Head and Neck Anatomy: Posterior Triangle

The posterior triangle is a space on the side of the neck
situated behind the sternocleidomastoid muscle

Boundaries

Anteriorly

Posterior border of sternocleidomastoid

Posteriorly

Anterior border of trapezius.

Inferiorly

Middle one-third of clavicle.

Apex

Lies on the superior nuchal line where the trapezius and sternocleidomastoid meet.

Roof

The roof is formed by the investing layer of deep cervical fascia,
The superficial fascia over the posterior triangle contains:

1. The platysma.
2. The external jugular and posterior external jugular veins.
3. Parts of the supraclavicular, great auricular, transverse cutaneous and lesser occipital nerves 4. Unnamed arteries derived from the occipital, transverse cervical and suprascapular arteries.
5. Lymph vessels which pierce the deep fascia to end in the supraclavicular nodes.

Floor

The floor of the posterior triangle is formed by the prevertebral layer of deep cervical fascia, covering the
following muscles:
1. Splenius capitis.
2. Levator scapulae.
3. Scalenus medius.
4. Semispinalis capitis may also form part of the floor.

Division of the Posterior Triangle

It is subdivided by the inferior belly of omohyoid into:

1. A larger upper part, called the occipital triangle.

2. A smaller lower part, called the supraclavicular or the subclavian triangle

Clinical Anatomy

The most common swelling in the posterior triangle is due to enlargement of the supraclayicular lymph nodes, While doing biopsy of the lymph node, one must be careful in preserving the accessory nerve which, may get entangled amongst enlarged lymph nodes
Supraclavicular lymph nodes are commonly enlarged in tuberculosis, Hodgkin's disease, and in malignant growths of the breast arm or chest.
Block dissection of the neck for malignant diseases is the removal of cervical lymph nodes along with other structures involved in the growth. This procedure does not endanger those nerves of the posterior triangle which lie deep to the prevertebral fascia, i.e- the brachial and cervical plexuses and their muscular branches.
A cervical rib may compress the second part of subclavian artery. In these case blood supply to upper limb reaches via anastomosis around the scapula.
Dysphagia caused by compression of the oesophagus by an abnormal subclavian artery is called dysphagia lusoria
Elective arterial surgery of the common carotid artery is done for aneurysms, AV fistulae or arteriosclerotic occlusions. It is better to expose the common carotid artery in its upper part where it is superficial. While ligating the artery care should be taken not to include the vagus nerve or the sympathetic chain.
Second part of the subclavian artery may get pressed by the scalenus anterior muscle, resulting in decreased blood supply to the upper limb. If the muscle is divided the effects are abolished.