Gamma knife surgery for trigeminal neuralgia: outcome, imaging, and brainstem correlates

To review our results with gamma knife surgery (GKS) in the treatment of trigeminal neuralgia (TN), and to determine whether pain relief, medication usage, and the development of facial numbness are affected by trigeminal nerve compression, MRI imaging quality, or brainstem radiation dose.

One hundred twelve patients with TN refractory to medical or surgical management were treated at the University of Maryland Gamma Knife Center between June 1996 and July 2001. Patients were treated using a 4-mm shot to the trigeminal nerve, at a point 2-4 mm anterior to the root entry zone of the nerve into the pons. The median dose prescribed was 75 Gy (range, 60-80 Gy). T1- and T2-weighted, axial, 1.5-mm-thick MRI images were obtained using three-dimensional gradient echo acquisition after contrast injection for treatment planning. MRI images were evaluated for imaging quality (i.e., the adequacy of visualization of the affected prepontine trigeminal nerve), the presence of trigeminal nerve compression, and the brainstem dose. Follow-up data were obtained via telephone interviews, and patients were asked to rate their pre-GKS and post-GKS pain using the Barrow Neurological Institute (BNI) Pain Intensity Scale. Patients were also asked about side effects from GKS and were asked to rate any facial numbness on the BNI Facial Numbness Scale. Medication use, time to pain response, and duration of relief were also evaluated.

Ninety-six patients who had follow-up data were included in the analysis. Eighty-six patients (89.6%) responded to GKS with an improvement in BNI pain class. Ten patients (10.4%) were found to have an MRI of poor quality, 30 (31.3%) fair quality, and 56 (58.3%) good quality. Forty-two (43.8%) received 10% of the maximal dose to the brainstem edge, whereas 54 (56.2%) received 20%. Eleven (11.5%) patients were found to have obvious nerve compression by MRI. Imaging quality (p = 0.1863), presence of compression (p = 0.1147), and brainstem dose (p = 0.3168) did not correlate with treatment response. There was also no correlation between these variables (MRI quality, compression, and brainstem dose) and medication use (p = 0.5372, p = 0.0913, p = 0.6832, respectively). Facial numbness was the only side effect experienced. Thirteen patients reported varying degrees of facial numbness, but there was no correlation between imaging quality (p = 0.0600), brainstem dose (p = 0.6773), and presence of compression (p = 0.5785) with the development of facial numbness.

Gamma knife surgery is effective in the treatment of TN and has a favorable side effect profile. Treatment response and the development of facial numbness do not correlate with MRI imaging quality, presence of nerve compression, or radiation dose to the brainstem.