Risk of intrafascicular spread after deliberate ex vivo intraneural injections of brachial plexus nerve roots.

Background: We investigated the intraneural spread of injected fluid in brachial plexus nerve roots, examining the potential for intrafascicular spread and identifying influencing factors.

Methods: Twelve deliberate ultrasound-guided intraneural injections were performed at the ventral rami of the brachial plexus nerve roots at their exits from the neuroforamina in six fresh, unembalmed, cryopreserved human cadavers. A 22-G, 30-degree bevel echogenic regional anaesthesia needle was used. Each injection contained 1 ml of heparinised erythrocytes as a marker. Nerve swelling observed on ultrasound images confirmed intraneural injection.

Results: Intraneural spread was observed in 12 ventral rami of the six brachial plexi: C5 (1), C6 (3), C7 (5), C8 (2), and T1 (1). Among these, intrafascicular spread was detected in eight cases, six in monofascicular roots and two in bifascicular roots, though none in roots with three or more fascicles. The fascicle diameters in these cases (2.1-3.8 mm) were at least twice the diameter of the needle orifice, measured at 0.9 mm, which was entirely inside the fascicles. In the four cases with intraneural but without intrafascicular spread, the fascicle diameters were about two times the diameter of the needle orifice in three instances, but the entire needle orifice was not always inside a fascicle.

Conclusions: In contrast with multifascicular peripheral nerves, intrafascicular spread was possible after deliberate intraneural injections near the neuroforaminal canal exit of the brachial plexus nerve roots in several monofascicular or bifascicular ventral rami if the fascicle diameter was more than twice the needle opening length and the entire opening was inside the fascicle.