Layered anatomy of the greater and lesser occipital nerves with photogrammetry-based three-dimensional models: a cadaveric study

The superficial neurovascular anatomy of the posterior occipital region is important for occipital nerve block, greater occipital nerve (GON) decompression, and posterior fossa incision planning. However, the continuous layered relationship between the medial GON-occipital artery (OA) region and the lateral lesser occipital nerve (LON) channel remains incompletely characterized.

This cadaveric study examined 10 formalin-fixed specimens (20 sides). Layer-by-layer dissection documented nerve courses, emergence points, diameters, terminal branches, neurovascular relationships, GON-LON communications, and relationships with the OA and adjacent muscles. Photogrammetry-based three-dimensional models were constructed for visualization, not quantitative measurement.

The GON and LON were identified on all 20 sides. The GON had 6.0 ± 1.4 terminal branches. Its trapezius muscle/fascial emergence point was located 25.4 ± 3.2 mm horizontally from the posterior midline and 14.0 ± 2.2 mm vertically from the external occipital protuberance (EOP) level. GON-OA relationships comprised a single crossing on 3 sides, multiple crossings on 8 sides, continuous contact on 5 sides, and coiling on 4 sides. The LON traversed a trapezius muscle-related plane on 9 sides and followed a posterior sternocleidomastoid muscle-border course on 11 sides. In descriptive side-level comparisons, the trapezius muscle-related emergence point was closer to the posterior midline and EOP level but farther from the mastoid reference line than the posterior sternocleidomastoid muscle-border emergence point. GON-LON communications were observed on 17 sides.

These findings support a layered, pathway-based, and conceptual zone-based model of posterior occipital neurovascular anatomy, rather than localization based only on isolated surface landmarks.