Curriculum · Gastroenterology
Lower gastrointestinal bleeding
What it is
Lower GI bleeding is GI bleeding from a source distal to the ligament of Treitz. The vast majority of cases of severe hematochezia are caused by a colonic source of bleeding; however, it can be caused by severe upper GI bleeding or by small bowel bleeding. Massive bleeding is defined as a significant loss of 30 to 50% in 3 hours with hemodynamic abnormalities.
Causes and risk
Acute, painless bleeding in older adult patients is usually caused by colonic diverticula or angiodysplasia. Anorectal causes, hemorrhoids and anal fissure, are the most common cause of rectal bleeding overall, particularly in young patients. The differential runs by pattern: painless, self-limited, massive hematochezia is diverticular bleeding, the most common overall cause; chronic blood loss or acute painless hematochezia in an older adult is colonic tumor, polyp or angiodysplasia; recent colonic polypectomy means postpolypectomy bleeding; evidence of vascular disease in an older adult with LLQ abdominal pain is ischemic colitis; aortic stenosis is angiodysplasia, that is Heyde syndrome; a history of bloody diarrhea, tenesmus, abdominal pain and fever is IBD; aortic aneurysm repair raises aortoenteric fistula, in which upper GI bleeding is the most common form; painless hematochezia in a young patient with normal upper endoscopy and colonoscopy is Meckel diverticulum; and mucocutaneous telangiectasias mean hereditary hemorrhagic telangiectasia. For massive bleeding in particular, the commonest cause is upper GI bleeding, with diverticulosis and angiodysplasia the others. Angiodysplasias have their own place here. They are also known as arteriovenous malformations, small ectatic blood vessels in the submucosa of the GI tract, and more than half of them are located on the right side of the colon. They are responsible for 3% to 20% of acute lower GI bleeds, and although angiodysplasia accounts for the most common cause of lower GI bleeding in younger patients, its incidence overall increases with age over 50 years. That first half stands against the line above, that anorectal causes are the most common cause of rectal bleeding particularly in young patients: the two come from different sources and neither is placed over the other. They are associated with many medical problems, including end-stage renal disease, aortic stenosis and von Willebrand disease, so painless hematochezia in a patient on hemodialysis is a familiar setting for them.