Two-Session Tumor and Retrogasserian Trigeminal Nerve-Targeted Gamma Knife Radiosurgery for Secondary Trigeminal Neuralgia Associated with Benign Tumors.

Objective: To investigate gamma knife radiosurgery (GKS) for benign tumor-associated secondary trigeminal neuralgia (TN).

Methods: Between 2006 and 2015, 21 patients with secondary TN due to meningioma were treated using GKS. Their mean age was 56.5 ± 12.2 years. The 50% isodose was 12.5 ± 1.1 Gy for the first GKS for the meningioma. Retrogasserian targeting of the trigeminal nerve at 90 Gy with a 4-mm collimator was used for the second GKS.

Results: The pain duration until GKS was 1.9 ± 1.9 years. The meningiomas were located in the cisternal space in 13 patients (56.5%) and involved the skull base in 8 patients (43.5%). The mean duration of follow-up was 3.7 ± 2.7 years. The pain control outcome was a Marseilles Pain Scale (MPS) score of I to IV in 15 patients (71%) and a score of V in 6 patients (29%). For these latter patients, we performed a second GKS targeting the trigeminal nerve and resulting in MPS scores of I to IV. The tumor size did not increase in any patient and decreased by >10% in 12 (80%) of the 15 patients who were followed for at least 1 year. Trigeminal nerve visibility may improve after tumor shrinkage. Retrogasserian trigeminal nerve targets may be used even with invisible trigeminal nerves using Meckel's cave as an anatomic marker.

Conclusions: Here we show the reproducible feasibility of a 2-session GKS procedure using higher radiation doses, the first dose to treat the tumor and the second to treat the trigeminal nerves using retrogasserian targeting.