Effects of the Accessory Infraorbital Nerve and Foramen on the Morphology of the Infraorbital Nerve and Foramen

Abstract

Title: Effects of the accessory infraorbital nerve on the morphology of the infraorbital nerve and foramen Problem: Anatomical variations of the infraorbital neurovascular bundle are frequently encountered during a host of oral surgical procedures involving the infraorbital region. The accessory infraorbital foramen (AIOF) and its nerve (AION) are variable, but clinical implications are common and include failure of loco-regional anesthesia, risk of neural damage, or hemorrhage following surgical interventions particularly involving the infraorbital nerve (ION) and foramen (IOF). Thus, morphological characterization of the AIOF and AION and relationships to the IOF and ION are essential for optimizing oral surgical procedures. Additionally, predictive features of the AION based on its relationship to ION morphology could facilitate predictive capabilities enabling the surgeon to anticipate its presence and proceed accordingly Purpose: The purpose of this study is to determine whether the presence of an AION affects the size, shape and composition of the infraorbital foramen and nerve. The specific hypothesis tested is that the topography and morphology of the ION and IOF differs between individuals possessing an AION and those lacking this anatomical variant. Data will serve to determine the potential field of innervation of the ION with and without the presence of AION and identify potential morphological correlates between ION and AION features. Procedure: Gross topographic features of IOF (84 hemifaces) were compared between specimens possessing (test) or lacking (control) an AIOF. Nerve fascicle features of ION (60 cadaveric sides) were examined histologically and compared morphometrically between specimen with or without an AION. Results: Occurrence of AIOF was determined as 47.6% of the skulls (20 crania), but only 32.1% of the sides (27 sides). A single AIOF was observed in 24 sides and double AIOF in 3 sides. AIOF occurred bilaterally in seven specimens (16.7%). The majority of AIOF (86.7%) were located superomedial to IOF, but overall a heterogeneous direction of the canal leading to AIOF was noted. A higher frequency of AION was found in left side compared to the right. The number and area of nerve fascicles were determined histologically. The size of the ION without an AION was not significantly different than the ION with AION (1.45x106/1.32x106, p < 0.35). However, the number of ION fascicles was greater in specimens without and AION compared to those with an AION (15.15/12.71, p <0.04) Conclusions: The data indicate that the area of the ION is not affected by an AION, suggesting that the field of innervation of this area will not be modified However the ION appears to divide more proxima in the cases when the AION is present.