ischemic colitis; ischemic bowel; colonic ischemia

Classification

• mild: 0-2 signs associated with poor outcomes & no peritonitis
• moderate: >= 3 signs associated with poor outcomes but no peritonitis
• severe: >= 3 signs associated with poor outcomes & peritonitis

* signs associated with poor outcomes from ischemic colitis include:

• right-side involvement
• peritoneal signs
• shock or systolic blood pressure <90 mmHg
• tachycardia
• absence of bleeding from the rectum
• history of atrial fibrillation
• blood hemoglobin <12 g/dL
• WBC count >15,000/uL
• serum sodium <136 mEq/L
• serum urea nitrogen >20 mg/dL,
• serum lactic dehydrogenase >350 U/L

Etiology

• arterial
  • hypoperfusion
    • decreased cardiac output
    • cardiac arrhythmias
    • sepsis with shock
    • vasocontriction due to vasopressors
    • diversion of blood supply
      • long-distance running
      • may be aggravated by high altitude
    • dehydration
  • thrombosis of the inferior mesenteric artery
  • embolic
    • arterial emboli
    • cholesterol emboli
• drug-induced
  • cocaine
  • digoxin
  • estrogens
  • pseudoephedrine
• post-operative
  • CABG
  • abdominal aortic aneurysm surgical repair
• vasculitis: systemic lupus erythematosus
• hypercoagulable state
• risk factors
  • hypertension
  • coronary artery disease
  • peripheral vascular disease
  • atrial fibrillation
  • diabetes mellitus
  • chronic renal failure

Epidemiology

• much more common than acute or chronic mesenteric ischemia
• occurs in older patients with atherosclerosis
• 90% of patients > 60 years of age
• occurs in others (see etiology)
• more common in women

Pathology

• most commonly affected sites
  • right colon (25%)
  • transverse colon (10%)
  • left colon (33%)
  • sigmoid colon (25%)
  • may involve watershed areas between arterial supply, such as splenic flexure & rectosigmoid
• involvement of the ascending colon (right side)
  • suggests concurrent mesenteric ischemia (right colon supplied by superior mesenteric artery)
  • associated with worse outcomes
• most commonly results from a nonocclusive low-flow state in microvessels that occurs with hypovolemia or hypotension

Clinical manifestations

• left lower quadrant pain is generally mild
• self-limited bloody diarrhea, urgent defecation, tenesmus
• rectal bleeding (BRBPR) or maroon color
• crampy lower abdominal pain followed by bloody diarrhea 24 hours later
  • bleeding is typically preceded by lower abdominal pain
  • abrupt onset of lower abdominal discomfort, followed by the urge to defecate & development of hematochezia
• bleeding insufficient to require transfusion
• mild abdominal tenderness over involved segment of colon
• hypoactive bowel sounds (case description)
• abdominal distension (case description)
• nausea may occur
• patients do not appear very ill
• hypovolemia & peritonitis herald intestinal gangrene, intestinal perforation or transmural necrosis

Laboratory

• complete blood count (CBC)
  • leukocytosis may be observed (case description)
    • leukocytosis of 16,000/uL gets broad spectrum antibiotics
• basic metbolic panel
  • serum glucose
  • serum creatinine
  • serum bicarbonate
• INR
• stool studies for Clostridium difficile (GRS9)*
  • presumably Clostridium difficile enterotoxin A+B in stool or Clostridium difficile toxin genes in stool with fast turnaround, but test specifics omitted in (GRS9)

* priority over colonoscopy due to concern for toxic megacolon (GRS9)

Diagnostic procedures

• colonoscopy within 48 hours
  • segmental involvement
  • sharply demarcated pale mucosa with petechial bleeding
  • hemorrhagic nodules
  • linear & circumferential ulceration
  • gangrene
  • edematous & friable mucosa with ulceration & submucosal hemorrhage
  • findings overlap with those of inflammatory bowel disease

Radiology

• abdominal CT with IV contrast
  • segmental colonic wall thickening of watershed areas between arterial supply, such as splenic flexure or rectosigmoid
  • MKSAP20 describes nonocclusive low-flow state in microvessels as patent arterial & venous vesssels
• CT angiography is diagnostic imaging modality of choice
  • MKSAP 20 states CT angiography of mesenteric vessels of low yield
  • exception is isolated right-sided colonic ischemia
    • may be the harbinger of acute mesenteric ischemia due to thrombus or embolus of the superior mesenteric artery
• angiography after revascularization plan established with CT angiography
• barium enema (no longer diagnostic procedure of choice)
  • thumbprinting representing submucosal hemorrahages
  • segmental wall thickening may be noted, especially at splenic flexure (GRS9)

Complications

• bowel infarction
• peritonitis
• hypovolemic shock
• septic shock

Differential diagnosis

• diverticulitis
  • diverticular bleeding (without diverticulitis) is painless except for abdominal cramping due to the cathartic action of colonic blood (MKSAP20)
• bleeding is preceded by lower abdominal pain with colonic ischemia

Management

• evidence base for management is weak
• identify & correct contributing factors if feasible
• mild disease
  • supportive
  • intravenous fluids
  • bowel rest (NPO)
  • most cases resolve spontaneously
• moderate disease: as for mild disease
  • also consider antibiotics to cover anaerobes & gram negative bacteria
  • MKSAP20 suggest broad spectrum antibiotics rather than CT angiography of mesenteric vessels
• immediate exploratory laparotomy if signs of
  • peritonitis
  • hypovolemic shock
  • septic shock
  • bowel infarction
• prognosis
  • overall mortality (12%), 20-22% with right-sided & pancolitis
  • 37% mortality associated with surgery
  • risk factors for failure of medical management
    • clopidogrel use
    • lack of rectal bleeding
    • intraperitoneal fluid identified on abdominal CT
    • low serum bicarbonate on hospital admission (metabolic acidosis)

More general terms

• mesenteric ischemia (ischemic enteritis)