Evaluation of Inferior Alveolar Nerve Disorders by 3.0T MR Neurography

Background: Traumatic injury of the inferior alveolar nerve (IAN) is not unusual during dental practice, resulting in persistent sensory disorders in its distribution. Although magnetic resonance neurography (MRN) is an effective tool for diagnosing various peripheral nerve diseases, the technique is not much utilized for imaging orofacial nerves. Objective: To evaluate symptomatic sensory disorder of IAN non-invasively, using high resolution three dimensional volume rendering (3DVR) MRN techniques based on a 3.0T system. Methods: Nine patients who complained of persistent sensory disturbance attributed to unilateral IAN injury participated in the investigation. 3D data set was obtained with a T1-weighted fast spoil Gradient echo (FSPGR) sequence and fat suppression, using an 8ch Neurovascular phased-array coil. 3DVR with multi planar reconstruction was conducted as post-processing. Results: In eight out of nine patients (89%), 3DVR MRN revealed the specific pathology of IAN: Deformities of IAN (50%) and/or abnormal growth of connective tissue surrounding IAN (75%). Two cases had subsequent surgical confirmation. In one case, a typical fusiform-shaped neuroma was detected with 3DVR MRN, while in the other case, 3DVR MRN demonstrated connective tissue overgrowth. Conclusion: 3DVR MRN provided hitherto unobtainable information directly useful for clinical judgment. The success owes to the appropriate use of a higher field system and the adaptation of 3DVR technique for IAN analysis. The study unequivocally demonstrated that high-resolution 3DVR MRN on a 3.0T system is a powerful means for evaluating post-traumatic sensory disorders of the IAN.

Supported by grants from the Ministry of Education, Culture, Sports, Science and Technology (Japan) and University of Niigata.