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.