The importance of the greater occipital nerve in the occipital and the suboccipital region for nerve blockade and surgical approaches--an anatomic study on cadavers.

Objective: Greater occipital nerve (GON) blockade is an effective method for treatment of occipital neuralgias. Occipital neuralgia or neuropraxis of this region may be seen particularly as a result of compression of the GON. This study shows the relationship between the GON and its external bone landmarks, in order to prevent complications and to perform nerve blockades safely. The study also defines the points where the GON pierces the semispinalis capitis (SSC) and the trapezius, and where the GON passes the obliquus capitis inferior (OCI), and identifies bone landmarks for places where the GON may be entrapped.

Materials And Methods: In the laboratories of Dokuz Eylül University, Faculty of Medicine Department of Anatomy, 12 GON's belonging to male adult cadavers fixed in formaldehyde were dissected. Colored silicone was injected to all cadavers and then microdissections were performed under a dissection microscope. The lesser occipital nerve, the GON, the greater auricular nerve, and the occipital artery (OA) were dissected. All measurements were made with a 0.1mm sensitive calipometer.

Results: The GON's diameter at the point where the GON pierces the SSC was found to be 2.5±0.3 mm. The distance between the point where the GON pierces the SSC and the external occipital protuberance (EOP) was 53.6±5.0 mm. The distance between this point and the midline was 9.0±1.9 mm, the distance between this point and the intermastoid line was 11.5±3.9 mm and the distance between this point and the mastoid process was 65.5±5.9 mm. The distance between the midline and the point where the GON pierces the aponeurosis of trapezius (AT) was 47.9±8.0 mm, the distance between this point and the EOP was 15.1±7.0 mm, the distance between this point and the intermastoid line was 17.1±2.8 mm, and the distance between this point and the mastoid process was 59.4±2.3 mm. We measured the distance between the OA and the intermastoid line to be 8.5±6.1 mm vertically and 32.3±3.9 mm horizontally to the midline.

Conclusion: In this study, we define the GON's route in the suboccipital and the occipital region where the nerve pierces the SSC and the AT and where blockade or surgery can be performed. These data will help the surgeon and clinician to avoid complications in this region.