous melanosis (NCM), the latter more often occurring in children. The diagnosis of PLM is challenging for clinicians because of its rarity and nonspecific neurological symptoms which clinically can mimic meningitis. Magnetic resonance images (MRI) can demonstrate a characteristic appearance because of the paramagnetic properties of melanin, but tissue biopsy is necessary for a definite diagnosis before treatment. Cerebrospinal fluid (CSF) analysis may demonstrate malignant cells containing melanin pigment, leading to difficult differential diagnoses including metastatic melanoma and other pigmented primary CNS tumours. Herein, we report a case of v-raf murine sarcoma viral oncogene homolog B1 (BRAF) negative and neuroblastoma RAS viral (v-ras) oncogene homolog (NRAS) positive PLM confirmed by immunocytochemistry and molecular testing using only the CSF sample.