Atrophic changes in the trigeminal nerves of patients with trigeminal neuralgia due to neurovascular compression and their association with the severity of compression and clinical outcomes

Abstract

S trong evidence suggests that in classic trigeminal neuralgia (TN) caused by neurovascular compression (NVC), the neuralgia is related to morphological and structural changes in the trigeminal nerve (TGN) that are probably the result of chronic vascular compression. Morphological changes in the nerve include nerve deviation, distortion, groove formation, and atrophy. 5 Atrophy of the nerve is seen in most cases of TN 20 and is probably attributable to structural abnormalities such as axonal loss and demyelination, 4,10,12,18 but these morphological changes are difficult to describe objectively. Object. The aim of this study was to prospectively evaluate atrophic changes in trigeminal nerves (TGNs) using measurements of volume (V) and cross-sectional area (CSA) from high-resolution 3-T MR images obtained in patients with unilateral trigeminal neuralgia (TN), and to correlate these data with patient and neurovascular compression (NVC) characteristics and with clinical outcomes.Methods. Anatomical TGN parameters (V and CSA) were obtained in 50 patients (30 women and 20 men; mean age 56.42 years, range 22-79 years) with classic TN before treatment with microvascular decompression (MVD). Parameters were compared between the symptomatic (ipsilateralTN) and asymptomatic (contralateralTN) sides of the face. Twenty normal control subjects were also included. Two independent observers blinded to the side of pain separately analyzed the images. Measurements of V (from the pons to the entrance of the nerve into Meckel's cave) and CSA (at 5 mm from the entry of the TGN into the pons) for each TGN were performed using imaging software and axial and coronal projections, respectively. These data were correlated with patient characteristics (age, duration of symptoms before MVD, side of pain, sex, and area of pain distribution), NVC characteristics (type of vessel involved in NVC, location of compression along the nerve, site of compression around the circumference of the root, and degree of compression), and clinical outcomes at the 2-year follow-up after surgery. Comparisons were made using Bonferroni's test. Interobserver variability was assessed using the Pearson correlation coefficient.Results. The mean V of the TGN on the ipsilateralTN (60.35 ± 21.74 mm 3 ) was significantly smaller (p < 0.05) than those for the contralateralTN and controls (78.62 ± 24.62 mm 3 and 89.09 ± 14.72 mm 3 , respectively). The mean CSA of the TGN on the ipsilateralTN (4.17 ± 1.74 mm 2 ) was significantly smaller than those for the contralateralTN and controls (5.41 ± 1.89 mm 2 and 5.64 ± 0.85 mm 2 , respectively). The ipsilateralTN with NVC Grade III (marked indentation) had a significantly smaller mean V than the ipsilateralTN with NVC Grade I (mere contact), although it was not significantly smaller than that of the ipsilateralTN with NVC Grade II (displacement or distortion of root). The ipsilateralTN with NVC Grade III had a significantly smaller mean CSA than the ipsilateralTN with NVC Grades I and II (p < 0.05). The TGN on the ipsilateralT...

Degree of distal trigeminal nerve atrophy predicts outcome after microvascular decompression for Type 1a trigeminal neuralgia

“…Another recent study, by Leal and colleagues, evaluated 50 patients with unilateral idiopathic TN to determine if there is a relationship among the characteristics of symptoms, NVC, and clinical outcomes after MVD. 10 They demonstrated that greater atrophy at the trigeminal root entry zone was associated with more severe vascular compression and significantly better clinical outcome, which is consistent with our observation that atrophy in the proximal nerve near the root entry zone is associated with a trend toward better outcome. However, that study did not evaluate the nerve along its entire course but only measured the midcisternal segment.…”

“…Our data suggest that the story may be a bit more complex: Atrophy of the nerve in the cistern seems to be associated with better prognosis, possibly due to its correlation with vascular compression, but more distal atrophy (i.e., away from the site of vascular compression) might represent a poor prognosis, possibly due to intrinsic changes in the nerve. 10 As such, we have been able to distinguish 2 types of trigeminal nerve atrophy with different implications for outcome after MVD.…”

“…viduals. 4,5,7,9,10,17 In a retrospective study of 30 patients with idiopathic TN, Ha and colleagues demonstrated that, on preoperative FIESTA MRI, there was significantly more atrophy at the cisternal segment of the trigeminal nerve on the affected side than on the unaffected side compared with the affected and unaffected sides of age-and sexmatched control patients with hemifacial spasm. 5 Of note, these authors also found a significant association between the sharpness of the trigeminal-pontine angle on the affected side compared with the unaffected side, which was not found in the control group.…”

“…8,10,13,21 Structural changes in the trigeminal nerve, leading to volume loss, have been well documented, 3,6,12 and a number of studies have demonstrated that nerve atrophy ipsilateral to the symptomatic side is visible on preoperative MRI. 1,4,5,7,9,15,17 Recently, Leal et al demonstrated that atrophy in the midcisternal region of the nerve is associated with more severe vascular compression, and these patients tend to exhibit greater clinical improvement following surgical decompression of the nerve.…”

“…1,4,5,7,9,15,17 Recently, Leal et al demonstrated that atrophy in the midcisternal region of the nerve is associated with more severe vascular compression, and these patients tend to exhibit greater clinical improvement following surgical decompression of the nerve. 10 However, it is unclear whether the nerve atrophy is entirely due to physical compaction by the compressing vessel or whether it is due, in part, to irreversible structural changes. DistinabbreviatioNs MVD = microvascular decompression; NVC = neurovascular conflict; TN = trigeminal neuralgia.…”