Vascular contact with the fifth cranial nerve at the pons in patients with trigeminal neuralgia: detection with 3D FISP imaging.

Objective: Vascular contact with the trigeminal nerve at the pons is known to cause trigeminal neuralgia; however, this finding also is present in some asymptomatic subjects. We evaluated the usefulness of high-resolution MR imaging and MR angiography of the posterior fossa to determine the presence or absence of vascular contact with the fifth cranial nerve at the pons in patients with trigeminal neuralgia and in control subjects.
Subjects and Methods: The trigeminal nerves in 40 symptomatic patients and 114 asymptomatic control subjects were examined for the presence or absence of vascular contact at the pons by using three dimension (3D) fast inflow with steady-state precession (FISP) imaging. 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 scan. Axial, coronal, sagittal, and maximum-intensity-projection images were reviewed by two observers who had no knowledge of the clinical details. The findings on MR images were prospectively compared with the surgical findings in 25 patients.
Results: On the unenhanced MR images, vascular contact with the trigeminal nerve at the pons was identified in 70% of 40 nerves in patients with trigeminal neuralgia and in a further 15% following injection of contrast medium. Contact between the nerve and two vessels at the pons was seen in 10% of cases, and deformity 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. Contact 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 vascular contact with the nerve at the pons (p < 0.001, x2 test), distortion of the nerve (p < .001), and contact between the nerve and two vessels (p < .001). The imaging findings were in agreement with the surgical findings regarding the presence or absence of vascular contact with the nerve in all 25 patients who had surgery. Complete or partial pain relief was achieved following microvascular decompression in all patients who had surgery.
Conclusion: Despite the fact that vascular contact with the trigeminal nerve at the pons is not specific for trigeminal neuralgia, high-definition unenhanced and enhanced 3D FISP imaging and MR angiography at 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 treatment of trigeminal neuralgia.