A Novel Ultrasonographic Method to Quickly and Accurately Access the C2 Dorsal Root Ganglion

BACKGROUND: Occipital neuralgia manifests as pain in the cutaneous distribution of occipital nerves, with the greater occipital nerve stemming from the C2 spinal nerve and the lesser occipital nerve originating from the C2 and C3 spinal nerves. While pulsed radiofrequency ablation of the C2 dorsal root ganglion (DRG) is an effective treatment for refractory occipital neuralgia, accessing the C2 DRG remains a clinical challenge even under fluoroscopic guidance. OBJECTIVE: We aimed to develop an ultrasonographic method for quickly and accurately accessing the C2 DRG. STUDY DESIGN: This is a prospective, observational cohort study. SETTING: Our study was conducted in the Department of Pain Management, Xuanwu Hospital, Capital Medical University, Beijing, China. METHODS: Unlike the C3-C8 foramina, which are ventral to the corresponding facet joints, the C2 foramen is positioned more posteriorly, dorsal to the C1-C2 atlantoaxial joint and longitudinally aligns with the cervical facet joints of C2-C3 and C3-C4. This unique anatomical feature allowed us to rapidly identify the C2 foramen in the sonographic longitudinal-axis view, what we call the "Stage-light Sign." Further exposure of the C2 DRG in the oblique-axis view we call the "Turtle Sign." The following procedural parameters were prospectively obtained: the time required to identify the C2 DRG target, the time needed to reach the target from the point of skin puncture, the number of puncture attempts required to reach the target, and the minimum sensory testing voltage to evoke paresthesia responses in the cutaneous occipital nerve distributions. Clinical outcomes were assessed by serial pain severity using the Numeric Rating Scale at baseline and up to 3 months post the C2 DRG pulsed radiofrequency ablation procedure. RESULTS: The correct placement of the needle tip was initially confirmed with fluoroscopy, with the injected contrast medium distributed along the C2 spinal nerve. Importantly, electrical sensory stimulation elicited paresthesia in the headache area in all patients, with the required voltage being 0.35 ± 0.02 V. Furthermore, treatment outcomes supported the correct needle tip position, as pulsed radiofrequency ablation treatment led to sustained pain reduction. It took 36.2 ± 2.2 seconds to obtain the final "TurtleSign" view of the C2 DRG. Once the target was identified, it required a single puncture attempt to reach it, with a duration of 36.3 ± 2.5 seconds from puncturing the skin to reaching the target. LIMITATION: We only followed patients for up to 3 months postprocedure. CONCLUSION: We have developed an ultrasonographic method to quickly and accurately access the C2 DRG, which has the potential to greatly facilitate treating the C2 DRG for managing occipital neuralgia.