What are the causes of mesenteric ischemia?

Causes of Mesenteric Ischemia

Mesenteric ischemia results from four primary mechanisms: arterial thrombosis (now the most common at 40%), arterial embolism (25%), non-occlusive mesenteric ischemia (NOMI, ~25%), and mesenteric venous thrombosis (<10%). 1

Arterial Causes

Acute Arterial Thrombosis

• Atherosclerotic disease at the origin of the superior mesenteric artery (SMA) is the predominant cause, typically occurring in patients with pre-existing chronic mesenteric ischemia 1
• The underlying atherosclerotic plaque progresses to critical stenosis, usually accompanied by celiac artery occlusion due to collateral development 1
• This has become the leading cause of acute mesenteric ischemia, increasing from 20-35% historically to 40% currently, partly explained by modern anticoagulant therapy for atrial fibrillation 1
• Less common arterial thrombotic causes include vasculitis, mesenteric dissection, and mycotic aneurysm 1

Arterial Embolism

• Emboli originate from the heart (atrial fibrillation, left ventricular dysfunction, valvular disease like endocarditis) or atherosclerotic aorta 1
• The SMA is particularly vulnerable due to its large diameter and low takeoff angle from the aorta 1
• Emboli typically lodge 3-10 cm distal to the SMA origin, sparing the proximal jejunum and colon 1
• Nearly 50% of patients with embolic acute mesenteric ischemia have atrial fibrillation, and approximately one-third have prior arterial embolic events 1
• This mechanism has decreased to 25% of cases in recent years 1

Non-Occlusive Mesenteric Ischemia (NOMI)

• NOMI results from SMA vasoconstriction associated with low splanchnic blood flow, occurring in approximately 20-25% of cases 1
• Patients typically have severe coexisting illness, most commonly cardiac failure precipitated by sepsis 1
• Key precipitating factors include:
  • Heart failure, renal failure, and hemodialysis 1
  • Cardiac surgery using cardiopulmonary bypass 1
  • Hypovolemia and vasoconstrictive agent use 1
  • High-dose vasoactive drugs in septic shock 1
• The incidence is increasing due to greater numbers of critically ill patients and improved intensive care 1

Mesenteric Venous Thrombosis

• Accounts for less than 10% of mesenteric infarction cases 1
• Caused by Virchow's triad: stagnant blood flow, hypercoagulability, and endothelial damage 1

Inherited Hypercoagulable States

• Factor V Leiden, prothrombin mutation, protein S deficiency, protein C deficiency, antithrombin deficiency, and antiphospholipid syndrome 1
• Fibrinolysis shutdown (resistance to tissue plasminogen activator) is a significant risk factor 1

Acquired Causes

• Malignancies, hematologic disorders, and oral contraceptives 1
• Inflammatory processes: acute pancreatitis or inflammatory bowel disease causing inflammation around the superior mesenteric vein 1
• Surgical trauma: splenectomy or bariatric surgery 1
• In young patients, 36% of cases occur without obvious cause 1

Additional and Emerging Causes

Chronic Mesenteric Ischemia Progression

• Occlusive chronic mesenteric ischemia is mostly caused by atherosclerosis, affecting females more frequently (65-72%) 2
• Symptoms typically manifest when at least two mesenteric vessels are involved due to extensive collaterals 2

Other Mechanisms

• Abdominal compartment syndrome with very high intra-abdominal pressure causing bowel ischemia 1
• COVID-19-related ischemia: large vessel thromboembolic events and small vessel thrombosis linked to hypercoagulability and fibrinolysis shutdown 1
• Strangulating bowel obstruction 3
• Rare causes include vasculitis, traumatic injury, aortic dissection, cholesterol emboli, and intestinal obstruction 4

Age-Related Epidemiology

• The incidence increases exponentially with age: an 80-year-old has roughly tenfold the incidence of a 60-year-old 1
• In patients aged 75 years or older, acute mesenteric ischemia is more prevalent than appendicitis as a cause of acute abdomen 1