Posterior Triangle of the Neck

regio cervicalis lateralis

The posterior triangle is the side region of the neck between the posterior border of sternocleidomastoid, the anterior border of trapezius and the middle third of the clavicle. The inferior belly of omohyoid crosses it and divides it into a large occipital triangle above and a small omoclavicular triangle below.

Anatomical Data

Boundaries & Contents

Location	Side of the neck, behind sternocleidomastoid.
Boundaries	Posterior border of sternocleidomastoid in front Anterior border of trapezius behind Middle third of the clavicle below Investing fascia as the roof Prevertebral fascia over splenius capitis, levator scapulae and the scalenes as the floor
Contents	Spinal accessory nerve Cervical plexus cutaneous branches Trunks of the brachial plexus Third part of the subclavian artery External jugular vein Transverse cervical and suprascapular vessels Lymph nodes

Biomechanics

Function & Actions

A descriptive region of the lateral neck that contains nerves and vessels passing to the upper limb.

Clinical Relevance

Clinical Notes

The accessory nerve crosses the triangle superficially, just under the investing fascia, and is the structure most often injured in lymph node biopsy here, causing trapezius weakness and shoulder drooping. Supraclavicular brachial plexus blocks and subclavian vein access are performed in its lower part.

Pathology

Common Injuries & Conditions

Accessory Nerve Injury

Damage to the spinal accessory nerve during posterior triangle node biopsy or surgery, causing trapezius weakness, shoulder pain and difficulty raising the arm above the head.

Supraclavicular Lymphadenopathy

Enlarged nodes in the lower posterior triangle, which may signal cancer in the chest or abdomen, such as Virchow node on the left.

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