Pleomorphic Xanthoastrocytoma

2.1 Overview • Pleomorphic xanthoastrocytoma (PXA) is an uncommon astrocytic lesion that despite its significant histologic pleo-morphism, generally behaves in a less aggressive fashion than similarly pleomorphic infiltrative gliomas; the latter affords it a WHO grade II designation. • The vast majority are sporadic, with only rare examples described in association with neurofibromatosis type I (NF1). • Previously referred to as fibroxanthoma and xanthosar-coma, they have also been misclassified as forms of giant cell glioblastoma or monstrocellular sarcoma. • Postulated to originate from subpial astrocytes, multipotential neuroectodermal precursor cells, or pre-existing hamartoma-tous lesions, PXAs represent distinctive astrocytic neoplasms with a variable degree of neuronal differentiation demonstra-ble by immunohistochemistry and electron microscopy. • Representing <1% of all astrocytic tumors, PXAs most frequently arise within the first three decades of life. No gender predilection is apparent, and occasional cases have been reported in the elderly. • Given their superficial " meningo-cerebral " localization, patients typically present with a history of seizures, often of a longstanding nature. • Headaches may also occur. • PXAs are almost always supratentorial and superficially-situated within the cerebral hemispheres (most commonly the temporal or parietal lobe) with involvement of the leptomeninges. • Rare sites include the cerebellum, spinal cord, thalamus, and cerebellopontine angle. • 70% arise as a cyst with solid mural nodule, the remainder being predominantly solid with variable small cystic areas. • Their solid component is iso to hypodense on CT, isoin-tense on T1-weighted MR imaging, mildly hyperintense on T2-weighted imaging, and strongly enhances following gad-olinium administration (Fig. 2.1a and b). • Intratumoral hemorrhage or calcifications are uncommon; peritumoral edema may be present, but is typically minimal. • They may rarely show multifocality or leptomeningeal dissemination. • Gross pathology: Operative sampling of PXAs yield solid firm tissue (+/-cystic component) with variable coloration ranging from tan to yellow, the latter areas corresponding to xanthoma-tous histology. • Leptomeninges are usually present in the sample, incorporated into the solid portion of the tumor. • Intraoperative cytologic imprints / smears: Cytologic samples are polymorphous, containing cells with quite variable cytomorphology; fibrillary astrocytic, spindled, and giant pleomorphic forms with abundant sometimes vacuolated cytoplasm may all be present. (Fig. 2.2a and b). • Eosinophilic granular bodies and scattered lymphocytes are often identifiable. • Histology: – PXAs as a group are quite heterogeneous in their histo-logic appearance, however several key features are consistently present in all: – They are composed of spindle cells …