Specific types of headache
Migraine, cluster headaches, post-concussion headache
Cervicogenic headache, occipital neuralgia
The basis of how occipital nerve block works in the primary headache is likely related to the convergence of the functional connection between the sensory inputs from the occipital segments with the nuclei of the trigeminal nociceptive system (the trigeminocervical complex). From there, the neural circuit connects further to thalamus and cortex. Temporary suppression of the inputs from the greater occipital nerve (GON) may lead to modulation of central nociceptive pathways and reducing central sensitization.
Traditionally, the GON block is performed with blinded approach relying on the anatomic landmarks at the level of the superior nuchal line. This approach poses a higher risk to injection in the occipital artery and/or block failure. Complication rates of 5–10% have been reported, including dizziness, blurred vision, and syncope. Use of ultrasound has been shown not only to reduce the risks but also to improve the block efficacy.
The greater occipital nerve (GON) originates from the medial branch of the dorsal ramus of the C2 spinal nerve, with contributions from the C3 dorsal ramus.
The GON exits below the posterior arch of the second cervical vertebra, curves around the inferior oblique capitis (IOC) muscle, and travels cephalad in an oblique trajectory between the inferior oblique capitis and semispinalis capitis (SSC) muscle. At this site, the GON is susceptible to potential entrapment. The GON then perforates the trapezius muscle and ascends medial to the occipital artery to innervate the posterior cutaneous aspect of neck and scalp (Fig. 2.1).
The lesser occipital nerve (LON) is the most cephalad branch of the superficial cervical plexus beneath the sternocleidomastoid muscle. It is formed by fibers of the ventral rami of C2 and C3 and curves around its posterior border to run cranially to the parieto-occipital area where it splits in its terminal branches to innervate the lateral part of the occiput (skin behind and above the ear) (Fig. 2.2).
The diagnosis of a specific headache type can be made according to the International Head Society (IHS) classification. The occipital nerve block plays a diagnostic role in the diagnosis of occipital neuralgia and cervicogenic headache. For the other aforementioned headaches, the nerve block can be considered in patient’s failure to respond to conservative management.
The Greater Occipital Nerve: Two Different Target Locations
Proximal Approach at Level of C2
Position: Prone with head and neck flexed
Probe: Linear, 12–18 MHz
The key landmarks are the spinous process of C2 and the inferior oblique capitis muscle.
Scan 1: Occipital protuberance (probe in transverse orientation (Fig. 2.3).
Scan 2: Spinous process of C2. It showed a bifid bone structure below the occiput (Fig. 2.4).
Scan 3: The transducer is moved laterally to visualize the inferior oblique capitis (IOC) muscle and semispinalis capitis (SSC) muscle; to maximize the image of this muscle, the lateral end of the probe is rotated slightly in a cranial direction to bring the transducer parallel to the long axis of the muscle (Fig. 2.5). With this movement, the C2 lamina appears boat-shaped, and IOC is cradled within it. The plane between the IOC and SSC is visualized. Greater occipital nerve (GON) is sandwiched between the IOC and SSC muscles. LON-lesser occipital nerve, SCM-sternocleidomastoid.