The patient went on to have surgery.

Histology

MICROSCOPIC DESCRIPTION: Sections of cerebellar tissue show a cohesive tumor surrounding an extensive areas of central necrosis. Tumor cells form diffuse sheets of cells with abundant eosinophilic cytoplasm, vesicular nuclei and small nucleoli. No glandular or squamous differentiation is seen. Frequent mitoses are present.

Immunohistochemical results show tumor cells stain: CK7+, CK20 focal+, CK5/6+, p40-, TTF1+, NapsinA+ and CD10+; consistent with poorly differentiated primary lung adenocarcinoma.

FINAL DIAGNOSIS: Cerebral metastases: poorly differentiated adenocarcinoma, consistent with a lung primary.

Discussion

Distinguishing metastases from abscess can be difficult when blood product or central necrosis results in low ADC values centrally. A good clue is the morphology of the enhancing component (usually smooth and regular in abscesses) and T2 / SWI dark rim (complete and regular in abscesses).