Presentation
Recurrent seizures, headache, gait abnormalities, visual impairment and vomiting.
Patient Data
There is a large midline posterior fossa mass with both solid and cystic components centered in the cerebellum/fourth ventricle with resultant supratentorial hydrocephalus and transependymal seepage. It measures 96x77x60 mm in its longitudinal, AP and transverse dimensions. The solid component shows avid heterogeneous enhancement while the cystic component shows rim enhancement post gadolinium administration. No diffusion restriction or blooming artefacts is seen. There is perilesional edema and associated mass effect evidenced by significant compression and thinning of the brainstem.
A defect is noted in the right occipital bone likely post intervention.
Ventriculoperitoneal shunt tip noted in the right lateral ventricle.
Case Discussion
The differential diagnosis of posterior fossa mass in a child include pilocytic astrocytoma, ependymoma and medulloblastoma. MRI findings of a predominantly cystic posterior fossa mass with an enhancing solid component is typical for pilocytic astrocytoma. Patient underwent craniotomy for tumor excision which was histologically confirmed.
HISTOLOGY:
Sections show a benign tumor composed of cells disposed in biphasic pattern with cellular areas alternating with hypocellular and microcystic areas. The tumor cells are fairly monomorphic, spindle to oval in shape with hyperchromatic nuclei, moderate eosinophilic cytoplasm and long (piloid) processes. Also seen are eosinophilic granular bodies, Rosenthal fibers and prominent vascular proliferation including glomeruloid bodies. There are also focal areas of necrosis seen.
DIAGNOSIS: Pilocytic astrocytoma.