The topographic description of the neck intends to serve as a guide in which the external and readily accessible superficial features of the neck provide essential landmarks for deep structures. This is a critical element in the examination and description of clinical findings.
From a topographic standpoint, the sternocleidomastoid muscle and the carotid sheath divide each side of the neck into two different spaces. Although pyramidal in shape, these spaces are known as the anterior and posterior triangles of the neck (Fig. 2-8). The posterolateral space has a cranial apex at the level of the mastoid and a base at the level of the clavicle. It does not have a definite anatomical boundary, because it merges into the axilla through the cervicoaxillary canal. The apex of the medial space is located at the bottom of the neck and its base lies at the level of the submandibular gland and tail of the parotid gland. These spaces contain the lymph nodes that drain most cervical structures.
The anterior triangle is bounded by the anterior midline of the neck, the anterior border of the sternocleidomastoid muscle, and the inferior border of the mandible. The jugular notch constitutes the apex, and the base is formed by the inferior border of the mandible. The posterior belly of the digastric muscle and the superior belly of the omohyoid further divide this space into several smaller triangles (i.e., submental, submandibular, carotid, and muscular) (Fig. 2-9).
The submental triangle is an unpaired space bounded on each side by the anterior belly of the digastric muscle, posteriorly by the body of the hyoid bone, and anteriorly by the inferior border of the mandible. The floor of the submental triangle is formed by the mylohyoid muscles, which meet in a median fibrous raphe. This space is occupied by fat and lymph nodes.
The submandibular triangle is limited on each side by the inferior border of the mandible and the anterior and posterior bellies of the digastric muscle. The muscular floor of the submandibular triangle is formed, from anterior to posterior, by the mylohyoid, hyoglossus, and middle constrictor of the pharynx. The mylohyoid muscle further divides it into supramylohyoid and
inframylohyoid spaces. The supramylohyoid space contains the sublingual gland. The submandibular gland and a variable number of lymph nodes are contained within the inframylohyoid space. The lingual nerve, the hypoglossal nerve, part of the facial artery and vein, and the submental artery pass through this triangle.
The carotid triangle (also known as the superior carotid triangle) is bounded superiorly by the posterior belly of the digastric muscle, inferiorly by the superior belly of the omohyoid muscle, and posteriorly by the anterior border of the sternocleidomastoid muscle. The carotid triangle provides an important surgical approach to the carotid system. The common carotid artery divides into the internal and external branches at the level of the superior border of the thyroid cartilage. Many important structures, such as the common carotid artery, internal jugular vein, vagus nerve, and sympathetic trunk, lie within the limits of this space. The inferior part of the carotid triangle contains the common carotid artery medially, the internal jugular vein laterally, the vagus nerve posteriorly, and the ansa cervicalis. Many deep cervical lymph nodes lie along the internal jugular vein, and between the vein and the common carotid artery, within the carotid sheath.
The muscular triangle (or inferior carotid triangle) is bounded by the superior belly of the omohyoid muscle, the anterior border of the sternocleidomastoid muscle, and the midline of the neck. It contains the strap muscles, the thyroid and parathyroid glands, the trachea, and the esophagus.
The posterior cervical triangle is bounded anteriorly by the posterior border of the sternocleidomas-toid muscle, posteriorly by the anterior border of the trapezius, and inferiorly by the middle third of the clavicle. Its floor is formed, from superior to inferior, by the splenius capitis, levator scapulae, and medial and posterior scalene muscles. The inferior belly of the omohyoid muscle crosses the space dividing it into two smaller triangles (Fig. 2-10), the occipital triangle above and the omoclavicular or subclavian triangle below. The occipital triangle contains the spinal accessory nerve and part of the cervical and brachial plexuses. The occipital artery crosses the upper part of this triangle. The omoclavicular triangle corresponds to the supraclavicular fossa.
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