Computed tomography-guided γ knife stereotactic radiosurgery for trigeminal neuralgia

Gamma knife stereotactic radiosurgery (GKSR) is an effective minimally invasive option for the treatment of medically refractory trigeminal neuralgia (TN). Optimal targeting of the retrogasserian trigeminal nerve target requires thin-slice, high-definition stereotactic magnetic resonance imaging (MRI). The purpose of this study was to evaluate management outcomes in TN patients ineligible for MRI and who instead underwent GKSR using computed tomography (CT).

The authors reviewed their experience with CT-guided GKSR in 21 patients (median age: 75 years) with idiopathic TN. Contraindications to MRI included implanted pacemakers (n = 16), aneurysm clips (n = 2), cochlea implants (n = 1), metallic vascular stents (n = 1) or severe obesity (weight of 163 kg, n = 1). Contrast-enhanced CT at 1- or 1.25-mm intervals was acquired in all patients. One patient also underwent CT cisternography. The median target dose for GKSR was 80 Gy. The median follow-up was 35 months after GKSR. Treatment outcomes were compared to 459 patients who underwent MRI-guided GKSR for TN at our institute in the same time interval.

Targeting of the trigeminal nerve guided by CT scan was feasible in all patients. Stereotactic frame titanium pin-related artifacts that interfered with full visualization of the trigeminal nerve were found in one patient who had the ipsilateral posterior pin placed near the inion. After GKSR, 90% of patients achieved initial pain relief that was adequate or better, with or without medication (Barrow Neurological Institute pain scores I-IIIb). Median time to pain relief was 2.6 weeks. Pain relief was maintained in 81% at 1 year, 66% at 2 years, and 46% at 5 years. Eight (42%) of 19 patients who achieved initial pain relief reported some recurrent pain at a median of 18 months after GKSR. Some degree of facial sensory dysfunction occurred in 19% of patients within 24 months of GKSR. These results are comparable to those of patients who had MRI-guided GKSR.

CT-guided GKSR provides a similar rate of pain relief as MRI-guided radiosurgery. The posterior pins should be placed at least 1 cm away from the inion to reduce pin and frame-related artifacts on the targeting CT scan. This study indicates that GKSR using CT targeting is appropriate for patients with medically refractory TN who are unsuitable for MRI.