Frozen section discrepancy in the evaluation of nonneoplastic central nervous system samples

Frozen section (FS) for intraoperative evaluation of central nervous system (CNS) lesions provides the neurosurgeon with a rapid preliminary pathologic diagnosis. Diagnosis of nonneoplastic lesions is particularly challenging in this venue. To highlight common diagnostic pitfalls, we sought to identify discrepancies between FS and final diagnoses among nonneoplastic CNS samples via a retrospective review of 303 FS cases encountered from 1997 to 2006. Thirty-nine (12.9%) discrepant diagnoses were identified, of which 27 were clinically suspected tumors. Final diagnoses in the discrepant group included the following: inflammatory lesions (n = 8, 20.5%), malformation of cortical development-cortical dysplasia (n = 5, 12.8%), gliosis (n = 5, 12.8%), vascular malformations (n = 5, 12.8%), demyelination/progressive multifocal leukoencephalopathy (n = 3, 7.7%), infarct (n = 3, 7.7%), hemorrhage/blood clot (n = 3, 7.7%), and no pathologic changes (n = 3, 7.7%). The remaining 4 (10.2%) discrepant cases involved one case each of amyloid angiopathy, nonspecific vasculopathy, vasculitis, and meningioangiomatosis. Nonneoplastic lesions are often more challenging than neoplastic lesions at FS, particularly because they are less commonly sampled for FS and, therefore, less familiar to pathologists.