Accuracy of frozen section in determining meningioma subtype and grade.

Frozen section intraoperative consultation is a well-established means of evaluating brain tumors at the time of surgery. Limitations to the procedure are also well recognized resulting in less than perfect specificity of diagnosis. This study retrospectively reviewed 424 consecutive meningioma cases (N = 310 females; mean age 57.3 years) to examine concordance between frozen section evaluation of meningioma subtype and grade as compared with the final diagnosis subtype and grade. A discrepancy between frozen section diagnosis and final diagnosis was observed in 114 (26.9%) of cases. Of the WHO grade I subtypes, the most common discrepancy involved transitional meningiomas (N = 31) which were most commonly diagnosed at frozen section as either fibrous (N = 18) or meningothelial (N = 13) meningiomas. None of the grade I tumors were diagnosed as higher grade lesions. Of the higher grade meningiomas (WHO grade II and III) (N = 145) reviewed, concordance between tumor type and grade was seen in only 26.2% of cases; most commonly, 73/98 atypical meningiomas were under-graded as some subtype of WHO grade I meningioma (71/73 cases). In conclusion, discrepancies at frozen section with respect to accurately identifying higher grade meningiomas and higher grade meningioma subtypes are common and are generally due to tumor sampling and heterogeneity.