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

Abstract

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