Post-traumatic Midface Pain: Clinical Significance of the Anterior Superior Alveolar Nerve and Canalis Sinuosus
Helen G. Hui-Chou, MD, J. Bryce Olenczak, MD; Demetrio J. Aguila III, MD; Catherine A. Shaeffer, MD; A. Lee Dellon, MD, PhD, and Paul N. Manson, MD
Johns Hopkins Hospital, Baltimore, MD
Purpose: Post-traumatic midface pain secondary to injury of the anterior superior alveolar nerve (ASAN) is characterized as pain localized to the central and lateral incisors, canines, and maxilla. This nerve is susceptible to injury and subsequent formation of neuromas following midface trauma. Surgical intervention requires an accurate and precise understanding of the course of the ASAN. Methods: Dissections of twelve human cadaver heads were conducted to identify the course of the ASAN through the canalis sinuosus (CS). Fifty random 1-mm slice maxillofacial CT scans were evaluated to document the radiographic dimensions and course of the CS. A case series of patients with midfacial pain had CT scans evaluated for injury pattern along the course of ASAN. Results: The ASAN branched laterally from the infraorbital nerve (ION) prior to reaching the infraorbital rim in all cadavers. The bifurcation occurred 18 mm posterior to the infraorbital rim (range 10-30 mm). The ASAN is found 3.4 mm lateral to the piriform aperture (range 3-4 mm) at a point 25 mm inferior to the infraorbital rim. The cadaveric study revealed that the ASAN is a single trunk instead of prior implications of a plexus across the midface. Radiographic analysis of normal CT scans of the midface demonstrated a 12.9 mm horizontal length of the CS across the antrum of the maxilla (standard deviation 2.2 mm), a distance of 4.8 mm between the piriform aperture and the CS (standard deviation 1.2 mm), and 11.7 mm vertical length of the CS along the piriform aperture (standard deviation 3.0 mm). All patients in the series had comminuted fractures of the midface and resultant obliteration of the canalis sinuosus and main infraorbital nerve. Conclusions: The ASAN maintains consistent coordinates at specific points along its course through the anterior maxillary bone. An improved understanding of the intraosseous course of the ASAN will guide future diagnosis of injury to this nerve and surgical intervention for patients with post-traumatic midface and incisor pain. Patients with midface fractures and nerve deficits including altered sensation or pain effecting the central incisors, lateral incisors and canines should be evaluated for injury to the ASAN. Thin slice maxillofacial CT scans may be utilized to evaluate for ASAN and CS injuries. Surgical interventions may be approached through the orbit, anterior maxilla or piriform aperture.
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