Carotid sheath

The carotid sheath is an anatomical term for the fibrous connective tissue that surrounds the vascular compartment of the neck. It is part of the deep cervical fascia of the neck, below the superficial cervical fascia meaning the subcutaneous adipose tissue immediately beneath the skin.
The deep cervical fascia of the neck includes four parts:
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. It extends from the base of the skull to the first rib and sternum, varying between C7 and T4. It merges with the axillary sheath when it reaches the subclavian vein.
Contents.
The four major structures contained in the carotid sheath are:
The carotid artery lies medial to the internal jugular vein, and the vagus nerve is situated posteriorly between the two vessels.
In the upper part, the carotid sheath also contains the glossopharyngeal nerve (IX), the accessory nerve (XI), and the hypoglossal nerve (XII), 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. The carotid sheath has limited loose connective tissue.
Relations.
The cervical part of the sympathetic trunk is embedded in prevertebral fascia immediately posterior to the sheath.
Clinical significance.
The carotid sheath may act as a conduit for infections, although this is rare due to the limited connective tissue.