Ultrasound-guided blockade of the third occipital nerve is useful in the diagnosis and treatment of cervicogenic headache, cervicalgia, and other pain syndromes subserved by the third occipital nerves. This technique is also useful as a prognostic indicator of the potential efficacy of destruction of the third occipital nerve with neurolytic agents such as phenol or radiofrequency lesioning. Traditionally, third occipital nerve block is performed under fluoroscopic guidance, but recent investigations by Narouze and others have demonstrated the utility of ultrasound guidance when performing this technique.

The third occipital nerve arises from medial branch fibers of the posterior division of the third cervical nerve at the level of the trapezius muscle (Fig. 26.1). The third occipital nerve courses dorsomedially around the superior articular process of the C3 vertebra (Fig. 26.2). Fibers from the third occipital nerve provide the primary innervation of the C2-C3 facet joints with some contribution from the C3 medial branch and small communicating fibers from the second cervical nerve. Fibers of third occipital nerve then course superiorly at a point medial to the greater occipital nerve to provide sensory innervation to the ipsilateral suboccipital region (Fig. 26.3). In most patients, there are communicating branches from the third occipital nerve with the greater occipital nerve.

Ultrasound-guided third occipital nerve block can be carried out by placing the patient in the lateral position. A total of 2 mL of local anesthetic is drawn up in a 10-mL sterile syringe. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic.

The mastoid process on the side to be blocked is then identified by palpation (Fig. 26.4). After preparation of the skin with antiseptic solution, a linear high-frequency ultrasound transducer is placed in a longitudinal plane with the cephalad end of the transducer resting at the base of the mastoid process, and the inferior border of the mastoid process is identified on ultrasound (Figs. 26.5 and 26.6). The transducer is then slowly moved in a posterior direction ¾ inch until the arch of C1 (atlas) and the articular pillar of C2 (axis) can be identified (Figs. 26.7 and 26.8). The transducer is then slowly moved in a caudad direction until the C2-C3 facet joints are visualized (Fig. 26.9). The ultrasound transducer is then slowly rotated toward the acoustic auditory meatus until the third occipital nerve is identified crossing just above the “hill” of the C2-C3 facet joint. The third occipital nerve will appear like a hyperechoic dot within a hypoechoic halo. The larger medial branch of the C3 can also be visualized in the “valley” between the articulations of the C2-C3 facet and the C3-C4 facet joints (Fig. 26.10).