Posterior triangle

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POSTERIOR TRIANGLE

Posterior triangle is a space on the side of the neck situated behind the sternocleidomastoid muscle.

01

Boundaries

Posterior triangle is a space on the side of the neck situated behind the sternocleidomastoid muscle.

Anterior

Posterior border of sternocleidomastoid.

Posterior

Anterior border of trapezius.

Inferior / Base

Middle 1/3rd of clavicle.

Apex

Lies on the superior nuchal line, where trapezius and sternocleidomastoid meet.

02

Roof

The roof is formed by:

1. Skin

2. Superficial Fascia

The superficial fascia contains:

  • Platysma.
  • External jugular vein and posterior external jugular vein.
  • Parts of:
    • Supraclavicular nerves.
    • Great auricular nerve.
    • Transverse cutaneous nerve.
    • Lesser occipital nerve.
  • Unnamed arteries derived from:
    • Occipital artery.
    • Transverse cervical artery.
    • Suprascapular artery.
  • Lymph vessels → pierce the deep fascia and end in the supraclavicular nodes.

3. Investing Layer of Deep Cervical Fascia

Structures Piercing the Roof

  • Lesser occipital nerve (C2).
  • Great auricular nerve (C2, C3).
  • Transverse cervical nerve (C2, C3).
  • Supraclavicular nerve (C3, C4).
  • External jugular vein.
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External Jugular Vein

  • External jugular vein lies deep to the platysma.
  • It is formed by union of:
    • Posterior auricular vein.
    • Posterior division of retromandibular vein.
  • It begins within the lower part of the parotid gland.
  • It crosses the sternocleidomastoid obliquely.
  • It pierces the anteroinferior angle of the roof of the posterior triangle.
  • It opens into the subclavian vein.

Tributaries of External Jugular Vein

  1. Posterior external jugular vein.
  2. Transverse cervical vein.
  3. Suprascapular vein.
  4. Anterior jugular vein.

Oblique Jugular Vein

  • Connects the external jugular vein with the internal jugular vein.
  • It crosses the middle one-third of the anterior border of sternocleidomastoid.
04

Floor

The floor of the posterior triangle is formed by the prevertebral layer of deep cervical fascia, covering the following muscles from above downwards:

  1. Splenius capitis.
  2. Levator scapulae.
  3. Scalenus medius.
05

Division of the Posterior Triangle

The posterior triangle is subdivided by the inferior belly of omohyoid into:

1. Occipital Part / Occipital Triangle

Larger upper part.

2. Supraclavicular Part / Subclavian Triangle

Smaller lower part.

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Contents of Occipital Triangle

1. Nerves

Spinal Accessory Nerve

Spinal accessory nerve.

Four Cutaneous Branches of Cervical Plexus

  1. Lesser occipital nerve (C2).
  2. Great auricular nerve (C2, C3).
  3. Anterior cutaneous nerve of neck (C2, C3).
  4. Supraclavicular nerves (C3, C4).

Muscular Branches

  1. Two small branches to levator scapulae (C3, C4).
  2. Two small branches to trapezius (C3, C4).
  3. Nerve to rhomboids [proprioceptive] (C5).

2. Vessels

  • Transverse cervical artery and vein.
  • Occipital artery.

3. Lymph Nodes

Along the posterior border of sternocleidomastoid:

  • More in the lower part → supraclavicular nodes.
  • A few at the upper angle → occipital nodes.
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Subclavian / Supraclavicular Triangle

1. Nerves

  • Root and trunk of brachial plexus.
  • Nerve to serratus anterior [long thoracic, C5–C7].
  • Nerve to subclavius (C5, C6).
  • Suprascapular nerve (C5, C6).

2. Vessels

  • 3rd part of subclavian artery.
  • Subclavian vein.
  • Suprascapular artery and vein.
  • Transverse cervical artery and vein.
  • Lower part of external jugular vein.

3. Lymph Nodes

A few members of the supraclavicular chain.

08

Clinical Anatomy

Jugular Venous Pressure (JVP)

  • The right external jugular vein is examined to assess the venous pressure.
  • The right atrial pressure is reflected in it because:
    • There are no valves in the entire course of this vein.
    • It is straight.

External Jugular Vein and Air Embolism

  • External jugular vein pierces the deep fascia.
  • The margins of the vein become adherent to the fascia.
  • If the vein gets cut:
    • It cannot close.
    • Air is sucked in due to negative intrathoracic pressure.
    • This causes air embolism.
  • To prevent this, the deep fascia has to be cut.

Supraclavicular Lymphadenopathy

  • The most common swelling in the posterior triangle is due to enlargement of the supraclavicular lymph nodes.
  • During biopsy of the lymph node, care should be taken to preserve the accessory nerve, which may get entangled amongst enlarged lymph nodes.

Enlargement of Supraclavicular Lymph Nodes

Supraclavicular lymph nodes are commonly enlarged in:

  1. Tuberculosis.
  2. Hodgkin’s disease.
  3. Malignant growths of:
    • Breast.
    • Arm.
    • Chest.

Virchow’s Lymph Nodes

  • Left supraclavicular lymph nodes are also called Virchow’s lymph nodes.
  • They are commonly involved in metastasis from tumours of:
    • Stomach.
    • Testes.
    • Other abdominal viscera.
  • Biopsy of supraclavicular nodes may reveal the cause of the enlargement.

Block Dissection of Neck

  • Block dissection of the neck for malignant disease involves removal of:
    • Cervical lymph nodes.
    • Other structures involved in the growth.
  • This procedure does not endanger those nerves of the posterior triangle which lie deep to the prevertebral fascia, including:
    • Brachial plexus.
    • Cervical plexus.
    • Their muscular branches.

Cervical Rib

  • A cervical rib may compress the 2nd part of the subclavian artery.
  • In these cases, blood supply to the upper limb reaches via anastomoses around the scapula.

Dysphagia Lusoria

Dysphagia caused by compression of the oesophagus by an abnormal subclavian artery is called dysphagia lusoria.

Surgery of Common Carotid Artery

Elective arterial surgery of the common carotid artery is done for:

  • Aneurysms.
  • AV fistulae.
  • Arteriosclerotic occlusions.

It is better to expose the common carotid artery in its upper part, where it is superficial.

While ligating the artery, care should be taken not to injure:

  • Vagus nerve.
  • Sympathetic chain.

Second Part of Subclavian Artery

  • The second part of the subclavian artery may get compressed by the scalenus anterior muscle.
  • This results in decreased blood supply to the upper limb.
  • If the muscle is divided, the effects are abolished.

Brachial Plexus Block

  • The brachial plexus can be blocked by injecting local anaesthetic between the 1st rib and the skin above the clavicle.
  • It may be required for upper limb surgeries.
POSTERIOR TRIANGLE
Head & Neck Anatomy Study Notes