Evaluation of trigeminal neurovascular compression in patients with trigeminal neuralgia with 3.0 T MRI

Objective: To identify anatomical characteristics of neurovascular compression associated with trigeminal neuralgia (TN). Methods: Fifty patients with TN (23 of 50 patients underwent microvascular decompression) and 50 patients without facial pain underwent 3.0 T MRI scanning for analysis of 50 trigeminal nerves ipsilateral to TN symptoms, 50 contralateral to TN symptoms, and 100 in asymptomatic patients. MRI sequences included balanced fast-field echo and 3D MR angiography. Images were fused and reconstructed into virtual cisternoscopy images to determine the degree (severity of compression was defined as follows: 1=no compression; 2 =compressed by a vein; 3 =contacted by an artery; 4 =indented by an artery; and 5 =nerve displaced or distorted by an artery) and site of neurovascular compression (the point of each offending vascular structure: proximal was defined as located in 1/3 length of the cisternal segment of the trigeminal nerve near root entry zone; the place of superior was defined as above the cisternal segment of the trigeminal nerve). Reconstructed MPR images were used to measure nerve length and cross sectional area. The chi-square test was used for all 2 × 2 contingency tables. The t-test was used for dependent samples. The Logistic regression was used for prediction of occurrence of the event of TN. Results: Twenty-three of 50 patients with TN underwent microvascular decompression, which confirmed predicted neurovascular relationships in all cases, and 21 of 23 patients were pain free after the operation. The incidence of neurovascular compression on asymptomatic nerves (no. of level 1=79, level 2=5, level 3 =8, level 4 =8), on nerves contralateral to TN symptoms (no. of level 1=27, level 2 =6, level 3 =9, level 4 =8), and on nerves ipsilateral to TN symptoms (no. of level 1=4, level 2 =12, level 3 =12, level 4 =7, level 5 =15) was 21.0% (21/100), 46.0% (23/50), and 92.0% (46/50), respectively. The difference between symptomatic and asymptomatic nerves was significant regarding nerve distortion (level 4 and 5, χ² =27.0, P<0.01), the point of compression (no. of proximal of symptomatic nerves =32, not proximal of symptomatic nerves =14, proximal of asymptomatic nerves =4, not proximal of asymptomatic nerves =17, χ² =14.8, P<0.01), the place of vascular compression (no. of superior of symptomatic nerves =36, not superior of symptomatic nerves =10, superior of asymptomatic nerves =5, not superior of asymptomatic nerves =16, χ² =18.0, P<0.01) and the mean cross-sectional area of the CPA cistern [ipsilateral: (183.9±52.5) mm², contralateral: (217.8±58.8)mm², t=-3.04, P<0.01]. Decreased nerve size was observed in patients with TN [the section area of ipsilateral nerve (6.3 ±1.3) mm², contralateral (7.7±1.6) mm², t=-4.80, P<0.01; length of ipsilateral nerve: (8.0 ±1.9) mm, contralateral: (9.0±2.0) mm, t=-2.64, P<0.05]. Conclusions: Trigeminal neurovascular compression can occur in asymptomatic patients, but is more severe, more proximal, more superior and with smaller size of cross-sectional area of the CPA cistern in patients with TN. This information may help identify patients who are likely to benefit from microvascular decompression. (authors)