The patient went on to have surgery which revealed that the lesion was a cerebral metastasis.

Histology

MICROSCOPIC DESCRIPTION: Sections of brain tissue show a cohesive tumor forming solid sheets with cells containing abundant amphophilic cytoplasm, vesicular nuclei and prominent nucleoli. Focally tumor cells form papillary structures and glands. Frequent mitoses and focal necrosis are present.

Immunohistochemical results show tumor cells stain:

CK7+, CK20-, ER- and PR-, TTF1+, NapsinA+, GATA3-, GCDFP-; HER2-, CDX2-, p63- and PAX8 focal+; consistent with primary lung adenocarcinoma. 

FINAL DIAGNOSIS: Poorly differentiated adenocarcinoma presumably from lung. 

Discussion

Having difficulty in distinguishing metastases from cerebral metastases is frustrating, however it is better (in the setting of prominent central restricted diffusion) to err on the side of favoring abscesses. 

Possibly the best clue in this case is the presence of incomplete T2 signal loss on SWI in the superior lesion (abscesses usually have a smooth complete ring) and the fact that the cerebellar lesion does not have prominent restricted diffusion. There is also a central area of more facilitated diffusion in the frontal lesion.