MR APPEARANCE OF TRIGEMINAL AND HYPOGLOSSAL MOTOR DENERVATION

PURPOSE: To illustrate and describe the appearance of both long-standi ng and relatively recently occurring motor denervation of the hypoglos sal nerve and of the third (mandibular) division of the trigeminal ner ve (V3), with emphasis on findings particular to MR imaging. METHODS: Findings from 11 patients with V3 denervation and from seven patients with hypoglossal denervation resulting from a Variety of abnormalities were reviewed retrospectively. The motor denervation appearance and f unctional compromise of the affected musculature are described in term s of the chronicity of the denervation process. RESULTS: The appearanc e of V3 and hypoglossal motor denervation Varies with the chronicity o f the process. Long-standing denervation results in extensive fatty re placement and a decrease in the size of the affected musculature. Rela tively recently occurring denervation results in abnormal contrast enh ancement and edemalike signal changes in the denervated musculature, F atty replacement was observed acutely in hypoglossal denervation but d id not manifest until the subacute stage in V3 denervation. Increased volume of the denervated musculature may also accompany acute denervat ion signal changes. CONCLUSION: V3 and hypoglossal denervation have a variable appearance depending on the chronicity of the process. Recogn ition of MR imaging patterns of denervation may allow earlier diagnosi s of a denervating lesion and may help to distinguish denervation from similar-appearing processes, such as infection or neoplasia.