Background: Total or subtotal surgical resection of WHO grade II glioma (diffuse low-grade glioma, DLGG) can significantly increase survival. Moreover, a supratotal resection, i.e., an extended resection with a margin beyond MR imaging abnormalities, could decrease the risk of malignant transformation. Here, the goal is to analyze the long-term functional and oncological outcomes following supratotal resection for DLGG.

Methods: Sixteen consecutive patients who underwent supratotal resection for a DLGG with a minimum follow-up of 8 years after surgery were included. The resection was continued up to functional cortical and subcortical structures defined by intrasurgical electrical mapping. The extent of resection was evaluated on postoperative FLAIR-weighted MR imaging. Data regarding clinicoradiological features, therapeutic management, and outcomes were analyzed.

Results: Seven men and nine women (mean age, 41.3 years, range, 26-63 years) were included (seizure in 15 cases, one incidental discovery). All patients resumed a normal life after surgery (no neurological deficits, no epilepsy). The volume of postoperative cavity was larger than the preoperative tumor volume in the 16 patients. Neuropathological examination confirmed the diagnosis of WHO grade II glioma in all cases. No adjuvant treatment was administrated after resection. The mean duration of postoperative follow-up was 132 months (range, 97-198 months). There was no relapse in eight cases. Eight patients experienced tumor recurrence, with an average time to relapse of 70.3 months (range, 32-105 months), but without malignant transformation. Five of them have been re-treated, with a reoperation (two cases), chemotherapy (three cases) and radiotherapy (two cases). All patients continue to enjoy a normal life.

Conclusions: This is the first series demonstrating the prolonged impact of supratotal resection on malignant transformation of DLGG. These original data may suggest to remove a margin around the FLAIR-weighted MR imaging abnormalities in a more systematic manner for DLGG not involving eloquent structures.