Acute mesenteric ischaemia (AMI) represents a critical vascular emergency resulting from a sudden, severe reduction in intestinal blood flow that threatens bowel viability and rapidly progresses to transmural infarction, intestinal gangrene, peritonitis, and death if left unrecognized and untreated1,4. Despite modern advances in critical care, cross-sectional imaging, and endovascular interventions, overall mortality remains unacceptably high, frequently exceeding 50%1,6. Timely diagnosis relies heavily on high clinical suspicion—particularly in elderly patients with cardiovascular comorbidities such as atrial fibrillation—and the immediate acquisition of dynamic contrast-enhanced computed tomography angiography (CTA)1,2,6. Prompt resuscitation, anticoagulation, and emergent revascularization are mandatory to salvage ischemic bowel and optimize survival3,5.

1. Etiology & Risk Factors

  • Acute Superior Mesenteric Artery (SMA) Embolism: Accounts for approximately 50% of cases. Typically originates from cardiac sources such as atrial fibrillation, recent myocardial infarction, or valvular heart disease, lodging downstream past the middle colic artery origin.
  • Acute SMA Thrombosis: Accounts for 15–25% of cases, usually occurring on the background of severe pre-existing atherosclerotic narrowing at the origin of the SMA, precipitated by low cardiac output or dehydration.
  • Mesenteric Venous Thrombosis (MVT): Accounts for 5–15% of cases. Associated with hypercoagulable states (e.g., factor V Leiden mutation, protein C/S deficiency, antithrombin III deficiency, myeloproliferative neoplasms, malignancy, intra-abdominal sepsis, or portal hypertension).
  • Non-Occlusive Mesenteric Ischaemia (NOMI): Accounts for 20–30% of cases. Caused by persistent splanchnic vasoconstriction in the setting of low cardiac output, shock, severe heart failure, sepsis, vasopressor administration, or cardiopulmonary bypass, despite patent mesenteric vessels.
  • Key Cardiovascular Risk Factors: Advanced age, atrial fibrillation, congestive heart failure, recent myocardial infarction, peripheral arterial disease, hypercoagulability, tobacco use, and recent major surgery or trauma1,3,6.

2. Pathophysiology

The pathophysiological cascade of acute mesenteric ischaemia is initiated by an abrupt decrease in macrovascular or microvascular perfusion to the intestines, most commonly affecting the superior mesenteric artery distribution4,6. As oxygen and nutrient delivery fall below baseline cellular requirements, mucosal cells—having the highest metabolic turnover—suffer immediate injury. This hypoxia forces cells into anaerobic metabolism, leading to rapid intracellular ATP depletion, failure of active ion transport, cellular swelling, and accumulation of lactic acid. As ischemia extends from the vulnerable mucosa through the muscularis propria to become transmural, the intestinal wall loses its barrier function. This permits bacterial translocation, the release of inflammatory cytokines, and localized hemorrhage into the bowel lumen and wall. Severe vasospasm, reperfusion injury upon restoration of blood flow, and progressive thrombosis of the microvasculature compound the initial insult, culminating in bowel infarction, perforation, peritonitis, septic shock, and multi-organ failure if revascularization is not achieved expeditiously3,5,6.

Acute mesenteric ischaemia — Pathophysiological Cascade & Clinical Flowchart 1 Trigger / Primary Insult Acute arterial embolus, thrombosis, or low-flow state abruptly reduces superior mesenteric blood flow. 2 Cellular / Pathophysiological Cascade Severe tissue hypoxia triggers mucosal cellular energy depletion, loss of barrier function, and profound anaerobic metabolism. 3 Target Organ / Structural Change Transmural bowel wall infarction occurs, leading to intestinal wall edema, hemorrhage, and pneumatosis intestinalis. 4 Hallmark Clinical & Diagnostic Manifestation Sudden agonizing abdominal pain out of proportion to physical exam findings, vomiting, and markedly elevated serum lactate. 5 Complications if Untreated & Therapeutic Target Rapid progression to bowel perforation, peritonitis, septic shock, and death, preventable by urgent revascularization.

3. Clinical Presentation & Classic Clinical Signs

  • History & Cardinal Symptoms: The hallmark presentation is sudden, severe, unrelenting abdominal pain that is strikingly out of proportion to the minimal findings elicited during abdominal palpation3. Patients frequently report agonizing periumbilical or diffuse pain accompanied by "gut emptying" manifestations, including forceful vomiting, nausea, and frequent bowel movements or watery diarrhea (sometimes progressing to bloody stools as mucosal sloughing occurs)3.
  • Physical Examination & Named Clinical Signs: Early in the clinical course, abdominal examination may reveal remarkably soft, non-tender quadrants despite excruciating patient distress. As ischemia progresses to full-thickness necrosis and transmural infarction, patients develop overt signs of peritonism, including abdominal distension, localized or diffuse abdominal tenderness, voluntary and involuntary guarding, rigidity, and absent bowel sounds. Hemodynamic instability, tachycardia out of proportion to fever, tachypnea, and signs of septic or hypovolemic shock herald advanced disease and peritonitis3,6.

4. Diagnostic Workup & Interpretation (Laboratory, Imaging & ECG/Pathology)

Diagnostic Modality / Test Expected Clinical & Radiological / Laboratory Finding
Gold-Standard InvestigationBiphasic CT Mesenteric Angiography (CTA) demonstrating abrupt cut-off or filling defect within the superior mesenteric artery, attenuated or absent bowel wall enhancement, bowel dilatation (>25 mm), mesenteric edema, venous thrombosis, or pneumatosis intestinalis1,2.
Laboratory PanelMarkedly elevated serum lactate, leukocytosis with left shift, metabolic acidosis with base deficit, elevated D-dimer (high sensitivity, low specificity), and elevated serum amylase, creatine kinase, and phosphate in advanced ischemia.
Imaging / Radiology (X-ray, US, CT, MRI)Plain abdominal radiographs are frequently normal early on or show nonspecific ileus; later findings include thumbprinting, dilated loops, and pneumoperitoneum. Duplex ultrasound can evaluate proximal SMA/venous flow but is limited by bowel gas. Non-contrast CT reveals high-attenuation thrombus in the SMA/SMV, while dynamic contrast CTA confirms vascular patency and bowel perfusion deficits.
ECG / Histopathology / Procedural12-lead ECG assessing for underlying atrial fibrillation, acute myocardial infarction, or arrhythmias as embolic sources. Histopathology of resected bowel reveals mucosal sloughing, coagulative necrosis, transmural neutrophilic infiltration, and bacterial colonisation. Diagnostic laparoscopy or exploratory laparotomy serves as the ultimate diagnostic and therapeutic procedure when imaging is equivocal in unstable patients.

5. Staging, Classification & Clinical Scoring Systems

Criterion / Stage / Score Component Clinical Threshold, Points & Management Implication
Aetiological ClassificationCategorized into four primary pathological processes: Arterial Embolism (50%), Arterial Thrombosis (15–25%), Mesenteric Venous Thrombosis (5–15%), and Non-Occlusive Mesenteric Ischaemia (NOMI, 20–30%), each dictating specific medical versus surgical revascularization strategies3.
Bowel Viability Grading (Intraoperative)Intraoperative assessment grading bowel from viable (normal pink color, active peristalsis, palpable mesenteric pulses, bleeding cut edges) to borderline/doubtful (dusky, sluggish Doppler signals) and non-viable (black, rigid, non-pulsatile, necrotic), guiding resection length and second-look laparotomy decisions.
Clinical Severity & Prognostic ScoringMultivariable risk models incorporating age, serum lactate, base deficit, presence of peritonitis, and comorbidities. High scores (>2.0 mmol/L lactate with systemic signs) indicate high risk of transmural infarction and mandate immediate operative intervention and intensive care unit admission.

6. Differential Diagnosis

Differential Condition Distinguishing Clinical, Biochemical & Imaging Features
Acute AppendicitisTypically presents with localized right lower quadrant pain starting periumbilically, preceded by anorexia and low-grade fever. Contrast-enhanced CT demonstrates a distended, thick-walled, non-compressible appendix with surrounding inflammatory fat stranding, without mesenteric vascular occlusion.
Acute PancreatitisPresents with severe, constant epigastric pain radiating to the back, associated with persistent vomiting and markedly elevated serum lipase (>3 times upper limit of normal). CT demonstrates pancreatic enlargement and peripancreatic fluid collections with normal mesenteric vessels.
Perforated Peptic UlcerPresents with sudden, severe, sharp epigastric pain with rapid generalization and board-like abdominal rigidity. Upright chest X-ray or CT confirms pneumoperitoneum (free air under the diaphragm) with normal superior mesenteric vasculature.
Acute Small Bowel ObstructionPresents with colicky crampy abdominal pain, nausea, vomiting, and obstipation. CT demonstrates a clear transition point with proximal bowel dilation and distal collapse, typically caused by adhesions, hernia, or volvulus, without primary mesenteric arterial/venous cutoff.

7. Management & Treatment Protocol

  • Initial Stabilization & Resuscitation: Immediate aggressive fluid resuscitation with crystalloids to restore effective circulating volume, placement of an indwelling urinary catheter for strict urine output monitoring, correction of electrolyte and acid-base disturbances, and avoidance of vasoconstrictive vasopressors where possible5.
  • First-Line Medical / Pharmacological Therapy (with exact adult dosing):
    • Intravenous unfractionated heparin: Bolus of 80 units/kg followed by a continuous infusion titrated to maintain an activated partial thromboplastin time (aPTT) ratio of 1.5 to 2.0, initiated immediately upon diagnosis unless absolute contraindications exist.
    • Broad-spectrum intravenous antibiotics: Empiric coverage for enteric gram-negative bacilli and anaerobes (e.g., piperacillin-tazobactam 4.5 g IV every 6 hours or meropenem 1 g IV every 8 hours) to prevent bacterial translocation sepsis.
    • Pain management: Adequate intravenous analgesia with opioid agents (e.g., morphine or fentanyl) titrated to patient comfort.
  • Surgical / Interventional Indications:
    • Endovascular Therapy: First-line approach for acute embolic or thrombotic SMA occlusion in patients without clinical peritonitis or radiological signs of bowel perforation/irreversible infarction. Techniques include catheter-directed thrombolysis, mechanical aspiration thrombectomy, and percutaneous transluminal angioplasty with stenting4.
    • Open Surgical Revascularization & Laparotomy: Indicated for patients exhibiting signs of peritonitis, hemodynamic instability, bowel perforation, or failed endovascular intervention. Involves open embolectomy/bypass grafting combined with exploratory laparotomy, resection of non-viable (necrotic) bowel, primary bowel anastomosis or stoma formation, and planned second-look laparotomy within 24–48 hours to reassess borderline bowel viability3,5.

8. Complications & Prognosis

  • Acute Complications: Transmural bowel necrosis, intestinal perforation, generalized purulent or fecal peritonitis, intra-abdominal abscess formation, septic shock, disseminated intravascular coagulation (DIC), acute kidney injury, and short bowel syndrome following extensive intestinal resection3,5,6.
  • Chronic Complications: Chronic malabsorption, short bowel syndrome requiring long-term parenteral nutrition, chronic mesenteric ischemia, stricture formation at anastomotic sites, and recurrent thrombosis.
  • Mortality and Prognosis: Overall mortality remains exceptionally high, ranging from 50% to over 90% depending on the speed of diagnosis and time to revascularization1,6. Prompt diagnosis prior to the onset of bowel necrosis drastically improves survival rates, highlighting that clinical suspicion and rapid CTA imaging are the single most critical determinants of patient outcome1,5.