The lateral cervical region of the neck, also known as the posterior triangle of the neck, contains important structures that connect the head and visceral neck to the arm and thorax. Several layers of important fascias surround and define the triangle. Muscles related to this triangle are responsible for neck flexion, head rotation, head extension, and movements about the shoulder girdle. Many terminal portions of neurovascular bundles cross through it on their way to/from more distal targets of the neck and shoulder muscles and skin. Lymphatic drainage returns to the venous system in this area.
Boundaries of the lateral cervical region of the neck
The lateral cervical triangle has the following boundaries and relationships:
- ANTERIOR: posterior border of the SCM (sternocleidomastoid muscle)
- POSTERIOR: anterior border of the trapezius muscle
- INFERIOR: middle 1/3 of the clavicle
- APEX: where the SCM and trapezius mm. meet at the superior nuchal line
- ROOF: investing layer of deep cervical fascia
- FLOOR: muscles covered by the prevertebral layer of deep cervical fascia (scalene mm., levator scapulae m., and splenius capitis m.)
The inferior belly of the omohyoid m. moves through the lower portion of the lateral cervical region to sub-divide the larger triangle into two sub-triangles:
- Occipital sub-triangle
- Superior to the omohyoid inferior belly, closer to the occiput (thus the name)
- Omoclavicular/subclavian/supraclavicular sub-triangle
- Small area between the omohyoid inferior belly and the clavicle, the main content of this sub-triangle is the subclavian vessels
- This sub-triangle has many names based on the relationships reviewed here – choose the one that is most memorable for you!
Contents of the lateral cervical region of the neck
The lateral cervical region of the neck contains many nerves, vessels, and lymphatic structures that serve several functions in the shoulder and neck.
- cutaneous branches from the cervical plexus providing sensory dermatomes over the anterior shoulder, the lateral and anterior skin of the neck, the skin behind the ear, and even a tiny bit of skin covering the angle of the mandible
- the spinal accessory nerve (cranial nerve XI, or 11) moves through this triangle to innervate both the sternocleidomastoid and trapezius mm.
- trunks of the brachial plexus on it’s way to the shoulder and arm
- inferior portion of the external jugular vein
- blood supply to shoulder muscles from the transverse cervical artery (also known as the cervicodorsal trunk) and suprascapular artery
- the third portion of the subclavian artery (that part lateral to anterior scalene m.) and sometimes the subclavian vein
- cervical and supraclavicular lymph nodes
Fascias bounding the lateral cervical region of the neck
Neck fascias are organized into superficial and deep layers. Each layer has sub-divisions thereof.
- Superficial fascia is related to skin and cutaneous neurovascular supply and innervation of this region.
- Unique in the human body, the superficial fascia of this region contains a flat, sheet-like muscle called the platysma m., technically a muscle of facial expression.
- Deep fascias enclose muscles and visceral compartments in the neck.
- They provide lubrication so structures glide past one another freely.
- They allow neurovascular bundles to pass between large regions like the head and neck, the neck and the arm, and into/out of the thorax.
Deep cervical fascia & sub-compartments
- Most superficial of the deep cervical fascias
- Completely surrounds the sternocleidomastoid (SCM) and trapezius muscles
- Extends like a sheet from the base of the cranium to the pectoral girdle
- Visceral layer of the pretracheal fascia encloses the thyroid, trachea, and the esophagus (visceral components of the neck)
- Muscular layer contains the muscles of the anterior triangle of the neck
- Surrounds scalene mm., prevertebral mm., and deep back muscles
- The carotid sheath is a fascial sleeve derived from the prevertebral layer of deep cervical fascias. Contents of this important fascial tube are the carotid arteries, the internal jugular vein, and the vagus n. (cranial nerve X, or 10). Left and right carotid sheaths are connected by a thin alar fascia.
The space between pretracheal and prevertebral layers of deep cervical fascia is known as the retropharyngeal space.