Posterior Triangle of neck

INTRODUCTION

Side of the neck

– The side of the neck appears quadrangular when viewed laterally.

Boundaries

• Anterior: The anterior midline of the neck.
• Posterior: The anterior border of the trapezius muscle.
• Superior: The lower border of the mandible and a line joining its angle to the mastoid process.
• Inferior: The clavicle.

Triangles on the side of neck

– The sternocleidomastoid muscle divides the side of the neck into two regions:

• Anterior triangle: A larger triangular area in front of the muscle.
• Posterior triangle: A smaller triangular area behind the muscle.

Surface Landmarks on the Side of the Neck

• Lower border of mandible: It extends from the chin to the angle of the mandible. It is easily palpable and separates the face from the neck.
• Mastoid process: It is a prominent bony projection palpable behind the lower part of the auricle.
• Clavicle: It is a subcutaneous bone that forms the boundary between the neck and thorax.
• Sternocleidomastoid muscle: It extends obliquely from the sternum and clavicle to the mastoid process. It becomes prominent when the head is turned to the opposite side.
• Lesser supraclavicular fossa: It is a small triangular depression between the sternal and clavicular heads of sternocleidomastoid, just above the medial end of the clavicle. The internal jugular vein lies deep to this region.
• Greater supraclavicular fossa: It is a depression above the middle third of the clavicle. The brachial plexus and third part of the subclavian artery lie deep to this region.

POSTERIOR TRIANGLE OF NECK

– The posterior triangle is a triangular region on the lateral side of the neck, behind the sternocleidomastoid muscle.

Boundaries

• Anterior: Posterior border of sternocleidomastoid.
• Posterior: Anterior border of trapezius.
• Inferior (base): Middle third of the clavicle.
• Apex: Meeting point of sternocleidomastoid and trapezius along the superior nuchal line.

Roof

– The roof consists of the following layers:

1. Skin.
2. Superficial fascia, containing:
   1. Platysma muscle.
   1. External jugular and posterior external jugular veins.
   1. Four cutaneous nerves of the cervical plexus.
   1. Cutaneous vessels and superficial cervical lymph nodes.
3. Investing layer of deep cervical fascia.

Floor

– The floor is formed by the prevertebral fascia covering the following muscles, from above downward:

1. Semispinalis capitis.
2. Splenius capitis.
3. Levator scapulae.
4. Scalenus medius.

– The posterior triangle lies between the investing and prevertebral layers of deep cervical fascia.

Structures Piercing the Roof

– The investing fascia is pierced by:

1. Lesser occipital nerve (C2).
2. Great auricular nerve (C2–C3).
3. Transverse cervical nerve (C2–C3).
4. Supraclavicular nerves (C3–C4).
5. External jugular vein.

External Jugular Vein

• Formation: It begins below the angle of the mandible by the union of the posterior division of the retromandibular vein and posterior auricular vein.
• Course: It descends superficial to sternocleidomastoid, deep to platysma.
• Termination: It pierces the investing fascia above the clavicle and drains into the subclavian vein.
• Tributaries: These commonly include the posterior external jugular, transverse cervical and suprascapular veins. The anterior jugular vein may also join it.

Oblique Jugular Vein

– It is a variable venous communication between the external and internal jugular veins, crossing the anterior border of sternocleidomastoid.

Divisions of Posterior Triangle

– The inferior belly of omohyoid divides the posterior triangle into two parts:

1. Occipital triangle: Larger upper part.
2. Supraclavicular (subclavian) triangle: Smaller lower part.

Contents of Posterior Triangle

Contents of occipital triangle

• Nerves: Spinal accessory nerve, four cutaneous branches of cervical plexus, dorsal scapular nerve, and muscular branches of C3–C4.
• Vessels: Occipital and transverse cervical arteries and accompanying veins.
• Lymph nodes: Occipital and cervical lymph nodes.

Contents of subclavian or supraclavicular triangle

• Nerves: Roots and trunks of brachial plexus, long thoracic nerve, suprascapular nerve, and nerve to subclavius.
• Vessels: Third part of subclavian artery, suprascapular and transverse cervical vessels, and terminal external jugular vein.
• Lymph nodes: Supraclavicular lymph nodes.

Important Nerves

– Spinal accessory nerve (XI): Supplies sternocleidomastoid and trapezius. It crosses the posterior triangle deep to the investing fascia before entering trapezius.

– Lesser occipital nerve (C2): Ascends along sternocleidomastoid and supplies the lateral occipital region.

– Great auricular nerve (C2–C3): Ascends over sternocleidomastoid and supplies the auricle, parotid region, and angle of mandible.

– Transverse cervical nerve (C2–C3): Crosses sternocleidomastoid horizontally and supplies the anterior neck.

– Supraclavicular nerves (C3–C4): Descend as medial, intermediate, and lateral branches to supply the skin over the clavicle, upper chest, and shoulder.

– Dorsal scapular nerve (C5): Pierces scalenus medius and supplies rhomboids and levator scapulae.

Nerve Point of Neck

• The four cutaneous branches emerge near the midpoint of the posterior border of sternocleidomastoid.
• This point is used for superficial cervical plexus block.

Important Arteries

• Subclavian artery: Its third part crosses the lower triangle toward the axilla.
• Transverse cervical and suprascapular arteries: Usually arise from the thyrocervical trunk.
• Dorsal scapular artery: Has variable origin and passes deep to levator scapulae.
• Occipital artery: Crosses the upper part of the triangle.

Brachial Plexus

• Ventral rami C5–T1 form upper (C5–C6), middle (C7), and lower (C8–T1) trunks between the scalene muscles.
• Their divisions pass behind the clavicle to form three cords.

Omohyoid

– The inferior belly extends from the scapula to the intermediate tendon. The superior belly continues to the hyoid bone.