Posterior abdominal split

Posterior abdominal split

Posterior abdominal wall is muscular and supports not only the retroperitoneal organs like kidney, ureter, duodenum but all the other organs and vessels, etc. of the biggest cavity of the body. It contains the lumber plexus, and part of the course of its branches. In addition, both the sympathetic and parasympathetic components of autonomic nervous system are visible here. The sympathetic is unsympathetic to gastrointestinal tract. It is seen in the form of Cornelia, superior and inferior mesmeric plexuses.

Abdominal aorta 

The abdominal aorta begins in the midline at the aortic opening of the diaphragm, opposite the lower border of vertebra T12. It runs downwards and slightly to the left in fornt of the lumber vertebrae, and ends in fornt of the lower part of the body  of vertebra L4, about 1.25 cm to the left of the median plane, by dividing into the right and left common iliac arteries. Due to the forward convexity of the lumbar vertebral column, aortic pulsations can be felt in the region of the umbilicus, particularly in slim persons.    

Dissection :Expose the centrally placed abdominal aorta and inferior vena cava to the right of aorta.Trace the ventral, lateral, posterior and terminal branches of abdominal aorta and the respective tributaries of inferior vena cava. Remove the big lymph nodes present in the posterior abdominal wall. Identify the muscles of the posterior abdominal wall by removing their fascial coverings. These are psoas major, quadratu lumborum, and iliacus. Avoid injury to the vessels and nerves related to the muscles. Detach psoas major from the intervertebral discs and vertebral bodies and trace the lumbar vessels and the rami communicans posteriorly deep to the tendinous arches from which psoas major arises. Dissect the genitofemoral nerve only on the anterior surface of psoas major. Trace the various branches of lumber plexus, e.g. iliohypogastric, ilioinguinal, lateral cutaneous nerve of thigh and femoral nerve. These exit from lateral border of psoas major. Identify obturator and lumbosacral trunk seen on the medial aspect of the muscle. Locate the lumbar part of the right and left sympathetic chains.Trace their branches into the coeliac and superior mesenteric plexuses of nerves in addition to giving rami communicans to the lumber spinal nerves.

Tributaries  

The common ilic veins formed by the union of the external and internal iliac veins unite to from the inferior vena cava. Each vein receives an iliolumbar vein. The median sacral vein joins the left common iliac vein. The third and fourth lumbar veins run along with the corresponding arteries and open into the posterior aspect of the inferior vena cava. The veins of the left side cross behind the aorta to reach the vena cava. The first and second lumbar veins end in the ascending lumbar vein, on the right side, or the hemiazygos vein on the left side. The ascending lumbr vein is an anastomotic channel which connects the lateral sacral, iliolumbar, and the subcostal veins. It lies of the psoas muscle, in fornt of the roots of the transverse processes of the lumbar vertebrac. On joining the subcostal vein it forms the azygos vein on the right side, and the hemiazygos vein on the left side.The right testicular or ovarian vein opens into the inferior vena cava just below the entrance of the renal veins. The left gonadal vein drains into the left renal vein. The renal veins join the inferior vena cava just below the transpyloric plane. Each renal vein lies in fornt of the corresponding artery. The
right vein is shorter than the left and lies behind the second part of the duodenum. The left vein crosses in front of the aorta, and lies behind the pancreas and the splenic vein. It receives the left suprarenal and gonadal veins. The right suprarenal vein is extremely short. It emerges from the hilum of the gland and soon opens into the inferior vena cava. The left suprarenal vein opens into the left vein.The hepatic veins are three large and many small veins which open directly into the anterior surface of the inferior vena cava just
before it pierces the diaphragm. These act as important support of liver.      

Cisterna chyli : This is an elongated lymphatic sac about 5 to 7 cm long. It is situated in front of the first and second lumber vertebrac, immediately to the right of the abdominal aorta. It is overlapped by the right crus of the diaphragm. Its upper end is continueous with the thoracic duct. It is joined by the right and left lumbar and intestinal lymph trunks the lumbar trunks arise from the lateral aortic nodes, and bring lymph from the lower limbs, the pelvic wall and viscera, the kidneys, the suprarenal glands, the testes or ovaries, and the deeper parts of the abdominal wall. The intestnal trunks bring lymph from the stomach, the intestine, the pancreas the spleen, and the anteroinferior part of the liver. The cisterna chyli may be replaced by anastomotic channels between the two lumbar trunks which join to from the thoracic duct. The intestinal trunks may thus join the cisterna chyli, the lumbar trunks, or the thoracic duct.

Posterior layer : Medially, the posterior layer  is attached to the tips of the lumbar and sacral spines and the interspinous ligaments. Laterally, it blends with the middle layer at the lateral border of the erector spinae. Superiorly, it continues on to the back of thethorax where it is attached to the vertebral spines and the angles of the ribs. Inferiorly, it is attached to the posterior one-fourth of  the outer lip of the iliac crest.

Middle layer : Medially, the middle layer is attached to the tips of the lumbar transverse preocesses and the inter-transverse ligaments. Laterally, it blends with the anterior layer at the lateral border of the quadratus lumborum. Superiorly, it is attached to the lower border of the 12th rib and to the lumbocostal ligament. Inferiorly, it is attached to the posterior part of the intermediate area of the iliac crest.

Anterior layer : Medially, the anterior layer is attached to the vertical ridges on the anterior surface of the lumbar transverse processes. Laterally, it blends with the middle layer at the lateral border of the quadratus lumborum. Superiorly, it forms the lateral arcuate ligament, extending from the tip of the first lumbar transverse process to the 12th rib. Inferiorly, it is attached to the inner lip of the iliac crest and the iliolumbar ligament.

Clinical anatomy 

Thrombosis in the inferior vena cava causes oedema of the legs and back.The collateral venous circulation between the superior and inferior venae cavae is established through the superficial or deep veins, or both. The participating superficial veins include the epigastric, circumflex iliac, lateral thoracic, thoracic, posterior intercostal, external pudendal and lumbovertebral  veins. The deep veins are the azygos, hemiazygos and lumbar veins. The vertebral venous plexus may also provide an effective collateral circulation between the two venac cavac. The inferior vena cava may sometimes be duplicated below the level of the renal veins. The psoas is enclosed in the psoas sheath,a part of the lumbar fascia.Pus from tubercular infection of the the thoracic and lumbar vertebrae may track dowen through the sheath into the thigh, producing a soft swelling in the femoral triangle. The typical posture of a laterally rotated lower limb following fracture of the neck of the femur is produced by contraction of the psoas muscle. Viscera are insensitivesto cutting, crushing or burning. The pain felt in the region of the viscus itself is known as true visceral pain. It is poorly localized and
is dull or heavy. Pain arising in viscera may also be felt in the skin or other sometic tissues,supplied by somatic nerves arising from the same spinal segment. This kind of pain is called referred pain. If the inflammation spreads from a diseased viscus to the perietal peritoneum it causes local somatic pain in the overlying body wall.

Nerves of the posterior abdominal wall

lLumbar plexus : The lumbar plexus lies in the posterior part of the substance of the psoas major muscle. It is formed by the ventral ramie of the upper four lumbar nerves. The first lumbar nerve receives a contribution from the subcostal nerve, and the fourth lumbar nerve gives a contribution to the sacral plexus. The branches of the lumbar plexus are summarized.

Genitofemoral nerve : The genitofemoral nerve ( L1,L2 ventral divisions ) emerges on the anterior surface of the psoas muscle near its medial border and runs downwards in front of the muscle. Near the deep inguinal ring it divides into femoral and genital branches. The femoral branch passes through the arterial compartment of the femoral sheath and its distributed to the skin of the upper part of the front of the thigh. The genital branch pierces the psoas sheath and enters the inguinal canal through the deep inguinal ring. In the male, it supplies the cremaster muscle, and in the female, it gives sensory branches to the round ligament of the uterus and to the skin of the labium majus.