Median Arcuate Ligament Syndrome (MALS) is a rare vascular compression disorder affecting the upper abdomen. It occurs when the median arcuate ligament (MAL), a fibrous band of the diaphragm, sits lower than normal and presses upon the celiac artery, the main blood vessel supplying the stomach, liver, and spleen. This compression restricts blood flow and irritates the surrounding celiac nerve plexus, causing debilitating symptoms. Diagnosing MALS is challenging because its vague symptoms mimic many common gastrointestinal conditions. The diagnostic process involves a multi-step pathway that first excludes common disorders before using specialized imaging and functional testing to confirm the anatomical compression.
Initial Clinical Assessment and Suspicion
The diagnostic journey begins with a detailed assessment of the patient’s clinical history, focusing on a specific triad of symptoms. The most prominent symptom is chronic, severe upper abdominal pain that consistently occurs after eating (post-prandial pain). This pain often leads to sitophobia (fear of eating) and significant, unexplained weight loss. Physicians also look for accompanying symptoms, including persistent nausea, vomiting, and bloating.
During a physical examination, the physician may listen for an abdominal bruit, a turbulent whooshing sound over the upper abdomen. This sound is caused by turbulent blood flow through the narrowed celiac artery. While suggestive, a bruit is present in less than half of MALS cases. Initial suspicion is built upon the combination of severe meal-related pain and weight loss that does not align with a typical digestive disorder.
Eliminating Gastrointestinal and Cardiac Mimics
MALS is considered a diagnosis of exclusion because its non-specific symptoms require systematically ruling out other common causes of abdominal pain. The initial workup focuses on excluding gastrointestinal and hepatobiliary diseases. This involves standard diagnostic tests, including upper endoscopy and colonoscopy, to check for conditions like peptic ulcers or inflammatory bowel disease.
Standard blood tests and motility studies are also used to exclude disorders such as gastroparesis or gallbladder dysfunction. The failure of these common tests to identify a source for the patient’s severe pain often directs the physician toward a rare vascular cause like MALS.
Standard cross-sectional imaging, such as CT or MRI, often fails to capture the compression. This is because these scans are typically performed with the patient lying flat (supine). When supine, the diaphragm relaxes and moves upward, temporarily releasing the pressure exerted by the median arcuate ligament on the celiac artery. This non-diagnostic result necessitates specialized imaging protocols that capture the dynamic nature of the compression.
Specialized Imaging for Vascular Compression
Specialized vascular imaging is used to visualize the anatomical compression and measure its functional impact on blood flow. The first specialized test is typically a mesenteric duplex ultrasound, a non-invasive study that assesses blood flow velocity in real-time. The ultrasound uses a breathing protocol (normal breathing, deep inspiration, deep expiration) designed to capture the dynamic change in compression.
In a positive MALS case, celiac artery blood flow velocity significantly increases during deep expiration, when the ligament compresses the artery. A peak systolic velocity exceeding 200 cm/s is a common cutoff indicating substantial narrowing. This dynamic visualization is often the first test to provide objective evidence of the syndrome.
Anatomical details are confirmed using Computed Tomography Angiography (CTA) or Magnetic Resonance Angiography (MRA). These tests provide high-resolution, three-dimensional images and must also be performed using a specific respiratory protocol, often imaging during deep expiration. The characteristic finding is a focal narrowing of the proximal celiac artery, appearing as a distinct “J-shaped” or “hooked” indentation. For detailed pre-surgical mapping, an invasive catheter angiography may be performed to image the artery and measure pressure gradients across the narrowed segment.
Functional Testing and Diagnostic Confirmation
The final step is a functional test linking the anatomical compression to the patient’s pain: the diagnostic Celiac Plexus Block (CPB). This involves injecting an anesthetic mixture near the celiac nerve plexus to temporarily numb the nerve bundle irritated by the compression.
A positive result is immediate, substantial, and temporary relief from abdominal pain, often defined as a 50% or greater reduction in severity. This successful blockade suggests the patient’s symptoms are mediated by the compressed nerves. The pain relief serves as functional proof that the anatomical abnormality is the source of the chronic pain.
A confirmed MALS diagnosis requires two components: clear anatomical evidence of celiac artery compression on specialized imaging, and functional evidence of pain relief following the nerve block. Once both criteria are met, the diagnosis is complete. The primary treatment is surgical decompression, known as Median Arcuate Ligament Release, which aims to cut the ligament and free the celiac artery and celiac plexus.