Posterior Triangle of the Neck

Location

Boundaries

Subdivisions

• Occipital triangle (larger, superior): the main portion of the posterior triangle above the omohyoid
• Omoclavicular (subclavian) triangle (smaller, inferior): below the omohyoid, at the base of the posterior triangle

Contents

Nerves

• Exits the skull via the jugular foramen and descends through the neck
• Pierces (or passes deep to) the SCM, which it innervates, then enters the posterior triangle within the investing layer of cervical fascia
• Crosses the triangle obliquely in a downward direction to reach the deep surface of the trapezius, which it also innervates
• Its superficial position within the posterior triangle makes it highly vulnerable to injury during lymph node biopsy or surgery

• Cutaneous (superficial) branches emerge beneath the posterior border of SCM at the midpoint ("nerve point"):
  • Lesser occipital nerve (C2) - skin of the lateral scalp and back of ear
  • Great auricular nerve (C2, C3) - skin over the parotid and mastoid regions, and lower ear
  • Transverse cervical nerve (C2, C3) - anterior neck skin
  • Supraclavicular nerves (C3, C4) - skin over the clavicle and shoulder
• Muscular (deep) branches include:
  • Phrenic nerve (C3-C5) - descends across the anterior scalene muscle within the prevertebral fascia to enter the thorax
  • Branches to prevertebral muscles and the ansa cervicalis (C1-C3, for infrahyoid muscles)

Arteries

• Transverse cervical artery (branch of thyrocervical trunk) - crosses the base of the triangle anterior to the anterior scalene and brachial plexus; divides into superficial and deep branches at the trapezius
• Suprascapular artery (also from the thyrocervical trunk) - passes across the lowest part of the posterior triangle, heading toward the superior border of the scapula
• Subclavian artery (third part) - crosses the base in the omoclavicular triangle, lateral to the anterior scalene
• Occipital artery may occasionally appear in the superior triangle

Veins

• External jugular vein - most superficial structure in the triangle; forms near the angle of the mandible, crosses the SCM, then descends vertically through the posterior triangle in the superficial fascia before draining into the subclavian vein just above the clavicle
• Subclavian vein - crosses the base of the triangle, lies anterior to and slightly below the subclavian artery; receives the external jugular vein here and then joins the internal jugular vein to form the brachiocephalic vein
• Transverse cervical and suprascapular veins accompany their respective arteries and drain into either the external jugular or subclavian veins

Lymph Nodes

Clinical Relevance

• Accessory nerve injury during posterior triangle surgery (e.g., lymph node biopsy) causes weakness of the trapezius, resulting in shoulder drop, pain, and lateral winging of the scapula
• Central venous access: the subclavian vein is accessed at the base of the triangle for central line placement
• Nerve blocks: the "nerve point" along the posterior SCM border is used for cervical plexus blocks; brachial plexus blocks can be performed in the supraclavicular region
• Cervical lymphadenopathy: the triangle is a common site for enlarged nodes in head/neck infections, lymphoma, and metastatic disease
• The phrenic nerve (C3-C5) crosses the anterior scalene muscle within the prevertebral fascia - deep procedures in this area risk phrenic nerve injury and consequent diaphragm paralysis