Neuropathology Entities Involving the Sinonasal Tract.

Neuropathologic entities uncommonly involve the sinonasal tract via several mechanisms: (1) ectopic tissue remnants or defects during embryologic development (anterior encephalocele, extracranial meningioma, ectopic pituitary adenoma); (2) extension of benign tumors from structures exiting the brain or in the sellar region (pituitary adenoma, craniopharyngioma, schwannoma, meningioma); and (3) invasion from high-grade intracranial tumors (glioblastoma, atypical teratoid/rhabdoid tumor of sella, anaplastic meningioma, solitary fibrous tumor). Because these entities are not always restricted to the intracranial space, it is important for surgical pathologists to consider them in the differential diagnoses of unusual sinonasal lesions.