Introduction
Headaches remain notoriously difficult to treat despite advances in therapy. This is in part due to difficulty of classification and contributions of referred pain. While traditional treatments targeted intracranial pathologies, substantial evidence now exists in support of extracranial components of headache. Disorders of the neck can contribute to this and are a cause of “secondary” headaches, one of which is termed cervicogenic headache.
While multiple efforts have been made to delineate criteria for cervicogenic headache, there remains significant variability in its definition and diagnosis. Initially, the original definitions put forth by the International Headache Society (IHS) and the Cervicogenic Headache International Study Group (CHISG) , differed significantly in their classification. This led to discrepancies in accurate patient diagnosis and optimal treatment. The IHS has since updated its definition to better align with the CHISG criteria to ensure consistency.
Despite the strides made in classifying cervicogenic headache, its definition is further complicated by the diversity of its etiologies, ranging from trauma to arthritis, and significant overlap with other disorders such as migraine and tension headache. , Indeed, other headaches including migraine, cluster headache, occipital neuralgia, and trigeminal neuralgia are notoriously difficult to treat. Given the significant burden of headache disorders on both patients and the healthcare system, effective treatment is necessary.
Radiofrequency ablation of the sphenopalatine ganglion has been found to be effective in the treatment of migraine and chronic cluster headaches. Specifically, ablation can significantly decrease both the frequency and intensity of attacks, and reduce disability associated with the headache disorder. These benefits appear to persist for more than 2 years. Sphenopalatine ganglion RFA may also be efficacious in the treatment of lesser studied headache disorders such as Sluder’s neuralgia and atypical facial pain.
Migraine headache is a common headache syndrome that can lead to significant functional impairment. Despite the many treatment regimens available, migraine headaches may remain refractory. Some migraine headaches may respond to ablations discussed previously, such as greater occipital nerve or lesser occipital nerve blocks, as well as supraorbital and supratrochlear nerve ablation.
In this chapter, we will explore literature on the indications, clinical applications, and technical approach to the use of radiofrequency ablation as a treatment modality for headache related pain.
Anatomy
Trigeminal cervical complex
The etiology of cervicogenic headache remains poorly understood but it is thought to relate to cervical neuralgia. This pain is believed to originate from the upper cervical spine at the trigeminocervical nucleus or trigeminal cervical complex (TCC), which is a convergence of descending fibers from the trigeminal nerve with sensory fibers from the upper cervical roots (C1–C3). , Irritation of these afferent fibers along the cervical processes commonly occurs due to arthritis or trauma, thereby leading to referred pain to the head or face and causing a headache.
Modern-day practice has focused largely on the zygapophyseal joints (z-joints), also known as facet joints, as targets for intervention. Innervated by the medial branches of adjacent spinal nerves, these joints assist with range of motion of the cervical spine. As these medial branches are responsible for nociception at each joint level, they are one potential nidus of referred pain. Damage to these joints and nearby articular processes are noted in 54% to 60% of cases of chronic neck pain, with the potential to be perceived as headache pain due to referral through the TCC. The joint spaces most frequently involved are C1–C2 and C2–C3. Therefore, the suboccipital nerve (dorsal ramus of C1) and C2 spinal nerve and its dorsal root ganglion, and the C3 spinal nerve and dorsal root ganglion, are potential sources of referred head pain. Of these, irritation of the dorsal rami is considered to be the most common cause of cervicogenic headache. Table 15.1 lists commonly implicated cervical levels, nerves involved, and pain distributions for cervicogenic headache. Fig. 15.1 depicts the distribution of pain associated with each cervical level.
| Cervical Spine Level | Corresponding DRG/Nerve Afferent | Corresponding Joint Affected or Innervated | Distribution of Pain |
| C1 | Suboccipital nerve (SON) | Atlanto-occipital joint | Occipital pain |
| C2 | C2 DRG/spinal nerve | Proximal to C1–C2 z-joint (atlanto-axial joint) Innervates C2–C3 z-joint | Occipital and suboccipital pain, interpreted as vertex, orbit, and ear pain Occipital/parietal pain |
| C3 | Third occipital nerve (TON) | Proximal to and innervates C2–C3 z-joint | Occipital/parietal region, extension to frontal region and periorbital region |
Damage to any of the structures noted previously, in the form of trauma or progression of chronic illness such as osteoarthritis, can lead to referred pain to the occipital, frontotemporal, and periorbital regions. Lower vertebrae (C3–C4 and C7–T1) may also be another source, but pain from these regions is more commonly localized to the upper lateral cervical neck.
The diagnostic criteria for cervicogenic headache have evolved considerably since inception. Originally, the definition put forth by the IHS differed significantly from that described by the CHISG. This led to inconsistencies in investigating, diagnosing, and treating cervicogenic headache. In 2013, the IHS updated their definition for diagnosis to better align with that of the CHISG. The diagnosis of cervicogenic headache according to the IHS criteria is as follows:
- A.
Any headache fulfilling criterion.
- B.
Clinical, laboratory and/or imaging evidence of a disorder or lesion in the cervical spine or soft tissues of the neck, known to be able to cause headache.
- C.
Evidence of causation has been demonstrated by at least two of the following:
- •
Headache that developed in temporal relation to the onset of the cervical disorder or appearance of the lesion
- •
Headache that has significantly improved or resolved in parallel with improvement in or resolution of the cervical disorder or lesion
- •
Cervical range of motion is reduced, and headache is made significantly worse by provocative maneuvers
- •
Headache is abolished following diagnostic blockade of a cervical structure or its nerve supply
- •
- D.
Not better accounted for by another ICHD-3 diagnosis
Evaluation for cervicogenic headache thus involves ruling out other more common causes of headache such as tension headache and migraines given the significant overlap of these disorders. , Diagnostic work-up includes a thorough history and physical examination, imaging (MRI), and diagnostic blockade which will be detailed in subsequent sections.
Sphenopalatine ganglion
The sphenopalatine ganglion is located in the pterygopalatine fossa, posterior to the middle nasal turbinate. Its location makes it an attractive site for anesthetic block using several approaches including the lateral (infrazygomatic, Fig. 15.2 ), transnasal, or via the greater palatine foramen. Anesthetic block for each of these approaches differs in topical application of anesthetic used for the transnasal approach versus local anesthetic injection used for the lateral or greater palatine foramen ( Figs. 15.3 , 15.4 ). However, the only approach of these that facilitates neuroablative techniques is the infrazygomatic approach.
Third occipital nerve
Occipital headache is similar in etiology and distribution to cervicogenic headache described previously ( Fig. 15.5 ). The most commonly implicated region is the C2–C3 facet (zygophyseal) joint ( Figs. 15.6 , 15.7 ). Radiofrequency ablation has been demonstrated as an efficacious treatment in patients refractory to conservative measures who experience relief following anesthetic block. The effectiveness of these techniques has been discussed previously.
Treatment
Good candidates for minimally invasive treamtent modalities are patients suffering from cervicogenic headache, migraine headache, occipital neuralgia, or trigeminal neuralgia whose pain is refractory to pharmaceutical intervention and noninvasive therapies (i.e., transcutaneous electrical nerve stimulation [TENS]). Radiofrequency ablation and pulsed radiofrequency are two such options. In this section we will explore candidacy for ablation or neuromodulation, the underlying mechanisms of these treatments, anatomic targets, and their possible complications.
Indications
As with any intervention, patient selection is paramount. Suitable candidates for radiofrequency ablation (RFA) or modulation have a long-standing history of neck and face pain, lasting months to years, that significantly limits their daily function. Even then, these treatments should be considered only after the patient has failed maximum conservative therapy including medical management, physical therapy, and TENS unit.
The medical exam to determine candidacy for RFA includes imaging such as with an MRI and fluoroscopy. These studies lend support to cervical pathology and localization of pain and exclude contraindications (i.e., disk herniation, skull pathology, and intracranial etiology) to the procedure. Once alternative etiology is ruled out, candidates should then undergo diagnostic anesthetic blocks.
Contraindications
Patients without an extracranial component of headache are not candidates for RFA as there is no target for lesioning. Furthermore, patients with prior neck surgery with resultant anatomy that would make ablation difficult, or other conditions that would alter anatomy or increase the risk associated with electrode placement, such as cervical spinal stenosis or disk herniation, are poor candidates. Patients with definitive structural abnormalities on CT or MRI of the brain or spine that could cause neurologic deficits are also poor candidates. Patients with other conditions that might confound success of an RFA, such as complex regional pain syndrome, should be adequately treated prior to intervention.
Diagnostic block
A diagnostic block with local anesthetic is used to determine whether significant pain relief would be achieved by ablation. The targets for anesthetic block differ based on headache type. For cervicogenic headache, migraine headache, and cluster headache as well as occipital neuralgia these are the spinal nerves and dorsal rami of C1–C3 (including the GON, LON, and TON); however, it is important to note the technical challenge of some of these blocks, particularly the C2 dorsal ramus and subsequent greater occipital nerve (GON). Further, GON blockade may not be specific for the diagnosis of cervical head/neck associated pain.
For pain associated with the C2–C3 z-joint, which accounts for approximately 70% of cases of cervicogenic headache, the third occipital nerve (TON) can be blocked as it crosses the joint. The patient is placed prone with flexion at the cervical spine. A lateral fluoroscopic view of the C2–C3 z-joint is obtained. A 22-gauge, 15cm needle is advanced through an introducer under fluoroscopy towards the midway point between the apex of C2 and the base of C3 ( Fig. 15.8 ). Needle placement is similarly confirmed with fluoroscopy ( Fig. 15.9 ) and motor stimulation to 50 Hz with 0.1 to 0.75 V. After local anesthetic injection, ablation is achieved at 80ºC for 90 s.
For pain associated with the C3–C4 z-joint, the medial branches of C3 and C4 can be blocked as they traverse the waist of the articular pillar. , Fig. 15.10 depicts the target site for the diagnostic block and subsequent electrode placement for ablation. The technique for diagnostic block uses the positioning and local anesthetic dose detailed in the International Spinal Injection Society guidelines. Generally, the patient is placed in the prone position with pillows under the thorax to accentuate the curve of the cervical spine ( Fig. 15.11 ). The spinal needle is advanced under fluoroscopic guidance to the target region, and 1 to 2 mL of 1% lidocaine is injected. The patient is then followed up several weeks later to determine the efficacy of the block in providing head and neck pain relief. It is important to note that there are several different approaches to diagnostic block. While some have used a diagnostic GON block with subsequent additional blocks, others have used a singular diagnostic block at the cervical medial branch. It should be noted that while a common site of headache pain, GON blocks can be technically challenging. The specific threshold of pain relief from diagnostic block is debated. Although 100% pain relief has been used to determine eligibility for RFA, more commonly 50% improvement in pain is deemed as sufficient. However, there is no clear consensus on the extent of pain relief from diagnostic block or time interval required between diagnostic block and radiofrequency ablation. Typically, patients should return several weeks after a diagnostic block and report the duration of pain relief.
