Ultrasound-Guided Lower Cervical Nerve Root Injectate Volumes Associated With Dorsal Root Ganglion and Epidural Spread.

Objectives: We aimed to estimate the spread of injections for ultrasound-guided cervical nerve root blocks and to determine the optimal injectate volume required in this procedure.

Methods: A total of 32 ultrasound-guided injections (C5-C8) were made in 4 fresh cadavers. The target on each cervical root was the space between the posterior tubercle and the cervical root at the most proximal location possible on the sonogram. After ultrasound-guided needle insertion, 0.5 mL of a contrast medium was injected 4 times. The dye flow patterns were confirmed with fluoroscopy each time, and we recorded whether the contrast medium reached the dorsal root ganglion level or the epidural space. After the injections, the needle tip location was determined by computed tomography and image reconstruction.

Results: All injections produced typical neurograms. The contrast medium reached the dorsal root ganglion in 29 of 32 (90.6%) injections (mean ± SD, 0.84 ± 0.42 mL of contrast medium) and the epidural space in 10 of 32 (31.3%) injections (1.30 ± 0.54 mL of contrast medium). The mean distance between the needle tip and neural foramen was 9.64 ± 3.68 mm, and this distance correlated positively with the volume of contrast medium necessary to reach the dorsal root ganglion or the epidural space.

Conclusions: Ultrasound-guided cervical nerve root blocks show potential utility for targeting an anesthetic into the cervical root area. This study may be helpful for deciding the most appropriate volume for the procedure.