The Value of Simpson I–II Resection in Deep-Seated and Skull Base WHO Grade I Meningioma

Background: The prognostic value of the Simpson grading scale for deep-seated and skull base WHO grade I meningiomas has recently been questioned. The availability of adjuvant radiosurgery and the possible morbidity associated with aggressive resection of these lesions has resulted in some neurosurgeons adopting less aggressive surgical strategies. We aimed to compare tumor control rates following complete resection with treatment of involved dura (Simpson I–II) to that of less aggressive resection (Simpson III) or incomplete resection with or without adjuvant radiosurgery (Simpson IV +/−RS).

Methods: We performed a retrospective review of all patients who underwent microsurgical resection of a deep-seated (intraventricular or pineal/tentorial) or skull base WHO grade I meningioma at our institution from 2008-2017 with at least 6 months of follow-up. Treatment failure was defined by the need for further surgical resection or radiosurgery after radiographic progression. Kaplan–Meier (KM) analysis and log-rank tests were utilized to assess and compare retreatment-free survival (RFS), respectively. This outcome was analyzed in 4 groups of patients: Simpson I–II, Simpson III, Simpson IV without adjuvant radiosurgery (Simpson IV −RS), and Simpson IV with adjuvant radiosurgery (Simpson IV +RS).

Results: The cohort included 300 patients with a mean (SD) follow-up period of 50 (31) months. Overall, treatment failure occurred in 36 patients (12%) at a mean (SD) duration of 35 (24) months from surgery. Based on the RFS curves, the KM analysis estimated the mean time to treatment failure to be 133.8, 91.5, 84.1, and 108.9 months for the Simpson I–II (n = 135), Simpson III (n = 45), Simpson IV −RS (n = 79), and Simpson IV +RS (n = 41) groups, respectively. RFS was superior in the Simpson I–II group compared to the Simpson III ([Fig. 1A]; p = 0.02) and Simpson IV −RS ([Fig. 1B]; p < 0.01) groups. The RFS analysis appeared to favor the Simpson I–II group over the Simpson IV +RS group, but it did not reach statistical significance ([Fig. 1C]; p = 0.06). RFS was superior in the Simpson III group compared to the Simpson IV −RS group (Fig. 2A; p = 0.03), but not the Simpson IV +RS group (Fig. 2B; p = 0.54). RFS was superior in the Simpson IV +RS group compared to the Simpson IV -RS group (Fig. 2C; p < 0.01). The rate of permanent neurological morbidity in the Simpson I–II, Simpson III, Simpson IV −RS, and Simpson IV +RS groups was 6.7, 11.1, 12.7, and 14.6%, respectively.

Conclusion: The Simpson grading scale remains an accurate predictor of tumor recurrence in the modern resection of deep-seated and skull base WHO grade I meningioma. In patients where it can be achieved, Simpson I–II resection leads to greater tumor control compared to Simpson III and IV resection without adjuvant radiosurgery. Adjuvant radiosurgery appears to improve short-term tumor control following Simpson IV resection. Future studies with longer follow-up periods are needed to evaluate our data's suggestion that Simpson I–II resection is superior to Simpson IV resection with adjuvant radiosurgery. The higher morbidity rate of less-aggressive resection observed in this retrospective study is likely an association with tumor complexity and not causative.

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Publication History

Article published online:
12 February 2021