Findings:
Multiple MR images show a heterogenously enhancing mass
in the midline cerebellum, extending into the fourth ventricle and causing
obstructive hydrocephalus. The mass has heterogenous signal characteristics
on all sequences.
Differential Diagnosis:
medulloblastoma, ependymoma, glioma
Discussion:
Medulloblastoma is a primitive neuroectodermal tumor
which originates from the cerebellar vermis in children and cerebellar
hemispheres in adults. The tumor is composed of both neuronal and glial
elements, with possible astrocyte differentiation. Peak ages of occurrence
are 4-8 and 15-35 with slight male predominance. 75% of tumors occur in
patients <15 yrs. The tumor is XRT/chemo sensitive, with a 5ysr of 50-70%.
imaging:
-solid, hyperdense on CT
-cystic/necrosis in 50%, calcification in
20%, rare hemorrhage
-hypo T1, variable T2
-intense, homogenous enhancement
-50% with subarachnoid spread (Zuckerguss)
-systemic mets in 5% (bone)