A 70 year old man was admitted for elective right hemicolectomy for a caecal tumour. The surgery was uneventful, however, on the 7th day, he became pale and clammy and developed abdominal distension and new onset atrial fibrillation. The abdomen was tender to palpate and distended, but there were no signs of peritonism. An emergency CT scan was performed to exclude an anastomotic leak. In view of marked derangement of his renal function, a non-contrast enhanced CT of the abdomen and pelvis was performed.
CT imaging did not demonstrate any anastomotic leak. However, there was evidence of small bowel ischaemia and infarction with thinning of the bowel wall, intramural gas (pneumatosis intestinalis), and extension of the intramural gas into the mesenteric veins and on into the SMV and portal veins. A large amount of portal venous gas was seen within the liver, extending into the peripheries. No free intraperitoneal gas was identified to suggest viscal perforation.
The patient had an emergency laparotomy which demonstrated gross bowel infarction. No bowel resection was performed. The patient passed away 24hours later.
Bowel / mesenteric ischaemia is usually due to arterial occlusion, be it occlusive or non-occlusive. Occlusive infarction has a 90% mortality and may be due to an embolus (50%) just distal to the middle colic artery or due to SMA thronbosis (20-40%) at origin and at site of atherosclerotic narrowing. Acute events are due to acute occlusive SMA embolus in 50%, usually at bifurcation of middle colic artery and SMA.
Risk factors includes a cardiac history and atheromatous disease ( our patient was a diabetic with a cardiac history and new onset AF). Typical presentation would be of initial crampy pains, leading to continuous abdominal pains followed by an acute event. The area of ischaemia may affect any segment of small bowel or distal transverse colon, splenic flexure and caecum.
Initial CT findings are of circumferential bowel wall thickening with a 'target sign', then bowel wall thinning may be seen as the bowel becomes gangrenous. There may be focal/ diffuse bowel dilatation due to arrested peristaltic activity. A variable enhancement pattern may be seen, from reduced enhancement due to interrupted arterial flow to increased wall enhancement due to hyperaemia. Oedema of the mesentery results in increased attenuation of the mesentery. Dissection of intraluminal gas into the bowel wall occurs due to compromised mucosa (pneumatosis intestinalis), this may extend into the mesenteric venous system and may propagate into the portal venous system. Pneumoperitoneum with/out ascites is seen when the infarcted bowel perforates. A hyperattenuating SMA may be seen in arterial occlusion on non-enhanced CT.
Prognosis depends on collateral flow; massive infarction of small and large bowel occurs when mesenteric embolisation occurs proximal to middle colic artery whilst focal segment on intestinal ischaemia is seen if embolisation occurs distal to the middle coloc artery. Mortality ranges from 70-92% for intestinal infarction.