Median Arcuate Ligament Syndrome (MALS) is a rare vascular disorder causing chronic, often severe abdominal pain. Also known as Celiac Artery Compression Syndrome (CACS) or Dunbar syndrome, MALS arises when a band of diaphragmatic tissue presses on the Celiac Artery, the main vessel supplying blood to the upper digestive organs. This anatomical compression restricts blood flow and irritates surrounding nerves, leading to debilitating symptoms that often mimic other gastrointestinal issues.
The Anatomy of Compression
MALS is an anatomical issue involving three specific structures in the upper abdomen. The Median Arcuate Ligament (MAL) is a fibrous arch connecting the two muscular portions of the diaphragm where they meet the spine. Normally, the MAL passes above the origin of the Celiac Artery (CA), the first major branch off the aorta.
In MALS, the ligament is positioned lower than usual, crossing directly over the Celiac Artery at its origin. This results in extrinsic compression, pinching the artery against the aorta. The compression is often dynamic, worsening significantly during exhalation as the diaphragm moves downward and tightens the ligament’s arch.
The compression also irritates the surrounding network of nerves called the Celiac Plexus. This dense bundle controls much of the sensation and function for the abdominal organs. While reduced blood flow (ischemia) was the original theory for the pain, irritation of the Celiac Plexus is now thought to be a major contributor to the chronic pain experienced by patients.
Etiology and Predisposing Factors
The precise cause of symptomatic compression is not fully understood, but it involves a combination of congenital and acquired factors. Many people are born with an anatomical variation where the Median Arcuate Ligament inserts lower than the Celiac Artery origin. This configuration is present in up to 24% of the population, yet only a small fraction develops symptoms, suggesting anatomy alone is insufficient to cause MALS.
Anatomical variations of the ligament itself, such as increased thickness or a downward trajectory, can also contribute to compression. The condition most commonly affects women between the ages of 20 and 40. Other factors may include prior abdominal or spinal surgery, blunt abdominal trauma, or rapid weight loss, which can remove a protective fat pad cushioning the artery and nerves.
Clinical Presentation and Manifestations
The most characteristic and debilitating symptom of MALS is chronic, recurrent abdominal pain, often localized to the upper abdomen (epigastric region). This pain is typically described as sharp or cramping and can be severe. A defining feature is that the pain is often triggered or significantly worsened after eating, known as postprandial pain.
Eating triggers this pain because the digestive system requires an immediate increase in blood flow to process food. When the compressed Celiac Artery cannot meet this increased demand, it potentially leads to relative ischemia in the abdominal organs. The pain can be so severe that patients develop a fear of eating, often leading to significant, unintentional weight loss.
Other common manifestations include nausea, vomiting, and diarrhea, which are often nonspecific and can overlap with many other gastrointestinal conditions. Patients may also notice that leaning forward or standing can temporarily lessen the pain, as these positions slightly relieve tension on the Median Arcuate Ligament. In some cases, a physician may hear a distinct whooshing sound, called an abdominal bruit, over the upper abdomen during an examination.
Diagnostic Procedures and Treatment Options
Diagnosing MALS is challenging because its vague symptoms mimic more common digestive disorders, making it a diagnosis of exclusion. The diagnostic process relies on specialized imaging tests to visualize the compression and assess blood flow. Duplex ultrasound is a common initial screening tool, as it noninvasively measures the speed of blood flow through the Celiac Artery during both inspiration and expiration. Significantly elevated velocities during exhalation are highly suggestive of compression.
To confirm anatomical compression, physicians often order Computed Tomography Angiography (CTA) or Magnetic Resonance Angiography (MRA). These advanced techniques provide detailed, cross-sectional views of the vessels and show the characteristic “hooked” appearance of the Celiac Artery where the ligament pinches it. Scans are often performed during both inspiration and expiration to capture the dynamic nature of the compression.
A Celiac Plexus Block (CPB) is sometimes used as a diagnostic step to confirm nerve involvement in the pain symptoms. This procedure involves temporarily injecting numbing medication into the Celiac Plexus. Significant, temporary pain relief strongly suggests the nerve compression component is responsible, helping determine which patients are most likely to benefit from surgery.
The only definitive treatment for symptomatic MALS is surgical decompression, also known as Median Arcuate Ligament release. The goal is to divide the fibrous arch of the MAL to relieve pressure on the Celiac Artery and the Celiac Plexus nerves. The procedure is often performed using a minimally invasive laparoscopic or robotic approach.
During decompression, surgeons meticulously cut the ligament’s fibers and often perform neurolysis—removing surrounding nerve tissue—to fully relieve irritation. If severe narrowing or damage to the artery wall persists after the ligament is cut, a vascular reconstruction procedure may be required to restore full blood flow. Surgical release provides symptomatic relief in a majority of carefully selected patients.