Anterior & Posterior Triangles of the Neck

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Introduction

The neck is a complex region containing numerous important anatomical and neurovasculature structures. Assessing neck lumps and understanding the surgical approaches for pathological lesions requires a sound understanding of neck anatomy.

This article will review the surface anatomy that represents the boundaries of the neck, its divisions into the anterior triangle and posterior triangle and their subdivisions. Relevant clinical and surgical applications will be discussed in relation to these regions.


Surface anatomy

The limits of the neck are:

  • Medial: midline of the neck
  • Lateral: anterior margin of trapezius
  • Superior: inferior border of the mandible
  • Inferior: superior border of the clavicle

The neck can further be divided into the anterior triangle and the posterior triangle. The muscle which delineates these two regions is the sternocleidomastoid (SCM).

Anterior and posterior triangles of the neck
Figure 1. Anterior and posterior triangles of the neck

Anterior triangle

The anterior triangle is bound by the midline of the neck, anterior border of SCM and the inferior border of the mandible.

This triangle is further subdivided into four sub-triangles by the hyoid bone, suprahyoid and infrahyoid muscles. These sub-triangles are the submandibular, submental, carotid and muscular triangles.

Submental triangle

Boundaries of the submental triangle include:

  • Medial: midline
  • Lateral: anterior belly of digastric
  • Inferior: body of hyoid bone
  • Floor: mylohyoid muscle
  • Roof: investing layer of deep cervical fascia

Contents of the submental triangle include submental lymph nodes that receive lymphatic drainage from the chin, the tip of the tongue, lower lip, lower incisor teeth and floor of the mouth and the anterior jugular vein.

Submental triangle boundaries
Figure 4. Submental triangle boundaries
Clinical relevance: lymph nodes

Odontogenic infection from the lower central and lateral incisor teeth can spread into the submental space contained within the submental triangle. This may require external incision and drainage.

For head and neck cancer staging, the neck is divided into six anatomic lymph node levels. The submental nodes are classed as level Ia.

Cervical lymph nodes and levels
Figure 5. Cervical lymph nodes and levels

Submandibular triangle

Boundaries of the submandibular triangle include:

  • Anterior: anterior belly of digastric
  • Posterior: the posterior belly of digastric and stylohyoid
  • Superior: inferior border of the mandible
  • Floor: mylohyoid muscle

A number of important structures are contained within the submandibular triangle including the marginal mandibular branch of the facial nerve, the lingual nerve, the hypoglossal nerve, the facial and lingual arteries (with their corresponding veins), the submandibular gland, and lymph nodes.

Submandibular triangle boundaries
Figure 6. Submandibular triangle boundaries
Clinical relevance: sialadenitis

Sialadenitis (inflammation of the salivary gland) is a common pathology of the submandibular gland. This is commonly due to a blocked salivary stone (sialolithiasis).

Common symptoms include post-prandial pain, foul taste in the mouth, submandibular swelling and overlying skin erythema.

Treatment is usually conservative with encouraging hydration, good oral hygiene and sialagogues. Occasionally antibiotics are required.

Should surgery to remove the gland be required due to recurrent episodes, there is a potential risk for marginal mandibular nerve damageย (a branch of the facial nerve)ย that can lead to weakness of the ipsilateral lower lip.

Right sided submandibular swelling secondary to salivary gland stone
Figure 7. Right-sided submandibular swelling secondary to a salivary gland stone.

Carotid triangle

Boundaries of the carotid triangle include:

  • Superior: the posterior belly of the digastric muscle
  • Anteroinferior: the superior belly of the omohyoid muscle
  • Lateral: medial border of SCM
  • Floor: hyoglossus, thyrohyoid, inferior and middle constrictors

Important contents include the common carotid artery and its bifurcation into the internal and external carotid arteries, the internal jugular vein, the vagus (CNX), hypoglossal (CNXII) and accessory nerves (CNXI).

Carotid triangle boundaries
Figure 8. Carotid triangle boundaries
Clinical relevance: carotid triangle

The carotid sinus, identifiable as a visible swelling at the start of the ICA, and the carotid body are located within this neck triangle.

The carotid sinus contains baroreceptors innervated by a branch of the glossopharyngeal nerve (CNIX) that detect changes in blood pressure and transmit these to the cardiovascular regions of the medulla. If the carotid sinus is oversensitive to manual stimulation, individuals can develop carotid sinus hypersensitivity, leading to hypotension, bradycardia and syncope.

The carotid body contains chemoreceptor cells that are stimulated by changes in arterial pO2, pCO2 and H+ ion concentration, leading to activation of cardiorespiratory centres.

Paragangliomas are a rare form tumour that can involve the carotid body. When located in the adrenal glands they are called a phaeochromocytoma.

Muscular triangle

Boundaries of the muscular triangle include:

  • Medial: midline of neck from hyoid to the sternum
  • Superolateral: the superior belly of omohyoid
  • Inferolateral: anterior border of SCM
  • Superior: hyoid bone

Important contents include the infrahyoid muscles, superior and inferior thyroid arteries, anterior jugular vein, larynx, trachea, oesophagus, thyroid and parathyroid glands.

Muscular triangle boundaries
Figure 9. Muscular triangle boundaries
Clinical relevance: muscular triangle

Common indications for surgical access to this area of the neck include thyroid surgery and tracheostomies.

A potential risk of both is damage to the recurrent laryngeal nerve. Other than the cricothyroid muscle, it supplies all the intrinsic muscles of the larynx, including the posterior cricoarytenoid; the only muscle that abducts the vocal cords. Injury can cause hoarseness, aphonia and dyspnoea.

Cadaveric anatomical dissection of neck midline structures
Figure 10. Cadaveric anatomical dissection of neck midline structures. Note the close relationship of the recurrent laryngeal nerves to the thyroid gland and trachea.

Posterior triangle

The posterior triangle is bound by the posterior edge of SCM anteriorly, the anterior border of the trapezius posteriorly and the middle 1/3 of the clavicle inferiorly.

The omohyoid is the important structure that subdivides the triangle into the occipital triangle above and the subclavian triangle below.

Posterior triangle of the neck
Figure 11. Posterior triangle of the neck

Occipital triangle

Boundaries of the occipital triangle include:

  • Anterior: posterior border of SCM
  • Posterior: anterior border of trapezius
  • Inferior: inferior belly of omohyoid
  • Floor: levator scapulae, splenius capitis, middle and posterior scalene muscles

Important contents include accessory nerve (CNXI), cutaneous and muscular branches of the cervical plexus, upper part of the brachial plexus, supraclavicular nerves and the transverse cervical artery.

Occipital triangle boundaries
Figure 12. Occipital triangle boundaries
Clinical relevance: occipital triangle

Lymph node biopsy in this area can cause damage to the accessory nerve and subsequently trapezius innervation, leading to inability of the patient to shrug their shoulder.

Subclavian/supraclavicular triangle

Boundaries of the subclavian/supraclavicular triangle include:

  • Anterior: posterior border of SCM
  • Superior: the inferior belly of omohyoid
  • Inferior: middle 1/3 of the clavicle
  • Floor: first digitation of serratus anterior, middle scalene and the first rib

Contents include theย third part of theย subclavian artery, the inferior aspect of the external jugular vein, trunks of the brachial plexus, nerve to subclavius and lymph nodes.

Subclavian triangle boundaries
Figure 13. Subclavian triangle boundaries
Clinical relevance: Virchow’s node

The left supraclavicular lymph node or Virchowโ€™s node is near the junction of the thoracic duct and the left subclavian vein. It receives lymphatic drainage from most of the body except the right arm, chest, head and neck.

Enlargement of this lymph node can indicate metastasis of gastrointestinal malignancy, though can also arise from ovarian, renal or testicular origin. The term Troisierโ€™s sign is used to describe this presentation.

CT scan demonstrating an enlarged Virchow node
Figure 14. CT scan demonstrating an enlarged Virchow node

Editor

Dr Chris Jefferies


References

Reference texts

  • Ellis, H and Mahadevan, V. Clinical Anatomy: Applied Anatomy for Students and Junior Doctors. Published in 2013.
  • Brennan, P., Mahadevan, V and Evans, BT. Clinical Head and Neck Anatomy for Surgeons. Published in 2016.
  • Kikuta, S., Iwanaga, J., Kusukawa, J and Tubbs, RS. Triangles of the neck: a review with clinical/surgical applications. Published in 2019. Available from: [LINK]
  • Radiopaedia Triangles of the neck. Published in 2020. Available from: [LINK]

Image references

  • Figure 1. Wikimedia Commons [image modified by Mark Lam]. Anterior and posterior triangles of the neck. Licence: [CC BY-3.0]
  • Figure 2. Geeky Medics. Anterior triangle of the neck midline view.
  • Figure 3. Geeky Medics. Anterior triangle of the neck boundaries.
  • Figure 4. Wikimedia Commons. Submental triangle boundaries. Licence: [CC BY-3.0]
  • Figure 5. Wikimedia Commons. Cervical lymph nodes and levels. Licence: [CC BY-3.0]
  • Figure 6. Wikimedia Commons. Submandibular triangle boundaries. Licence: [CC BY-3.0]
  • Figure 7. Wikimedia Commons. Right-sided submandibular swelling secondary to salivary gland stone. Licence: [CC BY-3.0]
  • Figure 8. Wikimedia Commons. Carotid triangle boundaries. Licence: [CC BY-3.0]
  • Figure 9. Wikimedia Commons. Muscular triangle boundaries. Licence: [CC BY-3.0]
  • Figure 10. Wikimedia Commons. Cadaveric anatomical dissection of neck midline structures. Licence: [CC BY-3.0]
  • Figure 11. Geeky Medics. Posterior triangle of the neck.
  • Figure 12. Wikimedia Commons. Occipital triangle boundaries. Licence: [CC BY-3.0]
  • Figure 13. Wikimedia Commons. Subclavian triangle boundaries. Licence: [CC BY-3.0]
  • Figure 14. Wikimedia Commons. CT scan demonstrating an enlarged Virchow node. Licence: [CC BY-4.0]

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