Nerve Atrophy and a Small Trigeminal Pontine Angle in Primary Trigeminal Neuralgia: A Morphometric Magnetic Resonance Imaging Study.

OBJECTIVE: To prospectively evaluate the morphological and structural changes in the trigeminal nerve in patients with trigeminal neuralgia (TN) compared with healthy controls.

METHODS: We conducted a prospective case-control study of 60 consecutive patients diagnosed with TN and 30 sex-and age-matched healthy controls. All subjects underwent high-resolution 3-dimensional magnetic resonance imaging (MRI). The volume and length of the cisternal segment of the trigeminal nerve and the angle between the trigeminal nerve and the anterior surface of the pons (trigeminal pontine angle) were measured and compared.

RESULTS: The mean volume of the affected trigeminal nerve was significantly reduced compared with that of the nonaffected side (65.8 ± 21.1 mm3 vs. 77.9 ± 19.3 mm3 ; P = 0.001) and controls (65.8 ± 21.1 mm3 vs. 74.7 ± 16.5 mm3 ; P = 0.003). The mean trigeminal pontine angle was 42.4 ± 8.7° on the affected side, 47.6 ± 9.2° on the nonaffected side, and 46.0 ± 7.2° in the controls. The trigeminal pontine angle on the affected side was significantly smaller than that on the nonaffected side (P = 0.005) and in controls (P = 0.01). There the was no statistically significant difference in the mean length of the cisternal segment of trigeminal nerve between the affected and nonaffected sides (P = 0.46).

CONCLUSIONS: TN is associated with atrophy and a small trigeminal pontine angle in the affected nerve. Nerve atrophy may be a late consequence of chronic physical stress and is likely involved in the pathogenesis of TN. A small trigeminal pontine angle may increase the risk of neurovascular conflict, and thus more likely to result in the genesis of TN.