An unusual cause of chronic abdominal pain: Median arcuate ligament syndrome

Clinical History

Young man with no significant past medical history presented with a few months history of dyspepsia, weight loss, nausea and postprandial abdominal pain.
Clinical examination was unremarkable. Routine laboratory tests, including coeliac disease antibodies, were within normal limits.
Abdominal US and upper gastrointestinal endoscopy revealed no abnormalities.

Imaging Findings

Contrast-enhanced abdominopelvic CT was performed to rule out pancreatic pathology. Arterial phase CT showed mild indentation on the superior aspect of the proximal coeliac trunk, causing an arterial focal narrowing up to 50%. No other possible cause of symptoms was identified.
Considering the findings, a CT angiographic study in deep expiration was realized and revealed a marked increase of the proximal coeliac stenosis in comparison to the inspiration study. In sagittal images, a hook appearance of the proximal coeliac trunk was identified, due to an abnormal low placement of the median arcuate ligament, causing a significant stenosis of the coeliac artery. In addition, poststenotic dilatation and prominent pancreaticoduodenal collateral vessels were present.

Discussion

The median arcuate ligament (MAL) is a tendinous band that connects the medial borders of the crura of the diaphragm on either side of the aortic hiatus, superior to the origin of the coeliac axis (at around the L1 level) [1, 2].
In 10-24% of cases, the MAL passes anterior to the coeliac axis, due to a more cephalad origin of the coeliac artery or a low insertion of the MAL, resulting in extrinsic compression of the proximal coeliac trunk and nearby structures. In a small part of these people, the compression of the coeliac artery may mean a significant haemodynamic compromise that would cause symptoms [1, 3]. Median arcuate ligament syndrome typically occurs in women aged 20-40 years. Clinical features include postprandial epigastric pain, nausea, and weight loss. At physical examination, abdominal bruit that increases with expiration may be audible in the midepigastric region [4].
The compression of the coeliac artery worsens with expiration as the diaphragm moves caudally during lungs expands. Postulated mechanisms for the cause of pain associated with median arcuate ligament syndrome include mesenteric ischaemia secondary to a “steal syndrome”, with blood flow diverted from the SMA to the coeliac and direct compression of celiac ganglia [1, 3, 5].
Typical findings can be seen at conventional mesenteric, CT, or MR angiography.
Angiography has been largely superseded by thin-section multidetector CT, with 3D software, sagittal reconstructions and maximum intensity projection for diagnosing median arcuate ligament syndrome. The main finding at CT angiography, as at DSA, is a characteristic focal narrowing during expiration (“J” or hook shape), at around 5 mm from the CA ostium on sagittal images. This finding differentiates this cause of narrowing from atherosclerotic stenosis, which typically occurs at the ostium. The ligament is visible as it crosses the artery and may be thicker than usual (4 mm or more)
[1, 4].
Compression is considered severe when it persists at end inspiration, when it causes a poststenotic dilatation of the coeliac artery, or when there is haemodynamic compensation by collateral vessels between branches of the coeliac axis and the SMA, usually via the pancreaticoduodenal arcade.
Duplex US is occasionally performed for suspected MALS and it characteristically shows increased flow velocities in the coeliac artery during deep expiration [1].
It is important to note that the median arcuate ligament syndrome is a diagnosis of
exclusion and the isolated finding of coeliac compression is not sufficient to make the diagnosis, unless haemodynamic alterations and clinical symptoms are also present [3].

Differential Diagnosis List

Final Diagnosis

Median arcuate ligament syndrome (MALS), also known as Dunbar’s syndrome.

URL:	https://www.eurorad.org/case/13473
DOI:	10.1594/EURORAD/CASE.13473
ISSN:	1563-4086