Mesenteric Ischemia

Clinical

Ischemia arises from inadequate blood flow to or from mesenteric vessels. It may be arterial or venous, occlusive or non-occlusive, acute or chronic, diffuse or focal. The SMA and IMA are more frequently affected than the celiac artery. The majority of mesenteric ischemia is arterial in origin. Acute ischemia results from thrombosis or embolism of a mesenteric artery. The classic presentation is that of “pain out of proportion to the physical exam.” This is a medical emergency and carries an extremely high mortality if not treated immediately. Chronic mesenteric ischemia, usually caused by atherosclerotic narrowing of two or more mesenteric branches, has a more indolent course. It usually presents as “intestinal angina,” caused by pain after eating associated with hypoperfusion of the bowel. Weight loss and fear of eating are common.  Both acute and chronic mesenteric ischemia are most commonly caused by atherosclerosis.

Radiological

Plain films are usually first imaging ordered in evaluation of mesenteric ischemia because symptoms are often non-specific.  Both erect and supine films are used primarily as a screening tool, looking for free air, obstruction, ileus, volvulus, intussusception. Plain films are often normal, but they can demonstrate thumbprinting, as well as findings of adynamic ileus. Pneumatosis (air within the bowel wall) and portal venous gas are late, ominous findings associated with infarction and necrosis.

Fluoroscopic finding result from edema and hemorrhage into the bowel wall, and include fold thickening and effacement (“thumbprinting”) and separation of bowel loops. The lumen can be either narrowed or dilated.

Mesenteric ischemia.  Note the separation of small bowel loops and fold thickening from edema.

CT is an important component of the evaluation of mesenteric ischemia, especially in the emergency setting. Oral and IV contrast are essential. The earliest CT findings are signs of functional obstruction or ileus (dilated loops of bowel, air-fluid levels) and bowel wall thickening. The enhancement pattern typically demonstrates decreased arterial and increased venous bowel wall enhancement. Pneumatosis intestinalis and portal venous gas are easily identified on CT, both representing late, ominous findings. With adequate IV contrast, CT can also occasionally identify the site of occlusion, usually manifest as an endoluminal filling defect.

Angiography and ultrasound are used to evaluate mesenteric vessels. Angiography is the gold standard for evaluating mesenteric ischemia. In addition, it offers both diagnosis and treatment.