1. Diverticulitis (Diverticulosis) Pictures Slideshow
2. Hemorrhoids Quiz: Test Your Medical IQ
3. Ulcerative Colitis Pictures Slideshow

Medical Author:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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Medical Editor:

Bhupinder Anand, MD

In this Article

• Rectal bleeding (blood in stool) facts
• What does rectal bleeding (blood in stool) mean?
• What are the causes of blood in the stool (rectal bleeding)?
• What diseases and conditions can cause blood in the stool (rectal bleeding)?
• Anal fissure
• Hemorrhoids
• Diverticulosis
• Colon cancer and polyps
• Polypectomy
• Angiodysplasias
• Colitis and proctitis
• Meckel's diverticulum
• Rare causes of rectal bleeding
• How is the cause and site of rectal bleeding determined?
• History and physical examination
• Anoscopy
• Flexible sigmoidoscopy
• Colonoscopy
• Radionuclide scans
• Visceral angiogram
• Video capsule and small intestine enteroscopy
• MRI and CT tomographic angiography
• Nasogastric tube aspiration
• Esophagogastroduodenoscopy
• Blood tests
• How is rectal bleeding treated?
• Diverticulitis (Diverticulosis) Pictures Slideshow
• Hemorrhoids Quiz: Test Your Medical IQ
• Ulcerative Colitis Pictures Slideshow
• Patient Comments: Rectal Bleeding - Share Your Experience
• Patient Comments: Rectal Bleeding - Treatment
• Find a local Gastroenterologist in your town
• Rectal Bleeding Index

Tumors of the colon and rectum are growths (masses) arising from the wall of the large intestine. Benign tumors of the large intestine are usually called polypoid in shape. Malignant tumors of the large intestine are called cancers, and most are believed to have developed from polyps. Bleeding from colon polyps and cancers tends to be mild (the amount of blood loss is small), intermittent, and usually does not cause low blood pressure or shock.

Cancers and polyps of the colon and rectum can cause bright red rectal bleeding, maroon colored stools, and sometimes melena. The colon cancers and polyps located near the rectum and the sigmoid colon are more likely to cause mild intermittent bright red rectal bleeding; while colon cancers located in the right colon are more likely to cause occult bleeding that over time can lead to moderate or severe iron deficiency anemia.

Colon polyps found during colonoscopy usually are removed, a process called polypectomy. Bleeding can occur at the site of the polypectomy days to weeks after the polyp is removed. Such bleeding is called delayed post-polypectomy bleeding. Smaller polyps (2-3 mm in size) can be removed with biopsy forceps. The amount of blood loss from the use of a forceps usually is minute, and there will be no delayed bleeding. However, larger polyps (larger than 5-10 mm) usually are removed with an electro-surgical snare. These snares are connected to a machine that generates an electrical current. The polyp is looped within a snare, and electrical current is passed through the snare. The electrical current cuts off the polyp and cauterizes ("heat seals") the tissue at the base of the polyps. Cauterization prevents bleeding during polypectomy; however, the site of cauterization heals with the formation of an ulcer. Rarely, these ulcers can bleed several days to up to 2-3 weeks after polypectomy. Post-polypectomy bleeding can at times be brisk and severe, and can be bright red, dark red, maroon colored, or black.