Neck Triangles: What are they? General Anatomy, Clinical Relevance, and Related Conditions

They are surgically centered divisions of the neck, first described from anatomical studies based on early dissection.

They preceded a cross-sectional anatomical description based on cross-sectional images.

The side of the neck has a quadrilateral contour, limited above by the lower border of the body of the mandible, and an imaginary line that extends from the angle of the mandible to the mastoid process; below, by the superior border of the clavicle; in front, along the midline of the neck; behind, by the anterior margin of the trapezius.

This space is subdivided into two large triangles by the sternocleidomastoid, which passes obliquely through the neck, from the sternum and clavicle below, to the mastoid process and the anterior occipital bone .

The triangular space in front of this muscle is called the anterior triangle; and behind that, the posterior triangle.

Anatomists use the term neck triangles to describe the divisions created by the major muscles in the region.

The anterior triangle is divided into muscular, carotid, submandibular and submental, and the posterior one into occipital and subclavian triangles.

General anatomy

The neck is divided into anatomical triangles to facilitate description and surgical localization. The two main triangles are the front and back triangles. They are separated by the sternocleidomastoid muscle (SCM).

The posterior triangle: it is delimited anteriorly by the sternocleidomastoid muscle, inferiorly by the clavicle, posteriorly by the anterior border of the trapezius muscle and superiorly by the superior nuchal line.

It can be further divided into the occipital and supraclavicular triangles by the lower belly of the omohyoid muscle that extends transversely.

The occipital triangle : it is the superior of the two and contains the superficial branches of the cervical plexus , as well as the trunks of the brachial plexus (PB) and the spinal accessory nerve or spinal accessory nerve. It is also the largest division of the posterior triangle.

It is delimited, in front, by the sternocleidomastoid; behind, by the trapeze; below, by the omohyoid.

Its floor is formed from top to bottom by the splenium of the head, the levator scapulae muscle, the middle scalene, and the posterior scalene. It is covered by the skin, the superficial and deep fascia, and the platysma below.

The accessory nerve runs obliquely through the space from the sternocleidomastoid, perforating to the lower surface of the trapezius; below, the supraclavicular nerves and the transverse cervical vessels and the upper part of the brachial plexus cross the space.

There is also a chain of lymph nodes that runs along the posterior border of the sternocleidomastoid, from the mastoid process to the root of the neck.

The supraclavicular triangle: also known as the omoclavicular or subclavian triangle, the subclavian triangle, the smallest division of the posterior triangle, is bounded, above, by the lower belly of the omohyoid; below, by the clavicle and its base is formed by the posterior border of the sternocleidomastoid.

Its floor is formed by the first rib with the first fingering of the serratus anterior. The size of the subclavian triangle varies with the extent of the union of the clavicular portions of the sternocleidomastoid and the trapezius, and also with the height at which the omohyoid crosses the neck.

Its height also varies according to the position of the arm, decreasing when raising the limb, due to the elevation of the clavicle, and increasing when pulling the arm down, when that bone is depressed.

This space is covered by the integument, the superficial and deep fascia, and the platysma, and crossed by the supraclavicular nerves.

Just above the level of the clavicle, the third portion of the subclavian artery curves outward and downward from the lateral border of the anterior scalene, through the first rib, to the axilla, and this is the most commonly chosen location for bind the glass.

Sometimes this vessel rises up to 4 cm. Above the clavicle; occasionally, it passes in front of the anterior scalene or pierces the fibers of that muscle.

The subclavian vein is located behind the clavicle and is usually not seen in this space; but in some cases it rises up to the artery, and it has even been seen that it passes with that vessel behind the anterior scalene.

The brachial plexus of nerves lies above and in close contact with the artery. Passing transversely behind the clavicle are the transverse scapular vessels; and crossing its superior angle in the same direction, the transverse cervical artery and vein.

The external jugular vein runs vertically down behind the posterior border of the sternocleidomastoid, ending at the subclavian vein; It receives the transverse cervical and transverse scapular veins, which form a plexus in front of the artery, and occasionally a small vein that crosses the clavicle from the cephalic.

The small subclavian nerve also crosses this triangle around its center, and some lymphatic glands are generally found in space.

The anterior triangle of the neck : It is more complicated and contains more anatomical structures than the posterior triangle. It is divided into at least four smaller triangles. The first, and the least complex, is the submental triangle.

It is an unpaired triangle that is bilaterally delimited by the mandibular symphysis, the hyoid, and the anterior bellies of the digastric muscles. The mylohyoid muscles form the floor of the triangle. Its content is largely veins and lymph nodes.

The carotid triangle : The carotid triangle contains the carotid sheath and is the site where the common carotid bifurcates into the external and internal carotid arteries. Several nerves also traverse the carotid triangle, including the hypoglossal nerve, exiting the submandibular triangle.

The lower carotid, or muscular triangle, is bounded in front by the midline of the neck from the hyoid bone to the sternum; behind, by the anterior margin of the sternocleidomastoid; above, by the upper belly of the omohyoid.

It is covered by the integument, superficial fascia, platysma and deep fascia, branching into which some of the branches of the supraclavicular nerves are found.

Beneath these superficial structures are the sternohyoid and sternothyroid, which, together with the anterior margin of the sternocleidomastoid, conceal the lower part of the common carotid artery.

Therefore, the common carotid artery and the internal jugular vein are not, strictly speaking, within this triangle, as they are covered by the sternocleidomastoid; that is, they lie below that muscle, which forms the back edge of the triangle.

But since they are very close to the structures that are actually contained in the triangle, and whose position it is essential to remember when operating on this part of the artery, it is convenient to study the relationships of all these parts together.

This vessel is enclosed within its sheath, along with the internal jugular vein and the vagus nerve; the vein is lateral to the artery on the right side of the neck, but overlaps below the left side; the nerve is located between the artery and the vein, in a plane posterior to both.

In front of the sheath there are some descending filaments of the hypoglossal loop; behind the sheath are the inferior thyroid artery, the recurrent nerve, and the sympathetic trunk; and on its medial side, the esophagus, trachea, thyroid gland, and the lower part of the larynx.

By cutting across the top of this space, and slightly displacing the sternocleidomastoid, the common carotid artery can join below the omohyoid.

The superior carotid, or carotid triangle, is limited, behind by the sternocleidomastoid; below, by the upper belly of the omohyoid; and above, by the stylohyoid and the posterior belly of the digastricus.

It is covered by the integument, superficial fascia, platysma, and deep fascia; branching into which are the branches of the facial and cutaneous cervical nerves. Its floor is made up of parts of the thyrohyoid, hyoglossus, and the middle and inferior constrictor constrictors.

This space when dissected is considered to contain the upper part of the common carotid artery, which bifurcates opposite the upper border of the thyroid cartilage towards the external and internal carotids.

These vessels are somewhat hidden from view by the anterior margin of the sternocleidomastoid, which overlaps. The external and internal carotids are located next to each other, the exterior being the more anterior of the two.

The following branches of the external carotid are also in this space, as are the upper thyroid, running forward and down; the lingual, directly forward; the external maxilla, forward and up; the occipital, backwards; and the ascending pharynx, directly upward on the medial side of the internal carotid.

The veins found are : the internal jugular, which is located on the lateral side of the internal and common carotid arteries; and veins corresponding to the aforementioned branches of the external carotid, namely the superior thyroid, lingual, common facial, ascending pharyngeal, and sometimes occipital, all of which terminate in the internal jugular.

The nerves in this space are as follows: In front of the common carotid sheath is the descending hypoglossal branch. The hypoglossal nerve crosses the internal and external carotids above, curving around the origin of the occipital artery.

Inside the sheath, between the artery and the vein, and behind both, is the vagus nerve; behind the sheath, the sympathetic trunk.

On the lateral side of the vessels, the accessory nerve spans a short distance before perforating the sternocleidomastoid; and on the medial side of the external carotid, just below the hyoid bone, the internal branch of the superior laryngeal nerve can be seen; and, even more inferiorly, the external branch of the same nerve.

The upper portion of the larynx and the lower portion of the pharynx also meet at the front of this space. The glossopharyngeal and vagus nerves are also contained in the deep tissue of these two triangles.

The submandibular (or digastric triangle) : corresponds to the neck region immediately below the body of the jaw.

It is limited, above, by the lower border of the body of the mandible, and a line drawn from its angle to the mastoid process; below, by the posterior belly of the digastric and stylohyoid; in front, by the anterior belly of the digastricus.

It is covered by the integument, superficial fascia, platysma, and deep fascia, branching out into the branches of the facial nerve and the ascending filaments of the cutaneous cervical nerve.

Its floor is formed by mylohyoid, hyoglossus, and superior pharyngis constrictor. It is divided anteriorly and posteriorly by the stylomandibular ligament.

The anterior part contains the submaxillary gland, superficial to which is the anterior facial vein, while embedded in the gland is the external maxillary artery and its glandular branches; Below the gland, on the surface of the mylohyoid, are the submental artery and the mylohyoid artery and nerve.

The posterior part of this triangle contains the external carotid artery, which rises deep into the substance of the parotid gland. This vessel is here in front of, and superficial to, the internal carotid, being crossed by the facial nerve, and emits in its course the posterior maxillary, superficial temporal and internal branches.

More deeply are the internal carotid, internal jugular vein, and vagus nerve, separated from the external carotid by the stigloglossal and stylopharyngeal, and the glossopharyngeal nerve.

The structures listed as contained in its posterior part are found, strictly speaking, below the muscles that form the posterior limit of the triangle; but since it is very important to take into account its close relationship with the parotid gland, all these parts are discussed together.

The submental triangle (or suprahyoid triangle) : it is limited behind by the anterior belly of the digastric, in front by the midline of the neck between the mandible and the hyoid bone; below, by the body of the hyoid bone; its floor is formed by the mylohyoid.

It contains one or two lymph nodes and some small veins; the latter join to form the anterior jugular vein.

A detailed understanding of the anatomy of the neck is a necessary precursor to an evaluation of nerve injuries in the neck, as well as their diagnosis and treatment.

Forgotten neck triangles

The neck is an area that lends itself to anatomical geometry, such as triangles. Many neck triangles have been described, and some are well known, however some have been almost forgotten, namely Lesser’s triangle, Farabeuf’s triangle, Pirogoff’s triangle, and Beclard’s triangle.

From an anatomical and surgical point of view, the neck is an incredibly interesting place. It is like a connection where crucial functional units meet and pass. The added surgical milestones are always helpful to the surgeon when dealing with the neck.

Farabeuf triangle

It is named after the French surgeon DR. Louis Hubert Farabeuf (1841-1910). This triangle is delimited posteriorly by the internal jugular vein, the common facial vein, and the hypoglossal nerve forms the base of this triangle superiorly.

The content of this triangle is a branch of the common carotid artery or carotid bifurcation and the jugulodigastric lymph node. Depending on the deviation, this triangle is another useful and neglected feature of the carotid anatomy that forms an admirable gathering point for the neck.

This triangle is a well-known sign for the identification of the common carotid artery bifurcation.

The submandibular triangle is bordered superiorly by the lower border of the body of the mandible and lies between the anterior and posterior belly of the digastric muscle. The submandibular triangle is subdivided anteriorly and posteriorly by the stylomandibular ligament.

The submandibular gland is the main content of this triangle and is present in the anterior part of this triangle, superficial to the anterior facial vein and below the gland, on the surface of the mylohyoid muscle, are the submental artery and the nerve and vessels mylohyoids.

At the back of this triangle is the external carotid artery, which rises deep into the substance of the parotid gland. The Beclard, Lesser and Pirogoff triangles which are also known as forgotten neck triangles, small are found within the submandibular triangle.

Lesser’s triangle

It is a triangle contained within the submandibular triangle. Its limits are the hypoglossal nerve and the anterior and posterior belly of the digastric muscle. This triangle was named after a German surgeon named Dr. Ladislao Leon Lesser , who lived from 1846 to 1925.

The anterior belly of the digastric tendon forms the lower limit, the upper border by the hypoglossal nerve, and the posterior border is formed by the posterior margin of the mylohyoid muscle in the intermediate tendon of the digastric muscle.

The floor of this is formed by the hyoglossus muscle and the mylohyoid muscle.

Pirogoff’s triangle

It was named after the Russian surgeon and scientist Dr. Nikolai I Pirogoff (1810-1881), who made the first description of this anatomical area of ​​the neck.

The following are the limits of this triangle : the upper limit is formed by the hypoglossal nerve, the lower limit is formed by the intermediate tendon of the digastric muscle, and the posterior border is formed by the posterior border of the mylohyoid muscle.

This triangle is also considered to be the posterior continuation of Lesser’s triangle.

Surgeon Dr. John Blair Deaver in his book “Surgical Anatomy of the Human Body” referred to this triangle as the Pinaud’s triangle and the hypoglossohyoid. Sometimes the lingual artery can be found in the Pirogoff triangle below the hyoglossus muscle fibers.

Beclard’s triangle

It is named after the French anatomist Dr. Pierre A. Beclard (1785-1825). Much of the hyoid bone forms the lower limit, the posterior belly of the digastric muscle forms the upper limit, and the posterior border of the hyoglossus muscle forms the posterior limit and its base.

It is also known as the posterior triangle of the lingual artery and the contents of this triangle are the lingual artery and the hypoglossal nerve.

Sometimes arcus raninus, that is, the anastomosis between the left and right final branch of the deep lingual artery, is also present in this triangle. This triangle also helps to tie off the external carotid artery.

Clinical relevance

The use of divisions described as neck triangles allows effective communication of the location of palpable masses located in the neck between health professionals.

The common anterior midline of swellings is:

  • Enlarged submental lymph nodes and sublingual dermoids in the submental region.
  • Thyroglossal cyst and inflammation of the subhyoid bursa just below the hyoid bone.
  • Goiter, carcinoma of the larynx, and enlarged lymph nodes in the suprasternal region.

Conditions present in the neck triangles

Neck triangle and tumors

Tumors of the larynx, hypopharynx, and anterior triangle of the neck may manifest clinical symptoms identical to those of hyoid syndrome.

Cervical lymphangioma occurs most often in the posterior triangle, but anterior triangle lesions tend to be more troublesome, interfering with the patient’s ability to breathe or swallow and extending up into the oral cavity or down into the mediastinum.

Neck triangle and cervical thymic cyst

Cervical thymus cysts are morphologically identical to their mediastinal counterparts.

They are found in the anterior triangle of the neck along the normal path of descent of the thymus, with or without parathyroid glands, and may have a fibrous band or a solid connection of the thymic cord to the pharynx or mediastinum.

Neck Triangles and Cranial Nerves

There are three main cranial nerves that are present in the anterior neck triangles on the left and right sides, these are the glossopharyngeal, vagus, and hypoglossal nerves.