This patient had a known history of lung carcinoma. He went on to have a craniotomy and excision of this cerebellar mass. 

Histology

MICROSCOPIC DESCRIPTION: The sections show features of metastatic small cell carcinoma infiltrating into the cerebellar parenchyma.  The tumor forms diffuse sheets.  Thick cuffs of tumor surround blood vessels.  The tumor cells have high N/C ratio with enlarged hyperchromatic nuclei, nuclear molding, granular chromatin, inconspicuous nucleoli and scanty cytoplasm.  Scattered mitoses and apoptotic bodies are present. Lymphovascular invasion is not seen. The tumor cells are CAM5.2, CD56, synaptophysin and TTF-1 positive.

FINAL DIAGNOSIS: Metastatic small cell carcinoma from the lung

Discussion

This case illustrates how in some instances the demographics of the patient are more important that the appearance of the abnormality. In a younger adult patient, the most likely differential would be hemangioblastoma, whereas in a child pilocytic astrocytoma would be more likely.