Anterior Triangle of the Neck and its Subdivisions
The anterior triangle of the neck is an anatomical division created by the muscles of the head and neck. It is used clinically to locate structures that pass through the neck. In this article, we shall look at the regional anatomy of the anterior triangle and its subdivisions.
It is important to note that all triangles mentioned here are paired – they will appear on the left and the right side of the neck.
The anterior triangle is situated at the front of the neck.
It is bounded:
- Superiorly – Inferior border of the mandible (jawbone)
- Laterally – Medial border of the sternocleidomastoid
- Medially – Imaginary sagittal line down midline of body
It can be subdivided into 4 further triangles, which we will look at later on.
The anterior triangle of the neck contains muscles, nerves, arteries, veins and lymph nodes.
The muscles in this part of the neck are divided as to where they lie in relation to the hyoid bone. There are four suprahyoid muscles (stylohyoid, digastric, mylohyoid, and geniohyoid) and four infrahyoid muscles (omohyoid, sternohyoid, thyrohyoid, and sternothyroid)
With respect to the vasculature, the common carotid artery passes through the anterior triangle, and bifurcates within the triangle into the external and internal carotid arteries. The internal jugular vein also can be found within this area. It drains blood from the head and neck.
Numerous cranial nerves are located in the anterior triangle. Some pass straight through, and others give off branches to innervate some of the other structures within the triangle. The cranial nerves in the anterior triangle are the facial [VII], glossopharyngeal [IX], vagus [X],accessory [XI], and hypoglossal [XII] nerves.
The hyoid bone, suprahyoid and infrahyoid muscles are used to further subdivide the anterior triangle into four triangles. We shall look at the borders and contents of each.
The carotid triangle of the neck has the following boundaries:
- Superior: Posterior belly of the digastric muscle.
- Lateral: Medial border of the sternocleidomastoid muscle.
- Inferior: Superior belly of the omohyoid muscle.
The main contents of the carotid triangle are the common carotid artery (which bifurcates within the carotid triangle into the external and internal carotid arteries), the internal jugular vein, and the hypoglossal and vagus nerves.
Clinical Relevance: Medical Uses of the Carotid Triangle
In the carotid triangle, many of the vessels and nerves are relatively superficial, and so can be accessed by surgery. The carotid arteries, internal jugular vein, vagus and hypoglossal nerves are frequent targets of this surgical approach.
The carotid triangle also contains the carotid sinus – a dilated portion of the common carotid and internal carotid arteries. It contains specific sensory cells, called baroreceptors. The baroreceptors detect stretch as a measure of blood pressure. The glossopharyngeal nerve feeds this information to the brain, and this is used to regulate blood pressure.
In some people, the baroreceptors are hypersensitive to stretch. In these patients, external pressure on the carotid sinus can cause slowing of the heart rate and a decrease in blood pressure. The brain becomes underperfused, and syncope results. In such patients, checking the pulse at the carotid triangle is not advised.
The submental triangle in the neck is situated underneath the chin. Its main content is the submental lymph nodes, which filter lymph draining from the floor of the mouth and parts of the tongue.
It is bounded:
- Inferiorly – Hyoid bone.
- Medially – Imaginary sagittal midline of the neck.
- Laterally – Anterior belly of the digastric.
The base of the submental triangle is formed by the mylohyoid muscle, which runs from the mandible to the hyoid bone.
The submandibular triangle is located underneath the body of the mandible. It contains the submandibular gland (salivary), and lymph nodes. The facial artery and vein also pass through this area.
The boundaries of the submandibular triangle are:
- Superiorly: Body of the mandible.
- Anteriorly: Anterior belly of the digastric muscle.
- Posteriorly: Posterior belly of the digastric muscle.
This anatomical area is situated more inferior than the triangular sub-divisions. It is a slightly dubious triangle, in reality having four boundaries. The muscular triangle is also unique in containing no vessels of note. It does however contain some muscles and organs – the infrahyoid muscles, the pharynx, and the thyroid, parathyroid glands.
The boundaries of the muscular triangle are:
- Superiorly: The hyoid bone.
- Medially: Imaginary midline of the neck.
- Supero-laterally: Superior belly of the omohyoid muscle.
- Infero-laterally: Inferior portion of the sternocleidomastoid muscle.