Variant Inferior Alveolar Nerves and Implications for Local Anesthesia
A sound knowledge of anatomical variations that could be encountered during surgical procedures is helpful in avoiding surgical complications. The current article details anomalous morphology of inferior alveolar nerves encountered during routine dissection of the craniofacial region in the Gross Anatomy laboratory. We also report variations of the lingual nerves, associated with the inferior alveolar nerves. The variations were documented and a thorough review of literature was carried out. We focus on the variations themselves, and the clinical implications that these variations present. Thorough understanding of variant anatomy of the lingual and inferior alveolar nerves may determine the success of procedural anesthesia, the etiology of pathologic processes, and the avoidance of surgical misadventure.
Diagrammatic representation of the normal anatomy of the mandibular nerve in the infratemporal fossa. In the infratemporal fossa, the mandibular nerve (a) descends and gives off several branches. One of its branches, the inferior alveolar nerve (b), descends in the fossa, gives off the nerve to the mylohyoid (d), and enters the mandible through the mandibular foramen. Within the mandible, the nerve innervates the mandibular molars, second mandibular premolar and the associated labial gingivae, before dividing into 2 terminal branches, incisive and mental nerves. The lingual nerve (c) enters the oral cavity, carrying general sensation from soft tissue structures.
Photographs of dissected right and left infratemporal fossae. (a) The right infratemporal fossa shows the right lingual nerve traveling medially to enter the oral cavity and the right inferior alveolar nerve located laterally and entering the mandibular canal through the mandibular foramen. The nerve to mylohyoid is seen as a branch from the inferior alveolar nerve, as expected. White asterisks and arrows indicate the splitting of the inferior alveolar nerve around the maxillary artery. The white hashtag and arrow points to a nerve connecting the lingual and inferior alveolar nerves. (b) On the left side of the same donor body, dissection revealed a similar splitting of the left inferior alveolar nerve to surround the maxillary artery, indicated by white asterisks and arrows.
Photograph of dissected left infratemporal fossa. The left infratemporal fossa shows the mandible hemisected and turned over to expose the mandibular foramen with the left inferior alveolar nerve entering into the mandibular canal. The left lingual and inferior alveolar nerves show expected anatomy. A distinct nerve connects the lingual and inferior alveolar nerves, indicated by white asterisk and arrow.
Summary diagram indicating variant branching patterns of the inferior alveolar nerve. (a) The inferior alveolar nerve can split high in the infratemporal fossa and then reunite to enter the mandibular canal as a single nerve. (b) During its course in the infratemporal fossa, the inferior alveolar nerve may be connected via small nerve branches to the lingual nerve. (c) A single inferior alveolar nerve entering the mandibular canal may course through the mandible as 2 distinct branches. These branches may be located within a single mandibular canal, or within 2 independent mandibular canals. (d) A single inferior alveolar nerve entering the mandibular canal may course through the mandible as 3 distinct branches. (e) Variations of the inferior alveolar nerve within the mandible may be unilateral. (f) A unilateral presentation of the inferior alveolar nerve may include a bifid nerve entering the mandibular canal as 2 distinct nerves, and continuing to course through the mandible as independent nerves.
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