Posterior fossa metastasis (breast cancer)

Centered just to the right of the midline in the posterior fossa is a 3.0 x 4.0 x 2.7 cm mass which has a broad dural attachment superiorly to the undersurface of the tentorium, without invasion of the torcula or transverse sinus. It is heterogeneous on T2 weighted images, with vivid but heterogeneous contrast enhancement, and no evidence of hemorrhage. MR spectroscopy demonstrates high choline, with little in NAA or creatine and elevation of lactate. Cerebral blood volume (CBV) is moderately elevated within the mass. (not shown)

The mass is surrounded by vasogenic edema involving both cerebellar  hemispheres, and exerts mass effect upon the 4th ventricle which is  distorted but does not appear effaced. No hydrocephalus is present at this  time. Basal cisterns remain open.

The mass has an isolated lesion and the remainder of the brain is unremarkable in appearance.

Conclusion:

Solitary posterior fossa lesion is most likely extra-axial, or centered  peripherally in a cerebellar folia, and most likely represents a metastasis,  especially in view of the surgical clips on the chest x-ray (not shown), which are  presumably within the right breast and suggest possible prior breast  malignancy correlation with history required). The differential is that of  a meningioma although the appearance is less typical of this and is thought  far less likely.