The median arcuate ligament is a fibrous arch formed by the convergence of the right and left diaphragmatic crura across the anterior surface of the aorta at the level of T12-L1. The aorta and thoracic duct pass posterior to this arch through the aortic hiatus. In most people the ligament passes well above the celiac trunk, but in approximately 10-24% of individuals it compresses the origin of the celiac artery from below, producing varying degrees of celiac axis stenosis.
Forms the anterior boundary of the aortic hiatus of the diaphragm, allowing the descending aorta to pass from the thorax to the abdomen while maintaining the diaphragmatic muscular seal.
Median arcuate ligament syndrome (MALS, Dunbar syndrome) occurs when the ligament compresses the celiac artery significantly, producing postprandial abdominal pain from celiac territory ischaemia after meals. The syndrome is controversial and overdiagnosed: celiac compression is common on imaging but causes symptoms in a minority. A celiac bruit and positional variation of the stenosis (worse in expiration) support the diagnosis. Surgical or laparoscopic division of the median arcuate ligament with or without celiac ganglionectomy is the treatment.
Compression of the celiac artery by a low-lying median arcuate ligament produces postprandial epigastric pain from foregut ischaemia, exacerbated in expiration when the diaphragm descends and worsens compression, treated by laparoscopic ligament division and celiac artery reconstruction when haemodynamically significant.
