Median Arcuate Ligament Syndrome Radiology Findings

Radiological imaging is the primary way median arcuate ligament syndrome (MALS) is identified, yet the diagnosis is never made on imaging alone. CT angiography, duplex ultrasound, MR angiography, and catheter angiography each capture a different piece of the picture, from the characteristic “hook sign” on CT to the dramatic velocity changes seen on ultrasound during breathing. The challenge for radiologists and clinicians is that the same compression pattern shows up in people who have no symptoms at all, making clinical correlation essential before anyone calls it a syndrome.

What Imaging Actually Shows

The median arcuate ligament is a fibrous arch that connects the two diaphragmatic crura, crossing the aorta near where the celiac artery branches off. In some people, this ligament sits lower than usual, or the celiac artery originates higher than usual, and the ligament ends up pressing on the artery. Anatomical studies using CT have measured the average ligament thickness at roughly 8 mm, with the celiac trunk typically originating around the level of the twelfth thoracic vertebra and the distance between the ligament’s center and the celiac trunk averaging only about 1.3 mm.¹ That tiny margin helps explain why even minor anatomical variation can produce significant compression.

The compressive tissue is not just the ligament itself. Surgical dissections reveal that the ligament and surrounding ganglionic tissue form a broad, multilayered band overlying the celiac artery.² This matters for imaging interpretation because the compression on a scan does not always correlate neatly with how much blood flow is actually restricted, or whether the patient’s symptoms are coming from the vessel narrowing at all.

CT Angiography and the Hook Sign

CT angiography (CTA) is typically the first cross-sectional imaging study that raises suspicion for MALS, and it remains the most commonly used modality for formal workup. The hallmark finding is a focal narrowing at the very beginning of the celiac artery, right where the ligament crosses over it. Unlike atherosclerotic narrowing, which tends to involve irregular plaque along the vessel wall, this compression produces a smooth indentation on the superior aspect of the artery. On sagittal reformats, the proximal celiac trunk takes on a distinctive downward-hooked shape rather than its normal gentle upward or horizontal course.³

This “hook sign” has been studied as a specific diagnostic marker. In one analysis, the hook sign was present in about 59% of patients ultimately diagnosed with MALS compared to roughly 29% of controls, and celiac stenosis itself was found in about 76% of MALS patients versus 45% of controls.⁴ The hook sign helps radiologists distinguish ligament-related compression from other causes of celiac narrowing, but it is not a perfect test. Some patients with genuine MALS lack a clear hook, and some asymptomatic individuals have one.

CTA also picks up secondary findings that support the diagnosis: prominent collateral vessels feeding the celiac territory from the superior mesenteric artery (particularly enlarged pancreaticoduodenal arteries), post-stenotic dilation of the celiac trunk, and soft-tissue thickening around the aortic hiatus. These secondary clues are often more convincing than the stenosis alone, because they indicate that the compression is hemodynamically significant enough for the body to have developed alternative blood supply routes.

Duplex Ultrasound and Breathing Dynamics

Where CT provides a static snapshot, duplex ultrasound adds something CT cannot: real-time assessment of how blood flow changes with breathing. Because the diaphragm moves downward during expiration, the ligament tightens over the celiac artery. During deep inspiration, the diaphragm rises and the compression often eases. This dynamic quality is central to MALS and gives ultrasound a unique diagnostic role.

The diagnostic criteria that have gained traction involve measuring the peak systolic velocity in the celiac artery during both respiratory phases. A flow velocity above 226 cm/s during expiration, combined with a drop of more than 68 cm/s during inspiration, carries high specificity for confirming celiac compression.⁵ Ultrasound research combining the hook sign with velocity measurements has found that patients with the hook sign had mean expiratory peak velocities around 305 cm/s, compared to about 158 cm/s in those without the sign, a difference that is hard to miss on the Doppler tracing.

Ultrasound does have limitations. It is operator-dependent, and a patient’s body habitus can make visualizing the celiac origin technically difficult. Bowel gas can obscure the view. Still, ultrasound is noninvasive, inexpensive, and repeatable, making it a natural first-line screening tool in many institutions, especially for follow-up after surgical treatment.

MR Angiography and Catheter Angiography

MR angiography plays a supporting role in MALS evaluation, particularly in younger patients or when CT is being avoided for radiation concerns. In children and adolescents, contrast-enhanced MR angiography has shown the same hook-shaped deformity of the celiac trunk seen on CT, and the findings resolve after surgical release of the ligament.⁶ MR angiography does not achieve the spatial resolution of CT for very small vessels, but it captures the characteristic proximal celiac compression well enough to confirm the diagnosis when combined with clinical findings.

Catheter angiography, while more invasive, used to be considered the confirmatory gold standard and still has a role in complex cases. It can demonstrate the dynamic nature of the compression in real time, with the stenosis worsening on forced expiration and improving on deep inspiration. In cases where the hemodynamic significance of the stenosis is in question, some investigators have used fractional flow reserve measurements during catheter angiography to quantify the pressure gradient across the compressed segment, directly proving that blood flow is restricted in a functionally meaningful way.⁷ In practice, though, catheter angiography is now reserved for situations where noninvasive imaging is equivocal or when endovascular intervention is being considered.

The Asymptomatic Compression Problem

One of the most persistent puzzles in MALS radiology is how often celiac compression appears in people who feel perfectly fine. Studies of CT angiograms performed for unrelated reasons have found that roughly 3 to 5% of asymptomatic individuals have more than 50% narrowing of the celiac artery by the median arcuate ligament.⁸⁹ That rate is far higher than the prevalence of symptomatic MALS, which suggests that compression alone is not enough to produce the syndrome.

This is the reason MALS remains a diagnosis of exclusion. Radiologists routinely note celiac compression as an incidental finding, but it should not trigger a MALS workup unless the patient has symptoms that fit. The classic symptom triad is postprandial abdominal pain, unintentional weight loss, and an abdominal bruit (a whooshing sound a clinician hears with a stethoscope over the upper abdomen).¹⁰ In practice, the full triad is often incomplete. Vascular anatomy varies from person to person, and collateral blood flow from adjacent vessels frequently compensates for the celiac stenosis, muting or eliminating symptoms entirely.¹¹

The practical takeaway for anyone reading their own imaging report: a mention of celiac compression or a low-riding median arcuate ligament on a CT scan is common and does not by itself mean you have MALS. If you have no abdominal pain, weight loss, or nausea, the finding is almost certainly incidental.

Is the Pain Actually From Blocked Blood Flow?

For decades, the assumption was straightforward: the ligament squeezes the artery, the organs downstream get less blood (especially after a meal, when they need more), and the patient hurts. But the evidence increasingly suggests that vascular compromise is not the whole story, and may not even be the main one.

One line of evidence comes from studying surgical outcomes. Research has found that symptoms associated with MALS do not reliably correlate with the degree of arterial stenosis, and that patients with atherosclerotic risk factors actually tend to do worse after treatment, a pattern that does not fit a purely vascular explanation.¹² A separate study using celiac plexus nerve blocks found that pain relief did not correlate with the presence of celiac arterial abnormalities, supporting the idea that irritation or compression of the celiac nerve plexus (the dense nerve network wrapped around the celiac artery origin) is the primary driver of symptoms.¹³ That same study went further, arguing that the absence of celiac stenosis on imaging should not be used to exclude MALS, because the nerve compression can cause symptoms even when blood flow looks adequate.

This has real consequences for how imaging findings are interpreted. A radiologist who sees mild celiac compression might downplay it, but if the patient has classic symptoms and responds to a nerve block, the imaging finding becomes clinically relevant regardless of its severity. Conversely, a dramatic-looking stenosis in someone with atypical symptoms may be a red herring.

Celiac Plexus Blocks as a Diagnostic Bridge

Because imaging cannot definitively prove that a patient’s pain is coming from MALS, celiac plexus blocks have emerged as a way to test the diagnosis before committing to surgery. The procedure involves injecting local anesthetic around the celiac plexus under CT guidance. If the patient’s pain resolves temporarily, the reasoning goes, the pain was likely neurogenic in origin and surgical release of the ligament is more likely to help.

The data on this approach is encouraging. In one cohort, 57 patients with suspected MALS underwent CT-guided celiac plexus block, and about two-thirds showed clinical improvement. Among those who improved and subsequently underwent open surgical release, 96% had favorable outcomes after surgery.¹⁴ The block essentially serves as a trial run: if it works, surgery is more likely to work too. Many centers now use a positive response to celiac plexus block as one of the criteria for proceeding with surgical ligament release.¹⁵

From a radiology perspective, the block is performed under CT or sometimes ultrasound guidance, adding the interventional radiologist to the diagnostic team rather than leaving the decision entirely to vascular surgeons. It also means that imaging of MALS has expanded beyond just looking at the vessel: the nerve plexus matters, and how the patient responds to a targeted intervention against it matters more than the degree of stenosis on a scan.

Collateral Pathways and Aneurysm Risk

When the celiac artery is chronically compressed, blood still needs to reach the liver, spleen, and stomach. It gets there through collateral pathways, most commonly the pancreaticoduodenal arteries that connect the celiac territory with the superior mesenteric artery. On CT angiography, these enlarged collateral vessels are a telltale sign that the compression is hemodynamically significant and has been present long enough for the body to adapt.

The downside of this adaptation is that the collateral arteries, which were never designed to carry high-volume flow, can develop aneurysms over time. One institutional review of CT reports found aneurysmal formation secondary to celiac artery stenosis in about 42% of MALS cases, with pancreaticoduodenal artery aneurysms specifically identified in roughly 5% of cases.¹⁶ These aneurysms develop because increased retrograde blood flow from the superior mesenteric artery pushes through vessels that are not built to handle the pressure.¹⁷

Although rupture is uncommon, it can be life-threatening when it occurs. Case reports describe retroperitoneal hemorrhage from ruptured pancreaticoduodenal artery aneurysms that were ultimately traced back to undiagnosed MALS.¹⁸ When radiologists encounter visceral artery aneurysms, especially along the pancreaticoduodenal arcade in a young patient without atherosclerosis, MALS should be on the differential diagnosis. This is one situation where imaging findings alone may justify further workup even in the absence of classic MALS symptoms.

Why Stenting Usually Does Not Work

A natural question for patients is whether a stent could simply hold the celiac artery open, avoiding surgery. The answer, based on accumulated experience, is that stenting alone performs poorly for MALS. The fundamental problem is that the compression is external and dynamic, caused by a fibrous band that moves with every breath. A stent placed inside the artery cannot relieve external pressure. Reports describe stent deformation and restenosis occurring within months: one case documented recurrence of abdominal pain six months after celiac artery stenting, ultimately leading to surgical ligament release as the definitive treatment.¹⁹ Stent fracture has also been reported as a complication, and because neuropathic mechanisms contribute to symptoms, a stent that addresses only the vascular component may leave the patient’s pain unchanged.²⁰

The standard treatment remains surgical release of the ligament, which can be done as an open or laparoscopic procedure.²¹ Both approaches divide the ligament fibers and surrounding tissue compressing the celiac trunk. Comparative data shows that the laparoscopic approach avoids the larger incision and is associated with shorter hospital stays and faster return to eating, while achieving similar safety profiles.²² Some surgeons also perform a celiac ganglionectomy (removal of the nerve tissue) at the same time, targeting the neurogenic component of the syndrome.

MALS in Children and Adolescents

MALS is not exclusively an adult diagnosis, and pediatric presentations have their own imaging characteristics. The condition appears to affect adolescent girls disproportionately. In one series of 46 pediatric patients, 91% were female, with a median age of about 16 and a half years.²³ These patients showed dramatically elevated celiac artery velocities on duplex ultrasound, averaging 381 cm/s during expiration, which dropped to an average of 197 cm/s with deep inspiration. That respiratory variation is the same dynamic pattern seen in adults, but the absolute velocities in children tend to be higher, possibly because the vessels are smaller and the compression proportionally more severe.

Contrast-enhanced MR angiography has been validated specifically in younger patients as an alternative to CT, confirming the hook-shaped celiac deformity without radiation exposure. Postoperative MR angiography in the same patients showed resolution of the hook sign and normalization of the vessel caliber.²⁴ Postoperative ultrasound velocities in that cohort dropped from a mean of 304 cm/s before surgery to 163 cm/s afterward, closely matching the velocities of healthy controls at 140 cm/s. For pediatric patients, ultrasound and MR angiography together can often establish the diagnosis without any CT radiation exposure.

Post-Operative Imaging and What Counts as Success

After surgical ligament release, imaging plays a role in confirming that the compression has been relieved and monitoring for complications. CT angiography performed after surgery typically shows enlargement of the previously compressed celiac artery, though the root diameter may remain somewhat smaller than the downstream vessel caliber, suggesting that the artery does not always spring back to a completely normal shape.²⁵ Duplex ultrasound is commonly used for longer-term follow-up, checking that celiac flow velocities have normalized and that no recurrent compression has developed.

Some surgeons now use intraoperative tools like transit-time flowmeters to confirm that blood flow has improved before closing, rather than waiting for a postoperative scan to check. This approach catches incomplete decompression at a stage when it can still be corrected on the table. For patients who have undergone prior stenting that failed, imaging after ligament release may also look for stent integrity and confirm that blood flow has been re-established through the native celiac artery rather than through collaterals.

One area where post-operative imaging is especially important is in patients who had collateral aneurysms before surgery. After the celiac artery is decompressed and normal antegrade flow is restored, the collateral pathways should carry less blood and the aneurysms should stop growing. Follow-up CT or ultrasound confirms this, and persistent or enlarging aneurysms after ligament release may need their own treatment through embolization or further surgery.²⁶