Unilateral anatomical variation of the ansa cervicalis.

The ansa cervicalis is a loop of nerves that is usually formed by the union of ventral rami of spinal nerves C1, C2, and C3. It is located in the carotid triangle of the neck, lying superficial to the carotid sheath. During routine dissection, unilateral variation of the ansa cervicalis was observed. The superior root, arising from hypoglossal nerve, was initially bifurcated and later united to form a single superior root. IN addition, the inferior root consisted of fibres arising from the spinal accessory nerve, C1, C2 and C3 spinal nerves that joined separately. Fibres from the spinal accessory and C1 joined to form a single root. Thus, a 'triple form' of ansa cervicalis was observed. An interconnection was observed between the C2 and C3 fibres. Knowledge of such anatomical variations is important for surgery, clinical intervention or trauma involving the carotid triangle or the structures within or deep to this region.