Figure 1. Pilocytic astrocytoma. Photomicrograph (original magnification, x40; hematoxylin-eosin stain) of a classic pilocytic astrocytoma reveals a biphasic appearance with a loose glial component (g) with numerous microcysts and vacuoles and more compact piloid tissue (p) with elongated bipolar cells (arrowhead) showing fine fibrillary processes. Rosenthal fibers (arrows) are also noted.