Anatomical Considerations of Abdominal aorta in Ultrasound

The abdominal aorta is entirely a retroperitoneal structure. It begins at the aortic hiatus of the diaphragm at approximately the 12th thoracic vertebrae and courses anterior to the spine before bifurcating into the common iliac arteries. The inferior vena cava (IVC) courses to the right of the abdominal aorta and may be confused for the abdominal aorta by novice sonologists. The psoas muscle and kidney are posterior-lateral to the abdominal aorta on the left side.
The left lobe of the liver is located anterior to the proximal abdominal aorta and acts as the primary acoustic window for this area of the vessel. More caudal, the aorta is posterior to the transverse colon, the pancreas, and proximal duodenum. The distal duodenum crosses over the abdominal aorta distal to the superior mesenteric artery. Other areas of the small bowel lie anterior to the abdominal aorta as it courses distally to its bifurcation at approximately the 2nd lumbar vertebrae (or umbilicus). Components of the gastrointestinal system may contain air that can block visualization of the abdominal aorta and its vascular branches.

Branches of the abdominal aorta and inferior vena cava. SMA = superior mesenteric artery

The abdominal aorta is 10–20 cm in length in adults with a maximum external diameter that is normally less than 3.0 cm (2.1 cm for men over 55 years and 1.8 cm for women over 55 years). It tapers to approximately 1.5 cm at the bifurcation, but it can be less than 1.0 cm in diameter in smaller adults. The first large branch of the abdominal aorta is the celiac trunk (The Figure below). It comes off the anterior wall of the abdominal aorta approximately 1–2 cm below the level of the diaphragm and courses anteriorly for 1–2 cm before splitting into the common hepatic and splenic arteries. The splenic artery courses to the left and follows the superior border of the pancreas before entering the spleen. The common hepatic artery courses to the right and supplies blood to the liver, stomach, pancreas, and duodenum. The superior mesenteric artery arises from the anterior wall of the aorta approximately 1 to 2 cm distal from the celiac trunk and courses caudally to supply blood to the small bowel. Both renal arteries come off the lateral wall of the abdominal aorta, just distal to the superior mesenteric artery; the right renal artery courses under the IVC. The paired gonadal arteries (testicular and ovarian) come off the anterior wall distal to the renal vessels. The inferior mesenteric artery comes off the anterior wall 2 to 3 cm proximal to the iliac bifurcation and supplies blood to the lower gastrointestinal tract. Both the gonadal vessels and inferior mesenteric artery are usually difficult to visualize by ultrasound and rarely contribute to evaluation and management of the patient.