Agreement between extent of meningioma resection based on the surgical Simpson Grade and based on postoperative MRI-findings

and Purpose: The surgical Simpson Grade, introduced in 1957 is the standard measure for meningioma resection and prediction of recurrences. We used an MR-based grading system for the radiological extent of resection, and assessed agreement of the extent of resection between the surgical Simpson Grade and the MR-based scale. Patients were prospectively included during a two-year period. Immediately after surgery the surgeon determined the Simpson Grade. MRI was performed within 72 hours and at three months after surgery. Scans were assessed by a neuroradiologist, blinded to the surgeon's grading. Intraclass correlation coefficient (ICC) and absolute agreement were used to evaluate agreement between both scales. Thirty-five patients (41 tumors) were included. Absolute agreement was 76%, with an ICC of 0.613. At three months postoperatively, the ICC and absolute agreement were 0.682 and 78%. In 20% of cases, the extent of resection was less favorable on the early postoperative MRI than the surgeon's Simpson Grade. Agreement for extent of meningioma resection between both scales was good in terms of ICC. When the surgical Simpson Grade is unclear, MR-imaging at three months after surgery may be used as a baseline for further follow-up. In a substantial portion of cases the extent of resection was less favorable on the early postoperative MRI than the surgeon's Simpson Grade. The predictive value of the radiological extent of resection for the risk of long-term recurrences is a subject for further research