Posterior abdominal wall Sanjaya Adikari Department of Anatomy

Objectives § Describe the arrangement of muscles and fascia in the posterior abdominal wall § Describe the structures found in the posterior abdominal wall § Describe the posterior abdominal viscera

Contents of abdominal cavity Contents removed

Posterior abdominal wall • A musculoskeletal wall between the lower border of the rib cage and the pelvic brim • Marks the posterior boundary of the abdominal cavity • Anteriorly lie the retroperitoneal organs and the parietal peritoneum • Posteriorly lie muscles, fascia and the lumbar spine

Structures forming the posterior abdominal wall Rib cage peritoneum Fat Fascia Muscles Bones Pelvic brim cavity mesentery

Retro-peritoneal structures Organs Abdominal aorta IVC, Portal vein Lymphatics Nerves Peritoneum

Paravertebral gutters lumbar lordosis Forward projection is enhanced by aorta and IVC Floor is formed by psoas and quadratus lumborum above and iliacus below the iliac crest Posterior part of the diaphragm also contributes

Psoas major and minor L 1 Fibrous arches Inguinal ligament

Psoas major muscle

Psoas major • Originates from bodies of T 12 to L 5, intervertebral disks and the medial end of transverse processors • Inserted into the lesser trochanter of the femur • Part above the medial arcuate ligament lies in the thoracic cavity • Flexes the hip and laterally flexes the lumbar spine • Both muscles acting together flexes the trunk

Quadratus lumborum Iliolumbar ligament Anterior sacroiliac ligament

Quadratus lumborum • Originates from transverse process of L 5, iliolumbar ligament and iliac crest • Inserted into the transverse processes of L 4 to L 1 and the 12 th rib medial half

Iliacus

Iliacus • Originates from upper 2/3 of iliac fossa and anterior sacroiliac ligament thereby filling the illiac fossa • Inserted into the lesser Psoas major muscle Iliacus trochanter of the femur trough a common tendon with the psoas major • Flexes the hip Common attachment

Fascia of the posterior abdominal wall • Psoas fascia • Iliac fascia • Lumbar part of the thoracolumbar fascia

Psoas fascia • Thick fascial sheath surrounding the psoas muscle • Arises as the muscle enters the abdominal cavity under the medial arcuate ligament • Ends at the pelvic brim as the muscle leaves the abdomen inferior to the inguinal ligament (does not extend into the thigh)

Thoracolumbar fascia • Extends from the back of sacrum to the neck • Binds erector spinae to vertebral column and encloses the quadratus lumborum • Very strong in the lumbar region • Laterally it gives origin to internal oblique and transversus abdominis muscles • Its lumbar part medially splits into three layers

Posoas fascia Transversus abdominis Anterior layer Posoas major muscle Middle layer Internal oblique Quadratus lumborum Posterior layer Erector spinae

L 1 Inguinal ligament

Psoas abscess • A focus of pus in the lumbar intervertebral disks can track down along the muscle and present as a lump in the groin • Tuberculosis of the spine gives rise to a psoas abscess

Skeleton of the posterior abdominal wall include A. Ischium B. 11 th rib C. 12 th vertebra D. Sacrum E. Intervertebral disks Correct: B, C, D, E

Muscles of the posterior abdominal wall include A. Iliopsoas B. Erector spinae C. Quadratus lumborum D. Diaphragm E. Transversus abdominis Correct: A, C, D

Lateral arcuate ligament Medial arcuate ligament Anterior layer of lumbar fascia Psoas fascia Iliac fascia

Arcuate ligaments L 1 Lateral arcuate ligament Median arcuate ligament Formed by tendinous fibres from medial edges of left and right crura of the diaphragm Median arcuate ligament

Medial and Lateral arcuate ligaments Subcostal vessels and nerve Iliohypogastric nerve Ilioinguinal nerve Sympathetic chain Abdominal aorta

Organs in the posterior abdominal wall Duodenum 2 nd and 3 rd parts Pancreas Kidneys and ureters Suprarenal glands

Vessels • Aorta and its branches • Inferior vena cava and its tributaries • Portal vein and its tributaries • Lymphatics and lymph nodes

Branches of abdominal aorta Main branches are in three categories • Single ventral arteries to gut and its derivatives – Coeliac trunk, superior and inferior mesenteric • Paired arteries to other viscera – Suprarenal, gonadal • Paired arteries to body wall – Inferior phrenic, lumbar

Branches of abdominal aorta T 12 Coeliac trunk R. inferior phrenic art. R. suprarenal art. Superior mesenteric a. R. renal art. R. gonadal art. R. 4 th lumbar art. Inferior mesenteric a. L 5 Median sacral artery

Related structures T 12 Coeliac trunk Splenic vein Body of pancreas T. P. P Superior mesenteric a. L. renal vein Un. pro. pancreas 3 rd part duodenum Inferior mesenteric a. L 5 Median sacral artery

Lymph nodes Lymphatics follow arteries • Single ventral arteries Pre-aortic nodes • Paired arteries to other viscera Para-aortic nodes • Paired arteries to body wall

Lymph nodes

Thoracic duct Pre-aortic nodes Cisterna chyli Para-aortic nodes Common iliac nodes External iliac nodes Internal iliac nodes

Lumbar plexus 1 st – 4 th lumbar spinal segments Embeded in the psoas Branches related laterally, medially or anteriorly to psoas

Branches of lumbar plexus & psoas muscle