Because of their critical location, petroclival meningiomas (PCM) are difficult to resect completely and surgery is associated with significant morbidity. Gamma Knife radiosurgery (GKR) can be proposed as unique treatment or as a complement after partial surgical resection of PCM.

     We evaluate the results of Gamma Knife irradiation in this indication using a 12-Gy dose.

     Sixty-one patients were treated by GKR for a PCM with a 12-Gy margin dose at the 50%-isodose. For 34 patients (56%) GKR was the unique treatment of the PCM; for 27 patients GKR was used for a residue of a recurrence of tumor after surgical removal. A neurological deficit related to the meningioma was present in 31 patients (51%) before GKR.

      Dosimetric planning was performed using a combination of 3 imaging modalities (axial 1-mm sliced Gadolinium-enhanced T1-weighted, T2-weighted and CT densitometric 3D volume acquisitions) and with multiple small collimators. Patients were followed clinically and by MRI performed once a year. Patients with a complete follow-up of minimum 2 years after treatment were included in the study.

     Mean tumor volume was 3.42 cc (SD 2.7). The Conformity Index ranged from 1.15 to 2.21 (median 1.44). A median number of 16 isocenters were used (range 2-36). Data of the follow-up of 46 patients were analyzed; the mean follow-up was 4.5y (range 2-9y). Local tumor control was achieved on last follow-up in all patients (100%). The tumor volume significantly decreased in 21 patients (46%) and remained unchanged in 25 patients (54%). Neurological status improved for 5 patients (11%) and was stable for 41 patients; no patient worsened. Two patients require surgery for an extension of the meningioma outside the radiosurgical target volume.

     This is a retrospective study.

     PCM treated by BGK with a 12-Gy margin dose can achieve high local tumor control rate and low morbidity.