Median Arcuate Ligament Syndrome (MALS) · What Is It, Causes, Symptoms, and More

Median arcuate ligament syndrome (MALS), also known celiac artery compression syndrome (CACS) or Dunbar syndrome, is an uncommon cause of abdominal pain that results from the compression of the celiac artery and surrounding structures by the median arcuate ligament of the diaphragm. This syndrome results in various degrees of abdominal pain; gastrointestinal symptoms, like nausea and vomiting; exercise-induced abdominal pain; and exercise intolerance. 

Median arcuate ligament syndrome is caused by the compression of the celiac artery by the median arcuate ligament of the diaphragm. The median arcuate ligament is a fibrous band that forms the anterior wall of the aortic hiatus, an opening in the diaphragm that allows passage of the aorta and other thoracic structures to the abdomen. Just beneath the aortic hiatus, the abdominal aorta gives rise to the celiac artery: a major blood vessel that supplies blood to the esophagus, stomach, proximal duodenum, liver, gallbladder, pancreas, and spleen.

With MALS, the celiac artery becomes trapped underneath the median arcuate ligament, reducing the flow of blood to the stomach, duodenum, liver, and other organs. Additionally, the median arcuate ligament compresses the bundle of nerves surrounding the celiac artery, causing nerve fiber irritation that leads to abdominal pain. It is thought that a higher origin of the celiac artery or lower insertion of the median arcuate ligament are likely to cause this syndrome. The structural anomaly can be congenital or acquired due to abdominal trauma or secondary to abdominal or spinal surgeries. In some individuals, MALS has been associated with connective tissue disorders like Ehler-Danlos syndrome.

Signs and symptoms of median arcuate ligament syndrome are often nonspecific and can include mild to severe upper abdominal pain, indigestion, nausea, vomiting, and constipation or diarrhea. The abdominal pain associated with MALS typically worsens after a meal as blood flow to the gastrointestinal tract attempts to increase to accommodate the high metabolic demands of digestion. Because MALS symptoms are worse during digestion, individuals often reduce their intake in an effort to improve the symptoms, resulting in weight loss. For some individuals, the abdominal pain may also be triggered by exercise, leading to exercise intolerance. Although not in all cases, a bruit (whooshing sound) may be heard with a stethoscope over the epigastric area, which is caused by the turbulent flow of blood through a narrowed blood vessel. 

Median arcuate ligament syndrome is diagnosed through its clinical presentation as well as demonstration of celiac artery compression by imaging techniques. Diagnosis of MALS requires exclusion of more common causes of abdominal pain, such as gastroesophageal reflux disease, chronic gastritis, cholecystitis, inflammatory bowel disease, or peptic ulcer disease.

If MALS is suspected, a screening test called a mesenteric duplex ultrasound may be performed to check blood flow through the celiac artery. With MALS, duplex ultrasound shows increased velocity of blood flow in the celiac artery, typically greater than 200 cm/second. An increase in velocity on deep expiration and a deflection angle between the aorta and the celiac artery of 50º between expiration and inspiration are also indicative of MALS. These changes upon respiration occur due to the downward movement of the diaphragm during inspiration, which relaxes the aortic hiatus and relieves compression on the celiac artery. 

Additionally, CT angiography (CTA) or MR angiography (MRA) may be conducted to identify the characteristic “hooking” of the celiac artery below the medial arcuate ligament. In some individuals, conventional angiography may be conducted as well. Conventional angiography remains the gold standard for vascular imaging, but it is an invasive procedure where a catheter is placed into the common femoral artery and guided to the affected artery. Subsequently, a contrast dye is injected, allowing the visualization of the arteries with a series of X-rays.

Finally, a frequent test is the celiac plexus block, which involves local injection of anesthetic and/or corticosteroids in the location of the celiac ganglion and adjacent nerves. This test may be conducted to identify those individuals that will benefit the most from removal of the celiac plexus during MALS surgery. 

Treatment of the median arcuate ligament syndrome involves the release of the celiac artery by open or laparoscopic removal of a portion of the median arcuate ligament. In some individuals, the surrounding celiac plexus and scar tissue may also be removed to improve pain and other associated symptoms. After the initial surgery, additional surgeries, angioplasty, or stenting may be needed to restore blood flow. When surgery is not possible, treatment focuses on managing the symptoms. In these cases, a celiac plexus block may be completed as a strategy to treat chronic abdominal pain that does not improve with pain-relief medications. 

Median arcuate ligament syndrome (MALS) is thought to be caused by the compression of the celiac artery and surrounding structures by the median arcuate ligament of the diaphragm. The compression causes decreased blood supply to the upper abdominal organs and/or nerve irritation, resulting in abdominal pain, nausea, vomiting, and exercise intolerance. Diagnosis of MALS is based on the clinical presentation and exclusion of more common causes of abdominal pain. Specific diagnostic tests to diagnose MALS include a mesenteric duplex ultrasound, CT and MR angiography, and conventional angiography. Standard treatment of MALS involves laparoscopic median arcuate ligament release to decrease the compression of the celiac artery.