Fig. 2.
Histopathology of pilocytic astrocytomas (PA) and other related pediatric low-grade gliomas. PAs are typically biphasic tumors containing piloid areas with (A) Rosenthal fibers and (B) oligodendrocyte-like areas with eosinophilic granular bodies. (C) Multinucleated cells in a loose myxoid stroma are found in a subset of cases. (D) In contrast, the pilomyxoid astrocytoma subtype has a monomorphous appearance embedded within a myxoid background and frequent perivascular aggregates. (E) Histologic features of anaplasia in PA may be recognizable as cellular aggregates in an otherwise conventional PA, (F) with increased mitotic activity. Subsets of pediatric low-grade astrocytomas with distinct alterations include (G) angiocentric glioma (with MYB-QKI fusions), (H) MYB-altered diffuse astrocytoma, and (I) pleomorphic xanthoastrocytoma, which frequently harbors BRAFV600E mutations. Magnification, ×400 (A, B, C, E, H, I), ×600 (F), ×200 (D, G).