Role of MR Neurography for the Diagnosis of Peripheral Trigeminal Nerve Injuries in Patients with Prior Molar Tooth Extraction

Abstract

Background and purpose: Clinical neurosensory testing is an imperfect reference standard to evaluate molar tooth extraction related peripheral trigeminal neuropathy. The purpose was to evaluate the diagnostic accuracy of MR neurography in this domain and correlation with neurosensory testing and surgery.

Materials and methods: In this retrospective study, nerve caliber, T2 signal intensity ratio, and contrast-to-noise ratios were recorded by 2 observers using MR neurography for bilateral branches of the peripheral trigeminal nerve, the inferior alveolar and lingual nerves. Patient demographics and correlation of the MR neurography findings with the Sunderland classification of nerve injury and intraoperative findings of surgical patients were obtained.

Results: Among 42 patients, the mean ± SD age for case and control patients were 35.8 ± 10.2 years and 43.2 ± 11.5 years, respectively, with male-to-female ratios of 1:1.4 and 1:5, respectively. Case subjects (peripheral trigeminal neuropathy or injury) had significantly larger differences in nerve thickness, T2 signal intensity ratio, and contrast-to-noise ratios than control patients for the inferior alveolar nerve and lingual nerve (P = .01 and .0001, .012 and .005, and .01 and .01, respectively). Receiver operating characteristic analysis showed a significant association among differences in nerve thickness, T2 signal intensity ratio, and contrast-to-noise ratios and nerve injury (area under the curve, 0.83-0.84 for the inferior alveolar nerve and 0.77-0.78 for the lingual nerve). Interobserver agreement was good for the inferior alveolar nerve (intraclass correlation coefficient, 0.70-0.79) and good to excellent for the lingual nerve (intraclass correlation coefficient, 0.75-0.85). MR neurography correlations with respect to clinical neurosensory testing and surgical classifications were moderate to good. Pearson correlation coefficients of 0.68 and 0.81 and κ of 0.60 and 0.77 were observed for differences in nerve thickness.

Conclusions: MR neurography can be reliably used for the diagnosis of injuries to the peripheral trigeminal nerve related to molar tooth extractions, with good to excellent correlation of imaging with clinical findings and surgical results.

Fig 1.

A, MIP coronal 3D PSIF image showing class II injury to the right IAN with mild increase in caliber (less than 50% of the left) and signal intensity of the right IAN (long arrow) in comparison with a normal left inferior alveolar nerve (short arrow). B, Sagittal reconstruction MIP 3D PSIF image showing increase in caliber and signal intensity of the right IAN (long arrow) proximal to injury site (arrowhead). C, Normal uniform caliber and signal intensity of the left IAN (short arrow).

Fig 2.

A and B, MIP 3D coronal PSIF images show a hyperintense left LN (long arrow) with a 3-mm neuroma in continuity (demarcated by 3 arrowheads) compatible with class IV injury. C and D, Sagittal reconstructions show the abnormal left LN neuroma (demarcated by 3 arrowheads) compared with a normal right LN (short arrow).

Fig 3.

Coronal 3D PSIF images showing A, localization of the site of the LN and IAN (short and long arrows, respectively) and B, signal intensity measurements on both sides.

Fig 4.

A, MIP 3D PSIF coronal image shows class IV/V injury of the left LN with excessive granulation and possible discontinuity of its distal end (long arrow). B, On surgery, it was also called class IV/V injury (arrow) with excessive scarring and granulation tissue and was resected. The final gap was 16 mm (C) and an allograft was placed for nerve reconstruction.

Fig 5.

κ correlations for A, MRN versus NST and B, MRN versus surgical classifications.

Fig 6.

Differences in thickness, T2SIR, and CNR among the case and control groups.

Fig 7.

ROC curves for A, IAN and B, LN.

Fig 8.

Correlations between differences in nerve thickness on MRN versus NST (A) and surgery (B).