Brachial plexus root injection in a human cadaver model: injectate distribution and effects on the neuraxis

The potential for injection into the brachial plexus root at cervical levels must be considered during interscalene block or chronic pain interventions in the neck, but this phenomenon has not been well studied. In this investigation, we performed injections into the brachial plexus roots of unembalmed cadavers, with real-time ultrasound guidance, to evaluate the proximal and distal spread of the injected fluids, the potential of the injectate to reach the neuraxis, and whether the injectate could migrate into the actual substance of the spinal cord itself. A solution of particulate dye mixed with local anesthetic was injected into 8 brachial plexus roots at a lower cervical level, in unembalmed cadaver specimens, utilizing an automated pump and pressure monitor. Two injections were made adjacent to nerve roots as controls. The specimens were then dissected, and gross and microscopic analysis utilized to determine the distribution of the dye and the structures affected. The mean peak pressure achieved during plexus root injections was 48.9 psi. After injections into the plexus root, dye was evident within the neural tissue at the level of injection and spread primarily distally in the plexus. In 1 of 8 injections into the brachial plexus root, the dye in the injectate spread proximally into the spinal canal, but in none of the injections was the spinal cord affected by the dye. Injection directly into the neural tissue of a brachial plexus root in a cadaver model produced high pressures suggestive of intrafascicular injection and widespread flow of the injectate through the distal brachial plexus. However, proximal movement of the dye-containing injectate was more restricted, with only 1 of the injections leading to epidural spread and no apparent effects on the spinal cord.