Cyst w/nodule shape Cyst w/nodule shape Gross picture - the cyst is surrounded by reactive gliosis
Cyst w/nodule shape This PA has a more irregular, multiloculated shape.

WHO Grade I

Cell of Origin: ASTROCYTE


Common Locations: cerebellum, diencephalon (especially the optic nerves and hypothalamus)

Demographics: 5-15yrs, with a peak around 10 years

Histology: Alternating dense and loose areas, fusiform "piloid" bipolar astrocytes, microcysts in loose areas may coalesce to form the macroscopic cysts. The presence of nuclear atypia (without mitotic activity) does not convey a worse prognosis. Vascular changes are usually limited to capillary proliferations that may include glomeruloid capillaries and endothelial proliferation. Eosinophilic "Rosenthal fibers" are characteristic. Calcification possible.

Special Stains: GFAP always +

Progression : Usually stable, rare cases of CSF dissemination and transformation reported

Radiology: Classically, these lesions present with an extratumoral fluid-filled "cystic" component. The wall of the cyst is often composed of non-neoplastic tissue, with the tumor limited to a "mural nodule". Enhancement is almost universal, and outlines the neoplastic tissue - i.e. part of the cyst wall may not enhance - this is the "classic " cyst-with-nodule appearance.