The carotid triangle is one of the natural geometrical formations of the neck. The triangle is located anterolaterally on each side of the neck. It is comprised of various anatomical structures that are noted as theoretical borders.
They surround other groups of anatomical structures (mainly vessels) ascending and descending in order to supply and drain the head and neck.
Each triangle has three sides which are known as borders. In this particular instance, the triangle happens to be a scalene triangle, where none of the sides are of equal length.
The posterior border which is the largest of the three sides or the base of the triangle is formed by the sternocleidomastoid muscle. Anteroinferiorly, the shortest side is composed of the omohyoid muscle and the anterosuperior border is limited by the posterior belly of the digastric muscle. The hyoid bone can be seen in the most anterior angle of the carotid triangle, with two of the three sides either originating or inserting upon it. Medially, the floor of the triangle is formed by parts of the thyrohyoid muscle, the hyoglossus muscle, and the middle and inferior pharyngeal constrictor muscles. It is covered laterally by the integument, the platysma, and the superficial and deep cervical fasciae.
As previously stated, the contents of the carotid triangle are made up of arteries, veins, and nerves. The points of interest are listed below according to the previously mentioned vessels.
Of the arteries in the triangle, the common carotid is the largest where it bifurcates in the upper corner of the triangle into the internal and external carotid arteries. Other arterial branches visible in this space are branches of the external carotid artery:
- the superior thyroid artery
- the lingual artery
- the facial artery
- the occipital artery
- the ascending pharyngeal artery
As for the veins, all branches correspond to a previously mentioned artery where they all drain into the internal jugular vein. The latter runs laterally to the common carotid artery. The list of branches includes the:
- superior thyroid vein
- the lingual veins
- common facial vein
- occipital vein
- ascending pharyngeal vein
When relating to the nerves, an important structure must first be mentioned before the other descending cranial nerves: the carotid sheath. It is formed by the middle cervical fascia where it encompasses the vagus nerve (CN X) as well as the internal jugular vein, the common carotid artery, and deep cervical lymph nodes. Superficial to the carotid sheath, the hypoglossal nerve (CN XII) also descends within the triangle, as does the accessory nerve (CN XI), and the ansa cervicalis profunda.
As mentioned above, the carotid triangle holds great importance for structures running through the neck. Some of these important structures are more superficial than others; carotid arteries, jugular veins, and vagus and hypoglossal nerves. These structures are often targets for various surgical approaches since they are relatively superficial.
The carotid triangle also houses the carotid sinus or bulb. This structure contains baroreceptors which are responsible in detecting stretch caused by pressure within a vessel and have a role in maintaining blood pressure (baroreceptor reflex). These receptors are innervated by a branch of the glossopharyngeal nerve and part of homeostatic mechanisms.