Topographic and morphometric anatomy of the greater occipital nerve

Knowledge of complex anatomy of greater occipital nerve is crucial for its decompression surgery and blockade. Consequently, this study was performed to investigate anatomical variations of the nerve in detail. Forty-one cadavers were dissected bilaterally. According to its morphologic properties, greater occipital nerve was classified into 4 main categories that included 15 subtypes. Potential compression points of the nerve were defined. The triangle located between emergence points of greater occipital nerve, lesser occipital nerve, and third occipital nerve was identified. Considering external occipital protuberance, measurements were carried out using ImageJ software. Type 2 (61 sides, 74.4%) was the most frequent one among main types while Type 2-A (44 sides, 53.6%) was determined to be the most frequent subtype. In addition to first potential compression point where greater occipital nerve and occipital artery cross each other, the second and third new potential compression points were observed. The vertical distances between second and third entrapment points and the vertical line that passes from external occipital protuberance were meanly 42.13±3,91mm and 46,74±8,72mm, respectively. Similarly, the vertical distances between second and third entrapment points, and the transverse line that passes from external occipital protuberance were meanly 7.36±7,94mm and 13.43±10.40mm, respectively. The area of triangle was measured meanly as 952.82±313.36mm² in male 667.55±273.82mm² in female, and there was a statistically significant difference between sexes (p=0.002). The novel anatomical findings described in this study may play a significant role for increasing the success rate of invasive interventions of greater occipital nerve and reducing the related complications. Key words: Greater occipital nerve, headache, blokage, decompression surgery, occipital artery