Fascia of the Neck
The cervical fascia consists of concentric layers of fascia that compartmentalize structures in the neck (Figure 25-1). These fascial layers are defined as the superficial fascia and the deep fascia, with sublayers within the deep fascia. The fascia of the neck can determine the direction in which infection in the neck may spread.
The superficial cervical fascia is the subcutaneous layer of the skin in the neck. This thin layer contains the muscles of facial expression, including the platysma muscle in the neck. The cutaneous nerves, superficial vessels, and superficial lymph nodes course within the superior cervical fascia.
The deep cervical fascia is deep to the superficial fascia. The deep cervical fascia is condensed in various regions to form the following sublayers: the investing layer of the deep cervical fascia, the pretracheal fascia, the prevertebral fascia, and the carotid sheath. The function of the deep fascia is to provide containment of muscles and viscera in compartments, to enable structures to slide over each other, and to serve as a conduit for neurovascular bundles.
The investing fascia attaches as follows:
- Posteriorly to the nuchal ligament, completely encircling the neck and splitting to enclose the sternocleidomastoid and trapezius muscles.
- Superiorly to the hyoid bone and then splitting to enclose the submandibular gland.
- Along the mandible and splitting to enclose the parotid gland.
- Superiorly to the mastoid process, occipital bone, and zygomatic arch.
- Inferiorly along the acromion, scapular spine, clavicle, and manubrium.
The pretracheal fascia forms a tubular sheath in the anterior part of the neck. The pretracheal fascia extends superiorly from the hyoid bone and inferiorly to the thorax, where it blends with the fibrous pericardium. The pretracheal fascia:
- Encloses the infrahyoid muscles.
- Encloses separately the thyroid gland, trachea, and esophagus.
- Blends laterally with the carotid sheath.
- Is contiguous inferiorly with the buccopharyngeal fascia of the pharynx.
The prevertebral fascia forms a tubular sheath around the vertebral column and the prevertebral muscles, which are attached to the vertebral column. The prevertebral muscles are:
- Anteriorly, the longus colli and capitis muscles.
- Laterally, the anterior, middle, and posterior scalene muscles.
- Posteriorly, the deep cervical muscles.
The prevertebral fascia:
- Attaches superiorly from the base of the skull and inferiorly to the endothoracic fascia in the thorax.
- Extends laterally as the axillary sheath, which surrounds the axillary vessels and brachial plexus of nerves to the upper limb.
- Contains, within its connective tissue fibers, the cervical sympathetic trunk and ganglia.
The carotid sheath also is a tubular fascial investment that extends superiorly between the cranial base and inferiorly to the root of the neck.
- The carotid sheath blends with the investing, pretracheal, and prevertebral layers of the deep cervical fascia.
- The carotid sheath contains the common and internal carotid arteries, internal jugular vein, and vagus nerve [cranial nerve (CN) X]. In addition, the carotid sheath contains deep cervical lymph nodes, sympathetic fibers, and the carotid sinus nerve.
The retropharyngeal space is a potential space consisting of loose connective tissue between the prevertebral and the buccopharyngeal fascia.
The retropharyngeal space serves as a potential conduit for the spread of infection from the pharyngeal region to the mediastinum.
Muscles of the Neck
The muscles of the neck are organized and grouped with the cervical fascia. The platysma muscle is located within the superficial fascia, and the sternocleidomastoid and trapezius muscles are located within the investing fascia (part of the deep cervical fascia). Vertebral muscles (prevertebral, scalene, and deep cervical) are located within the prevertebral fascia. The suprahyoid muscles are deep to the investing fascia, whereas the infrahyoid muscles are within the pretracheal fascia. The vertebral muscles are within the prevertebral fascia.
The platysma muscle is the most superficial muscle of the neck. Unlike most skeletal muscles, the platysma is located in the superficial fascia (Figure 25-2A and B). The muscle extends superiorly from the inferior border of the mandible and inferiorly to the clavicle to the fascia of the anterior shoulder and thorax. The platysma muscle is a muscle of facial expression and therefore is innervated by the facial nerve (cervical branch of CN VII). Upon contraction, the platysma depresses the mandible and wrinkles the skin of neck.
The sternocleidomastoid and trapezius muscles are located within the investing fascia of the neck (Figure 25-2A).
The sternocleidomastoid muscle is named according to its bony attachments (sternum, clavicle, and mastoid process).
- The sternocleidomastoid muscle creates the borders for both the anterior and the posterior triangles of the neck, and is innervated by the spinal accessory nerve (CN XI).
- This muscle flexes the neck, pulls the chin upward, and assists in elevating the rib cage during inspiration.
The trapezius muscle creates the anterior border of the posterior cervical triangle.
- The trapezius muscle attaches to the occipital bone, nuchal ligament, spinous processes of C7–T12, scapular spine, acromion, and the lateral part of the clavicle.
- The sternocleidomastoid muscle is innervated by CN XI.
During a physical examination, the functions of the sternocleidomastoid and trapezius muscles are evaluated together because they share the same innervation. During the examination, the physician looks for signs of muscle atrophy or weakness. To test the sternocleidomastoid muscle, the physician will place her hand on the patient’s chin and instruct him to rotate his head to the opposite side against resistance. If acting normally, the patient’s muscle can be seen and palpated. The physician next will instruct the patient to shrug his shoulders against resistance. Patients with damage to CN XI will have diminished shoulder strength while shrugging on the injured side.