Pilocytic astrocytoma

Pilocytic astrocytoma (PA), also known as juvenile pilocytic astrocytoma or cystic cerebellar astrocytoma, is a slow-growing (WHO grade I) brain tumor that arises from astrocytes, a type of glial cell in the central nervous system. It is the most common brain tumor in children, typically occurring in the cerebellum (posterior fossa), but can also develop in the optic pathways, hypothalamus, brainstem, and cerebral hemispheres. The tumor is generally well-circumscribed and often contains both solid and cystic components. Pilocytic astrocytomas are characterized histologically by biphasic architecture with compact bipolar (piloid) cells and loose-textured multipolar cells, along with Rosenthal fibers and eosinophilic granular bodies. Symptoms depend on the tumor's location and size. Cerebellar tumors commonly present with headaches, nausea, vomiting, balance difficulties (ataxia), and signs of increased intracranial pressure due to obstructive hydrocephalus. Optic pathway tumors may cause visual disturbances, proptosis, or hormonal abnormalities when the hypothalamus is involved. Pilocytic astrocytomas are frequently associated with neurofibromatosis type 1 (NF1), particularly optic pathway gliomas. The BRAF-KIAA1549 fusion gene is the most common molecular alteration found in sporadic cases, resulting in activation of the MAPK/ERK signaling pathway. The primary treatment is surgical resection, which is often curative when gross total removal is achieved, with excellent long-term survival rates exceeding 90% at 10 years. When complete resection is not feasible due to tumor location (e.g., hypothalamic or brainstem tumors), chemotherapy and/or radiation therapy may be employed. Targeted therapies, including MEK inhibitors and BRAF inhibitors, have shown promise in recurrent or progressive cases, particularly those harboring BRAF alterations. Overall, pilocytic astrocytoma carries one of the most favorable prognoses among all central nervous system tumors.

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