The aortomesenteric angle is an anatomical space in the abdomen, formed by the divergence of the abdominal aorta and the superior mesenteric artery. This space is significant because the third part of the duodenum, a section of the small intestine, passes through it.
Understanding the Aortomesenteric Angle
The abdominal aorta, the body’s largest artery, supplies blood to various organs, and the superior mesenteric artery (SMA) branches off it, supplying blood to much of the small intestine and the first part of the colon. The aortomesenteric angle, formed between these two arteries, typically ranges from 28 to 65 degrees in healthy individuals. The aortomesenteric distance, between the SMA and the aorta, is usually 10 to 34 millimeters. This configuration allows food and digestive contents to pass freely through the third part of the duodenum without obstruction. Surrounding fat and lymphatic tissues cushion the SMA, helping maintain this angle and distance.
Factors Affecting the Angle
Several factors can narrow the aortomesenteric angle, compressing structures within it. A common cause is significant, rapid weight loss, which depletes the mesenteric fat pad that cushions the vessels. This fat loss reduces the space between the aorta and the superior mesenteric artery, decreasing the angle. Conditions causing hypermetabolism, such as severe burns, trauma, anorexia nervosa, or malabsorptive diseases, can contribute to this fat loss. Anatomical variations can also predispose individuals to a narrowed angle, including exaggerated lumbar lordosis (an increased inward curve of the lower spine), body casts for spinal conditions, or prolonged bed rest.
Superior Mesenteric Artery Syndrome
A narrowed aortomesenteric angle can lead to Superior Mesenteric Artery (SMA) Syndrome, a rare digestive condition where the third part of the duodenum is compressed between the abdominal aorta and the superior mesenteric artery. The reduced aortomesenteric angle can drop to between 6 and 22 degrees, with the distance between the vessels shrinking to 2 to 8 millimeters. This compression hinders the normal passage of food, leading to a partial or complete obstruction of the small intestine. Symptoms include post-meal abdominal pain, nausea, and recurrent vomiting (often about half an hour after eating), early satiety, bloating, fullness, and significant weight loss. The cycle of nausea and vomiting can lead to inadequate food intake, exacerbating weight loss and worsening the compression.
Recognizing and Addressing Issues
Recognizing a narrowed aortomesenteric angle and SMA syndrome involves clinical assessment and imaging studies. Doctors use imaging techniques to visualize the anatomical relationship between the abdominal aorta, the superior mesenteric artery, and the duodenum. Computed tomography (CT) scans, particularly CT angiography, are frequently used to measure the aortomesenteric angle and distance, and to confirm duodenal compression. Barium swallow with fluoroscopy can also show the obstruction and delayed transit of contents through the duodenum. Treatment for a narrowed aortomesenteric angle and SMA syndrome generally begins with conservative measures. Nutritional support is a primary focus, often involving small, frequent, high-calorie meals and supplements to encourage weight gain. The goal is to increase the mesenteric fat pad, which can help to widen the aortomesenteric angle and relieve duodenal compression. In some cases, total parenteral nutrition (TPN), where nutrients are delivered intravenously, may be necessary. If conservative approaches are not successful, surgical intervention, such as a duodenojejunostomy, may be considered to bypass the obstructed section of the duodenum.