VASCULAR CONTACT WITH THE 5TH CRANIAL NERVE AT THE PENS IN PATIENTS WITH TRIGEMINAL NEURALGIA - DETECTION WITH 3D FISP IMAGING

OBJECTIVE. Vascular contact with the trigeminal nerve at the pens is k nown to cause trigeminal neuralgia; however, this finding also is pres ent in some asymptomatic subjects. We evaluated the usefulness of high -resolution MR imaging and MR angiography of the posterior fossa to de termine the presence or absence of vascular contact with the fifth cra nial nerve at the pens in patients with trigeminal neuralgia and in co ntrol subjects. SUBJECTS AND METHODS. The trigeminal nerves in 40 symp tomatic patients and 114 asymptomatic control subjects were examined f or the presence or absence of vascular contact at the pens by using th ree dimension (3D) fast inflow with steady-state precession (FISP) ima ging. Imaging parameters were 35/7/15 degrees (TR/TE/flip angle) with a slab thickness of 55 mm and 64 partitions. Contrast-enhanced imaging was done in 10 of 12 patients with normal findings on an unenhanced s can. Axial, coronal, sagittal, and maximum-intensity-projection images were reviewed by two observers who had no knowledge of the clinical d etails. The findings on MR images were prospectively compared with the surgical findings in 25 patients. RESULTS. On the unenhanced MR image s, vascular contact with the trigeminal nerve at the pens was identifi ed in 70% of 40 nerves in patients with trigeminal neuralgia and in a further 15% following injection of contrast medium. Contact between th e nerve and two vessels at the pens was seen in 10% of cases, and defo rmity of the nerve was present in 30% of cases. In the control group, vascular contact with the nerve was identified in 8% of 114 nerves. Co ntact between the nerve and two vessels or deformity of the nerve was not identified in any control subject. The difference between the two groups was highly significant regarding the presence or absence of vas cular contact with the nerve at the pens (p < .001, x(2) test), distor tion of the nerve (p < .001), and contact between the nerve and two ve ssels (p < .001). The imaging findings were in agreement with the surg ical findings regarding the presence or absence of vascular contact wi th the nerve in all 25 patients who had surgery. Complete or partial p ain relief was achieved following microvascular decompression in all p atients who had surgery. CONCLUSION. Despite the fact that vascular co ntact with the trigeminal nerve at the pons is not specific for trigem inal neuralgia, high-definition unenhanced and enhanced 30 FISP imagin g and MR angiography of the posterior fossa are useful in determining the presence or absence of vascular contact with, or deformity of, the fifth cranial nerve in patients for whom surgery is planned for treat ment of trigeminal neuralgia.