Cystic supratentorial brain tumors in adults, the usual and the unusual. Non-exhaustive list of differential diagnostic considerations. The PA had a nice mural nodule, not shown on this figure. #radres #neurorad #FOAMrad #FOAMed #MedEd #RadEd 
impossible to tell which is which on only T1-images with GD. Whenever I see an intra-axial tumor in an adult, I automatically consider GBM and metastases as they are the most frequent brain tumors in adults, so even when the tumor looks strange or atypical, they are a good bet.
Brain abcess and epidermoid cyst are pretty straightforward on diffusion-weighted images as their content is very diffusion restrictive. Brain abscess has a thick enhancing capsule, epidermoidcyst doesn't.
Ganglioglioma is a cortical based tumor and often presents as a large cyst with an enhancing mural nodule. They are most frequent in the temporal lobe, followed by the frontal lobe, and often associated with epilepsy. Patients are typically younger.
Pilocytic astrocytoma is a tumor we associate with childhood cerebellar masses, but they can also occur in adults. In adults, they are more frequently found in the supratentorial brain parenchyma, an atypical location in children. Mural nodule was present (not on the image).
ependymomas are tumors we associate with fourth ventricular masses, but they can also occur supratentorially and in that case are found extraventricularly (in the brain parenchyma) in about 50% of cases.
Each time I see a very strange looking intra-axial tumor in an adult and I have no clue whatsoever what it could be, I suggest: "maybe extraventricular ependymoma" and I'm suprisingly right a lot of times. So extraventricular ependymoma is my: "I have no clue" tumor.
Please feel free to add your own cases, thoughts or considerations...
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