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Triangles Of The Neck

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September 24, 2024

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Anatomy of the Triangles of the Neck

Introduction

There are 2 large triangles in the neck; Anterior triangle; and Posterior triangle. They are separated by the sternocleidomastoid (SCM). Each is divisible into smaller triangles. The anterior triangle is situated at the front of the neck. It is used clinically to locate structures that pass through the neck.

Anterior Triangle of the Neck

Boundaries

Boundaries of the anterior cervical triangle include:

• Anterior border: Midline of the neck
• Posterior border: Anterior border of SCM
• Lateral border: Medial border of the SCM
• Medial border: Imaginary sagittal line down the midline of the body
• Apex: Lower border of mandible, and a line drawn from the mandibular angle to the mastoid process
• Base: Manubrium sterni
• Floor: Pharynx, Larynx, and Thyroid gland
• Roof: Skin, Subcutaneous tissue, and Investing layer of cervical fascia

Contents

• Muscles: They are divided as to where they lie in relation to the hyoid bone
  • Suprahyoid muscles:
    • Stylohyoid
    • Digastric
    • Mylohyoid
    • Genohyoid
  • Infrahyoid muscles:
    • Omohyoid
    • Sternohyoid
    • Thyrohyoid
    • Sternohyoid
• Neurovasculature:
  • Arteries: Common carotid artery
  • Veins: Internal jugular vein
  • Nerves:
    • Facial nerve (CN VII)
    • Glossopharyngeal nerve (CN IX)
    • Vagus nerve (CN X)
    • Accessory nerve (CN IX)
    • Hypoglossal nerve (CN XII)

Subdivisions

The hyoid bone, suprahyoid and infrahyoid muscles are used to further subdivide the anterior triangle into 4 triangles. The anterior triangle is subdivided into 4 smaller triangles by:

• Hyoid bone
• Digastric and superior belly of omohyoid
• Suprahyoid, and
• Infrahyoid

They are:

• Carotid triangle
• Submental triangle (unpaired)
• Digastric/submandibular triangle; and
• Muscular triangle

Carotid Triangle

• Superior border: Posterior belly of digastric and stylohyoid
• Lateral border: Medial border of SCM
• Anteroinferior border: Omohyoid (superior belly)
• Posterior border: SCM
• Floor:
  • Middle and inferior pharyngeal constrictors
  • Hyoglossus
  • Thyrohyoid
• Contents:
  • Upper part of common carotid artery
    • Bifurcates within the carotid triangle at C3 (upper border of thyroid cartilage) into the external and internal carotid arteries
  • Commencement of internal carotid artery
    • An upward continuation of common carotid artery
    • Occupies the carotid sheath
  • External carotid artery, and some of its branches which include:
    • Superior thyroid artery
    • Facial artery
    • Lingual artery
    • Occipital artery
    • Ascending pharyngeal artery
  • Internal jugular vein (largely overlapped by SCM)
  • Part of hypoglossal nerve
  • Some fibres of ansa cervicalis
  • Vagus nerve (in the carotid sheath)
  • Deep cervical lymph nodes

Submental Triangle

It is an unpaired triangle situated underneath the chin.

• Apex: Symphysis menti (chin)
• Base: Body of hyoid bone
• Medial border: Imaginary sagittal midline of the neck
• Right and left lateral border: Anterior bellies of the digastric
• Floor: Mylohyoid muscles, which run from the mandible to the hyoid bone (united by a median raphe)
• Contents:
  • Submental lymph nodes – drain the tip of the tongue and central part of lower lip. They become swollen and tender following infection of the floor of the mouth, chin and apex of the tongue or lower lip.
  • Small veins that form the anterior jugular vein

Digastric (Submandibular) Triangle

It is located underneath the body of the mandible.

• Superior border:
  • Inferior border of the body of mandible; and
  • A line that joins the mandibular angle to the mastoid process
• Anteroinferior border: Anterior belly of the digastric
• Posteroinferior border: Posterior belly of the digastric and stylomastoid
• Roof: Skin, Subcutaneous tissue, Deep fascia
• Floor:
  • Mylohyoid
  • Hyoglossus
  • Middle pharyngeal constrictor
• Contents:
  • Superficial part of submandibular gland (salivary)
  • Submandibular lymph nodes
  • Parts of facial artery and vein
  • Mylohyoid artery and nerve
  • Submental artery (branch of facial artery), and
  • Part of hypoglossal nerve

Muscular Triangle

They are paired and situated more inferior than the triangular subdivisions. It is unique in containing no vessels of note.

• Superior border: The hyoid bone
• Medial border: Imaginary midline of the neck
• Anterior border: Midline (below the hyoid)
• Posterosuperior border: Omohyoid (superior belly)
• Posteroinferior border: Anterior border of the SCM (inferior portion)
• Contents:
  • Infrahyoid muscles (e.g. sternohyoid, sternothyroid)
  • Pharynx
  • Thyroid gland
  • Parathyroid gland

Posterior Triangle of the Neck

It is also known as the lateral cervical region. The posterior triangle is covered by the investing layer of fascia and the floor is formed by the prevertebral fascia.

Boundaries

• Anterior border: Posterior border of the SCM
• Posterior border: Anterior margin of trapezius
• Apex: Located at the junction of trapezius and SCM
• Base: Middle 3rd of the clavicle
• Roof: Investing layer of deep cervical fascia
• Floor:
  • Prevertebral fascia, and
  • Underlying muscles
    • Scalene medius and posterior
    • Levator scapulae
    • Splenius capitis, etc.

Contents

• Muscles:
  • Omohyoid
  • Vertebral muscles (covered by prevertebral fascia) which form the floor
    • Splenius capitis
    • Levator scapulae
    • Anterior scalene
    • Middle scalene
    • Posterior scalene
• Neurovasculature:
  • Arteries:
    • The distal part of the subclavian artery
    • Transverse cervical artery
    • Suprascapular artery
  • Veins:
    • External jugular vein
    • Subclavian vein
    • The transverse cervical vein
    • Suprascapular vein
  • Nerves:
    • The accessory nerve (CN XI)
    • The cervical plexus
    • The trunks of the brachial plexus

Subdivisions

The omohyoid muscle splits the posterior triangle of the neck into 2:

• The occipital triangle
• The subclavian (supraclavicular) triangle

belly)

• Inferior border Middle 3rd of clavicle Anterior border SCM

• Floor Scalene medius 1^st slip of serratus anterior 1^st rib

• Roof Skin Superficial fascia (containing platysma)
  • Deep fascia
  • 3^rd part of subclavian artery Here, it can be compressed against the 1st rib Its pulse can be felt Subclavian vein (occasionally)
  • Anterior to subclavian artery Supraclavicular part of brachial plexus Lies above and behind the subclavian artery Suprascapular nerve From superior trunk (C5, C6) of brachial plexus Suprascapular artery From thyrocervical trunk of subclavian artery Suprascapular vein Suprascapular lymph nodes Nerves to subclavius

[N.B. – transverse cervical artery is located in the roof of the subclavian triangle]

Carotid Pulse And Bruits

• Carotid pulse Can be taken in the carotid triangle between the thyroid cartilage and SCM
  • Or just below the angle of the jaw Each pulse is usually taken one at a time Bruits (vascular murmurs) in this region may suggest; Carotid arterial stenosis (e.g., from atherosclerosis), and Turbulent flow With risk of stroke

Supraclavicular Nodes

• Swelling and tenderness of supraclavicular nodes may suggest; Lung infections/malignancy (case of sentinel lymph node)
  • Breast infections/cancer Dissection of supraclavicular nodes; Supraclavicular part of brachial plexus and subclavian artery are at risk

Severance Of The External Jugular Vein

• The external jugular vein has a relatively superficial course down to the neck, leaving it vulnerable This is a medical emergency, managed by the application of pressure to the wound, stopping the bleeding, and the entry of air

Cervical Plexus Nerve Block

• For anaesthesis of the neck, a cervical plexus block is used This type of nerve block is not usually carried out on patients with pulmonary or cardiac problems, as it runs a high risk of damaging the phrenic nerve