pilocytic astrocytoma
Pronunciation: py-low-SIT-ik as-tro-sy-TOH-mah
A WHO Grade I brain tumor representing the most common primary brain tumor in children, characterized by slow growth and excellent prognosis when completely resected.
Full Definition
Pilocytic astrocytoma is a benign, slow-growing glioma that accounts for approximately 20% of all pediatric brain tumors. These tumors most commonly arise in the cerebellum, optic pathway, hypothalamus, and brainstem in children and young adults. Histologically, they are characterized by biphasic architecture with compact areas containing Rosenthal fibers and loose microcystic regions with eosinophilic granular bodies. The majority harbor KIAA1549-BRAF fusion or BRAF V600E mutations, leading to constitutive activation of the MAPK pathway. Complete surgical resection is often curative, with 10-year survival rates exceeding 95%. When located in surgically inaccessible areas like the optic pathway, these tumors may be managed with observation or targeted therapy, as they rarely undergo malignant transformation.
Usage
Usage note: Specify WHO grade when first mentioned to distinguish from higher-grade astrocytomas.
In Context
- "MRI demonstrated a well-circumscribed cystic lesion with an enhancing mural nodule consistent with pilocytic astrocytoma." — Radiology report
- "The pilocytic astrocytoma was successfully gross-totally resected without neurological deficit." — Operative note