The carotid sheath is one of four accumulations of deep cervical fascia or fibrous connective tissue of the neck which surrounds the great vessels of the neck. It extends from the base of the skull caudally to the first rib on the sternum. More precisely, it starts bilaterally at the level of the oropharynx on the lateral side of the retropharyngeal space, beneath the sternocleidomastoid muscle. It joins up medially with the prevertebral fascia and communicates inferiorly with the mediastinum. In this article, the fascial layers and relations, the contents of the carotid sheath and its pathology will be discussed.
Fascial Layers and Relations
The deep cervical fascia of the neck has four layers, listed from superficial to deep. The first is known as the investing layer and surrounds the sternocleidomastoid muscle and the trapezius muscle. The second that of the current topic, the carotid sheath which encompasses the vascular region of the neck. The third is called the pretracheal fascia and encloses the visceral region of the neck. Lastly, the fourth fascial layer is the prevertebral fascia and it surrounds the vertebral region of the neck. The carotid sheath itself is an accumulation of three of the layers of the deep cervical fascia. These layers include the investing fascia, the pretracheal fascia and the prevertebral fascia. An important adjacent anatomical structure which can be seen just behind the carotid sheath is the cervical part of the sympathetic trunk which is embedded in the prevertebral fascia.
The carotid sheath surrounds the following anatomical structures:
- The common carotid artery (CC)
- The internal carotid artery (I See = IC)
- The internal jugular vein (IV)
- The vagus nerve (CN X) (10 = CN 10)
- The deep cervical lymph nodes
- Sympathetic nervous fibers
In order to remember this list of the main carotid sheath contents, a popular mnemonic is well worth learning: ‘I See 10CC’s in the IV’ (See list above for correlations)
Pathological conditions that directly affect the carotid sheath are rare and it is much more common to see disorders that affect the contents of the sheath. Vascular disorders, neurological disorders or lymphatic diseases would affect the sheath and the rest of the contents secondarily. One scenario however that does involve the sheath is that of an extensive dental infection. The spreading of untreated dental focus can lead to cellulitis within the spaces of the head and neck. Should the fascia of the carotid sheath become involved, the infection could easily spread to the mediastinum and cause mediastinitis or even endocarditis.