19th July 2023

Ischaemic Bowel Disease

Ischaemic bowel disease is a heterogeneous group of conditions characterised by reduced blood flow to the bowel, resulting in ischaemia which may lead to infarction and necrosis. Ischaemic colitis affects the large bowel, whilst mesenteric ischaemia affects the small bowel.

Ischaemic Colitis

This is the most common type of bowel ischaemia, caused mainly by arterial (but occasionally venous) embolism or thrombus. It usually affects the watershed areas of the large bowel that lack a collateral blood supply – the splenic flexure and rectosigmoid junction. Risk factors include older age, recent cardiac or vascular surgery, irritable bowel syndrome and constipation. It often presents with sudden onset worsening left iliac fossa pain, often with concurrent passage of loose bloody stool. CT abdomen and pelvis with contrast is often the first line investigation, however, findings may not be specific or diagnostic. Colonoscopy may be required to confirm the diagnosis. Most cases resolve spontaneously. If there are persistent symptoms, patients may require hospital admission with a course of antibiotics, low molecular weight heparin, bowel rest and monitoring. Surgical intervention is required for associated complications (peritonitis, massive GI bleeding, fulminant colitis) – usually segmental bowel resection with stoma formation.

Acute Mesenteric Ischaemia (AMI)

AMI is a medical emergency where the small bowel becomes acutely ischaemic from one of the following 4 mechanisms: acute arterial embolism (50%), intestinal hypoperfusion (20-30%), arterial thrombosis (15-25%) or mesenteric venous thrombosis (5%). It typically affects older patients with cardiovascular risk factors, including atrial fibrillation, previous myocardial infarction, atherosclerosis, smoking and congestive heart failure. It presents with sudden onset severe periumbilical pain out of keeping with examination findings. 90% of patients will have leukocytosis. In suspected cases, an urgent contrast CT abdomen and pelvis and CT angiography are required. Once AMI is confirmed, early surgical and intensive care review is needed. Antibiotics should be started as the intestinal mucosal barrier can be damaged by ischaemia causing bacterial translocation. Management options include interventional radiology (IR)-guided endovascular treatment (thrombolysis, transjugular intrahepatic portosystemic shunt and thrombectomy) or urgent laparotomy with bowel resection if there is bowel infarction, perforation or peritonitis.

Chronic Mesenteric Ischaemia (CMI)

CMI is caused by chronic hypoperfusion of the small bowel, usually because of progressive atherosclerosis. It is more common in older female patients with risk factors including atherosclerosis, left ventricular dysfunction, chronic low blood pressure and constipation. It usually presents with recurrent episodes of mild self-limiting generalised abdominal pain, worse after eating, associated with weight loss from food avoidance. Signs include an abdominal bruit and electrolyte and nutrient deficiencies. Diagnosis is confirmed on CT angiography. Asymptomatic patients can be managed with lifestyle interventions, antiplatelet and lipid-lowering therapies. If symptomatic, surgical or IR-guided revascularisation can be performed.