Carotid triangle of the neck

Layer-by-layer structure of the region

Access to deep structures of the carotid triangle requires sequential dissection of several anatomical layers, each with its own characteristics:

1. Skin and superficial fascia. The skin here is thin and quite mobile. The first fascia of the neck is tightly fused with the skin, and it is within its thickness that the platysma muscle (m. platysma) lies. This muscle forms a broad sheet that completely covers the boundaries of the carotid triangle.
2. Subplatysmal tissue. Important neural and venous pathways run in the loose tissue between the first and second fasciae. Here lies the cervical branch of the facial nerve (ramus colli n. facialis) and, in some cases, the upper branch of the transverse cervical nerve (n. transversus colli). Among the venous collectors, the anterior jugular vein (v. jugularis anterior) stands out, actively anastomosing with the external jugular and retromandibular veins.
3. Second (proper) fascia of the neck. It runs from the anterior border of the sternocleidomastoid muscle (m. sternocleidomastoideus) to the midline of the neck. By fusing with the corresponding layer of the opposite side, it forms the linea alba of the neck.
4. Through the posterior wall of the fascial sheath, deep main structures begin to show through: the internal jugular vein and the common carotid artery.

Neurovascular bundle

The main value of the carotid triangle is the powerful neurovascular bundle enclosed in a common fascial sheath.

The bundle includes:

• Common carotid artery (a. carotis communis).
• Internal jugular vein (v. jugularis interna).
• Vagus nerve (n. vagus).
• Deep cervical lymph nodes (nodi lymphatici cervicales profundi).

The topography of the bundle elements is strictly ordered. The vagus nerve lies between the vein and the artery, slightly posterior to them. The anterior wall of the fascial sheath is often pierced by the facial nerve vein, which drains into the internal jugular. Descending over the fascial sheath is the superior root of the cervical loop (radix superior). Joining with the inferior root, it forms the ansa cervicalis (ansa cervicalis), the fibers of which provide motor innervation to the infrahyoid muscles.

Nervous structures of the carotid triangle

In addition to the main trunk of the vagus nerve, a number of critically important neural structures are located within the triangle:

• Superior cervical ganglion of the sympathetic trunk. Located within the thickness of the prevertebral fascia, posterior and slightly medial to the vagus nerve.
• Superior laryngeal nerve (n. laryngeus superior). This branch departs from the inferior ganglion of the vagus nerve and crosses the triangle posterior to the branches of the external carotid artery. It divides into two portions. The internal branch (sensory) pierces the thyrohyoid membrane and innervates the laryngeal mucosa above the vocal fold. The external branch runs to the cricothyroid muscle, the inferior constrictor of the pharynx, and the thyroid gland.
• Superior cervical cardiac branches (rr. cardiaci cervicales superiores). These contain the depressor nerve, which heads toward the reflexogenic zone of the carotid artery bifurcation.

Bifurcation and reflexogenic zones

The division of the common carotid artery into external (a. carotis externa) and internal (a. carotis interna) most frequently (54%) occurs at the level of the upper border of the thyroid cartilage. In 29% of cases, the bifurcation is located higher—at the level of the hyoid bone, and extremely rarely reaches the angle of the mandible. Important topographic rule: the external carotid artery is usually located medial and anterior to the internal.

The bifurcation zone plays a colossal role in homeostasis regulation due to two structures:

1. Carotid sinus (sinus caroticus). Represents a dilation of the initial segment of the internal jugular artery (internal carotid artery). Contains baroreceptors that respond to changes in blood pressure. Innervated by a powerful periarterial plexus (sinocarotid nerve, branches of the vagus and sympathetic trunk).
2. Carotid body (glomus caroticum). A small (grain-of-rice-sized) yellowish-red structure on the posterior surface of the bifurcation. This is a cluster of chemoreceptors that detect oxygen deficiency and excess carbon dioxide, participating in the fine regulation of respiration and hemodynamics parameters.

Briefly: answers to topical questions

What else to study on this topic

• Topography of the adjacent submandibular triangle (Trigonum submandibulare)
• Surgical approaches to the major vessels of the neck
• Vagoganglion / vagosympathetic block technique
• Lymph drainage from neck structures and deep cervical lymph nodes
• Clinical significance of anterior jugular vein anastomoses

Other topics in "Topographic Anatomy of the Neck"

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