Posterior Triangle of the Neck By Prof. Dr. Muhammad Imran Qureshi For the purpose of anatomical description the neck is sub divided into two major triangles, the Anterior and the Posterior by muscle bellies and bones. The Sternocleidomastoid muscle separates the posterior triangle from the anterior. Each of these is further divided into sub triangles. The Posterior triangle: There is one triangle on each side of the neck and each is bounded by: The Sternocleidomastoid The Trapezius and The middle third of the Clavicle. The Posterior triangle is divided by the Inferior belly of the Omohyoid muscle into: The Occipital triangle (bounded by the Sternocleidomastoid, Trapezius and Inferior belly of Omohyoid muscle) The Subclavian / Supraclavicular / Omoclavicular triangle (bounded by the Sternocleidomastoid, middle third of the Clavicle and the Inferior belly of Omohyoid). The Occipital triangle is larger than the Subclavian triangle The Anterior triangle: There is one triangle on each side of the neck and each is bounded by: The Sternocleidomastoid The Inferior border of the Mandible, and The Midline of the Neck. It is further subdivided into: The Digastric triangle, bounded by the anterior and posterior bellies of the Digastric muscle and the inferior border of the Mandible. The Submental triangle, bounded by the two anterior bellies of the Digastric muscles and the body of the Hyoid bone. The Carotid triangle bounded by the Sternocleidomastoid, the Posterior belly of the Digastric muscle, and the Superior belly of the Omohyoid muscle, and The Muscular triangle, which is bounded by the Sternocleidomastoid, Superior belly of the Omohyoid and the Midline of the Neck. 1 P age
The Posterior Triangle Boundaries: Anterior: Posterior border of Sternocleidomastoid muscle Posterior: Anterior border of Trapezius muscle Inferior (Base): Middle third of the Clavicle Roof: Investing layer of deep Cervical fascia. It encircles the neck, covers the posterior triangle, splits to envelop the Sternocleidomastoid and Trapezius and attaches to the clavicle. In the lower part, Platysma also forms part of the roof Floor: the floor is formed (from above downwards) by the Splenius capitis, Levator scapulae, Scalenus anterior, Scalenus Medius and Scalenus posterior muscles. These muscles are covered by the Prevertebral fascia CONTENTS OF THE POSTERIOR TRIANGLE: Cutaneous Nerves and Spinal part of Accessory Nerve The External Jugular Vein Brachial Plexus (Roots and Trunks) Inferior belly of Omohyoid muscle Lymph nodes Subclavian artery and vein, Suprascapular and transverse cervical arteries, Dorsal scapular artery and Occipital artery STRUCTURES DEEP TO THE STERNOCLEIDOMASTOID: The Carotid Sheath The Internal Jugular Vein THE CAROTID ARTERIES Sternocleidomastoid & Trapezius: These split from one sheet of embryonic muscle. Above, these two muscles have a continuous 2 P age
attachment extending from the mastoid process (behind the ear) to the inion (in the midline). Since this attachment is aponeurotic, it produces a ridge, the Superior Nuchal line. These two muscles separate as they descend below. Therefore, they have discontinuous attachment on the clavicle. A part of the sternocleidomastoid crosses the sternoclavicular joint. Spinal Part of the Accessory nerve: It is the nerve to sternocleidomastoid and Trapezius muscles and spans the gap between the two. Here it is quite superficial It divides the triangle into nearly two equal parts: The upper part is carefree part for there is no important structure to damage but below one must be very careful As it emerges from the jugular foramen (Accompanied with other nerves and vessels) it passes obliquely downwards and backwards from the transverse process of the atlas to the superior angle of the scapula. Along its course it burrows through the sternocleidomastoid a short distance below the mastoid process. Here lymph nodes surround it. It crosses the posterior triangle and disappears under cover of the trapezius, just above the clavicle. Sensory twigs from C2, C3 and C4 join it. Injury to this nerve in the posterior triangle results in a dropping of the shoulder downward and forward. In the posterior triangle there is an area about the size of a coin whose center is at the midpoint of the posterior border of the sternocleidomastoid muscle. From here, the cutaneous nerves of the cervical plexus radiate. All of them leave the triangle in various directions. The lesser occipital (from cervical segment C2) parallels the posterior border of the sternocleidomastoid muscle after hooking around the 11 th nerve and ascends to the occipital region; The great auricular (C2 and C3) crosses the sternocleidomastoid obliquely toward the lobe of the ear; The anterior / transverse cutaneous (C2 and C3) 3 P age
leaves the triangle by crossing the sternocleidomastoid muscle transversely to reach the skin of the anterior triangle. The medial, intermediate, and lateral supraclavicular nerves stem from a trunk formed by anterior rami of C3 and C4 and supply the skin over the lower part of the posterior triangle. In addition, the medial and intermediate supraclaviculars cross the clavicle to supply the skin of the upper pectoral region. The lateral supraclavicular crosses the anterior border of the trapezius muscle superficial to the angle of the trapezius and clavicle to supply the skin over the shoulder tip. Inferior belly of Omohyoid Muscle: It passes about an inch above the clavicle to which it is bound by an inverted sling of fascia. It subdivides the posterior triangle into a smaller lower subclavian triangle and a larger upper occipital triangle. External Jugular vein: This large vein descends subcutaneously across the sternocleidomastoid and pierces the deep fascia to end in the subclavian vein. Its tributaries in the posterior triangle are the transverse cervical, suprascapular, and anterior jugular veins. The last communicate with each other. The Floor: The fibres of the muscles of the floor run obliquely downward and backward. Levator scapulae occupies a middle position. It lies deep to the accessory nerve and runs parallel to it. Above it lies the Splenius Capitis. Below it are the three Scalene muscles. Above the Splenius Capitis a small part of Semispinalis capitis can sometimes be seen. The muscular floor of the triangle is carpeted with a layer of fascia (The prevertebral fascia). This carpet covers the subclavian vessels and the roots of the brachial plexus and thus provides them with a covering (the Axillary sheath) as they enter the axilla. It also covers and guards the motor nerves to four important muscles (Levator scapulae, Rhomboids, Serratus anterior and Diaphragm) Lymph Nodes: They are embedded in the fat between the fascial roof and the fascial floor and form the lateral group of Inferior deep cervical (Supraclavicular) lymph nodes. 4 P age
They drain the back of the scalp and neck. Usually they receive some efferent vessels from the upper deep cervical, axillary and deltopectoral nodes. These nodes empty into the subclavian lymph trunk. The axillary nodes empty into the subclavian lymph trunk, which follows the subclavian vein to the thoracic or right lymph duct. They Get enlarged in Infections of the Scalp and Rubella. Subclavian Artery: Its only branch given off in the posterior triangle is the dorsal scapular artery. The branches from the subclavian artery usually come from the second part (behind scalenus anterior) and first part (proximal to that muscle). Other Arteries in the Posterior Triangle: The Suprascapular and Transverse cervical arteries, which arise from the first part of the artery via thyrocervical trunk. They pass laterally in front of the scalenus anterior and its fascia and the phrenic nerve. Across the apex of the triangle one can have the glimpse of the occipital artery Brachial Plexus: Roots are located behind the Scalenus anterior muscle. Trunks are located in the lower part of the triangle. The roots receive gray rami from the middle and inferior cervical ganglia and first and second thoracic ganglia. Cutaneous Nerves: C1 has no cutaneous branch. The ventral rami of C5 to T1 form the brachial plexus. Thus C2, C3 and C4 supply the cutaneous territory between the Trigeminal nerve above and T2 below. They do this by means of FOUR nerves that radiate from about the middle of the posterior border of sternocleidomastoid The Lesser Occipital Nerve (C2, C3): It hooks around the accessory nerve and ascends just behind and parallel to the posterior border of the sternocleidomastoid to supply the scalp. The Greater Auricular Nerve (C2, C3): It runs vertically across the sternocleidomastoid to the lobe of the ear, with the external jugular vein. It has mastoid, auricular and facial branches 5 P age
The Anterior Cutaneous Nerve of the Neck / Transverse Cervical nerve (C2,C3): It crosses the sternocleidomastoid and the external jugular vein and supplies the skin between the jaw and the sternum The Supraclavicular Nerves (C3, C4): These are three sensory branches to the lower part of the posterior triangle and upper chest wall down to the level of the second rib. 6 P age