Clinical meaning
Gastrointestinal (GI) bleeding is classified by anatomical location relative to the ligament of Treitz (which suspends the duodenojejunal junction). Upper GI bleeding (UGIB) originates proximal to the ligament (esophagus, stomach, duodenum) and accounts for approximately 80% of GI bleeds. Lower GI bleeding (LGIB) originates distal to the ligament (jejunum, ileum, colon, rectum) and accounts for the remaining 20%.
The most common cause of UGIB is peptic ulcer disease (35-50% of cases), where acid-mediated erosion of the gastric or duodenal mucosa damages underlying blood vessels. When a peptic ulcer erodes into an artery (particularly the gastroduodenal artery posteriorly or the left gastric artery along the lesser curvature), massive hemorrhage can result. Other UGIB causes include esophageal varices (from portal hypertension in cirrhosis), Mallory-Weiss tears (mucosal tears at the gastroesophageal junction from forceful retching), erosive gastritis (NSAID use, alcohol, stress), and less commonly, arteriovenous malformations, Dieulafoy lesions (aberrant submucosal artery), and malignancy.
Esophageal variceal bleeding deserves special attention due to its severity. Portal hypertension in cirrhosis causes blood to be diverted through portosystemic collateral vessels, including submucosal veins in the distal esophagus. These varices develop thin walls under high pressure and are prone to rupture, causing massive hemorrhage with mortality rates of 15-20% per episode even with modern therapy.
LGIB most commonly results from diverticular bleeding (30-40%), which occurs when a branch of the vasa recta (arteriole supplying the colon wall) is eroded by a diverticulum. Other LGIB causes include colonic angiodysplasia (arteriovenous malformations, common in elderly), hemorrhoids, colorectal neoplasms, inflammatory bowel disease, ischemic colitis, and post-polypectomy bleeding.