Atrophy of the tongue following complete versus partial hypoglossal nerve transection in a canine model

OBJECTIVES/HYPOTHESIS: The hypoglossal nerve (XII) has been used as a donor nerve in facial and laryngeal reinnervation. The purpose of this study was to investigate the neuromuscular changes that occur within the tongue following partial or complete transection of XII using a canine model. STUDY DESIGN: Histopathological comparison of tongue denervation following two types of XII resection in a canine model. METHODS: Ten adult canines underwent complete unilateral resection of XII or resection of only the medial terminal branch of the hypoglossal nerve (mXII). After 6 months of recovery, tongue specimens were analyzed histopathologically using whole cross-sections. Routine histologic sections were assessed by two neuropathologists blinded to the type of denervation. The cross-sectional area was calculated of both sides of the tongue, and the amount of myosin was quantified morphometrically using immunohistochemistry for myosin (antimyosin heavy chain, fast isotype). Statistical comparison between partial and complete denervation was performed using the Student t test. RESULTS: Six months following XII transection, quantitative measures of the cross-sectional area of the tongue and content of myosin demonstrated severe muscle atrophy on the operated side of the tongue for both groups, compared to the nonoperated side. For partial transection involving only mXII, the degree of atrophy was less severe (P < .05). CONCLUSIONS: This study provides new histological information demonstrating that partial resection of the hypoglossal nerve, sacrificing only the proximal medial branch of the hypoglossal nerve (mXII), results in less severe atrophy of the tongue than complete transection of the entire hypoglossal nerve. LEVEL OF EVIDENCE: NA Laryngoscope, 126:2689-2693, 2016.