Fascial layers of the neck and carotid sheath

The Fascial layers of the neck (cervical fascia) can be divided into two parts:

Superficial cervical fascia
Deep cervical fascia

SUPERFICIAL CERVICAL FASCIA

This later is the superficial (outer) layer is between Dermis and Deep cervical fascia.Structures in the superficial fascia are:

Platysma muscle
Superficial veins (example- external jugular vein)
Cutaneous neurovascular supply
Superficial lymph nodes & Fat

DEEP CERVICAL FASCIA

This layer is further divided into various layers. These are (from superficial to deep):

Investing layer
Pretracheal layer
Prevertebral layer
Carotid sheath
Buccopharyngeal fascia
Pharyngobasilar fascia

INVESTING LAYER

It encloses 2 muscles (sternocleidomastoid and trapezius), 2 glands (Submandibular gland and Parotid gland) and 2 spaces (suprasternal space of Burns and supraclavicular space).

This cut section of the neck shows the investing layer:

Attachments :

Superiorly – external occipital protuberance, superior nuchal line, mastoid process and the base of mandible
Inferiorly -spine of scapula, acromion process, clavicle and manubrium sterni
Anteriorly -symphysis menti and hyoid bone (Above and below the hyoid bone the fascia is continuous)

PRETRACHEAL FASCIA

This layer encloses and suspends Thyroid gland and forms its “false capsule”. Posteriorly it thickens and forms the suspensory ligament of Berry which is attached to cricoid and thyroid cartilages, thus providing support to the thyroid gland. The fascia being smooth and slippery allows free moment of the trachea during deglutition.

Attachments :

Superiorly -Hyoid bone, oblique line of thyroid cartilage and cricoid cartilage
Inferiorly -blends with arch of aorta
On either side – forms the front of Carotid Sheath

PREVERTEBRAL FASCIA

Around the Vertebrae and prevertebral muscles. Forms that floor of the Posterior triangle of Neck and the posterior part of the carotid sheath. A portion of this fascia extends out with the brachial plexus and is called as the Axillary Sheath (containing trunks of brachial plexus and Subclavian artery; however, Subclavian vein lies outside the Axillary Sheath)

Attachments :

Superiorly – base of the skull
Inferiorly –(in the mediastinum) splits into Anterior and Posterior layer; anterior layer blends with buccopharyngeal fascia while the Posterior layer attached to the anterior longitudinal ligament of the Vertebrae.
On either side -fascia of sternocleidomastoid

CAROTID SHEATH

Formed anteriorly by the pretracheal fascia and posteriorly by the pre vertebral fascia.

Contents of Carotid Sheath :

Common Carotid artery (splits into internal and external carotid arteries, out of which the internal carotid artery remains within the sheath while the external branch pierces out)
Internal Jugular vein
Vagus nerve (CN X)
CN IX, CN XI, CN XII also present in the upper part of the sheath, but they pierce out.

Relations :

Anterior wall related to Ansa cervicalis
Posterior wall related to Cervical Sympathetic chain

OVERVIEW

NOTEWORTHY POINTS :

The investing layer of deep cervical fascia forms the “pulleys” for digastric and omohyoid muscle tendons
Investing layer also forms the stylomandibular ligament and the parotidomasseteric fascia
Cutting of the external jugular vein in the supraclavicular space may cause air embolism, due to the firm attachment of the fascia To the vein, which prevents the cut margins from joining and healing.

Buccopharyngeal fascia : covers the superior constrictor muscle externally; parallel to the prevertebral fascia.
Retropharyngeal space = space between the buccopharyngeal fascia and the prevertebral fascia.
Pharyngobasilar fascia : prominent between the superior constrictor muscle and the base of the skull.
The buccopharyngeal fascia is outside the pharynx and the pharyngobasilar fascia is deep to the pharyngeal muscles.