Cervicogenic headaches, a type of headache originating from the cervical spine, have been a focus of research and treatment since the early 1900s. These headaches, caused by pain referred from the upper cervical nerve roots, are relatively rare, affecting an estimated 0.4% to 2.5% of the population. They are often encountered in patients with chronic headaches who seek treatment at pain clinics.
The anatomy implicated in cervicogenic headaches includes cervical synovial joints, muscles, intervertebral discs, arteries, and the dura mater. The convergence of nociceptive fibers from these structures explains the referred pain. The most common sources of cervicogenic headaches are the C2-C3 zygapophyseal joints, followed by the lateral atlantoaxial joints. The unique and complex anatomy of the upper cervical spine, with its proximity to vital structures and limited space, presents challenges for interventions.
This article delves into the anatomical and technical considerations of CT-guided C1-C2 lateral joint interventions. It covers the anatomy of the C1-C2 joints, their innervation, and potential pathologies. The article also discusses the variability and subjectivity of cervicogenic headache pain, which can lead to inaccurate diagnoses. Standardized diagnostic criteria, such as those provided by the International Headache Society, aim to address this challenge.
Therapeutic options for cervicogenic headaches are limited due to the unique innervation of the C1-C2 joint. Patients may try physical therapy and anti-inflammatory medications, but their effectiveness is often minimal to moderate. More invasive options include instrumented arthrodesis of the C1-C2 joint, which carries significant risks and limits head rotation. Injections into the C1-C2 facet joints and neurectomy of occipital nerves have also shown some success in providing relief.
The primary indication for C1-C2 lateral mass articulation injections is diagnostic, to determine if the C1-2 facet joint is the source of a patient's headaches. MRI can also help identify edema or joint effusions. The absence of these findings on MRI suggests that the C1-2 articulation is unlikely to be the cause of neck pain or headaches. Patients often present with symptoms similar to occipital neuralgia, which can be attributed to joint arthrosis and impingement of the C2 dorsal root ganglion (DRG).
The approach to injecting the C1-C2 lateral mass joints using fluoroscopy is well-established, but CT-guided injections offer benefits such as improved depth perception and soft tissue visualization. However, CT-guided injections have limitations, including beam hardening and streak artifacts caused by amalgam or spinal hardware. Metal artifact reduction techniques can help improve image quality.
Before performing a C1-C2 lateral mass articulation injection, several factors must be considered. The C1-C2 lateral mass articulations should be identified as the probable pain source based on clinical examination and imaging. The injection can be performed for diagnostic or therapeutic purposes, and absolute contraindications are similar to those for fluoroscopically guided injections. The risks, benefits, and alternatives of the injection should be discussed with the patient to obtain informed consent.
The selection of injectate depends on the purpose of the injection. For diagnostic injections, 1% lidocaine is commonly used due to its short-acting effect. For symptomatic relief, various steroids can be considered, with dexamethasone being a preferred option due to its non-particulate nature, reducing the risk of catastrophic embolization in the cervical spine.
Understanding the anatomy surrounding the joint is crucial to ensure the safest trajectory for the injection. Medially, the thecal sac and its contents are present, and deviation can lead to intrathecal injectate administration or spinal cord injury. Laterally, the vertebral artery poses a risk of intravascular injection and posterior circulation embolization. Ventrally, the internal carotid artery is present, and advancing the needle too far anteriorly carries risks of extension into the oropharynx. Dorsally, along the preferred trajectory, the dorsal root ganglion is highly sensitive and can be easily encountered. A venous plexus may also be present in this area, which should be considered if the patient has a bleeding diathesis.
Patient positioning is crucial to ensure comfort and maintain a neutral neck position. Fiducial markers are placed on the posterior upper neck, and scout imaging is performed. The patient must remain still during the procedure to ensure accurate needle placement. Conscious sedation may be beneficial for anxious or sensitive patients if trained staff and continuous hemodynamic monitoring are available.
CT image acquisition and contrast administration are carefully planned to minimize risks. The total volume of contrast used is small (1-2 mL), and the opacification pattern can vary. The risks of contrast reactions are similar to those outlined in the ACR contrast manual. Alternatives to iodinated contrast, such as air or gadolinium, must be used judiciously due to their inherent risks.
The procedure tools and considerations for CT-guided injections are outlined in detail. The marking laser on the CT is used to mark the needle puncture site. The skin over the site is sterilized, and a drape is applied. A 25-gauge anesthetic needle is advanced slowly, with 1% lidocaine administered gradually. The spinal needle is advanced in short increments, with CT imaging performed between each step to ensure accuracy. If diagnostic aspiration is required, a 20-gauge needle may be preferred.
The CT-guided injection technique involves loading the initial measured trajectory to determine the needle angle. The skin is sterilized, and a sterile field is established. The 25-gauge needle is exchanged for a 3.5-inch 22-gauge spinal needle, and the same trajectory is maintained. The needle is advanced until adequate tissue purchase is achieved. The ideal trajectory is in-plane in a single slice, and the clinician should be confident in the needle position before advancing it to the posterior aspect of the joint.
Once at the joint capsule, an arthrogram is performed by slowly injecting contrast. The joint's volume is limited (2-3 mL), so it is important to reserve space for the injectate. Approximately 1 mL of steroid is then injected, followed by 0.5 mL of lidocaine. Care must be taken to avoid injecting against resistance, as this can lead to extravasation beyond the joint. In patients with advanced disease, the joint capsule may be deficient, allowing contrast to spread to adjacent regions.
In summary, C1-C2 lateral mass injections have been shown to provide temporary relief from cervicogenic headache symptoms. The delicate anatomy surrounding the C1-C2 joint allows for a limited safe trajectory and a narrow target area at the posterior joint line for intra-articular access. Image guidance is crucial for the effectiveness and safety of these injections. Recognizing potential pitfalls, such as intravascular injections and nerve damage, is essential for successful outcomes.
