OBJECT: Meningiomas treated by subtotal or partial resection are associated with 
significantly shorter recurrence-free survival than those treated by gross-total 
resection. The Simpson grading system classifies incomplete resections into a 
single category, namely Simpson Grade IV, with wide variations in the volume and 
location of residual tumors, making it complicated to evaluate the achievement 
of surgical goals and predict the prognosis of these tumors. Authors of the 
present study investigated the factors related to necessity of retreatment and 
tried to identify any surgical nuances achievable with the aid of modern 
neurosurgical techniques for meningiomas treated using Simpson Grade IV 
resection.
METHODS: This retrospective analysis included patients with WHO Grade I 
meningiomas treated using Simpson Grade IV resection as the initial therapy at 
the University of Tokyo Hospital between January 1995 and April 2010. 
Retreatment was defined as reresection or stereotactic radiosurgery due to 
postoperative tumor growth.
RESULTS: A total of 38 patients were included in this study. Regrowth of 
residual tumor was observed in 22 patients with a mean follow-up period of 6.1 
years. Retreatment was performed for 20 of these 22 tumors with regrowth. Risk 
factors related to significantly shorter retreatment-free survival were age 
younger than 50 years (p = 0.006), postresection tumor volume of 4 cm(3) or more 
(p = 0.016), no dural detachment (p = 0.001), and skull base location (p = 
0.016). 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.