Atypical Meningiomas Compared to Other WHO Grade 2 Meningiomas: Histological Features and Prognosis

Background: The 2021 WHO classification of meningiomas describes atypical meningiomas as having one major feature (4–19 mitotic figures/10 high power field or brain invasion) or 3 out of 5 minor features (small cells with high N/C ratio, large and prominent nucleoli, patternless or sheet-like growth, foci of spontaneous or geographic necrosis). Many meningiomas with one or two atypical features, but not enough to fulfill the criteria to be atypical meningioma are reported as grade 1 meningioma. The significance of each atypical feature on the prognosis or how it affects and changes the natural history of the disease is not yet clear. In this study, we studied each atypical feature in atypical meningioma versus other grade 2 meningiomas and its possible relation to recurrence.

Methods: We have conducted a retrospective study of patients with WHO grade 2 meningioma operated in our institution between January 2008 and December 2020. Demographic, radiological, and operative data were collected from the patient's chart, operative notes, and pathology reports. Pathology features are collected and analyzed in atypical meningioma and other WHO grade 2 meningiomas. The rates of recurrence, reoperation, and readmission were recorded during the follow-up period. A statistical analysis was done to determine the significance of each pathological feature in regard to recurrence.

Results: A total of 230 patients with meningioma were operated in this period. Only 74 patients were included as WHO grade 2 meningioma with 60 (81%) patients having an atypical meningioma and 14 (19%) patients with chordoid or clear cell meningioma. The mean age was 51 ± 14 years. The most common location was meningioma abutting the frontal lobe (convexity). Major atypical features (4–19 mitotic figures or brain invasion) were more noted in the atypical meningioma. Increased Nuclear cytoplasmic ration and cellularity were found significantly more in atypical meningioma. The recurrence rate was 16.2% (12 patients). Recurrence was seen in 10 (21.3%) of atypical meningioma patients and in 2 (16.7%) of other grade 2 meningioma patients. Neither specific pathology feature (major or minor) nor the type of Grade 2 meningioma was significantly related to recurrence.

Conclusion: The types of WHO grade 2 meningiomas (atypical, chordoid, or clear cell) have similar prognosis and recurrence rates. There is no significant difference between the atypical features in indicating a more aggressive nature or risk of recurrence in grade 2 meningiomas.

Publication History

Article published online:
01 February 2023