Melanoma is the most deadly form of skin cancer and is the third most common form of cancer to spread to the brain. Approximately 30% of patients with metastatic melanoma will experience involvement of the brain and CSF. Once melanoma has spread to the brain, it is no longer curable.
The top image shows a CSF cytospin from a teenage patient who presented with headaches, mental status changes, and new onset of seizures. There had been no prior recognition of a melanoma and there was no evidence of such on the physical exam.
The CSF showed a few cells with the "classic" look of melanoma - a "shaggy" mesothelial cell with blue-black melanin inclusions. This is very typical of metastatic melanoma.
Sometimes the melanin granules can be so sparse that they are difficult to find, as shown in the bottom image.