Pilocytic astrocytoma

Findings

CT shows a mixed cystic-solid mass in the left basal ganglia extending into the left anterior thalamus and left cerebral peduncle. There is associated mild effacement of the left foramen of Monroe with symmetric mild hydrocephalus involving the lateral ventricles. MR confirms the CT findings and demonstrates mild enhancement of the solid portion of the mass with essentially no surrounding edema.

Differential diagnosis of supratentorial partially cystic, partially solid mass in a child:
- Pilocytic astrocytoma
- PNET (primitive neuroectodermal tumor)
- Hemorrhage


Diagnosis: Pilocytic astrocytoma


Key points

Pilocytic astrocytomas are the most common infratentorial neoplasm in the pediatric age group and are classified as WHO grade I.
They typically are round, well defined, and have a solid center piece and cystic peripheral portion.
60% occur in the posterior fossa, but they can also occur in the hypothalamus or along the optic pathways.
On unenhanced CT they are hypodense. Postcontrast, the solid portion enhances.
Calcification is uncommon (<10%); a cystic component is very common (60-80%); hemorrhage is rare.
Pilocytic astrocytomas have an excellent prognosis (5 year survival >90%).