Rectal Bleeding (cont.)
Angiodysplasias
Abnormal collections of enlarged blood vessels frequently occur
just under the inner lining of the colon. These abnormal vessels are called
angiodysplasias. Angiodysplasias usually can be seen easily during colonoscopy
as bright red, spider-like lesions just beneath the colon's lining. Although
angiodysplasias may occur anywhere in the colon, they are most common in the
right colon. The cause of angiodysplasias is unknown, but they occur with
increasing frequency as people grow older. Bleeding from angiodysplasias is
painless and can result in bright red, dark red, maroon, or black stools.
Angiodysplasias also can cause occult bleeding and iron deficiency anemia.
Colitis and proctitis
Colitis means inflammation of the colon. Proctitis means
inflammation of the rectum. Several different diseases can cause colitis and
proctitis; they include bacterial or viral infection, ulcerative colitis or
proctitis, Crohn's colitis, ischemic colitis, and radiation colitis or
proctitis.
Ulcerative colitis, ulcerative proctitis, and Crohn's colitis are
chronic inflammatory diseases of the colon due to overactivity of the body's
immune system. These diseases can cause abdominal pain,
diarrhea, and bloody
diarrhea (diarrhea mixed with blood). Occasionally, moderate or severe rectal
bleeding may occur. The bleeding originates from ulcerations in the colon. (For
more information, please see the Crohn's
Disease and Ulcerative Colitis
articles.)
Like ulcerative colitis and Crohn's colitis, infection--bacterial
and, less commonly, viral--can inflame the colon, leading to abdominal pain,
diarrhea, and even bloody diarrhea. Rarely, infections may cause moderate or
severe rectal bleeding. Examples of infections causing rectal bleeding include
salmonella, shigella, Campylobacter, C. difficile, E. Coli O157:H7, and
cytomegalovirus (the last in patients with
HIV infection).
Ischemic colitis is
inflammation of the colon that is caused when the supply of blood to the colon
is reduced suddenly. This is most often due to a blood clot that obstructs a
small artery supplying blood to a portion of the colon. The most common part of
the colon affected by ischemic colitis is the splenic flexure (the part of the
colon where the transverse colon joins the left colon). The sudden reduction in
the flow of blood can lead to ulceration of the colon and cause the sudden onset
of severe lower abdominal, cramping pain followed by rectal bleeding. The amount
of blood lost during an episode of ischemic colitis usually is small. Rectal
bleeding and the abdominal pain of ischemic colitis usually subside on their own
after several days. The colonic ulcers usually heal after a few more days.
Radiation treatment for cancers of the abdomen can cause radiation colitis
acutely, but permanent changes to the inner lining of the colon and the colonic
blood vessels occur, which can result in bleeding many years after treatment. A
common example is radiation proctitis that results from pelvic radiation for the
treatment of prostate cancer. Rectal bleeding from radiation proctitis usually
is mild, but occasionally can be chronic enough to cause anemia.
Meckel's
diverticulum
A Meckel's diverticulum is an out-pouching (sack) that protrudes
from the small intestine near the junction of the small intestine and the colon.
It is present from birth, and occurs in approximately 2% of the population. Some
Meckel's diverticula can secrete acid, like the stomach, and the acid can cause
ulcerations in the inner lining of the diverticulum or the tissues of the small
intestine adjacent to the diverticulum. These ulcers can bleed. Bleeding from a
Meckel's diverticulum is the most common cause of gastrointestinal bleeding
among children and young adults. Bleeding from a Meckel's diverticulum is
painless but can be brisk and can cause bright red, dark red, or maroon stools.
Rare causes of rectal bleeding
Rarely, rapid and severe bleeding from the upper gastrointestinal
tract (for example, ulcers of the stomach or duodenum) can cause bright red
rectal bleeding. Other rare causes include leaking of blood into the
gastrointestinal tract when a blood vessel ruptures. This may occur when an
ulcer of the gastrointestinal tract erodes into a nearby artery or when an
arterial graft, for example, an aortic graft used to repair an aortic aneurysm,
erodes into the gastrointestinal tract. Even more rare is bleeding from a rectal
ulcer, or tumors of the small intestine.
Next: How is the cause and site of rectal bleeding determined? »
- Colonoscopy - Learn about the colonscopy procedure, what it is, why it is performed, preparation, complications, alternatives and the after effects of the screening exam on MedicineNet.com
- Abdominal Pain - Learn about abdominal pain (pain in the stomach / abdomen) including causes, symptoms, how abdominal pain is diagnosed, and how abdominal pain is treated.
- Fecal Occult Blood Test - Read about the fecal occult blood test in which there are two types, chemical and immunologic. Fecal occult blood tests are used to screen for colon cancer and colon polyps.
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