Supraorbital nerve exits: positional variations and localization relative to surgical landmarks

Significant variations exist in the occurrence, form, and position of supraorbital nerve exits through the frontal bone. Detailed knowledge of the positional variations of supraorbital exits is important to ensure safe and successful regional anesthesia, and to avoid iatrogenic nerve injuries during surgery of the orbitofacial region. Supraorbital nerve exits from 116 sides of 58 dry intact adult skulls (37 male and 21 female) in a Sri Lankan population were examined to determine the morphological features and the precise position in relation to the facial midline, temporal crest of frontal bone, and frontozygomatic suture. A majority of supraorbital nerve exits existed as notches (73.8%) and the rest as foramina (26.2%). Accessory exits were seen in 18.9% skulls. Of the skulls examined, 55.1% displayed bilateral supraorbital notches, 8.6% had bilateral supraorbital foramina, and 36.3% had a notch on one side and a foramen on the contralateral side. In males, the supraorbital nerve exit was located $23.64{\pm}3.49mm$ laterally from the facial midline, $27.86{\pm}2.76mm$ medially from the temporal crest of the frontal bone, $28.66{\pm}2.56mm$ from the frontozygomatic suture, and $2.12{\pm}1.07mm$ above the supraorbital margin in the case of a foramen, and in females $22.69{\pm}3.28mm$ laterally from the facial midline, $26.32{\pm}3.02$ medially from temporal crest of frontal bone, $27.29{\pm}3.05$ from the frontozygomatic suture, and $2.99{\pm}1.49mm$ above the supraorbital margin when it existed as a foramen. The observations made in this study will be useful when planning a supraorbital nerve block and surgery in the supraorbital region.