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Acute Mesenteric Ischaemia

1. ANATOMY

  • Celiac trunk supplies foregut, hepatobiliary system, spleen
  • Superior mesenteric artery (SMA) supplies the small bowel, proximal and mid colon
  • Inferior mesenteric artery (IMA) supplies the distal colon and rectum
  • The GIT has many arterial collateral vessels between all 3 major vessels to protect from gut ischemia
    • Collaterals between the celiac trunk and SMA – via the gastroduodenal artery
    • Collaterals between the SMA and IMA – via the arc of Riolan and the marginal artery of Drummond

2. GENERAL FEATURES OF ACUTE MESENTERIC ISCHAEMIA

  • Causes of mesenteric ischaemia
    • Arterial – embolism, thrombus, non-occlusive
    • Venous thrombosis
  • Regardless of the cause, acute mesenteric ischaemia can lead to intestinal mucosal sloughing within 3 hours of onset and full-thickness intestinal infarction by 6 hours
  • General clinical features
    • Generalised abdominal pain – out of proportion to clinical exam
      • Initially pain is around the umbilicus, later becomes diffuse and constant
    • Nausea and vomiting
    • Tenderness
    • Rebound tenderness (Blumberg sign)

3. ARTERIAL ISCHAEMIA

Mesenteric Embolism

  • Embolism most commonly occurs in the SMA
  • It is the most dangerous type of mesenteric ischaemia

Etiology – cardiac origin

  • Atrial fibrillation
  • Mural infarct
  • Endocarditis vegetations

Investigations

  • Angiogram

Treatment

  • If diagnosis is within 6 hours
    • Thrombolytics – streptokinase within 6 hours
    • Heparin – to stop formation of new thrombus
  • Diagnosis after 12 hours
    • Embolectomy
    • Surgery with intestinal resection

Mesenteric thrombosis

  • Most common in the inferior mesenteric artery (IMA)

Etiology

  • Atherosclerosis
  • Buerger’s disease

Pathogenesis/clinical features

  • Thrombus formation leads to decreased blood supply, however there is development of collaterals
  • Abdominal angina – pain after eating
    • Because there is a threefold increase in blood requirement during digestion, so ischemia occurs faster and causes pain
  • Vomiting, diarrhoea, dehydration
  • As patient deteriorates – oliguria, abdominal distension, metabolic acidosis
  • In severe cases – perforation, peritonitis, ileus

Investigations

  • Angiogram

Treatment

  • Transcatheter therapy
  • Surgical exploration – for necrosis

Non-occlusive mesenteric ischaemia

  • Diffuse, intense splanchnic arterial vasospasm

Etiology – systemic hypoperfusion due to several causes

  • Shock – cardiogenic, hypovolemic or septic shock
  • Post operative – cardiac or abdominal surgery
  • Blunt abdominal trauma
  • Medication induced mesenteric vasospasm – digoxin, amphetamines, cocaine

Investigations

  • Mesenteric angiogram

Treatment

  • Antispasmodics – papaverine
  • Vasodilators
  • Heparin

4. MESENTERIC VENOUS THROMBOSIS

  • Thrombosis of the superior mesenteric or portal vein can be due to two main mechanism

Descending/central mechanism

Etiology – due to low flow states in the mesenteric venous circulation

  • Portal hypertension
  • Liver cirrhosis
  • Congestive heart failure
  • Autoimmune vasculitis
  • Congenital hypercoagulable states – e.g. thrombophilia, protein C and S deficiency

Clinical features

  • Diffuse pain
  • Patients can have symptoms for days without ischemia
    • Due to development of collateral circulation

Investigations

  • CT and Doppler US

Treatment

  • Heparin
  • Thrombolytics
  • If patient presents with acute abdomen then surgery is required

Ascending/peripheral mechanism

  • Venous thrombosis associated with intra-abdominal infections from organs that drain into the mesenteric veins
    • Appendicitis, diverticulitis, pancreatitis
  • Clinical features are usually milder
    • Therefore patients are more likely to seek treatment at a later stage when they present with acute abdomen
    • By this stage there can be extensive necrosis and peritonitis
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