Summarize vascular ileus, including its acute presentation and chronic abdominal angina.

Vascular Ileus: Acute and Chronic Mesenteric Ischemia

Acute Mesenteric Ischemia (Acute Vascular Ileus)

Acute mesenteric ischemia is a life-threatening emergency with mortality rates approaching 60-70% despite treatment, requiring immediate recognition and aggressive intervention to prevent bowel infarction and death 1, 2, 3.

Clinical Presentation

The hallmark presentation is severe, sudden-onset periumbilical abdominal pain that is "out of proportion to physical findings" - meaning intense pain with minimal tenderness on examination initially 1. This occurs predominantly in elderly patients (median age 70 years, two-thirds female) with pre-existing cardiovascular disease 1.

Key clinical features:

• Abdominal pain is always present - anterior, periumbilical, severe enough to seek immediate medical attention 1
• Initially absent peritoneal signs (no guarding/rigidity early on)
• Common embolic sources: atrial fibrillation, recent MI, left ventricular dysfunction 3
• May have history of chronic abdominal pain and weight loss preceding acute event 1

Etiology

The causes break down as follows 3:

• Arterial embolism: 50% (most common, typically lodges in proximal SMA)
• Arterial thrombosis: 15-25% (occurs on pre-existing atherosclerotic disease)
• Non-occlusive mesenteric ischemia (NOMI): 25% (vasoconstriction from low-flow states)
• Mesenteric venous thrombosis: 5-15% (least lethal form)

Diagnosis

CT angiography (triple-phase: non-contrast, arterial, portal venous) is the gold standard and must be performed emergently 2, 4, 5. This identifies:

• Arterial occlusion/thrombosis
• Bowel wall thickening, distention
• Pneumatosis intestinalis and portal venous gas (late, ominous findings) 1
• Intra-abdominal fluid
• Perforation

Laboratory findings are non-specific but typically show:

• Leukocytosis and lactic acidosis 1
• Elevated amylase (50% of patients) 1
• Occult blood in stool (25% of patients) 1
• Elevated D-dimer 5

Critical pitfall: Duplex ultrasound is contraindicated in acute settings due to bowel distention, gas, and time delays 1.

Treatment Algorithm

The treatment approach depends critically on whether bowel infarction is present:

IF PERITONEAL SIGNS PRESENT (guarding, rigidity, pneumoperitoneum, intramural air on CT):

• Proceed directly to emergency laparotomy 6
• Surgical revascularization (embolectomy or bypass)
• Resection of non-viable bowel
• Scheduled "second-look" operation at 24-48 hours to reassess viability 1

IF NO PERITONEAL SIGNS AND NO BOWEL INFARCTION:

• Endovascular intervention is now first-line 6, 2, 6
• For embolic occlusion: aspiration embolectomy ± thrombolysis 2, 6
• For thrombotic occlusion: PTA with stenting 6
• Catheter-directed vasodilator infusion for associated vasospasm 6

Endovascular therapy advantages (compared to open surgery) 6:

• Decreased bowel resection rates
• Lower incidence of renal/respiratory failure
• Lower subsequent short bowel syndrome
• Lower mortality

Critical caveat: Even with successful endovascular revascularization, up to 70% may still require laparotomy for bowel assessment 2. Reperfusion of infarcted bowel can cause sudden endotoxin release leading to DIC, ARDS, and cardiovascular collapse 1.

Special Consideration: Non-Occlusive Mesenteric Ischemia (NOMI)

NOMI has the highest mortality (up to 70%) due to delayed diagnosis 6. Suspect in:

• Patients with cardiogenic shock or low-flow states 1
• Patients receiving vasoconstrictors (cocaine, ergots, vasopressin, norepinephrine) 1
• Post-cardiac surgery or coarctation repair 1

Diagnosis: Conventional angiography showing peripheral vessel narrowing with alternating dilation/narrowing pattern 6

Treatment: Intra-arterial vasodilators (nitroglycerin, papaverine, glucagon) or high-dose IV prostaglandin E1 6, 1

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Chronic Mesenteric Ischemia (Abdominal Angina)

Chronic mesenteric ischemia presents as the classic triad: postprandial abdominal pain, weight loss, and sitophobia (fear of eating) 6.

Pathophysiology

Almost always caused by atherosclerotic occlusive disease of mesenteric arteries (celiac axis, SMA, inferior mesenteric artery) 6. Due to extensive collateral circulation, symptoms typically require stenosis/occlusion of at least 2 of 3 main vessels 6.

Clinical Features

• Postprandial pain: Occurs 15-30 minutes after eating, subsides in 1-2 hours 7
• Weight loss: From food aversion and malabsorption
• Sitophobia: Fear of eating due to predictable pain
• Often coexists with atherosclerotic disease in other vascular beds

Diagnosis

Non-invasive imaging options 6:

• CTA with sagittal reformatting (excellent for ostial lesions)
• MRA (preferred in renal insufficiency or contrast allergy)
• Duplex ultrasound (>90% accuracy for ostial disease, operator-dependent) 6

Conventional angiography remains gold standard for peripheral vessel evaluation 6

Treatment

Endovascular revascularization (PTA with stenting) has supplanted open surgical repair as preferred therapy 6.

Advantages of endovascular approach:

• Lower mortality and morbidity compared to open repair 6
• Can be performed at time of diagnostic angiography

Disadvantage:

• Higher recurrent symptom rates requiring reintervention compared to open surgery 6

Open surgical bypass should be considered for:

• Complex anatomy 6
• Failed endovascular revascularization 6

Complications of endovascular treatment 6:

• Distal embolization
• Branch perforation
• Dissection
• Stent dislodgement/thrombosis

Natural History

Untreated chronic mesenteric ischemia can progress to acute mesenteric ischemia 1. The risk of developing symptoms from asymptomatic but significant disease is 86% with 40% overall mortality 8. Early intervention is vital to prevent life-threatening acute-on-chronic presentation.

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Key Clinical Pitfalls

1. Delayed diagnosis kills: The mortality remains 60-70% because diagnosis is often delayed until bowel infarction has occurred 1

2. Normal labs don't exclude the diagnosis: No specific laboratory findings exist for acute mesenteric ischemia 1

3. Don't waste time on duplex ultrasound in acute settings - it's contraindicated 1

4. Beware reperfusion injury: Restoring flow to infarcted bowel can cause catastrophic endotoxin release 1

5. Chronic can become acute: Patients with chronic symptoms may present with acute thrombosis - maintain high suspicion 1