The carotid sheath is an anatomical term for the fibrous

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

that surrounds the vascular compartment of the neck. It is part of the

deep cervical fascia The deep cervical fascia (or fascia colli in older texts) lies under cover of the platysma, and invests the muscles of the neck; it also forms sheaths for the carotid vessels, and for the structures situated in front of the vertebral column. Its a ...

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: * The investing layer (encloses the SCM and Trapezius) * The carotid sheath (encloses the vascular region of the neck) * The pretracheal fascia (encloses the visceral region of the neck) * The prevertebral fascia (encloses the vertebral region of the neck)

Structure

The carotid sheath is located at the lateral boundary of the retropharyngeal space at the level of the

oropharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...

on each side of the neck and deep to the

sternocleidomastoid muscle The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck. The sternocleidomastoid is innervated by the access ...

. It extends from the base of the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

to the first rib and

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...

, varying between C7 and T4. It merges with the axillary sheath when it reaches the

subclavian vein The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorptio ...

The four major structures contained in the carotid sheath are: * the

common carotid artery In anatomy, the left and right common carotid arteries (carotids) (Entry "carotid"
in
*parts of the

internal carotid artery The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these ...

and the

external carotid artery The external carotid artery is a major artery of the head and neck. It arises from the common carotid artery when it splits into the external and internal carotid artery. External carotid artery supplies blood to the face and neck. Structure T ...

. * the

internal jugular vein The internal jugular vein is a paired jugular vein that collects blood from the brain and the superficial parts of the face and neck. This vein runs in the carotid sheath with the common carotid artery and vagus nerve. It begins in the poste ...

. * the

vagus nerve The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and righ ...

. *part of the

recurrent laryngeal nerve The recurrent laryngeal nerve (RLN) is a branch of the vagus nerve ( cranial nerve X) that supplies all the intrinsic muscles of the larynx, with the exception of the cricothyroid muscles. There are two recurrent laryngeal nerves, right and ...

. * the deep cervical lymph nodes. In the upper part, the carotid sheath also contains the

glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior (closer to the nose) to the vagus nerve. ...

(IX), the

accessory nerve The accessory nerve, also known as the eleventh cranial nerve, cranial nerve XI, or simply CN XI, is a cranial nerve that supplies the sternocleidomastoid and trapezius muscles. It is classified as the eleventh of twelve pairs of cranial nerv ...

(XI), and the

hypoglossal nerve The hypoglossal nerve, also known as the twelfth cranial nerve, cranial nerve XII, or simply CN XII, is a cranial nerve that innervates all the extrinsic and intrinsic muscles of the tongue except for the palatoglossus, which is innervated ...

(XII), which pierce the fascia of the carotid sheath.

Relations

Posterior to common carotid artery is

sympathetic trunk The sympathetic trunks (sympathetic chain, gangliated cord) are a paired bundle of nerve fibers that run from the base of the skull to the coccyx. They are a major component of the sympathetic nervous system. Structure The sympathetic trunk lies j ...

. The sympathetic trunk is separated from the transverse processes of C4 to C6 vertebrae by prevertebral muscles. Medially are trachea and oesophagus with

in between them. At higher levels, larynx, pharynx, recurrent laryngeal nerve, and thyroid gland are located medially to common carotid artery. Anterolaterally, the artery is covered by sternocleidomastoid and strap muscles. Above the cricoid cartilage, the artery is only covered by skin and fascia. Posterior to internal carotid artery are sympathetic trunk, transverse processes of C1 to C3 vertebrae, and prevertebral muscles. Medial to the internal carotid artery is the lateral wall of pharynx. Anterolaterally, it is covered by sternocleidomastoid muscle throughout its length. The upper part of internal carotid artery is separated from external carotid artery by styloid process and its muscles. At the level of

base of skull The base of skull, also known as the cranial base or the cranial floor, is the most inferior area of the skull. It is composed of the endocranium and the lower parts of the calvaria. Structure Structures found at the base of the skull are for ...

, internal carotid artery passes in front of internal jugular vein and enters the

carotid canal The carotid canal is a passageway in the temporal bone of the skull through which the internal carotid artery enters the middle cranial fossa from the neck. Structure The carotid canal is located within the middle cranial fossa, at the petrous ...

. Meanwhile, the internal jugular vein and the vagus nerve enter the

jugular foramen A jugular foramen is one of the two (left and right) large foramina (openings) in the base of the skull, located behind the carotid canal. It is formed by the temporal bone and the occipital bone. It allows many structures to pass, including the ...

. The

ansa cervicalis The ansa cervicalis (or ansa hypoglossi in older literature) is a loop of nerves that are part of the cervical plexus. It lies superficial to the internal jugular vein in the carotid triangle. Its name means "handle of the neck" in Latin. Bra ...

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

is embedded in prevertebral fascia immediately posterior to the sheath.

Layers

The three major fascial layers in the neck contribute to the carotid sheath: the investing fascia, the

pretracheal fascia The pretracheal fascia is a layer of the deep cervical fascia at the front of the neck. It attaches to the hyoid bone above, and - extending down into the thorax - blends with the fibrous pericardium below. It encloses the thyroid gland and parat ...

, and the prevertebral fascia. The carotid sheath has limited

loose connective tissue Loose connective tissue, sometimes called areolar tissue, is a cellular connective tissue with thin and relatively sparse collagen fibers. Its ground substance occupies more volume than the fibers do. It has a viscous to gel-like consisten ...

Clinical significance

The carotid sheath may act as a conduit for

infections An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

, although this is rare due to the limited

Additional images

Image:Gray794.png, Hypoglossal nerve, cervical plexus, and their branches. Image:Gray1031.png, Muscles of the pharynx, viewed from behind, together with the associated vessels and nerves.

References

External links

* * () *
Cross section at tufts.edu
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