Pilocytic astrocytoma is classically associated with which histologic feature?

• A. Psammoma bodies
• B. Auer rods
• C. Rosenthal fibers
• D. Hyaline necrosis

Answer: (C)

Rosenthal fibers are the hallmark feature here. They are thick, elongated eosinophilic glial processes that often have a corkscrew or curly appearance within astrocytes. In pilocytic astrocytoma, especially in the dense fibrillary areas of the tumor, these fibers are prominent and help distinguish it from other gliomas. This tumor is typically a circumscribed, slow-growing lesion seen in children, often with a biphasic pattern of microcystic and fibrillary areas, and Rosenthal fibers are a key histologic clue tying the diagnosis together.

For context, psammoma bodies are laminated calcifications seen in meningiomas and some papillary carcinomas; Auer rods are needle-like cytoplasmic inclusions seen in acute promyelocytic leukemia; hyaline necrosis is not a characteristic feature of pilocytic astrocytoma and is more commonly discussed in the context of high-grade gliomas showing necrosis patterns like pseudopalisading.