الفهرس 
Anatomic backgroundOnly 14 pages are availabe for public view
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Abstract
Three large, unpaired midline arteries supply the majority of organs enclosed by the outer envelope of parietal peritoneum. Two of these, the celiac and superior mesenteric arteries, arise within centimeters of each other at the level of the first lumbar vertebra (the celiac at the upper border,the superior mesenteric at the lower border).The inferior mesenteric artery, arises from the anterior wall of the aorta at the level of the third lumbar vertebra.
In AMI, the risk factors that most often have been associated, in different case series, with this disease are atherosclerosis, heart disease, systemic hypertension, atrial fibrillation, smoking, digitalis use and obesity.
Arterial emboli are the most common cause of AMI, The proximal source of the embolus is frequently intracardiac mural thrombus that develops in patients with atrial tachyarrhythmias myocardial infarction, cardiomyopathy, and cardiac tumors. Endocarditis can result in septic emboli from affected valve leaflets. Mural thrombus in proximal aneurysms in the thoracic or proximal abdominal aorta. The SMA is the most common final destination for mesenteric emboli.
Arterial thrombosis constitutes the next most common cause of AMI, Preexisting atherosclerotic plaque affecting all visceral vessels is the most common finding. Hypercoagulability syndromes can also predispose to acute visceral artery thrombosis. The affected segment of SMA is usually its origin at the level of the aorta. Patients with acute arterial thrombosis frequently have preexisting symptoms of CMI.
Nonocclusive Mesenteric Ischemia (NOMI) Involves 15 % of AMI cases. Central to NOMI is SMA spasm, itself a result of excessive sympathetic outflow. Further, spasm may exist even after treatment of the precipitating event, and reperfusion injury contributes to the final clinical presentation. NOMI is associated with shock, hypovolemia, use of vasopressor agents and digitalis, and cardiopulmonary bypass.
Venous Thrombosis accounts for only 1–10 % of AMI. The superior mesenteric and splenic veins are most frequently involved, although it is possible for the portal and inferior mesenteric veins to be affected.
In CMI, The most common source is atherosclerotic occlusion or severe stenosis of the vessels accounting for more than 90% of instances. Well-known risk factors for atherosclerosis are also applicable to CMI such as hyperlipidemia, diabetes, and smoking. The pathogenesis of chronic mesenteric ischemia is the inability to achieve postprandial hyperemic intestinal blood flow.
The median arcuate ligament is the fibrous edge of the diaphragmatic crura that crosses anterior to the aorta and above the origin of the celiac axis. Extrinsic compression of the celiac axis by fibers of the median arcuate ligament or fibrotic celiac ganglion, chronic compression of the celiac axis can cause a syndrome of postprandial abdominal pain, nausea, vomiting, and weight loss.
Patients with acute mesenteric ischemia may initially present with classic “pain out of proportion to examination, patients with mesenteric venous thrombosis, as compared with those with acute arterial occlusion, tend to present with a less abrupt onset of abdominal pain. Nonocclusive mesenteric ischemia occurs most frequently in elderly, such patients are often intubated and sedated and, therefore, are unable to alert the clinician to their symptoms.
That the typical CMI complaints (postprandial pain, adapted eating pattern, fear of eating, weight loss), Abdominal pain 30 to 60 minutes after eating is common and is often self-treated with food restriction, resulting in weight loss and, in extreme situations, fear of eating, or “food fear.”
Ileus through abdominal X-ray may be an early finding consistent with mesenteric ischemia and advanced cases of intestinal ischemia may show evidence of bowel wall edema (“thumbprinting”) or pneumatosis. Plain abdominal radiography is most useful in excluding other causes of abdominal pain, such as bowel obstruction or perforation.
Duplex ultrasonography can visualize stenosis or occlusions in the celiac or superior mesenteric arteries. However, this study is often technically limited by distended, air-filled bowel loops, so duplex ultrasound has limited role in diagnosing AMI. It is an excellent screening study in patients with abdominal pain or an epigastric bruit in whom mesenteric artery disease is suspected.
CTA provides a significant amount of information about the central arterial and venous circulations. CT can also exclude other causes of abdominal pain and assess bowel perfusion to some extent. . Computed tomography is more sensitive in diagnosing venous thrombus than other types of AMI and is the investigation of choice in suspected cases of MVT. CTA has the highest spatial resolution and finest image detail and is considered by most the best study to evaluate anatomic characteristics (calcification, thrombus, diameters, and lengths) that are important to plan mesenteric interventions
Traditional catheter-based arteriography is the definitive diagnostic study for occlusive forms of AMI. Mesenteric arteriography is rarely needed to confirm the diagnosis, and it typically does not add anatomic detail to plan an intervention. it is obtained in conjunction with a planned endovascular intervention
Magnetic resonance angiography (MRA) of the splanchnic vessels is theoretically interesting because it is noninvasive, avoids the risk of allergic reaction and nephrotoxicity associated with iodinated contrast agents.
The primary treatment of NOMI is medical, with extensive critical care support and prompt arteriography. Operative exploration is reserved for signs of peritonitis suggesting the presence of gangrenous bowel that requires excision.
Fluid resuscitation of a patient with AMI should begin immediately. Surgical exploration is required for all patients who have evidence of any threatened bowel, regardless of the underlying cause. Superior Mesenteric Artery Embolectomy, Superior Mesenteric Artery Bypass and Hybrid Procedure (Retrograde Open Mesenteric Stenting) are the ways to revascularization in AMI. After revascularization has been accomplished, the viability of the bowel must be reassessed. If possible, 20 to 30 minutes of reperfusion time should be permitted. Also Duplex ultrasound seems to be the most reasonable, cost-effective way to obtain objective data for clinical decision making after various forms of mesenteric revascularization.
In CMI, Angioplasty with stenting exceeded open bypass as the first option and is currently used in more than 70% to 80% of the patients treated for chronic mesenteric ischemia. Mesenteric bypass offers improved patency, with lower rates of re-interventions and better freedom from recurrent symptoms. Revascularization should not be excessively delayed. Patients who present with deterioration of symptoms should be admitted, prescribed intravenous heparin, and treated urgently within 24 to 48 hours.
Diagnostic angiography is most often done immediately before a planned intervention, Antegrade Supraceliac Aorta to Celiac and SMA Bypass, Retrograde Iliac Artery or Infrarenal Aortic to SMA Bypass, Retrograde SMA Stent (Hybrid Revascularization) and endarterectomy are the ways to revascularization in CM.