Multivariate analysis revealed that no dural detachment (hazard ratio [HR]6.42, 95% CI 1.41-45.0; p = 0.02) and skull base location (HR 11.6, 95% CI 2.18-218; p = 0.002) were independent risk factors for the necessity of early retreatment, whereas postresection tumor volume of 4 cm(3) or more was not a statistically significant risk factor.CONCLUSIONS: Compared with Simpson Grade I, II, and III resections, Simpson Grade IV resection includes highly heterogeneous tumors in terms of resection rate and location of the residual mass. Despite the difficulty in analyzing such diverse data, these results draw attention to the favorable effect of dural detachment (instead of maximizing the resection rate) on long-term tumor control. Surgical strategy with an emphasis on detaching the tumor from the affected dura might be another important option in resection of high-risk meningiomas not amenable to gross-total resection.