Carotid sheath

The carotid sheath is a tubular fascial compartment derived from the deep cervical fascia that encloses several vital neurovascular structures as they pass between the thorax and skull base. It extends from the arch of the aorta inferiorly to the base of the skull superiorly, where it surrounds the margins of the carotid canal and jugular fossa.

Within the carotid sheath lie the common and internal carotid arteries, internal jugular vein, and vagus nerve (cranial nerve X), accompanied by sympathetic nerve fibres and deep cervical lymph nodes. The glossopharyngeal (IX), accessory (XI), and hypoglossal (XII) nerves may lie along or briefly within its walls before branching anteriorly. The ansa cervicalis is typically embedded in its anterior wall.

The carotid sheath receives fascial contributions from the investing, pretracheal, and prevertebral layers of the deep cervical fascia. Within the sheath, the internal jugular vein lies laterally, the carotid artery medially, and the vagus nerve between and posterior to them.

Functionally, the carotid sheath protects, separates, and supports the major neurovascular structures of the neck, allowing their mobility during swallowing and head movement. Clinically, its continuity with the mediastinal fascia provides a potential route for the spread of deep cervical infections into the thorax.