Does Presurgical MRN Predict Neuroma and Surgical Gap Size in Peripheral Trigeminal Nerve Injuries?
John R Zuniga, DMD, MS, PhD, Omar abdelBaky, DDS MD, Yin Xi, MD and Avneesh Chhabra, MD, University of Texas Southwestern, Dallas, TX
Magnetic Resonance Neurography (MRN) findings associated with Sunderland Class IV and V injuries of the peripheral trigeminal nerve exhibit excellent correlation with intraoperative findings and good inter-read reliability in identifying neuromas and abnormal nerve structure. It is not known how well the MRN determined size of abnormal nerve and neuroma correlate with final nerve gap to be grafted. We tested the hypothesis that presurgical MRN correlates with neuroma size and the final surgical gap size.
We performed a retrospective, single-blinded, non-randomized cohort study on 43 patients. All had Sunderland Class IV and V injuries of the Inferior Alveolar (IAN) or the Lingual Nerve (LN). The MRN maxillofacial protocol was performed on a 3T scanner which included 2D and 3D anatomic and diffusion imaging sequences. MRNs were read by two fellowship-trained musculoskeletal radiologists to determine the maximum size of neuroma and the abnormal nerve segment in two dimensions. Two independent variables were recorded from the surgical procedures: 1. the length of the neuroma; and 2. the length of the gap size created. The maximum length of the neuroma was also recorded from the histopathology reports.
There were 7 IAN and 36 LN cases analyzed. The mean time in months from injury to MRN was 6.97±9.18, range 1 to 51, median was 4. The mean interval time from MRN to surgery was 1.21 ± 1.4, 0 to 7, median of 1 month. The mean length of the neuromas at the time of surgery was 7.22 ± 2.78 mm, range 2-12, median size was 7mm. The mean greatest dimension in histologic evaluation was 10.65 ± 5.05 mm, range 3 to 22 with median of 12mm. The mean gap size was 12.02 ± 4.41 mm, range 3 to 22 mm, median was 12mm. ICC agreement was fair for abnormal nerve thickness and neuroma length (0.28, 0.39) while it was moderate for neuroma thickness and abnormal nerve length (0.50, 0.59). There was no significant correlation between MRN based measurements and surgical gap size (p>0.05).
Abnormal nerve and neuromas of the peripheral trigeminal nerve are easily identified on MRN imaging but there is no correlation of abnormal nerve segment or neuroma with the final size gap after the removal of neuroma. Although findings may be confounded by a small sample size of the study, MRN detected size of abnormal nerve or neuroma cannot be used for pre-surgical planning for determining the graft size.
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