Surgical “Safe Zone”: Rapid Anatomical Identification of the Lesser Occipital Nerve

Abstract

Background Surgical intervention has established a vital role in the management of chronic headaches. The lesser occipital nerve (LON) is a common target in patients suffering from occipital neuralgia and is often resected as a first-line option. We endeavored to define the relationships of the LON in the posterolateral neck to facilitate its safe and rapid intraoperative identification. Methods Seven fresh cadavers (14 nerves) were dissected, and their relationships to the mastoid prominence and nearby spinal accessory nerve (SAN) and greater auricular nerve were noted. Results The distance from the mastoid to the emergence of the LON along the posterior sternocleidomastoid ranged from 36 to 51 mm (mean: 45.2 mm), with relative symmetry between the two nerves in the same cadaver. The SAN emerged an average of 54 mm from the mastoid prominence. Conclusion Exploration for the LON should begin at a point 40 mm from the mastoid prominence along the posterior border of the sternocleidomastoid muscle. If the point of exit of the LON is not identified within 10 mm of this exposure, our dissection continues cranially along the posterior border of the sternocleidomastoid, anterior to the trapezius. In rare cases the nerve may pierce the fibers of the muscle and ascend directly on top of the muscle belly. By limiting the caudal extend of the dissection, we can avoid exposure of the SAN and minimize the risk of iatrogenic nerve injury.

The spinal accessory nerve and its entry point into the posterior triangle of the neck

“…There have been many attempts within the literature to describe the course of the spinal accessory nerve and to define its point of entry into the posterior triangle of the neck in relation to surrounding structures [8]. This includes distance from the clavicle [8,9], the mastoid process [3,4,8,11,12,23], the angle of the mandible [23], the greater auricular nerve [21] as well as, similar to this study, the distance along the posterior border of sternocleidomastoid from its superior insertion point [1,2,13,21,22].…”

Single midline incision approach for decompression of greater, lesser and third occipital nerves in migraine surgery

“…The great auricular nerve (GAN) and spinal accessory nerve (SAN) can be encountered in this area, but course differently than the LON. The GAN and SAN also emerge posterior to the SCM, but the GAN courses more anterior than the LON, while the SAN runs inferiorly and obliquely to the LON and varies in caliber from 1 to 4 mm in size [20][21][22]. Following the LON to the superior posterior occiput can help confirm its identity.…”

Peripheral Occipital Nerve Decompression Surgery in Migraine Headache

“…Research initially began to find a reason why patients were unresponsive or partially responding to surgery. 23 , 51 LON arises from C2 and/or C3 spinal nerves 52 with an exit point along the posterior border of the sternocleidomastoid muscle, 53 which does not seem to be a point of compression, whereas an intimate relationship between LON and OA (both as single interaction and as intertwinement) as well as with fascial bands are often present. A target zone for surgical release of LON has therefore been identified by Lee et al 54 The TON is the dorsal ramus of C3, its exit point is located closer to the midline than the previous two, but cadaver studies described a greater variability.…”