Pilocytic Astrocytoma

Findings:
A cystic mass with strongly enhancing mural nodule is present in the right posterior frontal region, without significant mass effect or surrounding edema.

Differential Diagnosis:
pilocytic astrocytoma, pleomorphic xanthoastrocytoma, less likely hemangioblastoma or ganglioglioma

Discussion:
Pilocytic astrocytomas are low grade glial neoplasms, 60% of which arise in the posterior fossa. 50% have a cyst/mural nodule appearance. Prognosis is excellent, with 25 yr survival rate in excess of 90% if resection is complete. Calcification is uncommon, seen in up to 25%. The cystic portion contains proteinaceous fluid and no capsule. Surrounding edema is rare. The mural nodule is usually iso-hypo T1, hyper T2. A solid, centrally necrotic subtype represents the other 50% of PA, which has a more guarded prognosis.

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