A rectal biopsy is a procedure used to extract a tissue sample from the rectum for laboratory analysis. The rectum is the lowest 6 inches of the large intestine, and is located just above the anal canal. Its purpose is to store the body’s solid waste until it is released.
A rectal biopsy is an important tool for determining the causes of abnormalities in the rectum. It helps to diagnose problems that are identified in screening tests such as anoscopy or sigmoidoscopy.
Anoscopy and sigmoidoscopy each use a different type of scope to observe the inner lining of the colon and rectum. The tests can identify the presence of conditions such as tumors, polyps, bleeding, or inflammation. However, these tests are limited in determining the causes of these abnormalities. Your doctor may have to order more tests before they are able to give you a diagnosis.
Your physician may recommend a rectal biopsy to:
- identify the cause of blood, mucus, or pus in your stool
- determine the causes of tumors, cysts, or masses identified in a rectal screening test
- confirm a diagnosis of amyloidosis (a condition in which abnormal proteins called amyloids build up in your organs and spread through your body)
- make a definitive diagnosis of rectal cancer
To get the most reliable results from your rectal biopsy, it is necessary for your physician to see the rectum clearly. This requires that your bowels are empty. You will typically be given an enema or laxative to help you empty your bowels.
You should tell your physician about any prescription or over-the-counter medications you are taking. Discuss how they should be used before and during the test.
Your physician may provide special instructions if you are taking medications that could affect the procedure, especially if your biopsy is part of a sigmoidoscopy. These medications may include:
- anticoagulants (blood thinners)
- nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin or ibuprofen
- any medications that affect blood clotting
- herbal or dietary supplements
Tell your physician if you are pregnant, or think you might be pregnant, to ensure that your fetus is not harmed.
A rectal biopsy usually is performed during an anoscopy or sigmoidoscopy. These tests are outpatient procedures typically done by a gastroenterologist or surgeon.
An anoscopy is typically performed in a physician’s office. This test uses a lighted scope called an anoscope. The scope allows the physician to view the lowest 2 inches of the anal canal and the lower rectum. A proctoscope, which is longer than an anoscope, may also be used.
A sigmoidoscopy can be performed in a hospital, an outpatient surgical center, or in a specially equipped physician’s office. This test uses a much longer scope. A sigmoidoscope enables the physician to see further into the large intestine, past the rectum, and into the colon. It is a flexible, lighted tube that is over 2 feet long. It has a camera that transmits video images to a monitor. The images help the physician guide the sigmoidoscope through the rectum and colon.
Preparations for both types of procedures are similar. The sigmoidoscopy, which is the more complicated procedure, takes about 20 minutes to perform. Taking a rectal biopsy can slightly extend the time the procedure will take.
Typically, general anesthesia, sedatives, and painkilling medication are not administered for the procedures. You will be positioned lying on your left side on an examining table. You will pull your knees toward your chest.
Your doctor will perform a digital rectal examination. A lubricant will be applied to a gloved finger, which will be inserted gently into your anus. The initial exam is to check for obstructions that may interfere with the scope. You shouldn’t feel any pain during the digital rectal examination, but you may feel pressure. Your physician will then insert the lubricated scope. You will feel pressure when the scope is inserted and you may feel cramping, as though you need to pass gas or have a bowel movement.
If you are having a sigmoidoscopy, air will be inserted into the colon through the scope. The air will inflate the colon to allow the physician to see the area more clearly. If fluid or stools are in the way, your physician may use suction to remove them. You may be asked to change position to allow the physician to alter the position of the scope.
Your physician will remove a sample of any abnormal tissue they find in the rectum. The biopsy will be extracted with forceps, a brush, swab, or suction catheter. Typically, a patient does not feel pain from the tissue removal.
Electrocauterization, or heat, may be used to stop any bleeding that results from tissue being removed. When the procedure is over, the scope is removed slowly from your body.
The degree to which you need to recover will depend on the type of procedure that was used to collect your rectal biopsy.
If a flexible sigmoidoscopy was used, you may experience bloating from the air that was introduced into the colon. This may result in abdominal discomfort or passing gas for a few hours after the procedure.
It is not uncommon to find a small amount of blood in your first bowel movement after your rectal biopsy. However, you should contact your physician if you experience:
- extreme abdominal pain
- more than one bloody bowel movement, especially if bleeding is heavy or clotted
- a feeling of faintness
You can resume your normal diet and activities as soon as the procedure is over.
A rectal biopsy can provide valuable data for diagnosing abnormal tissue in the rectum. In cases where cancer is a concern, the procedure can provide a definitive diagnosis.
However, a rectal biopsy, like any invasive procedure, carries the risk of internal damage to the targeted organ or nearby areas. Potential risks of a rectal biopsy include:
- bowel perforation (tearing of the bowel)
- difficulty with urination
These risks are very rare.
The tissue sample that was retrieved during your rectal biopsy will be sent to a laboratory for examination. A pathologist — a physician who specializes in disease diagnosis — will examine the tissue. A report on the findings will be sent to your physician.
If the results of your rectal biopsy are normal, the findings will indicate:
- the anus and rectum are normal in size and appearance
- there is no bleeding
- no polyps, hemorrhoids, cysts, or tumors were found
- no abnormalities were noted
If the results of your rectal biopsy are abnormal, the physician may have found:
- polyps or other abnormal growths
Abnormal results of your rectal biopsy also may indicate a positive diagnosis for:
- Crohn’s disease: an inflammatory bowel disease that affects the gastrointestinal tract
- Hirschsprung’s disease: an intestinal disease that can cause an obstruction
- ulcerative colitis: an inflammatory bowel disease that affects the colon and rectum
Your doctor may order more laboratory tests or physical exams before they are able to give you a diagnosis.