Carotid sheath

The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the internal carotid artery and related structures in the neck.

Structure
The carotid sheath is located at the lateral boundary of the retropharyngeal space at the level of the oropharynx on each side of the neck and deep to the sternocleidomastoid muscle, extending from the base of the skull to the first rib and sternum.

Contents
The three major structures contained in the carotid sheath are:
 * the internal carotid artery (arising from the common carotid artery)
 * internal jugular vein
 * the vagus nerve

The carotid artery lies medial to the internal jugular vein, and the vagus nerve is situated posteriorly between the two vessels.

The carotid sheath also contains the deep cervical lymph nodes.

In the upper part, the carotid sheath also contains the glossopharyngeal nerve, the accessory nerve, and the hypoglossal nerve, which pierce the fascia of the carotid sheath.

The ansa cervicalis is embedded in the anterior wall of sheath. It is formed by "descendens hypoglossi" (C1) and "descendens cervicalis" (C2-C3).

Layers
The three major fascial layers in the neck contribute to the carotid sheath: the investing fascia, the pretracheal fascia, and the prevertebral fascia.

Relations
The cervical part of the sympathetic trunk is embedded in prevertebral fascia immediately posterior to the sheath.