CT-Guided Block and Radiofrequency Ablation of the C2 Dorsal Root Ganglion for Cervicogenic Headache

Patient Selection

Complete patient selection criteria are beyond the scope of this technical report; suggested indications and contraindications are outlined in the Table. Briefly, patients should be considered for C2 DRG RF ablation if they present with occipital-distribution pain of a cervicogenic origin and have failed conservative therapy, including medication and physical therapy. An occipital nerve block is often performed initially to exclude a peripheral occipital nerve entrapment. CT and/or MR imaging of the cervical spine should be performed to evaluate the upper cervical nerve roots and facet joints. Classically, an asymmetric pattern of C1–C2 facet osteoarthrosis is seen with loss of cartilage and subchondral sclerosis (Fig 1). Posterior osteophyte formation may narrow the C1–C2 foramen and impinge on the C2 DRG, resulting in occipital neuralgia. Corresponding subarticular bone marrow edema may further suggest the C1–C2 joint as the pain generator (Fig 1).

• Download figure
• Open in new tab
• Download powerpoint

Fig 1.

A, Sagittal STIR sequence reveals increased T2-hyperintense signal in the right C1–C2 joint and periarticular bone marrow edema (circle). B, Coronal CT scan shows asymmetric marked osteoarthrosis of the right C1–C2 articulation, with loss of joint height, cortical irregularity, and subchondral sclerosis (circle).

Technique

Patients should be placed head first on the CT gantry table in the supine or prone position with the head in neutral alignment facing the ceiling or in slight rotation away from the painful side. Moderate sedation may be offered for patient comfort; however, it is important that the patient remain awake for RF ablation sensory testing. Scout topograms of the craniocervical junction are acquired in the frontal and lateral planes. An axial CT stack can then be prescribed from the skull base through C3. The C2 dorsal root ganglion can be visualized in the axial plane just dorsal to the C2 lateral mass (Fig 2). An adequate CT dose is necessary for visualization, and the authors recommend 120 kV and 100–200 mA (diagnostic dose) at 2.5 mm (reconstructed to 0.625-mm bone and standard algorithms) for the initial preprocedural planning scan. The dose may be reduced to 10–50 mA for subsequent procedural scans acquired for needle localization. Serial CT or CT fluoroscopy can be used on the basis of the interventionalist's preference. If preoperative angiography or MR imaging is not available, a targeted CT angiogram may be performed with intravenous contrast. It is important to identify relevant vertebral artery variants that may be present in up to 31% of patients at the C1–C2 level.⁶ Due to the transient nature of intravenous CT contrast, the authors recommend that if performed, a procedural CTA scan be obtained once the needle entry site has been selected and the patient's head immobilized because the CTA may be of limited utility if the patient is significantly repositioned (On-line Video).

• Download figure
• Open in new tab
• Download powerpoint

Fig 2.

Axial CT angiogram showing the left C2 dorsal root ganglion (arrow) positioned behind the left C2 lateral mass. The left proximal V3-segment vertebral artery is highlighted (dashed arrow) anterolateral to the target.

C2 Nerve Block

In preparation for needle insertion, the skin is sterilized and buffered 1% lidocaine is instilled subcutaneously for local anesthesia. A 22-ga, 2.5- to 3.5-inch Quincke-type spinal needle is then inserted. By means of intermittent CT guidance, the needle is advanced to approximate the C2 dorsal root ganglion. Care should be taken to avoid advancing the needle medial to the DRG, given the close proximity to the dura. If blood is seen in the hub, the needle may be carefully repositioned. There is a rich venous plexus surrounding the C2 DRG; a small volume (0.2–0.3 mL) of iohexol (Omnipaque 180; GE Healthcare, Piscataway, New Jersey) 180 or 240 contrast diluted with normal saline should be injected to ensure appropriate positioning and exclude inadvertent arterial or dural puncture. Once the appropriate position is confirmed, a 1- to 2-mL 1:1 mixture of preservative-free dexamethasone, 10 mg/mL, and 0.5% or 0.75% of bupivacaine is prepared and slowly instilled through the needle. The needle is then removed with the stylet in place.

Radiofrequency Ablation

For RF ablation, the authors recommend a 22-ga, 5- or 10-cm-length cannula with a 5-mm uninsulated tip. A grounding pad is placed on the upper thigh. Following the steps described above, an RF ablation canula is substituted for the spinal needle. Once the appropriate position is confirmed on CT, the stylet is removed and the radiofrequency probe is inserted (Fig 3). Impedance levels should be checked and are typically <300 Ω. Sensory testing is then performed at 50 Hz up to 2 V. Pain should be elicited in the distribution of the ipsilateral occipital nerve. Motor testing at 2 Hz may then be performed, which may evoke mild local contraction of the paraspinous musculature. Then, 0.5 mL of unbuffered 1% lidocaine is instilled in the RF cannula, and a CT scan is obtained with the RF probe in place for final confirmation of positioning. Thermal RF ablation is then performed at 80°C for 90 seconds. The patient may experience local discomfort during the thermal ablation and should be encouraged to hold still for the duration of the ablation. Discomfort during the ablation typically improves as the ablation continues. If the pain is severe and/or persistent, the ablation should be stopped and the needle withdrawn slightly before re-ablating, or alternatively, pulsed radiofrequency ablation may be considered. If pulsed RF ablation is desired, identical treatment steps may be followed, but the RF generator should be set to pulsed RF at 42°C for 120 seconds.

• Download figure
• Open in new tab
• Download powerpoint

Fig 3.

Intraprocedural axial CT scan showing appropriate placement of a 5-cm RF cannula targeting the right C2 DRG.

Following RF ablation, the probe is removed and a nerve block can be performed through the canula with dexamethasone and bupivacaine as described above to decrease postprocedural inflammation and discomfort. The canula is then removed with the stylet in place, and a sterile bandage is applied. Patients may experience a flare of symptoms for 24–72 hours following thermal RF ablation; oral nonsteroidal anti-inflammatory drugs are generally adequate for pain control. In cases of severe postoperative pain inadequately controlled with nonsteroidal anti-inflammatory drugs, a methylprednisolone (Medrol) dose pack may be helpful to decrease inflammation and discomfort.