“An important function of the cervical fascia is to guide against the spread of pus and debris (abscesses) resulting from diseased or abnormal tissues, however, a potential pathway for spread of infection exists...”
As applies to most walls of several regions of the body, structures making up the neck are surrounded by a layer of subcutaneous tissue called the superficial cervical fascia, and are compartmentalized by a second group of fasciae referred to as deep cervical fascia.
Superficial Cervical Fascia
This is a thin layer of subcutaneous connective tissue that lies between the dermis of the skin and the investing layer of deep cervical fascia. It is thinner on the anterior aspect of the neck where it houses the platysma muscle. It also surrounds and contains the cutaneous nerves, blood and lymphatic vessels, superficial lymph nodes, and variable (usually thinner compared to other regions) amounts of fat, which is its distinguishing characteristic. Because of this unusually thin amount of fat, some experts do not consider the superficial cervical fascia as a free fascia but rather as a part of the Panniculus adiposus.
Deep Cervical Fascia
The deep cervical fascia acts to compartmentalize most structures of the neck and prevents the spread of infections. It consists of three fascial layers (or sheaths), which are:
- The investing layer of deep cervical fascia
- Pretracheal layer of deep cervical fascia
- The prevertebral layer of deep cervical fascia.
These layers of the deep cervical fascia also function to support the viscera of the neck (e.g., the thyroid gland), muscles, blood and lymphatic vessels, and deep lymph nodes. They also form the carotid sheath that wraps around vessels like the common carotid arteries, internal jugular veins, and the vagus nerves. They also serve as landmarks and natural planes through which tissues may be separated during surgery.
In addition, these layers of deep cervical fascia provide flexibility and slipperiness that allows structures in the neck to glide over one another without difficulty, such as when swallowing and turning the head and neck.
Furthermore, some authors consider the deep cervical fascia to be made up of four parts, with the carotid sheath being the fourth, and the above three layers, the first three parts.
This layer of the deep cervical fascia is a collar of fascia surrounding the whole neck and contains the trapezius and sternocleidomastoid muscles. The investing layer is comparable to deep fascias of other regions of the body. It is the most superficial deep fascial layer. At the four midpoints (anterior, posterior and two lateral) of the neck, this investing layer splits into superficial and deep layers to invest the above muscles which have the same embryonic origin and nerve supply as this layer of deep cervical fascia.
Inferiorly, the investing layer attach to the manubrium of sternum, spine of the scapular, acromion of scapular and the clavicles. Superiorly to the cranial base [more specifically to the superior nuchal line of the occipital bone, mastoid processes of the temporal bones, zygomatic arches, inferior border of the mandible, hyoid bone (hence the chin and Adams apple of man in profile) and the spinous processes of the cervical vertebrae]. Posteriorly, this layer of deep cervical fascia is continuous with the periosteum covering the C7 spinous process, and with the ligamentum nuchae.
Inferior to its attachment to the mandible, the investing layer splits to enclose the submandibular gland, while posterior to the mandible, precisely between the angle of the mandible and the tip of the mastoid process, it also splits to form the fibrous capsule of the parotid glands.
As the name implies, this layer of the deep cervical fascia forms a tubular sheath for the vertebral column and the muscles (such as the longus colli and longus capitis) associated with the vertebral column.
Superiorly, this layer is attached to the cranial base, and it extends downwards to the lower limit of the longus colli muscle at the level of the body of T3 vertebral column where it blends with the endothoracic fascia peripherally (laterally) and to the anterior longitudinal ligament centrally. It also extends laterally as the axillary sheath, surrounding the axillary artery , the axillary vein and brachial plexus (the network of nerves supplying the upper limbs).
The prevertebral layer contains the cervical parts of the sympathetic trunks, the above mentioned muscles, the scalenus muscles and deep cervical muscles. Functionally, this layer provide a fixed basis on which the pharynx, oesophagus and carotid sheaths (4th part of deep cervical fascia) can glide during neck movements and swallowing, undisturbed by any movements of the prevertebral muscles.
This is the fourth part or layer of the deep cervical fascia. It is a tubular fascial investment that extends from the cranial base to the root of the neck. Anteriorly, this sheath blends with the investing and pretracheal layers of the deep cervical fascia, posteriorly it is continuous with the prevertebral layer, and it contains the common carotid arteries, internal carotid arteries, internal jugular vein, the vagus nerve (CN X), some deep cervical lymph nodes, carotid sinus nerve, and sympathetic nerve fibres (carotid periarterial plexuses).
Inferiorly, the carotid sheath and pretracheal fascia communicate freely with the mediastinum of the thorax, and also communicate with the cranial cavity superiorly. Thus, although a primary aim of the deep cervical fascia is to prevent the spread of abscesses, those communications with the mediastinum and cranial cavity represent potential pathways for the spread of infection and extravasated blood.
This layer of deep cervical fascia is a thin fascia limited to the anterior part of the neck. It is named after the trachea, to which it provides a slippery surface for up and down gliding during swallowing and neck movements.
It extends inferiorly from the hyoid into the thorax, where it blends with the fibrous pericardium of the heart. It is made up of two parts, a muscular part and a visceral, and contains the trachea, infrahyoid muscles, thyroid gland and the oesophagus. Posteriorly, it is continuous with the buccopharyngeal fascia of the pharynx, and laterally with the carotid sheaths.
The most significant clinical importance of the cervical fascia is prevention of the spread of pus and debris. However, this function is mainly restricted to the deep cervical fascia which lies closer to the neck viscera and muscles. For example, if an infection occurs between the investing layer of deep cervical fascia and the muscular part of the pretracheal fascia surrounding the infrahyoid muscles, the infection will usually not spread beyond the superior edge of the manubrium. Pus from an abscess posterior to the prevertebral layer of deep cervical fascia may extend laterally in the neck and form a swelling posterior to the sternocleidomastoid muscle. Such pus may perforate the prevertebral layer and enter the retropharyngeal space, producing a bulge in the pharynx, a condition referred to as retropharyngeal abscess which may cause difficulty in swallowing (dysphagia) and speaking (dysarthria). Infections in the head may also spread inferiorly, through the carotid sheath, to the mediastinum.