It is usually sudden in onset, painless and substantial. Diverticulosis is the cause in 30 to 50 percent of cases with massive bleeding from the colon. However, the bleeding stops spontaneously in most patients. In some cases, the bleeding may continue intermittently for a few hours to a few days before resolving. Chronic intermittent bleeding due to diverticulosis is unusual.
Some people believe that the diverticula bleed when they are inflamed.
Actually, it is quite the opposite. Bleeding is usually not seen during an acute episode of acute diverticulitis. Diverticula bleed when they are otherwise healthy. Diagnostic strategy in cases of rectal bleeding is directed at localizing the site and the cause since there are no clinical features to reliably distinguish diverticular bleeding from other causes of gastrointestinal hemorrhage. Treatment includes intravenous fluids and blood products, plus attempts to stop bleeding if it persists.