Posterior abdominal wall

The posterior abdominal wall is a musculoskeletal structure with numerous vascular and lymphatic structures formed by thelumbar vertebrae and their intervertebral discs, pelvic girdle, posterior abdominal wall muscles and their fascia. It supports the retroperitoneal viscera and neurovascular structures.

Gross anatomy

Musculotendinous

The muscles of the posterior abdominal wall attach to the lumbar vertebral body, the transverse process and the 12th rib. The lumbar vertebrae have a forward convexity and paravertebral gutters lie deep to each side of this convexity. The paravertebral gutters contain the psoas major muscle and psoas minor muscle, quadratus lumborum and also below the iliac crest lies the iliacus muscle.

The crura of the diaphragm have attachments at the level of T12 and L1, circumscribing the retrocrural space, and are also a part of the posterior abdominal wall.

A layer of fascia lies between the parietal peritoneum and the muscles of the posterior abdominal wall and is a continuation of transversalis fascia of the anterior abdominal wall. It is named according to the muscle it covers. Psoas fascia covers psoas major muscle and thoracolumbar fascia covers the quadratus lumborum and deep back muscles.

Blood supply

The abdominal aorta enters the abdominal cavity at the level of T12 through the retrocrural space, and travels downwards behind the peritoneum and on the bodies of the lumbar vertebrae. It bifurcates into the right and left common iliac arteries in the pelvis. The branches to the posterior abdominal wall are paired inferior phrenic arteries and lumbar arteries.

The inferior vena cava receives the lumbar veins draining the lateral and posterior abdominal wall. The right lumbar veins are shorter and enter the posterior surface of the inferior vena cava directly. On the left hand side the veins pass behind the aorta and they communicate via the ascending lumbar vein on the left side parallel to the inferior vena cava. The first and second lumbar vein on the left side usually don't reach inferior vena cava and joint the ascending lumbar vein. The 3rd and 4th lumbar veins enter the inferior vena cava posteriorly. The ascending lumbar vein ascends on the vertebral bodies at the root of the transverse process deep to the psoas muscle on the right and left and joins the subcostal vein to form azygos vein on the right and hemiazygos vein on the left side to enter thorax.

Lymphatic drainage

Retro-aortic lymph nodes and lateral aortic lymph nodes are responsible for drainage of the soft tissue and musculoskeletal structures of the posterior abdominal wall. The upper half of the posterior abdominal wall drains into the axillary lymph nodes on either side.

Innervation

The nerve fibers of the lumbar plexus leave the spinal cord and give rise to its six braches as it pierces the psoas major muscle. In the lateral border of the psoas muscle lies the femoral nerve.

Radiographic features

CT and MRI

The ascending lumbar veins, azygos and hemiazygos veins can become more visible if enlarged in inferior vena cava or superior vena cava obstruction.

Related pathology

• psoas muscle abscess
• lumbar hernias