EXTRACRANIAL NERVES IN THE POSTERIOR PART OF THE HEAD - ANATOMIC VARIATIONS AND THEIR POSSIBLE CLINICAL-SIGNIFICANCE

Study Design. An anatomic study of the peripheral nerves innervating t he occipital region. Objectives. To study the topography of the extrac ranial occipital nerves, to define optimal locations for anesthetic ne rve blockades, to provide guidelines to use with the suboccipital surg ical approach, and to search for structures with putative pathogenetic implications in cases of unilateral headache. Summary of Background D ata. There is little consensus in the literature concerning the sensor y innervation of the scalp. Previous clinical and morphologic studies have not proven the existence of an entrapment mechanism in cases of u nilateral head pain. Specific sites for anesthetic blockades have been defined only partly with reference to topographic landmarks. Methods. The topography of the greater occipital (n = 20), the minor occipital (n = 19), and the greater auricular nerves (n = 17) was studied by di ssection of 10 embalmed cadavers. Measurements of internerve distances and distances to defined landmarks were supplemented by drawings and photographs. Results. A great variability in nerve topography was seen interindividually and intraindividually. The greater occipital nerve ascended between 5 mm and 28 mm from the midline along the intermastoi d line. The minor occipital nerve was found between 32 mm and 90 mm fr om the midline along the same landmark. In most cases, both the greate r occipital nerve and the minor occipital nerve pierced the aponeurosi s after branching. Thirteen greater occipital nerves and eight minor o ccipital nerves also were embedded in this tissue. Twelve of the 20 gr eater occipital nerves formed a rich network around the occipital arte ry. However, anatomic structures with an imminent risk of causing entr apment were not observed. Conclusion. The results of this study sugges t that optimal locations for blockade techniques should be reconsidere d. The acquired knowledge concerning greater auricular and minor occip ital nerves behind the sternocleidomastoid muscle may aid in preventin g intraoperative injuries.