Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Cervical Adenopathy and Neck Masses
Classification
Cancer of the head and neck, which includes cancers of the larynx, nasal passages and nose, oral cavity, pharynx, salivary glands, buccal regions, and thyroid, is the sixth most frequent cancer worldwide. Neck masses can be grouped into two major types: nodal masses and nonnodal masses. Both types can appear as benign or malignant lesions. Most malignant nonnodal masses are epithelial malignancies of the mucous membranes of the upper aerodigestive tract, known as head and neck squamous cell carcinoma (SCC). A second major group of head and neck nonnodal masses arises from the glandular tissue, including thyroid and salivary glands. Less frequent head and neck nonnodal neoplasms include soft tissue and bone tumors (e.g., sarcomas), neuroectodermal tissue tumors (e.g., paragangliomas, malignant melanomas), and skin cancer (e.g., SCC, basal cell carcinoma).
Epidemiology
Chronic consumption of alcoholic beverages and smoking are accepted risk factors for head and neck cancer. In the upper aerodigestive tract, local morphologic, metabolic, and functional alterations lead to increased susceptibility to carcinogens and cell proliferation in the mucosa, resulting in genetic changes with the development of dysplasia, leukoplasia, and carcinoma. Also, radiation exposure is an established environmental factor for the development of glandular neoplasia.
Nodal masses in the head and neck result from regional metastases of malignant lesions of the head and neck or represent reactive enlargement due to inflammatory lesions or benign neoplasms. Lymphoma of the head and neck also presents with enlarged nodes. Cervical node metastases have variable incidence rates, and their presence is associated with a decrease in global survival to roughly half of affected patients; in addition, they are associated with higher recurrence rates.
Normal Anatomy
Gross Anatomy
The neck is composed of the posteriorly located nucha and the anteriorly located cervix. The nucha consists primarily of the vertebral column and its associated musculature, and the cervix (which also means “neck”) can be thought of as a cylinder of soft tissue whose superior extent is a line connecting the occiput and the tip of the chin and whose inferior extent parallels the course of the first rib at the thoracic inlet.
Muscles and Bones.
The most important landmarks to be grossly identified when one is studying the neck in any plane are the sternocleidomastoid muscle and the hyoid bone. The sternocleidomastoid muscle takes its origin from the mastoid tip and digastric notch at the skull base and extends anteriorly, inferiorly, and medially on each side to insert as two heads on the medial third of the clavicle and the manubrium. The course of the sternocleidomastoid muscle divides the soft tissues of the neck into two paired spaces, the anterior triangles and the posterior triangles (one on each side) ( Fig. 24-1 ). All structures located anterior to the sternocleidomastoid muscle lie within the anterior triangles, and structures deep and posterior to it are in the posterior triangles. The anterior triangles have a common side abutting each other in the midline, and their superior border is the mandible. The hyoid bone divides these triangles into a suprahyoid portion and an infrahyoid portion. The suprahyoid division contains the laterally located submandibular triangles and the medially located submental triangle. Superiorly these triangles are separated from the oral cavity by the mylohyoid muscle. By definition, structures above the mylohyoid muscle are in the oral cavity; those below are in the neck.
The base of each submandibular triangle is formed by the body of the mandible. The other two sides of each submandibular triangle are formed by the anterior and posterior bellies of the digastric muscle. The digastric muscle takes its origin from a depression on the skull base between the mastoid tip and the styloid process known as the digastric notch. The posterior belly of the digastric muscle extends anteriorly, inferiorly, and medially from the digastric notch to the greater cornu of the hyoid bone. The anterior belly of the digastric muscle extends from the greater cornu anteriorly, superiorly, and medially to insert on the internal surface of the mandible inferior to the attachment of the mylohyoid muscle. The base of the submental triangle is formed by the hyoid bone. The other two sides of the submental triangle are formed by the anterior bellies of the digastric muscles.
The infrahyoid division of each anterior triangle is divided by the superior belly of the omohyoid muscle into two parts, the carotid triangle superolaterally and the muscular triangle inferomedially. The infrahyoid portion of the anterior triangle contains the larynx, hypopharynx, trachea, esophagus, lymph nodes, and thyroid and parathyroid glands.
The two sides of each posterior triangle are the sternocleidomastoid muscle anteriorly and the trapezius muscle posteriorly. The base of each triangle is formed by the clavicle. The inferior belly of the omohyoid muscle crosses the inferior aspect of the posterior triangle and divides it into two unequal parts, the occipital triangle superiorly and the subclavian triangle inferiorly. The major structures located within the occipital triangle are the spinal accessory nerve (cranial nerve XI) and its associated chain of lymph nodes. The major structures located within the subclavian triangle are the transverse cervical vessels and their associated chain of lymph nodes.
Fasciae and Spaces of the Neck.
Interest in the fasciae of the neck stems from early anatomic investigations performed by surgeons who were seeking ways to predict the spread of infection. The importance of the fasciae of the neck lies in their ability to limit the spread of infections and some tumors.
There is no consistent definition of what constitutes fascia, so there are varied descriptions of the anatomic boundaries of the fasciae ( Figs. 24-2 and 24-3 ). Traditionally there are two major cervical fasciae, the superficial cervical fascia (SCF) and the deep cervical fascia (DCF).
Superficial cervical fascia.
The SCF is a layer of fatty loose connective tissue that covers the head, face, and neck and contains the thin platysma muscles, the muscles of facial expression, the subcutaneous nerves and lymphatics, and portions of the anterior and external jugular veins. Its primary function is to allow the skin to glide easily over the deeper structures of the neck. Infections that track along the SCF are often secondary to skin infections and rarely track deeper into the neck.
Deep cervical fascia.
The DCF is made up of thinner but denser, better-defined layers and extends in the neck below the skull base and encloses the muscles of the neck, the mandible, and the muscles of mastication and deglutition. It consists of three layers: (1) the superficial (or investing) layer (SLDCF) surrounding all the important structures of the neck; (2) the middle layer, with the pretracheal and visceral layers (MLDCF) surrounding the aerodigestive tract; and (3) the deep layer (DLDCF) surrounding the vertebral column and paravertebral muscles. The DLDCF has two divisions separated by a potential space: the alar layer anteriorly and the prevertebral layer posteriorly. All three layers are closely associated in the anterolateral neck, where they contribute to the formation of the carotid sheath, which surrounds the carotid artery, internal jugular vein, and vagus nerve.
Superficial layer of the deep cervical fascia.
The SLDCF is attached posteriorly to the ligamentum nuchae and the spinous processes of the cervical vertebrae. As it extends anteriorly the fascia splits to envelop the trapezius and sternocleidomastoid muscles, crossing the posterior triangle of the neck. In the suprahyoid neck, the SLDCF passes over the muscles below the floor of the mouth, splits to surround the submandibular glands, and when it reaches the mandible, divides into superficial and deep leaflets that enclose the muscles of mastication and form the masticator space. The SLDCF is attached superiorly to the external occipital protuberance, mastoid process, and skull base.
In the infrahyoid neck, the SLDCF encircles the strap muscles (sternothyroid, sternohyoid, and thyrohyoid muscles) anterior to the larynx and trachea (although some authors believe this fascia is part of the MLDCF). The fascia also invests the omohyoid muscle, holding the muscle close to the clavicle so that contraction of the muscle results in a downward rather than a lateral pull on the hyoid bone. Caudally in the midline the SLDCF splits into two layers enclosing the manubrium. This creates the variably sized suprasternal space of Burns (or Gruber), which contains fat and a communicating vein between the left and right anterior jugular veins. If this space is entered during a tracheostomy, inadvertent transection of the communicating vein may result in considerable blood loss. Caudally the SLDCF is attached into the pectoral and axillary regions.
Middle layer of the deep cervical fascia.
The MLDCF is the most arbitrarily described of the fascial layers. The MLDCF in the infrahyoid neck is most commonly considered the fascia between the sternocleidomastoid muscles, passing behind the strap muscles and lying in front of the thyroid gland and trachea (many authors consider this loose connective tissue about the trachea and thyroid gland not to be part of the MLDCF). The deepest portion of the MLDCF is closely adherent to the muscular walls of the pharynx and esophagus and extends ventrally via the pterygomandibular raphe over the buccinator muscles (buccopharyngeal fascia). Inferiorly the MLDCF extends behind the sternum into the origin of the strap muscles and fuses into the fibrous pericardium (at about the level of the fourth thoracic vertebra), forming the anterior border of the retropharyngeal space. Cranially the MLDCF fuses with the thyroid cartilage and the hyoid bone, and laterally it contributes to the carotid sheath on either side of the neck.
The MLDCF in the suprahyoid neck extends from the skull base and follows the outer surface of the pharyngobasilar fascia (cranial continuation of the superior pharyngeal constrictor muscle) and the pharyngeal constrictors. Here the fascia is firmly adherent to the muscular wall of pharynx and esophagus, although some authors argue for the existence of a potential visceral space between the fascia and the viscera.
Deep layer of the deep cervical fascia.
The DLDCF, like the SLDCF, begins in the posterior midline and extends to the side, covering and investing the muscles that form the floor of the posterior triangle. The deep layer is attached laterally to the posterior tubercles of the transverse processes of the vertebrae, where it splits into the anterior alar and posterior prevertebral layers as they extend anterior to the vertebral body (between them lies a layer of loose connective tissue). The alar and prevertebral layers have different craniocaudal extensions. Although both attach superiorly at the skull base, the alar layer blends with the visceral layer along the posterior margin of the esophagus at the level between the sixth cervical and fourth thoracic vertebrae; the prevertebral layer extends from the skull base to the coccyx. The proximal portion of each phrenic nerve lies deep to the prevertebral fascia on the anterior face of each anterior scalene muscle. On each side of the neck, the DLDCF extends laterally from the transverse process of the seventh cervical vertebra, covers the dome of the pleura, and attaches to the rib medially. This fascia separates the lower neck from the thorax and is called Sibson's fascia.
Neck spaces.
The three layers of the DCF delineate spaces in and through which bacterial infections can spread in the infrahyoid neck.
Visceral space.
The visceral space includes all structures within the confines of the MLDCF (pharynx, cervical esophagus, trachea, thyroid gland, parathyroid glands, larynx, recurrent laryngeal nerves, and portions of the sympathetic trunk) and is continuous with the anterior mediastinum. It is considered to have two subdivisions: an anterior pretracheal space and a more posterior retrovisceral space (see later), which communicate freely around the sides of the larynx, the lowermost pharynx, and the upper cervical esophagus between the levels of the thyroid cartilage and the inferior thyroid artery. Caudal to this level, the pretracheal space is separated from the retrovisceral space by dense connective tissue. The posterior margin of the retrovisceral space is the alar layer of the DLDCF.
Retropharyngeal space.
The retropharyngeal space is situated in the midline directly posterior to the pharynx. The anterior boundary of the retropharyngeal space is formed by the MLDCF fascia, and the posterior boundary is formed by the DLDCF. The retropharyngeal space can be further divided by the alar layer of the DLDCF into the retrovisceral space anteriorly and the danger space posteriorly. Depending on its location, infection in the retropharyngeal space can extend inferiorly in the retrovisceral and pretracheal space (it is common that a retropharyngeal abscess can affect the thyroid gland and anterior mediastinum) to the level of approximately C7 (where the alar layer and the visceral layer fuse) or in the danger space just above the level of the diaphragm, where the fused alar and visceral fasciae fuse with the prevertebral fascia. Because the danger space is a closed one, the infection must penetrate its walls to enter the space. Because it is impossible to separate these two smaller spaces radiographically, the retropharyngeal space may be considered a single radiographic space, with the recognition that all infections in the retropharyngeal space must be evaluated in full, and scans of either the superior mediastinum or entire chest may be necessary ( Fig. 24-4 ).
Prevertebral space.
The vertebral space is a potential space that includes those structures (vertebral bodies, paravertebral and scalene muscles, vertebral arteries) that are surrounded by the DLDCF. Infections of the prevertebral space are usually secondary to vertebral infection (osteomyelitis) or posterior extension arising in the retropharyngeal space. The vast majority of the pathology that affects this space arises from the adjacent vertebral bodies, disks, and nerves.
Carotid space.
The carotid space is a potential space within the carotid sheath. Investigators doubt whether this cavity can act as a space that allows spread of infections. Furthermore, because little areolar tissue is present within the sheath, actual infection of the carotid space is rare. The most accepted theory is that the carotid sheath may be a true space only below the carotid bifurcation and above the root of the neck. Similarly there is controversy over whether the carotid sheath in the suprahyoidal neck should be considered a separate “carotid space” or part of the parapharyngeal space. We support the latter opinion, which follows the anatomic and surgical literature. Remarkably the carotid sheath, with its contributions from all three layers of the deep cervical fascia, can act as a conduit of infection from one space to another. Septic or reactive thrombosis of the internal jugular vein may produce swelling within the carotid space. The internal jugular vein and its associated chain of lymph nodes closely parallel the deep surface of the anterior margin of the sternocleidomastoid muscle, thereby bridging the anterior and posterior triangles. The arterial and neural components of the carotid sheath, common carotid artery, internal carotid artery, and vagus nerve also traverse the neck within the anterior triangle.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here