الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 165 |  |  |
| | | from | 165 | | |
Abstract
Summary
Mesenteric ischemia occurs when perfusion of the visceral organs fails to meet normal metabolic requirements. This disorder is categorized as either acute or chronic, based on the duration of symptoms. Acute mesenteric ischemia (AMI) occurs rapidly over hours to days and frequently leads to acute intestinal infarction requiring resection. The most common causes are embolization to the mesenteric arteries or acute thrombosis related to a preexisting plaque. Chronic mesenteric ischemia (CMI) is a more insidious process and progresses over weeks to several months. The most common cause is progressive occlusive disease of the visceral arteries, usually related to atherosclerosis. It is often unrecognized by physicians and is frequently misdiagnosed as a gastrointestinal disorder (Jimenez et al., 2010).
The disorders of the visceral circulation are infrequent mainly because of the very extensive and efficient collateral system connecting the celiac, superior mesenteric, and inferior mesenteric arteries. However, there is a lot of interest in the optimal management of these conditions, because of their catastrophic outcomes that are usually associated with a high morbidity and mortality (Geroulakos et al., 2006).
Summary
133
The differential diagnosis of AMI includes intestinal obstruction, perforated viscus, pancreatitis, cholecystitis, appendicitis and diverticulitis. Diagnosis is often delayed due to the nonspecific presentation, and extensive infarction may develop. Therefore, this diagnosis should be considered and investigated in any patient with acute, severe, persistent (> 2 hours) and unexplained abdominal pain (Gardiner et al., 2013).
The sine qua non of CMI is postprandial abdominal pain (Schwartz et al., 2013), which some authors have described as intestinal angina. The pain is characteristically dull and crampy, occurring primarily in the epigastrium or midabdomen. The temporal relationship between pain and food ingestion often leads to ’’food fear”, another classic but not invariable complaint. The lack of specificity of the signs and symptoms of this syndrome often leads to a delay in diagnosis, and it is common for affected patiens to have undergone myriad interventions, including antacid or antireflux therapy, cholecystectomy, hysterectomy, and adhesiolysis (Schwartz et al., 2013). These patients have other stigmata of peripheral vascular disease such as a history of cardiac disease, stroke, claudication, or previous vascular operative procedures (Freischlag et al., 2004).
Plain abdominal radiographs may provide helpful information to exclude other causes of abdominal pain such
Summary
134
as intestinal obstruction, perforation, or volvulus, which may exhibit symptoms mimicking intestinal ischemia. Pneumoperitoneum, pneumatosis intestinalis, and gas in the portal vein may indicate infarcted bowel. In contrast, radiographic appearance of an adynamic ileus with a gasless abdomen is the most common finding in patients with acute mesenteric ischemia (Bechara et al., 2010).
Duplex ultrasonography is a valuable noninvasive means of assessing the patency of the mesenteric vessels. Moneta and associates evaluated the use of duplex ultrasound in the diagnosis of mesenteric occlusive disease in a blinded prospective study. A peak systolic velocity in the SMA >275 cm/s demonstrated a sensitivity of 92%, specificity of 96%, and an overall accuracy of 96% for detecting more than 70% stenosis. The same authors found sensitivity and specificity of 87% and 82%, respectively, with an accuracy of 82% in predicting more than 70% celiac trunk stenosis. Duplex has been successfully used for follow-up after open surgical reconstruction or endovascular treatment of the mesenteric vessels to assess recurrence of the disease (Bechara et al., 2010).
Finally, spiral computed tomography with three-dimensional reconstruction as well as MRA have been promising in providing clear radiographic assessment of the mesenteric vessels (Bechara et al., 2010).
Summary
135
The definitive diagnosis of mesenteric vascular disease is made by biplanar mesenteric arteriography, which should be performed promptly in any patient with suspected mesenteric occlusion. It typically shows occlusion or near-occlusion of the CA and SMA at or near their origins from the aorta. In most cases, the IMA has been previously occluded secondary to diffuse infrarenal aortic atherosclerosis. The differentiation of the different types of mesenteric arterial occlusion may be suggested with biplanar mesenteric arteriogram. Mesenteric emboli typically lodge at the orifice of the middle colic artery, which creates a ”meniscus sign” with an abrupt cutoff of a normal proximal SMA several centimeters from its origin on the aorta. Mesenteric thrombosis, in contrast, occurs at the most proximal SMA, which tapers off at 1 to 2 cm from its origin. In the case of chronic mesenteric occlusion, the appearance of collateral circulation is typically present. Nonocclusive mesenteric ischemia produces an arteriographic image of segmental mesenteric vasospasm with a relatively normal appearing main SMA trunk (Bechara et al., 2010).
Surgical revascularization in the presence of an embolism is performed with balloon embolectomy usually with patch angioplasty of the SMA. Patients with chronic proximal occlusion or stenosis undergo revascularization with bypass grafting. The thrombotic process occurs in a
Summary
136
severely atherosclerotic proximal SMA. Therefore, these patients require placement of a bypass graft to the SMA distal to the occlusive segment. Antegrade or retrograde bypass may be performed depending on anatomical considerations or according to surgeon preference. Thrombolytic therapy is a potential consideration in patients with acute thrombosis and no clinical signs of peritonitis. Successful lysis returns the mesenteric circulation to its chronic, stable state. Subsequent operative revascularization or balloon angioplasty of the stenotic vessel can be undertaken electively. However, this does not allow inspection for bowel viability following reperfusion and may delay operative revascularization if thrombolysis is unsuccessful. Thrombolysis in AMI therefore should be reserved for selected patients (Geroulakos et al., 2006).
The essential treatment of mesenteric venous thrombosis is systemic anticoagulation. Initiation of an unfractionated heparin bolus, followed by continuous infusion, is critical. Secondary therapies include bowel rest, nasogastric decompression, and the intravenous administration of broad-spectrum antibiotics to guard against sequelae of bacterial translocation. Patients who develop peritoneal signs will require exploration and bowel resection. There have been conflicting reports about the utility of percutaneous, transhepatic catheter-directed thrombolysis in these patients. Most patients can be treated
Summary
137
conservatively with anticoagulation, bowel rest, and observation. Those patients requiring more aggressive intervention after failure to respond to conservative measures have been shown to have a worse prognosis (Bobadilla, 2013).
Both endovascular and open revascularization options exist for the treatment of chronic mesenteric ischemia. However, open surgical revascularization remains the treatment of choice when the patient’s condition allows, either by bypass or endarterectomy. Visceral bypass can be performed either antegrade, using the supraceliac aorta for inflow, or retrograde, using the common iliac artery for inflow. Native venous conduit is ideal when suitable segments can be obtained. If native vein is not available, prosthetic or cryopreserved alternatives may be used (Bobadilla, 2013).
Many groups have noted a reduced early mortality when endovascular techniques are used. As with many endovascular techniques, the reduced early complication rate and mortality reduction comes with reduced long term durability and increased need for reintervention (Bobadilla, 2013). Earlier studies had found high restenosis rates; however, stenting has significantly improved outcomes (Cho et al., 2012).