Mesenteric Ischemia

Overview

Definition

Mesenteric ischemia is a condition caused by hypoperfusion of the intestine, resulting in ischemia and necrosis. Mesenteric ischemia is categorized based on the time course:

• Acute mesenteric ischemia: caused by a sudden decrease in blood flow
• Chronic mesenteric ischemia: episodic, recurrent, or constant intestinal hypoperfusion

Anatomy

The main vessels affected in mesenteric ischemia include:

• Superior mesenteric artery (SMA):
  • Most commonly affected
  • Supplies the midgut (distal duodenum to proximal ⅔ of the transverse colon)
• Inferior mesenteric artery: supplies the hindgut (distal ⅓ of transverse colon to anal canal above pectinate line)

Pathophysiology

• The intestinal tract has a ↑ metabolic rate → requires ↑ blood flow
• Disruption in blood flow → ischemic changes within 15 minutes:
  • May cause a reactive vasospasm → ↓ collateral blood flow
  • Bowel hypoxia → bowel wall spasm → symptoms:
    • Vomiting
    • Diarrhea
  • May depend on:
    • Adequacy of perfusion
    • Any collateral circulation
    • Number of vessels affected
• Mucosal damage and sloughing occurs within 3 hours and can lead to:
  • Gastrointestinal bleeding and visceral pain
  • Release of vasoactive mediators, bacteria, and toxic byproducts; resulting in:
    • Cardiac failure
    • Systemic inflammatory response syndrome (SIRS)
    • Multisystem organ failure
• Bowel wall becomes cyanotic and edematous → fluids released into peritoneal cavity
• Necrosis occurs within 6 hours → peritoneal signs

Acute Mesenteric Ischemia

Epidemiology

• Exact prevalence is unknown.
• Accounts for 0.1% of all hospital admissions
• Generally seen in patients > 60-years-old
• Mortality rate: 60%

Etiology

• Arterial embolism:
  • Most common type (50%)
  • Median age is 70-years-old.
  • Frequently due to a cardiac embolus:
    • Atrial dysrhythmias, such as atrial fibrillation
    • Congestive heart failure
    • Myocardial ischemia or infarction
    • Ventricular aneurysm
    • Valvular disease and endocarditis
  • Most commonly affected artery is the SMA due to: 
    • Large caliber
    • Acute angle of departure from the aorta 
• Arterial thrombosis:
  • 2nd most common type (25%)
  • Often seen in individuals with a history of chronic mesenteric ischemia symptoms
  • Acute occlusion occurs in severely narrowed segments of the vessel: 
    • Usually due to underlying atherosclerosis
    • Most often at the vessel origin
  • Risk factors include: 
    • Diabetes
    • Hypertension
    • Tobacco use
    • Hyperlipidemia
• Non-occlusive mesenteric ischemia:
  • 3rd most common type (5%–15%)
  • Can result in recurrent and repetitive injury to the bowel
  • Causes: 
    • Hypoperfusion states (e.g., sepsis, hypovolemia, ↓ cardiac output, hemodialysis) 
    • Vasospasm or vasoconstriction (e.g., vasopressors, cocaine)
• Venous thrombosis:
  • Least common type (5%–10%)
  • Frequently involves superior mesenteric vein 
  • Risk factors include: 
    • Thrombotic disorders or hypercoagulable states (e.g., young women taking oral contraceptives)
    • Malignancy causing venous compression
    • Inflammation (e.g., pancreatitis, intra-abdominal infection)
    • Venous congestion (e.g., portal hypertension from cirrhosis)
    • Trauma

Clinical presentation

• Classic triad:
  1. Diffuse abdominal pain out of proportion to the physical exam:
     • Severe pain 
     • Not worsened or reproduced with palpation
     • Abdomen remains soft
     • May be unresponsive to pain medication
  2. Gut emptying:
     • Vomiting
     • Diarrhea
  3. History of cardiovascular disease or embolic event
• Indications of bowel infarction:
  • Peritonitis:
    • Rigidity
    • Guarding
    • No bowel sounds
  • Septic shock:
    • Fever
    • Tachycardia
    • Hypotension
  • Hematochezia

Diagnosis

Acute mesenteric ischemia requires a high index of suspicion to allow a timely diagnosis.

• Laboratory studies:
  • Nonspecific
  • Findings that should draw suspicion:
    • ↑ Lactic acid and lactate dehydrogenase
    • Metabolic acidosis (↓ bicarbonate)
    • Leukocytosis with a left shift
    • ↑ amylase
• Electrocardiogram (ECG) should be performed to evaluate for cardiac dysrhythmia.
• Imaging studies:
  • Radiographs: 
    • Nonspecific
    • Possible findings: ileus and pneumatosis intestinalis (gas within the wall of the intestine)
    • Rule-out free air (perforation)
  • Duplex ultrasound of mesenteric vessels: assesses the SMA and celiac artery for blood flow
  • Computed tomography (CT) with angiography:
    • Preferred method for diagnosis
    • Requires intravenous (IV) contrast (no oral contrast)
    • Identifies occluded mesenteric vessels
    • Collateral vessels may be present.
    • Evaluates bowel for signs of ischemia (e.g., wall thickening, pneumatosis intestinalis, portal venous gas)
    • Bowel dilation and lack of bowel wall enhancement may be seen.
  • Mesenteric angiogram:
    • Identifies occluded mesenteric vessels in real-time under fluoroscopy
    • Used for endovascular interventions, such as angioplasty and/or stenting
    • May be used for surgical planning
    • Limited availability, requires an endovascular specialist
    • Requires IV contrast
• Exploratory laparotomy:
  • Imaging may be skipped in patients with clear evidence of advanced ischemia (e.g, sepsis, peritoneal signs); it may be safer and more expedient.
  • Goal is to identify and prevent impending perforation.

Management

• Initial management:
  • Early fluid resuscitation with crystalloid to maintain hemodynamic stability
  • Broad-spectrum antibiotics to cover anaerobic and gram-negative organisms
  • Nasogastric (NG) tube for decompression of distended stomach and small bowel
  • Correction of any electrolyte abnormalities
  • Pain control
  • Avoid vasopressors, if possible. Options if vasopressors must be used include dobutamine, low-dose dopamine, or milrinone.
• Systemic anticoagulation:
  • Heparin
  • Used to prevent thrombus formation or propagation
• Endovascular angioplasty: 
  • With stenting, embolectomy, or thrombolytics
  • Indications:
    • Severe comorbidities
    • No signs of advanced bowel ischemia or peritonitis
    • Short duration of symptoms
• Surgery:
  • Indications:
    • If endovascular approach fails
    • If any concern for bowel ischemia on exam
  • Options:
    • Exploratory laparotomy
    • Open embolectomy
    • Mesenteric bypass
• Special considerations:
  • Venous thrombosis:
    • Anticoagulation is the treatment. 
    • Thrombolysis may be considered in severe cases.
    • Patients with peritoneal signs require surgical consultation.
  • Non-occlusive mesenteric ischemia:
    • Reverse the cause of hypoperfusion or vasospasm
    • Vasodilators may be considered.

Complications

• Reperfusion injury 
• Infection and sepsis
• Short bowel syndrome

Chronic Mesenteric Ischemia

Epidemiology

• Rare
• 60% of cases are inpatients > 60-years-old.
• More common in women

Etiology

Chronic mesenteric ischemia is caused by a progressive stenosis of ≥ 2 arteries, resulting in episodes of blood flow supply and demand mismatch (usually after eating).

• The majority of cases are due to atherosclerotic disease narrowing the origin of the mesenteric vessels.
• Rare causes: 
  • Vasculitis
  • Fibromuscular dysplasia
  • Artery dissection
  • Retroperitoneal fibrosis
  • Median arcuate ligament syndrome: celiac artery compression by the arcuate ligament of the diaphragm
  • Endovascular repair of the aorta

Clinical presentation

• Episodic abdominal pain:
  • Referred to as “intestinal angina” 
  • Dull and crampy
  • Epigastric
  • Varies in intensity
  • Postprandial:
    • Occurs within 1 hour after eating
    • Resolves over the following 2 hours
• Food fear:
  • Due to postprandial pain
  • Leads to significant weight loss in 80% of patients
• Abdominal bruit: present in 50% of patients
• Less common signs and symptoms:
  • Nausea and vomiting
  • Early satiety
  • Diarrhea
  • Gastrointestinal bleeding
• Beware of acute-on-chronic mesenteric ischemia:
  • May occur due to thrombus formation in a patient with chronically stenotic vessels.
  • Associated with a ↑ morbidity and mortality
  • Symptoms similar to acute mesenteric ischemia.

Diagnosis

Vascular imaging studies are used to make the diagnosis.

• CT angiography: 
  • Preferred diagnostic modality
  • Should demonstrate high-grade stenosis of ≥ 2 major mesenteric arteries
• Duplex ultrasound of mesenteric vessels: can be used as a screening study

Management

• Conservative treatment:
  • Preferred for:
    • Incidental diagnosis
    • No overt clinical manifestations
  • Focuses on limiting the progression of atherosclerosis:
    • Smoking cessation
    • Glycemic control
    • Antiplatelet therapy
• Nutritional support:
  • Necessary in patients with significant weight loss
  • Parenteral nutrition may be considered for severe cases.
• Revascularization:
  • Indications:
    • Symptoms and documented stenosis on imaging
    • Peritonitis
    • Gastrointestinal hemorrhage
  • Goal: Prevent future bowel infarction.
  • Options:
    • Endovascular approach with stenting and/or angioplasty
    • Open surgical approach for endarterectomy or bypass

Differential Diagnosis

• Small bowel obstruction: an interruption of intraluminal contents through the small bowel due to a mechanical or functional problem. Patients present with abdominal pain, distention, nausea, vomiting, and obstipation. Diagnosis is confirmed with abdominal imaging. Conservative management is usually the 1st step; nil per os (NPO), IV fluids, and NG tube decompression. Some patients fail conservative management and require surgery to relieve the obstruction.
• Spontaneous bacterial peritonitis (SBP): an acute bacterial infection of the peritoneal fluid (a well-known complication in patients with cirrhosis). Individuals present with abdominal pain, distension, fever, and chills. Physical exam demonstrates a significantly tender abdomen. If SBP is suspected, patients require paracentesis with ascitic fluid analysis and culture. The treatment of choice is antibiotics.
• Acute cholecystitis: inflammation of the gallbladder resulting from sustained gallstone impaction of the cystic duct. Patients present with colicky, upper abdominal pain, nausea, and vomiting. Inflammation of the gallbladder and gallstones are seen on ultrasound or CT. Management includes IV fluids, antibiotics, and cholecystectomy.
• Peptic ulcer disease: ulcerations located in the stomach and/or duodenum. Peptic ulcer disease may be caused by Helicobacter pylori (H. pylori) infection, medications (e.g., nonsteroidal antiinflammatory drugs), lifestyle factors, or hypersecretory conditions. Patients may have dyspepsia, postprandial pain, early satiety, nausea, or evidence of bleeding. The diagnostic test of choice is an upper endoscopy. Management includes lifestyle changes, H. pylori treatment, and proton pump inhibitors.
• Diverticulitis: inflammation or infection of a colonic diverticulum; potentially complicated by perforation, abscess, or fistula formation. Patients present with diffuse or left lower quadrant abdominal pain, nausea, vomiting, and fever. Diagnosis is made with a CT scan. Management includes antibiotics and, in cases of perforation, surgical bowel resection.