01OverviewDefinition, clinical context and the essential points that orientate the chapter.
The median arcuate ligament crosses the proximal coeliac artery. A relatively low ligament or high coeliac origin can produce eccentric, hooked compression, greatest during expiration. This configuration is common on imaging and usually asymptomatic. MALS is the controversial clinical syndrome in which otherwise unexplained chronic postprandial symptoms coexist with substantial dynamic external compression. Proposed mechanisms include foregut ischaemia and coeliac plexus irritation; neither explains every case or supplies a definitive test.
ESVS 2025 deliberately restricts the label to highly selected patients. Its footnoted criteria combine postprandial pain with dietary modification, unexplained weight loss or diarrhoea; at least 70% external stenosis on two imaging techniques, including inspiratory and expiratory thin-slice CTA; and no abnormality on abdominal ultrasound or oesophagogastroduodenoscopy. Respiratory-phase duplex is the initial vascular test. Specialist MDT agreement precedes treatment because surgery is only class IIb, level C, and reported symptom improvement is vulnerable to selection and publication bias.
Key points
- MALS is a diagnosis of exclusion: do not convert incidental coeliac indentation into a pain diagnosis.
- The complete ESVS selection requires postprandial pain plus food modification, unexplained weight loss or unexplained diarrhoea; at least 70% external coeliac stenosis on two imaging techniques including inspiratory and expiratory 1 mm CTA; and normal abdominal ultrasound and gastroscopy. Imaging alone is insufficient.
- Start with mesenteric duplex during inspiration and expiration, then use a specialist MDT. Surgery may be considered only for selected confirmed MALS (class IIb, level C); when operating, laparoscopic or video-assisted retroperitoneal release may be preferred, and release precedes any selected revascularisation.
- ESVS selected criteria require at least 70% external coeliac stenosis demonstrated by two imaging techniques, including inspiratory and expiratory 1 mm CTA, plus normal abdominal ultrasound and gastroscopy.
- A specialist multidisciplinary team should agree the diagnosis and examine gastrointestinal, vascular, pain and psychological contributors without dismissing symptoms.
- Surgical ligament release may be considered only in selected patients; evidence is low and symptom response is not guaranteed.
- When operating, laparoscopic or video-assisted retroperitoneal release may be preferred; primary coeliac revascularisation is unsupported.
- Persistent symptoms and stenosis after adequate release prompt reassessment of diagnosis and only then selected consideration of revascularisation.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Anatomical relationship
A low median arcuate ligament or high coeliac origin permits the diaphragmatic band to cross and externally compress the proximal coeliac artery.
Predisposing phenotype
Reported intervention cohorts are predominantly younger women, but demographic pattern is not diagnostic and must never substitute for symptoms and exclusion work-up.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Respiratory compression
Expiration elevates the diaphragm and can intensify focal coeliac narrowing, whereas inspiration may partially relieve it and lower measured velocity.
- 2Foregut hypoperfusion
Demand after meals may exceed flow through a substantially compressed coeliac origin, although collateral circulation makes simple ischaemia an incomplete explanation.
- 3Neurogenic contribution
Compression or irritation around the coeliac plexus may contribute to pain, helping explain why anatomical severity and symptom response do not correlate perfectly.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Reproducible postprandial epigastric pain leading to smaller meals or food avoidance, with unexplained weight loss or diarrhoea, is more persuasive than constant nonspecific discomfort.
Coeliac indentation without characteristic symptoms is common. It should remain an imaging finding while clinicians investigate more likely gastrointestinal, hepatobiliary, pancreatic and functional causes.
The proximal coeliac artery narrows and velocity rises most during expiration, sometimes with a hooked contour and post-stenotic dilatation; respiratory change supports external compression.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Inspiratory and expiratory mesenteric duplexFirst step - Why
- Demonstrate dynamic coeliac compression as the first vascular examination.
- Interpretation and limitations
- Compare morphology and velocities across respiration. An isolated high velocity is not diagnostic; technique, fasting state, angle and symptoms affect interpretation.
- 02
Thin-slice inspiratory and expiratory CTA - Why
- Confirm external compression, quantify stenosis and map adjacent anatomy.
- Interpretation and limitations
- Selected ESVS criteria use at least 70% stenosis and 1 mm respiratory-phase imaging. Look for a hooked focal origin rather than diffuse calcified plaque.
- 03
Abdominal ultrasound and gastroscopy - Why
- Exclude common structural causes required by the selected diagnostic framework.
- Interpretation and limitations
- Abnormal findings redirect management. Normal tests do not prove MALS; the symptom pattern and dynamic vascular evidence must still align.
- 04
Broader gastrointestinal assessment - Why
- Evaluate pancreatic, biliary, coeliac, inflammatory, motility, malignant and functional disorders according to the history.
- Interpretation and limitations
- Testing is hypothesis-led rather than a ritual panel. Failure to pursue credible alternatives invalidates a diagnosis of exclusion.
- 05
Functional or coeliac plexus testing - Why
- Provide additional physiological or neurogenic information in specialised centres.
- Interpretation and limitations
- Tonometry, visible-light spectroscopy and coeliac plexus block remain selective tools with incomplete validation; response does not independently establish the diagnosis.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Peptic or biliary disease
Ulceration, gallstones and functional biliary disorders commonly cause meal-related upper abdominal pain and require targeted ultrasound, endoscopy and laboratory assessment.
Pancreatic disease
Chronic pancreatitis or pancreatic malignancy can cause postprandial pain, weight loss and food avoidance, often with imaging or biochemical clues.
Atherosclerotic mesenteric ischaemia
Diffuse vascular risk, calcified ostial plaque and multivessel disease indicate occlusive chronic mesenteric ischaemia rather than isolated dynamic external compression.
Disorders of gut-brain interaction
Functional dyspepsia and centrally mediated abdominal pain remain possible after structural exclusion and need positive, respectful assessment rather than diagnostic dismissal.
Additional chapter-specific clues
Older age, smoking, diffuse calcification and multivessel disease point toward atherosclerotic chronic mesenteric ischaemia, which has a different revascularisation pathway.
Sudden severe pain, shock, peritonism or bowel injury on CT suggests acute mesenteric ischaemia, perforation, pancreatitis or another emergency rather than uncomplicated MALS.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Worked casePostprandial pain with coeliac compressionFirst stepA young adult has meal-related pain, food avoidance, weight loss and coeliac indentation reported on routine CT.+
- 1First separate emergency features and document timing, meal relation, weight trajectory, bowel symptoms, vascular risk and previous investigations; incidental compression alone is not the answer.
- 2Exclude plausible gastrointestinal disease, including abdominal ultrasound and gastroscopy, then obtain expert mesenteric duplex during inspiration and expiration.
- 3If the clinical pattern and duplex remain convincing, confirm at least 70% external stenosis with a second technique including inspiratory and expiratory thin-slice CTA and review in a specialist MDT.
- 4The MDT either identifies another cause and redirects care, or reaches a selected MALS diagnosis and explains the low-certainty option of ligament release.
- 5Verify the decision after treatment by tracking the original meal-related symptoms, nutrition and weight, and reassess both diagnosis and residual stenosis if benefit is absent.
02Selection boundaryWhen not to operateCompression is present but symptoms, exclusion work-up or dynamic confirmation is incomplete.+
- 1Do not label MALS from imaging alone; treat identified gastrointestinal, functional or atherosclerotic disease and review the response.
- 2Avoid primary coeliac stenting because it does not remove external compression and creates mechanical failure risk.
- 3Reconsider specialist referral only if the selected symptom complex persists and a complete two-technique dynamic evaluation supports the syndrome.
03Treatment pathwaySelected ligament releaseA specialist MDT agrees that clinical and dynamic diagnostic criteria are met and expected benefit justifies intervention.+
- 1Use shared decision-making to explain low-certainty evidence, realistic symptom-response rates, recurrence and operative risks.
- 2PreferredWhen surgery is chosen, laparoscopic or video-assisted retroperitoneal coeliac release may be preferred to open release in an experienced centre.
- 3If symptoms persist, repeat clinical and vascular assessment; consider revascularisation only for selected residual stenosis after adequate release, not as the initial procedure.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Malnutrition
Food avoidance can produce progressive weight loss, micronutrient deficiency, deconditioning and increasing procedural risk even before a final diagnosis is secured.
Persistent pain
Symptoms may continue after technically successful release when selection was poor, another disorder coexists or the pain mechanism is not corrected.
Residual stenosis
Fibrotic arterial change may remain after decompression; it warrants reassessment only in the context of persistent compatible symptoms.
Procedural injury
Release near the aorta, coeliac origin and pancreas can cause haemorrhage, arterial injury, lymphatic injury or conversion to open surgery.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Track the exact pre-treatment symptom—meal-related pain frequency and severity—rather than using a vague global improvement score.
- Record weight, dietary restriction and nutritional risk; dietetic support is appropriate while investigation or recovery continues.
- After release, monitor bleeding, pancreatic or vascular injury and early return of oral intake according to the operative pathway.
- If symptoms fail to improve, reassess alternative diagnoses before attributing failure to residual coeliac stenosis.
- Repeat duplex or cross-sectional imaging when symptoms persist or recur; anatomical patency alone does not establish clinical success.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Common anatomy, rare syndrome
The central diagnostic error is confusing prevalence of compression with prevalence of symptomatic MALS. Clinical selection is the safeguard against overtreatment.
Expiration matters
A standard inspiratory CT can understate compression, while a single expiratory appearance can overcall disease. Dynamic comparison gives the finding physiological context.
Exclusion is active reasoning
A diagnosis of exclusion is not made by ordering everything. It requires testing credible alternatives and showing why they do not explain the particular symptom pattern.
Mechanism remains unsettled
Improved microcirculation after release supports an ischaemic component in selected cohorts, while plexus-block observations suggest neurogenic contribution; neither supplies a universal predictor.
Release before reconstruction
A stent placed into a still-compressed coeliac origin is exposed to respiratory and angular forces. Persistent stenosis is assessed only after adequate decompression.
11Common pitfallsFrequent interpretation and management errors.
- 01
Diagnosing MALS from a radiology report alone medicalises a common asymptomatic configuration.
- 02
Using constant nonspecific pain without meal relation, food adaptation, weight loss or diarrhoea weakens the selected clinical case.
- 03
Skipping gastrointestinal investigation defeats the diagnosis-of-exclusion requirement.
- 04
Quoting a duplex velocity without respiratory phase, technique and confirmatory imaging overstates specificity.
- 05
Promising symptom cure ignores low-certainty evidence, heterogeneous definitions and the possibility of another pain mechanism.