❓What❓
- ↓ bowel wall transcapillary pressure due to not only acute arterial occlusion, but also venous occlusion, incomplete arterial occlusion, & bowel strangulation
❓Epidemiology❓
💀 Acute vs. Chronic 💀
- Acute (~95%) > Chronic (~5%)
💀 Small vs. Large 💀
- Acute mesenteric ischemia (Small intestine = Celiac/SMA)
- Occlusive (~2/3)
- Arterial thromboembolism
- Venous thrombosis (e.g. PVT)
- Strangulation (mixed arterial & venous features)
- Non-occlusive (~1/3)
- Shock (any type)
- Vasospasm (e.g. amphetamines, cocaine)
- Extrinsic compression (e.g. tumor)
- Ischemic colitis (Large intestine = IMA)
- Non-occlusive > Occlusive DDx
❓Anatomy❓
💀 Inflow 💀
💀 Outflow 💀
❓Presentation❓
Can be thought of as “inside-out” destruction of bowel (lumen → wall → serosa):
💀 Early = Lumen 💀
Radiographic
- Dilated small/large bowel (”adynamic ileus”)
- Fluid-filled large bowel (↓ colonic absorption)
- Mucosal enhancement (white arrowhead above)
Clinical
- “Pain out of proportion” to exam (i.e. no peritoneal signs)
⚪ The finding of “adynamic ileus” is akin to the finding of acute foot drop in acute limb ischemia (i.e. complete loss of blood flow to nerves → true paralysis)
⚪ The lack of a (+) lactic acid in the early stages of acute mesenteric ischemia is akin to the entity “unstable angina” within the ACS spectrum (UA → NSTEMI → STEMI)
💀 Intermediate = Wall 💀
Radiographic
- Bowel wall thickening
- Pre-contrast
- Hyperattenuation = hemorrhage
- Hypoattenuation = edema
- Post-contrast
- Hyperenhancement = hemorrhage (implies ongoing blood flow & bowel viability)
- Hypoenhancement = arterial occlusion (impending infarction)
Clinical
- 3 to 6 hour deceptive pain-free interval (death of intramural pain receptors)
⚪ The finding of mural hyperenhancement (i.e. intramural hemorrhage) usually signifies venous occlusion, ischemic bowel, *or* arterial reperfusion
⚪ Of note, different patterns of enhancement may occur simultaneously
💀 Late = Serosa 💀
Radiographic
- Pre-perforation
- Bowel wall thinning & Intraluminal gas (”e-g” above)
- Mesenteric fat stranding
- Interloop ascites
- Perforation
- Pneumoperitoneum (thin arrows in “b” above)
- Portomesenteric venous gas
Clinical
- True peritonitis (”pain-in-proportion”)
- ↑ lactic acid, distributive shock
- Polymicrobial bacteremia
❓Diagnosis❓
- Not so terrible to diagnose via CT angiography if you don’t fall into 3 traps:
- “Normal lactate” — this is a late finding & a prognostic marker rather than a diagnostic test. (Lactates will be serially normal up until the patient has a catastrophic event.)
- Subtle imaging findings — mural hypoenhancement & adynamic ileus are somewhat subtle findings if the clinician is not thinking “acute mesenteric ischemia.”
- Deceptive pain free interval — don’t mistake resolution of pain for resolution of disease if the pre-test probability for disease is high.
📚 References 📚
