Greater occipital nerve (GON) intervention is indicated for managing different types of headache disorder including chronic migraine, occipital neuralgia, cervicogenic headache, and cluster headache. 1 The hypothesis behind using this intervention in headache management comes from the evidence of the transmission of sensory information to the fifth nerve nucleus neurons from both cervical and trigeminal fibers, thereby resulting in an antagonizing "wind-up-like effect". 2 In the past, landmark-guided GON intervention, based on anatomy, has been performed, which yielded variable results. The classical method of anatomical or landmarkguided GON intervention involves initial palpation of occipital artery at the level of the superior nuchal line. Once pulsations of occipital artery are felt, thumb is placed over it and negative aspiration injection is performed from medial to artery ( Fig. 1). Now various studies have revealed that ultrasound-guided GON intervention is the gold standard, which not only helps the interventionist to exactly localize the nerve but also increases the success rate of this intervention with even the smallest amount of the local anesthetics. On the contrary, ultrasonography (USG) does not compromise patient safety when compared with landmarkguided procedures.
AnAtomy o f GreAter occipitAl nerveIt is the sensory branch of the dorsal rami of the second spinal nerve, i.e., C2. Along with the lesser occipital nerve, it supplies the skin involving C2 and some part of C3 dermatome, i.e., areas adjoining the vertex. 3 After exiting the second spinal nerve, it appears at the lower border of the obliquus capitis inferior muscle (OCIM). Thereafter, it parallels between the OCIM and the semispinalis capitis muscle (SsCM). At last, it terminates in relation to trapezius and sternocleidomastoid, i.e., either penetrates the trapezius muscle or it travels as sandwiched between the trapezius muscle and the sternocleidomastoid muscle. In the short-axis view, the GON is seen as a hypoechoic structure sandwiched between the SsCM dorsally and the OCIM ventrally. 4
UltrAsoUnd-GUided intervention• Place the patient in prone position with neck flexed on a head ring or pillow. • Adjust the knobology component on the USG machine in terms of depth of gain and field to improve the image resolution. • A high-frequency linear (10-12 MHz) USG probe is placed over the occiput to get a short-axis view. Image is adjusted, so that the external occipital protuberance lies in the midline.• Now probe is oriented in an oblique manner, so that medial part of the probe points toward the C2 spinous process, which can be identified as a bifid structure and the lateral part of probe is directed toward the transverse process of the C1 vertebrae. • Now move the probe downwards to visualize the short-axis view of atlas to locate its arch. • Move the probe further downward to the C2 level to obtain bifid spinous structure along with left and right tubercles. It confirms the axis vertebrae.