An Update on Acute Mesenteric Ischemia

Abstract

Acute mesenteric ischemia (AMI) is an uncommon yet highly lethal cause of acute abdomen in the emergency setting. Computed tomography (CT) imaging, in particular a biphasic protocol consisting of angiographic and venous phase scans, is widely used to corroborate non-specific clinical findings when suspicions of AMI are high. Techniques such as low kilovoltage peak scanning, dual energy acquisition, or a combined arterial/enteric phase can improve iodine conspicuity and evaluation of bowel enhancement. Biphasic CT with CT angiography is mandatory to directly assess for the 3 primary etiologies of AMI—arterial, venous, and non-occlusive mesenteric ischemia (NOMI), and the CT angiographic findings may be the first visible in the disease. In addition, numerous non-vascular CT findings have also been reported. Bowel wall thickening, mesenteric stranding, and ascites are common but non-specific findings that correlate poorly with disease severity. Pneumatosis intestinalis and portomesenteric venous gas, while not pathognomonic for ischemia, are highly specific in cases of high clinical suspicion. Bowel wall hypoenhancement is an early and specific sign but requires a protocol optimizing iodine conspicuity to confidently identify. Finally, intraperitoneal free air and solid organ infarcts are also highly specific ancillary findings in AMI. AMI occurs as a complication in 10% of small bowel obstruction (SBO) patients, and understanding imaging findings of ischemia in the context of SBO is necessary to aid in treatment planning and reduce over- and under-diagnosis of strangulation. Familiarity with the imaging features of ischemia by radiologists is vital to establish an early diagnosis before irreversible necrosis occurs.

Acute Mesenteric Ischemia: Anatomy, Imaging Techniques, and Pathophysiology

“…This may lead to bacterial translocation and systemic infection via the portal system, subsequent inflammatory/septic response, and bowel perforation. 3 Complete vascular occlusion can result in irreversible intestinal injury within 6 hours. 1,15 Depending on timing of reperfusion, pro-inflammatory changes and oxygen free radicals may lead to further cell injury.…”

“…Arterial causes represent approximately three-fourths of all acute mesenteric ischemia with the most common cause being embolic, accounting for nearly two-thirds of arterial occlusive cases. 2,3 The SMA is particularly susceptible to embolic occlusion due to its angle of origin from the aorta with the embolism commonly lodging about 3 to 10 cm from the SMA ostia (Figure 3). 1,9 Emboli from cardiac sources are most frequent, followed by thrombosis and emboli of proximal aortic plaques, and SMA pseudoaneurysms/dissection.…”

Understanding CT imaging findings based on the underlying pathophysiology in patients with small bowel ischemia

“…Unlike acute mesenteric arterial occlusion and NOMI, the onset of mesenteric venous thrombosis is characterized by sub-acute abdominal pain that may appear in the course of 2-4 weeks; patients may suffer nausea and vomiting. Even in patients with an extensive clot burden, ischemia develops more gradually than in patients with arterial acute mesenteric arterial occlusion or NOMI and they typically do not suffer infarction unless there is extensive involvement of the upstream peripheral arcade or the vasa recta branches [48].…”

Discrimination between normal and necrotic small intestinal tissue using hyperspectral imaging and unsupervised classification

“…Particularly in preterm infants, the mortality rate approaches 50% when accompanied by diffuse peritonitis, massive intestinal bleeding, and infectious shock [3,4]. In elderly, acute mesenteric ischemia often causes necrosis of the small intestinal tissue [5][6][7] that is more common than acute appendicitis and aortic aneurysm [8]. Arrhythmic diseases such as age-related myocardial infarction, arterial hypertension, and atrial fibrillation are more likely to lead to acute mesenteric ischemia [9,10].…”