Remember to distinguish ACUTE mesenteric ischemia from CHRONIC mesenteric ischemia, can sometimes see Acute on Chronic ischemia. 

Acute: SUDDEN onset abdominal pain due to intestinal hypoperfusion ~50 % mortality if not treated

Chronic: gradual chronic abdominal pain due to intestinal hypoperfusion (intestinal angina)

Etiology (Acute): Arterial embolism (eg: dislodged thrombus from LA/LV/cardiac valve, septic emboli from IE, hx of A.fib not on anticoagulation), or arterial thrombosis.

Etiology (Chronic):Most common cause of chronic mesenteric ischemia is atherosclerosis, commonly affecting SMA or celiac arteries

Risk factors: History of atrial fibrillation, atherosclerotic disease (CAD, MI, PAD, smoking, DMII), for chronic mesenteric ischemia, age>60, female 3x>male, smoking, 50 % of patients with CAD, CVA, PAD

Acute mesenteric ischemia S&S: pain out of proportion to exam, severe pain, guarding (no time to form collaterals!), nausea/vomiting

Chronic mesenteric ischemia S&S: recurrent episodes of acute abdominal pain after eating, can lead to weight loss: Triad includes postprandial pain,food phobia , and weight loss. 

Diagnosis: CTA has high sensitivity/specificity, can also use Duplex ultrasound but more variability in sensitivity as operator dependent

For chronic mesenteric ischemia, must see high grade mesenteric vascular stenoses in at least 2 major vessels (usually one vessel alone will

Treatment of ACUTE mesenteric ischemia: broad spectrum abx, anticoagulation (heparin), open embolectomy, aorto-mesenteric bypass, laparotomy to remove necrosed bowel, and use of Vasodilators if non-occlusive.
Treatment of CHRONIC mesenteric ischemia: supportive care, if severe symptoms, can do revascularization with angioplasty +- stenting, aorto-mesenteric bypass

Comparing Mesenteric Ischemia and Ischemic Colitis