Both sigmoidoscopy and colonoscopy are used as screening tools for certain types of cancer, including colon cancer. Both of these methods employ the use of a thin, flexible tube with a camera attached to visualise the inside of the colon. The difference lies in which areas of the colon they can see.
- A colonoscopy examines the entire colon
- A sigmoidoscopy examines only the left side of the colon
A sigmoidoscopy is less intensive than the colonoscopy and involves significantly less preparation and sedation. The issue lies in the fact that it is only a partial examination and there might be problems in the unexamined portion.
A colonoscopy examines the entire colon and is thus more comprehensive, but involves intensive preparation, sedation or sometimes even anaesthesia which is more invasive and harder on patients.
What is a Sigmoidoscopy?
Your colon as a whole is responsible for absorbing water and nutrients from the body, but the last third, namely the sigmoid colon, which is the part of the colon that is connected to the rectum. Thus a sigmoidoscopy is a procedure to inspect this particular part of the colon.
The procedure makes use of a flexible tube that contains a light and camera, which helps your doctor with various diagnoses:
- ulcers
- abnormal cells
- polyps
- Cancer
Typically, biopsies of tissue will be taken to check for any abnormal cells or changes, usually in response to certain symptoms:
- changes in bowel habits
- rectal bleeding
- abdominal pain
- unexplained weight loss
These signs can be symptomatic of various colon diseases and a sigmoidoscopy may help with the diagnosis thereof. It is also used as a screening tool for colon cancer.
The preparation for a sigmoidoscopy is similar to that of a colonoscopy and will involve an enema usually 2 hours before the procedure. In certain occasions, the colon will need to be emptied entirely and thus similar preparation to a colonoscopy need to be adhered to. This involved a clear liquid diet for one to three days prior to the procedure and possibly a laxative to help cleanse the bowel.
The procedure requires the patient to lie on their left side and a thin, flexible tube is inserted into the anus and moved along the sigmoid colon. The tube can also inflate the colon which helps clear the field of vision for the doctor to examine adequately. The procedure is uncomfortable but not painful and thus people are usually not sedated. The doctor may ask the patient to shift their position from time to time to allow better penetration of the scope. If there are abnormal areas, small pieces of tissue may be removed for further testing.
The risks are not particularly large but tearing and minimal bleeding can occur. The entire procedure takes about 10 to 20 minutes and due to the fact most patients are not sedated, driving after the fact is allowed.
What is a Colonoscopy?
A colonoscopy is a procedure that enables a doctor to examine the entirety of the colon. The colonoscope is a flexible tube that measures about four feet in length and is as thick as a finger with a camera and light source at the end. Similarly, the tip of the colonoscope is inserted into the anus and then pushed into the rectum and through the colon, usually as far as the caecum.
As with the sigmoidoscopy, colonoscopies are performed as a screening test for colon cancer, after certain symptoms are reported by the patient:
- Blood in the stool
- Abdominal pain
- Diarrhoea
- Changes in bowel habits
- Abnormalities found on x-rays or CT scans
- Those with a history of polyps or colon cancer, or family history thereof
It is recommended that once one reaches the age of 50 and every decade thereafter, a colonoscopy be performed to remove polyps before they become cancerous.
The preparation for the colonoscopy is more thorough that with the sigmoidoscopy, as the entire colon needs to be cleaned. This cannot be achieved by an enema alone, but consists of the administration of a cleansing preparation or several days of a clear liquid diet and laxatives and enemas prior to the procedure. This is to ensure a good clear field of vision during the procedure.
There are various prescription and over the counter medications that can interfere with the procedure and thus special instructions will be given by your gastroenterologist. Some such medications include:
- Aspirin
- Warfarin or coumarin
- Insulin
- Iron medications
Furthermore, certain foods should be avoided in the days preceding the procedure. These include:
- Stringy foods
- Seeded foods
- Foods with red food coloring such as red Jello
The procedure itself necessitates an intravenous drip, as well as vital signs monitoring. Sedatives are administered into the IV line, which relaxes the patient and reduces pain. The colonoscopy can cause a feeling of pressure, cramping and bloating in the abdomen. The patient will need to lie on their left side or back as the colonoscope is advanced up the colon. The procedure takes 15 to 60 minutes.
If irregularities are found during the procedure, a biopsy can be performed and the tissue submitted for examination or culture, depending on the problem detected. Should the reason for the colonoscopy be bleeding, the cause of the bleeding can be identified and samples taken if necessary. Polyps can also be removed through the colonoscope and presents an important method for colorectal cancer prevention.
After the procedure, patients will be kept for observation for 1 – 2 hours until the medication has worn off and generally are not allowed to drive themselves. If they have had polyps removed, there will be certain activity restrictions on returning home. Colonoscopy complications are typically rare, but can include:
- Bleeding (which is usually minor and self-limiting)
- Perforations or tearing
- Reactions to sedatives
- Local irritation of the vein due to the IV line
A colonoscopy is the best practice to detect, diagnose and consequently tread irregularities found in the colon.
The Difference between Sigmoidoscopy and Colonoscopy
- By Definition
A colonoscopy examines the entire colon, as opposed to a sigmoidoscopy which examines on the last third of the colon, namely the sigmoid colon.
Comparison between Sigmoidoscopy and Colonoscopy
| Sigmoidoscopy | Colonoscopy |
| Examines the sigmoid colon | Examines the entire colon |
| Makes use of a thin flexible sigmoidoscope with a light and camera at the tip | Makes use of a finger-width tube with a light and camera at the tip |
| No sedatives used prior to procedure | Sedatives used prior to procedure |
| Preparation is minimal, including a 1 – 2 day clear liquid diet and a laxative | Preparation includes a bowel cleanser or several day clear liquid diet and laxative |
| Further procedures need to be scheduled | Can involve further surgery within the procedure such as polyp removal |
| Can drive home afterwards | Cannot drive themselves after the procedure |
| Usually painless | Can be painful |
| Procedure takes 10 – 15 minutes | Procedure takes 15 – 60 minutes |
Summary
- Sigmoidoscopy is a relatively painless, quick procedure used as a screening test for colon cancer.
- Colonoscopy is a more in depth, uncomfortable procedure that is also used for colon cancer screening
- Sigmoidoscopy involves little preparation and the patient suffers very few after effects or complications
- Colonoscopy involves complete colonic clearing and the patient can suffer cramps or bleeding after the procedure.