The major vessels of the abdomen, including the abdominal aorta and the inferior vena cava, course along the posterior abdominal wall. Branches and tributaries of these vessels help supply and drain the posterior abdominal wall, and the abdominal viscera. Important lymphatic vessels that help with drainage of the lower body are also found in this area.
Let’s start off with the abdominal aorta, which gives rise to most of the arteries supplying the posterior abdominal wall. It transitions from the thoracic aorta to the abdominal aorta starting at the aortic hiatus, located within the diaphragm, at the level of the T12 vertebra. Then, it descends anterior to the vertebral bodies and ends at the level of the L4 vertebra.
From superior to inferior, the abdominal aorta has a number of structures associated with it anteriorly. These include the celiac plexus and ganglia, the body of the pancreas, the splenic vein, the left renal vein, the horizontal part of the duodenum and the coils of the small intestine.
Structures to the right of the abdominal aorta include the inferior vena cava, azygos vein, cisterna chyli, and the thoracic duct. Posteriorly, the left lumbar veins pass behind the aorta to reach the inferior vena cava.
Now, let’s talk about the various branches that arise from the abdominal aorta. These can be organized in three categories based on the “vascular plane” or direction in which the arteries branch from the abdominal aorta: first, there are paired visceral branches, that travel in the lateral plane; second, there are paired parietal branches, which travel in the posterolateral plane; and third, there are the unpaired visceral branches in the anterior midline plane.
The paired visceral branches include the middle suprarenal arteries, the renal arteries and the gonadal arteries which supply the suprarenal glands, kidneys, and the testicles or ovaries, based on the biological sex.
Next up are the paired parietal branches, which include: the inferior phrenic arteries and the lumbar arteries which supply the inferior surface of the diaphragm and posterior abdominal wall. The subcostal arteries are paired parietal branches of the thoracic aorta, but they emerge below the diaphragm to supply the posterior abdominal wall.
Finally, the unpaired visceral branches include the celiac trunk, the superior mesenteric artery and the inferior mesenteric artery which supply the foregut, midgut and hindgut structures respectively.
The abdominal aorta terminates at the level of the L4 vertebra, where it bifurcates into the right and left common iliac arteries. The two arteries diverge and run inferolaterally following the medial border of the psoas muscles to the pelvic brim. At this point, each common iliac artery divides into an external iliac artery and internal iliac artery. The external iliac arteries follow the iliopsoas muscle.
Before leaving the abdomen, the external iliac arteries give rise to the inferior epigastric arteries and deep circumflex iliac arteries, which supply the anterolateral abdominal wall. The internal iliac artery passes medially over the pelvic brim and descends into the pelvic cavity to supply various structures of the pelvis.
Time for a quick quiz. Let’s see if you can remember the unpaired, and paired visceral branches of the abdominal aorta.
Great! Let’s talk about the venous drainage of the posterior abdominal wall, which are mainly tributaries of the inferior vena cava. The inferior vena cava begins anterior to the L5 vertebra through the union of the common iliac veins just right of the median plane, inferior to the aortic bifurcation and posterior to the proximal part of the right common iliac artery. The inferior vena cava then travels superiorly on the right side of the bodies of the L3 through L5 vertebrae and just to the right of the abdominal aorta. Finally, the inferior vena cava leaves the abdomen by passing through the caval opening in the diaphragm at the level of the T8 vertebra.