Accessory phrenic nerve

The accessory phrenic nerve is an anatomical variant seen in a little over one third of patients (36%). It most commonly arises from the ansa cervicalis, or slightly less commonly, the subclavian nerve. It is unknown as to how much the accessory phrenic nerve contributes to diaphragmatic function in these individuals.

Gross Anatomy

Origin

The accessory phrenic nerve most commonly arises from the ansa cervicalis (45%) or the subclavian nerve (43%).

Rarely, it has also been seen to arise from the C3, C4 or C5 nerve roots, supraclavicular nerve, spinal accessary nerve, nerve to sternohyoid muscle or hypoglossal nerve.

Course

The accessory phrenic nerve most commonly joins with the phrenic nerve within the thorax (two-thirds) with the other third being within the neck at various locations.