Castillo-Rebolledo, Daniela; Riveros, Andrés; Sousa-Rodrigues, Celio Fernando & Olave, Enrique

The great occipital nerve (GON) is formed from the dorsal branch of the C2 spinal nerve and ascends between the posterior cervical musculature to innervate the skin of the scalp. Various authors have described its course, however, there is little information regarding the relationship that this nerve presents with the obliquus capitis inferior (OCI) and its intramuscular path. The objective of this study was to determine the route and relationships that the GON established in the interval between the OCI muscles and the trapezius muscle (T). For this, the vertical and horizontal distances were measured at the height of the external occipital protuberance and median line, and the OCI muscle was divided into thirds to observe variations in the path of this nerve. Along with measuring the diameter of the GON, the vertical and horizon- tal distances of this nerve were measured through five muscle reference points and one vascular reference point. These muscle points were: a) on the belly of the OCI muscle (point 1); b) in the deep face of the semispinalis capitis muscle (SCM) (point 2); c) on the surface of the SCM (point 3); d) on the deep face of the T (point 4); and e) on the surface face of the T (point 5). To this was added point 6, in which the vertical and horizontal distances were established with the occipital artery at the height of the superficial face of the T. For this, 18 heads (36 suboccipital triangles) of Brazilian adult corpses belonging to the Anatomy laboratory of the Universidade Federal de Alagoas (UFAL), Maceió, Brazil, were dissected. The vertical and horizontal distances obtained with respect to the six points were: 63.67 and 27.15 mm (point 1); 53.89 and 21.44 mm (point 2); 30.61 and 14.49 mm (point 3); 20.39 and 22.8 mm (point 4); 5.86 and 33.46 mm (point 5); 5.99 and 35.56 mm (point 6), respectively. In relation to the OCI, the GON was located in 72.22 % of the samples in the middle third of this muscle, 19.44 % in its lateral third and 8.33 % in its medial third. All these findings should be considered when correctly diagnosing possible entrapments of GON in the deep cervical region, being a contribution to the success of surgical procedures in this region.

KEY WORDS: Anatomy; Innervation; Great Occipital Nerve; Obliquus Capitis Inferior; Suboccipital triangle; Anatomical Variations.

CASTILLO-REBOLLEDO, D. ; RIVEROS, A.; SOUSA- RODRIGUES, C. F. & OLAVE, E. Great occipital nerve: Course, anatomical relations and clinical implications of their potential entrapment sites. Int. J. Morphol., 38(4):1235-1243, 2020.