Given the history of previous lung cancer, the hemorrhagic right cerebellar lesion with moderate local mass effect is favored to represent a solitary metastasis. A glial tumor is the main differential diagnosis.

The most common cause of a solitary tumor in the posterior fossa in an adult patient is a metastatic lesion.

The lesion was resected.

MICROSCOPIC DESCRIPTION:

The sections show features of metastatic poorly differentiated non-small cell carcinoma, adjacent to cerebellar cortex. The tumor forms anastomosing trabeculae and nests with some areas of necrosis. Glandular structures are absent. The tumor cells have enlarged nuclei, prominent nucleoli and moderate amounts of cytoplasm. There is no evidence of keratinization. No evidence of lymphovascular invasion is seen. The tumor cells are diffusely p63 positive. There is focal staining for CK5/6 and less so with CK7. TTF-1 is negative.

DIAGNOSIS: 

R cerebellar lesion: Metastatic poorly differentiated squamous cell carcinoma, consistent with lung primary.