A spiralling origin of the median nerve around an accessory coracobrachialis brevis muscle.

During an ultrasound-guided axillary brachial plexus block, sonoanatomy demonstrated a delayed formation of the lateral root to the median nerve from the lateral cord, an accessory coracobrachialis brevis muscle, and a course of the lateral root to the median nerve 'spiralling' around the accessory muscle prior to locating lateral to the brachial artery. This rare variant is further discussed in the context of median, musculocutaneous and coracobrachialis variations.