Breaking down the Abdominal Aorta
The abdominal aorta for the purpose of ultrasound is classified by anatomical compartment below the diaphragm muscle. After leaving the heart, the aorta is shaped like a curvaceous candy cane with lots of branches. It arcs upward towards the left clavicle and then down through the aortic hiatus in the central diaphragm muscle, the muscle below the lungs separating the thoracic cavity from the abdominal cavity. The portion from the diaphragm muscle to the umbilicus is referred to as the abdominal aorta.
General sonographers evaluate the abdominal aorta frequently for anomalies like abdominal aortic aneurysms, also known as an AAA. A normal abdominal aorta is roughly the diameter of a garden hose and runs from the central chest to the umbilicus. It will bifurcate into the common iliac arteries near the umbilicus.
The Celiac Artery
The first main artery to brach off of the abdominal aorta is the celiac artery, also known as the celiac trunk. It is approximately 1.25 cm in length and branches at approximately the T12 level anatomically if you are trying to relate it to other things you may have studied in radiology/medicine. This little trunk of an artery gives rise to 3 vessels, the common hepatic artery, the left gastric artery and the splenic artery. I will dive more into this on a later post.
The Superior Mesentaric Artery
The second main artery to branch from the abdominal aorta is the superior mesenteric artery, SMA. It arises inferior to the celiac trunk and follows as a small vessel anterior to the abdominal aorta. The left renal vein can be seen in a cross section posterior to the SMA shortly after it branches off the aorta. It supplies blood to the intestines and will be discussed again in a later post because it is sometimes evaluated in patients with extreme post prandial pain, nausea, and vomiting.
The Inferior Mesentaric Artery
The third main artery to branch off the abdominal aorta is the inferior mesenteric artery, IMA. It supplies blood to the sigmoid colon and rectum. It is not always easily visible on ultrasound but can often be located at approximately the L3 level midway between the point where the renal arteries branch off the aorta and the bifurcation of the common iliac arteries occur.
The Common Iliac Arteries
The fourth main branch of the aorta is the common iliac bifurcation. It occurs at the level of the umbilicus. These arteries will course towards each leg as they will eventually branch into the internal and external iliac arteries. The external iliac artery will become the common femoral artery when it crosses the inguinal ligament within the pelvis. The internal iliac artery (also known as the hypogastric artery) is the main artery of the pelvis suppling blood to all of its smaller branches.
I hope that was a helpful simple breakdown of the abdominal aorta. I will be blogging more about normal human anatomy, how it relates to ultrasound, anomalies and disease processes in the future.
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