CSF cytology diagnosis of NRAS‐mutated primary leptomeningeal melanomatosis with neurocutaneous melanosis

Primary leptomeningeal melanomatosis is an extremely rare, diffuse, malignant melanocytic neoplasm without a localised mass. In this case, both immunocytochemistry and molecular testing were successfully completed using a CSF sample, allowing confirmation of the diagnosis and determination of the mutational status of the melanoma.