Acute mesenteric ischaemia: a pictorial review

Abstract

Acute mesenteric ischaemia (AMI) is an uncommon cause of acute hospital admission with high mortality rates (50-90%) that requires early diagnosis and treatment. With the increase in average life expectancy, AMI represents one of the most threatening abdominal conditions in elderly patients. Untreated, AMI will cause mesenteric infarction, intestinal necrosis, an overwhelming inflammatory response and death. Early intervention can reverse this process leading to a full recovery, but the diagnosis of AMI is difficult. The failure to recognise AMI before intestinal necrosis has developed is responsible for the high mortality of the disease. Unfortunately, common CT findings in bowel ischaemia are not specific. Therefore, it is often a combination of nonspecific clinical, laboratory and radiological findings that helps most in the correct interpretation of CT findings. The purpose of this article is to provide an overview of the anatomy, physiology of mesenteric perfusion and discussions of causes, pathogenesis and CT findings in various types of acute bowel ischaemia. Familiarity with various imaging features of mesenteric injury is essential to make a timely diagnosis that will lead to improved patient outcomes. TEACHING POINTS: • AMI is a potentially life-threatening disorder whose prognosis depends on early recognition, accurate diagnosis and timely intervention. • Arterial inflow occlusion due to thrombosis or embolisation is the most common cause of AMI. • Four aetiological types of AMI have been associated with different characteristics and risk factors (EAMI, TAMI, VAMI and NOMI). • Physical examination and laboratory findings are not sensitive or specific for diagnosing AMI; therefore, MDCT is still the first-line imaging method in suspected AMI. • Although a number of scoring systems for prognosis have been proposed, these have not been validated in large-scale studies.

Keywords: Computed tomography; Ischaemia/diagnosis; Mesenteric ischaemia; Mesenteric vascular occlusion/diagnosis; Pneumatosis intestinal.

Fig. 1

Anatomy. Sagittal CT MIP (maximum intensity projection) image shows three major arteries that supply the bowel, coeliac trunk (asterisk), superior mesenteric artery (white arrow) and inferior mesenteric artery (orange arrow), which are visceral branches of the abdominal aorta (+)

Fig. 2

Arterial occlusion. Contrast-enhanced CT image of the abdomen in a 54-year-old female with superior mesenteric arterial thrombosis. a, b: Contrast-enhanced axial CT scan demonstrates a thrombus in the superior mesenteric artery in coronal (a) and axial plane (b) (white arrow)

Fig. 3

Ischaemic colitis in a 74-year-old male with vasculitis who presented with abdominal pain and bloody diarrhoea. (a, b) Contrast-enhanced CT scan reveals involvement of the sigmoid colon and splenic flexure (orange arrows) with marked wall thickening and pericolic streakiness (asterisk). Diagnosis was confirmed at colonoscopy and biopsy. The ischaemic process resolved

Fig. 4

Venous occlusion. Contrast-enhanced CT image of the abdomen in 49-year-old female with superior mesenteric vein thrombosis. (a) Contrast-enhanced axial CT scan shows a thrombus in the superior mesenteric vein in axial plane (orange arrow); (b) wall thickening of the ascending colon (white arrow). Ascites (*) is also visible

Fig. 5

Contrast-enhanced CT image of the abdomen in an 82-year-old male with embolism of the superior mesenteric artery. (a) Contrast-enhanced axial CT shows pronounced intrahepatic portal venous gas (branching hypoattenuating areas) extending into the periphery of the left liver lobe (red arrow). (b) Contrast-enhanced axial CT scan shows dilated and gas-filled loops with an extreme thinning of the bowel wall, a “paper thin wall”, due to transmural small-bowel infarction (orange arrow). Pneumatosis (white arrow) is also seen; fat stranding (*) and gas in mesenteric veins (white arrowhead)

Fig. 6

Gasless abdomen. Contrast-enhanced CT image of the abdomen in a 62-year-old female with small bowel wall ischaemia due to venoocclusive disease. Contrast-enhanced CT image of the abdomen shows dilated and mainly fluid-filled bowel loops and gasless abdomen (white arrow). Ascites (*) and vascular engorgement (orange arrow) are also seen

Fig. 7

Bowel wall enhancement. Contrast-enhanced axial CT scan shows normal dilated loops with a diffuse hypointense segment of small bowel wall (white arrow) with reduction of bowel wall thickness due to superior mesenteric artery occlusion

Fig. 8

Bowel wall enhancement. Coronal contrast-enhanced CT shows “pale arterial ischaemia” with absent mural enhancement in a segment of small bowel (white arrow). An adjacent segment of small bowel shows mucosal hyperenhancement of thick-walled small bowel (orange arrow), indicating bowel reperfusion injury

Fig. 9

Shock bowel. Contrast-enhanced axial CT images in 56-year-old male with severe head trauma and bleeding from a large scalp laceration. Findings of shock bowel include diffuse intense mucosal enhancement (orange arrow) and submucosal oedema (white arrow)

Fig. 10

Bowel wall thickness and enhancement. a Contrast-enhanced axial CT images show a target sign (larger white arrow) in the small bowel wall due to mesenteric venous occlusion. b The vascular engorgement (*) and oedema of the bowel wall in turn lead to leakage of extravascular fluid into the bowel wall and mesentery. The resultant oedematous bowel may have a “halo” or “target” appearance due to mild mucosal enhancement (straight white arrow), submucosal and muscularis propria nonenhancement (red arrow), and mild serosal/subserosal enhancement (orange arrow). Bowel wall thickness is greatly increased measuring up to 1.5 cm

Fig. 11

Pneumatosis. A 91-year-old male with mesenteric infarction. Contrast-enhanced CT images of the lower abdomen show gas in the bowel wall (white arrow)

Fig. 12

A 56-year-old male with mesenteric infarction. Axial enhanced CT shows various hypointense rounded regions of infarction in the hepatic parenchyma and wedge shaped in peripheral spleen parenchyma (white arrows) in a patient who has a mesenteric infarction. It also shows pneumatosis involving the gastric wall (orange arrow) and diffuse pneumo- and retropneumoperitoneum (*)