Axial contrast-enhanced CT brain image in a 68-year-old man with known prostate carcinoma osseous metastases (not shown), demonstrating a hypoattenuating mass with a large enhancing peripheral nodule (arrow), predominantly involving the left cerebellar hemisphere, with mass effect on the fourth ventricle and resulting obstructive hydrocephalus. Biopsy with immunohistochemistry indicated metastatic prostatic adenocarcinoma.