Pilocytic astrocytoma and pleomorphic xanthoastrocytoma: glioneuronal tumors or variants of ganglioglioma?

Neoplasms of the central nervous system (CNS), when examined macroscopically, may be circumscribed or diffusely infiltrating. Circumscribed glial and mixed glial-neuronal neoplasms include, among others, pilocytic astrocytoma (PA), pleomorphic xanthoastrocytoma (PXA) and ganglioglioma (GG). Besides being circumscribed, these neoplasms share several similarities: they affect mostly children, adolescents and young adults; they are often cystic; they may present a mural nodule; they have low proliferative potential . Among the microscopic findings, we highlight the presence of eosinophilic granular bodies (PA, PXA and GG), Rosenthal fibers and microvascular proliferation (PA and GG), a network of reticular fibers and perivascular lymphocytic infiltrate (PXA and GG) and invasion of the leptomeninges (PA, PXA and GG). The variable mix of neurons and glial cells is the major finding for the diagnosis of GG. However, neurons can also be found in some PAs and PXAs, including tumors resulting from the combination of GG and PXA, which maximizes the similarity among these neoplasias.