Imaging the trigeminal nerve and pons before and after surgical intervention for trigeminal neuralgia

OBJECTIVE: To study the various imaging changes occurring in the trigeminal nerve and brainstem in patients before or after trigeminal neuralgia surgery. METHODS: During a 7-year period, 275 patients with trigeminal neuralgia underwent high-resolution, contrast-enhanced magnetic resonance imaging (MRI) of the pens during gamma knife radiosurgery. Ninety-seven patients had no previous surgical intervention for trigeminal neuralgia, and 178 patients had undergone one or move previous procedures. Two independent observers, one of whom was blinded to patients' clinical details, reviewed MRI scans retrospectively. The analysis of the independent observers was then correlated with all previous therapeutic interventions. RESULTS: One hundred one MRI scans demonstrated no radiological changes related to trigeminal neuralgia, and 174 MRI scans exhibited some radiological abnormality. The average axial plane diameter of the nerve for all patients was 4 mm (range, 2-6 mm). In the group that had not undergone previous surgery, 65 patients (67%) exhibited vascular compression. In the 88 patients who had undergone previous microvascular decompression, 21 (24%) had evidence of a pontine infarction. Twenty-six patients experienced facial sensory loss, 22 (88%) of whom had undergone previous surgery with evidence of a pontine infarction (n = 11) or perineural scarring (n = 6). CONCLUSION: The majority of patients who had undergone previous trigeminal neuralgia surgery demonstrated readily identifiable abnormalities of the trigeminal nerve or brainstem. The frequency of such changes correlated with the type and number of procedures. Evidence of vascular compression was detected in the majority of patients. Most patients with postoperative facial sensory loss demonstrate changes in the nerve or pens on MR images.