Virtual Medical Centre

Symptoms

Rectal bleeding

• Definition
• Causes

Definition

Rectal bleeding, also known as haematochezia, refers to the passage of bright blood (often mixed with clots or stools) via the rectum. The rectum is the final 15cm of the colon (large intestine) where faeces accumulate before being expelled from the body via the anal canal. Rectal bleeding can be due to bleeding from anywhere in the lower gastrointestinal tract namely the colon, rectum or anus. Rectal bleeding is a very common complaint in the general population and affects up to 15% of adults. Unfortunately not all these people report their symptoms to their doctors which is dangerous as a small proportion of rectal bleeding is due to an underlying colorectal carcinoma. The majority of cases however will be due to a self-limiting condition affecting the anus or rectum but it is still important that you see a doctor. The severity of rectal bleeding varies widely. Some patients will only have a few small drops of blood that stain the toilet water or are detected on wiping, whilst others will pass several bowel motions containing large quantities of blood and clots. In some patients the amount of blood loss is severe enough to cause weakness, light-headedness, low blood pressure and symptoms of anaemia. In these cases hospital admission is often needed. The colour of the blood gives the doctor a clue to the likely site of origin of the gastrointestinal bleeding. Generally speaking, the closer the lesion is to the anus the brighter the blood lost. The image to the right shows fresh bleeding from a polypoid (protruding) lesion within the rectum, as seen by colonoscopy.

Bleeding from the first parts of the large intestine (the ascending and transverse colon) on the other hand will cause passage of dark red or maroon blood. Bleeding from much further up the gastrointestinal tract such as the stomach doesn't normally cause the loss of fresh blood but produces black and tarry stools called melena. Rectal bleeding is a symptom itself and should not be confused with the term faecal occult blood. The latter has similar causes to rectal bleeding but does not result in any colour changes to the stool or presence of fresh blood in the rectum. Faecal occult (hidden) blood is only detected when stool samples are examined at a laboratory. This may be done for the purpose of investigating the cause of iron deficiency anaemia.

Causes of rectal bleeding

The most frequent causes of lower gastrointestinal or rectal bleeding include:

• Diverticular disease- Diverticulosis refers to the presence of small out-pouchings (sacks) within the wall of the intestine which affects most people to som degree by the age of 50-60 years. The precise cause for the condition is not known and it generally doesn't cause a problem unless the pouches rupture or become inflamed (diverticulitis). Both diverticulitis and diverticulosis can cause the sudden loss of large amounts of blood via the rectum into the toilet bowl. In the latter case this blood loss is painless. Diverticular disease is the most common cause of rectal bleeding in the elderly and due to the large amount of blood loss often requires hospitalisation and blood transfusion.
• Inflammatory bowel disease- Crohn's disease and ulcerative colitis are the most common causes of inflammatory bowel disease which are characterised by damage and inflammation of the lining of the bowel. Both these conditions can cause rectal bleeding that is often mixed with mucus in a loose stool. Lack of blood supply to area of the bowel called ischaemic colitis may also damage the wall and later lead to bleeding.
• Benign anorectal diseases (harmless diseases of the anus and rectum)- Haemorrhoids are masses or clumps (cushions) of tissue in the anal canal that contain blood vessels. If large enough they can cause mild bleeding that often presents as bright red blood on toilet paper or on the outside of the stools. Associated symptoms include discomfort and pruritus ani (itchy bottom). Anal fissures refer to painful tears in the skin lining the lower anal canal often caused by straining or constipation. Once a tear is present, later efforts to pass stool are very painful and may lead to bleeding. Fistula-in-ano refers to abnormal connections between the anus and other organs or tissues. Fistulae are typically painful and may present as abscesses or loss of bright red blood on toilet paper and the surface of the stool.
• Polyps- These are benign tumours or growths in the large intestine that can predispose to cancer. The bleeding associated with polyps tends to be mild and intermittent. Removal of polyps during colonoscopy (polypectomy) can also cause later rectal bleeding days to weeks after the procedure.
• Neoplasia- Cancer of the colon typically causes blood to be mixed with the stool. Colon cancer can also cause occult blood loss and be diagnosed following investigation of symptoms of weight loss or anaemia.
• Coagulopathy- Certain drugs that thin the blood (e.g. warfarin) or inherited clotting disorders can predispose to bleeding from the gastrointestinal tract.
• Arteriovenous malformation- Angiodysplasia refers to abnormal connections between the veins and arteries in the walls of the intestines. These vessels are prone to rupture and are a common cause of fresh rectal bleeding in the elderly.
• Very rarely rectal bleeding may originate from the upper gastrointestinal tract from an ulcer or other lesion of the stomach or small intestine. Bright red rectal bleeding will only occur in these circumstances if the blood loss is very rapid and severe, otherwise these lesions will normally produce dark stools (melena) and bloody vomit.