C2 suboccipital plane block (SOB-C2) for cervicogenic headache: a cadaveric study

Background and aims Cervicogenic headache is mediated by nociceptive input from upper cervical structures, including the C1–C3 spinal nerves, cervical joints, suboccipital muscles, and associated myodural bridges. The C2 dorsal root ganglion (DRG) represents an important convergence site within this nociceptive network. The suboccipital plane block targeting the C2 DRG (SOB-C2) has been described as an approach to these structures. This cadaveric study investigated the spread of injectate following SOB-C2 and determined whether the technique encompasses the suboccipital triangle and its neurovascular contents. Methods Bilateral ultrasound-guided SOB-C2 injections were performed in two unembalmed adult cadavers, yielding four hemispecimens. With the cadavers in the prone position, a needle was advanced in-plane from lateral to medial to a position deep to the obliquus capitis inferior muscle. A 2 mL of saline containing India ink was injected into each specimen. 1 hour after injection, layered anatomical dissection was performed to assess the distribution of injectate relative to the C2 DRG, suboccipital triangle, vertebral artery and C1–C2 joint. Results A tissue plane deep to the obliquus capitis inferior muscle was consistently identified in all four hemispecimens. Injectate staining consistently involved the deep surface of the obliquus capitis inferior muscle and its associated myodural bridges, the C2 DRG, and the floor of the suboccipital triangle, including the posterior atlanto-occipital membrane and underlying dura. The contents of the suboccipital triangle, particularly the vertebral artery were consistently stained. The posterior capsule of the C1–C2 joint was also stained in all specimens. The suboccipital nerve could not be reliably distinguished because of extensive staining within the triangle. Conclusions In this cadaveric study, the SOB-C2 injection consistently spread beyond the C2 DRG and myodural bridges to encompass the suboccipital triangle, including the vertebral artery with its surrounding sympathetic plexus, as well as the posterior capsule of the C1–C2 joint. These findings suggest that SOB-C2 may influence multiple anatomical structures implicated in cervicogenic headache. Further clinical and imaging studies are warranted to determine the clinical significance of this spread and to characterize the safety profile of the technique.