Abstract
Primary malignant melanoma of the brain is extremely rare, accounting for only 1% of all melanomas. We report a case of primary malignant melanoma of the brain in which the identification of atypical cells in the spinal fluid of a patient led to early diagnosis and treatment of cancerous meningitis. The patient, a 40-year-old woman, was diagnosed with primary malignant melanoma of the brain two years ago and treated with nivolumab after removal of the melanoma, but after six months, stereotactic radiotherapy was added because of recurrence. Approximately 2 weeks ago, she started feeling dizzy and nauseated, and her eyes were unable to focus, so a head MRI was performed. Meningitis was suspected from the contrast lesions along the meninges, and lumbar puncture diagnosed aseptic meningitis. The number of cells in the CSF was increased with predominance of mononuclear cells, and morphological evaluation by Samson’s stain showed atypical cells. The N/C ratio was high, the nuclei were irregularly sized, the nucleoli were markedly enlarged, and brownish-brown granules appeared sporadically in the cytoplasm. Since the granules were brown even without staining, the first possibility was that they were melanin granules. Based on the above findings, intrathecal dissemination of malignant melanoma was most suspected, and this was promptly reported to the attending physician. At the same time, cytological diagnosis was proposed, and Papanicolaou staining led to a definitive diagnosis of carcinomatous meningitis due to malignant melanoma. Although rarely encountered, cancerous meningitis is a serious disease whose prognosis depends on prompt diagnosis and treatment. It is essential to work closely with physicians and other departments including pathology on a daily basis, and to make efforts for early diagnosis and treatment.
