Sigmoidoscopy is one of the most useful diagnostic and screening exams available for detecting colon cancer and other conditions in the large intestine. Know about the types, procedure, limitations and risk factors of this test.

What is Sigmoidoscopy?

It is a medical test used to examine the part of the large intestine between the rectum and the terminal part of colon. It is considered to be a minimally invasive examination used for the large intestine.

It is performed for confirming the results of some other tests like X-ray as well as for diagnosing the reasons behind various health abnormalities like:

  • Severe abdominal pain
  • Diarrhea
  • Sudden weight loss

The test is commonly used for diagnosing:

  • Ulcerative Colitis
  • Microscopic Colitis
  • Various inflammatory bowel diseases
  • Crohn’s disease

Sigmoidoscopy is similar to another medical exam known as colonoscopy. However, there are various differences between them.

Sigmoidoscopy Types

There are two different types of this medical test:

Flexible Sigmoidoscopy

Also known as flexi sig exam, it is used for evaluating the colon or lower portion of the large intestine. It can also be used for evaluating the left colon to look for a sign of colitis. In this exam, the diagnostician inserts a thin and flexible tube (known as Sigmoidoscope) into the rectum of a patient. There is a tiny video camera attached at the top of the tube, which produces a live visual image of the interiors of the rectum and a large area of the sigmoid colon. The test allows the diagnostician to look at the last 61 cm of the large intestine. It is also possible to collect tissue samples for biopsy using the tubular instrument while performing a Flexible sigmoidoscopy.

This procedure can be used for finding the cause of different conditions including diarrhea, constipation and abdominal pain. It is also useful for detecting signs of early cancer as well as malignant and benign polyps in the lower part of the colon and rectum. By performing Flexible sigmoidoscopy, a physician can also notice:

  • Abnormal rectal growths
  • Rectal inflammation
  • Bleeding ulcers inside the rectum
  • Descending colon

It is not possible to view the entire colon through this type of the test. Naturally, any polyps or cancers growing farther inside the colon cannot be detected with this exam.

The flexi sig is considered to be safe during pregnancy and is used for evaluating the colon in pregnant women. It can also be performed during menstruation.

Rigid Sigmoidoscopy

Rigid sigmoidoscopy or rigid sig can be used in pediatrics and general practice for detecting ano-rectal diseases like bleeding per rectum and inflammatory rectal disease. This endoscopic exam of the rectum to recto-sigmoid junction is done by passing a sigmoidoscope through the anal canal. It is performed for the purpose of detecting conditions like colonic neoplasia and also to collect biopsies of pathologies within its range.

Both are very useful diagnostic tools. However, the former is more commonly used compared to the latter.

Sigmoidoscopy Instruments

The main Instrument used in this examination is Sigmoidoscope – a long tube with a small video camera attached to its top. The length of the tube ranges from 35 cm to 60 cm and it is as thick as a human finger. Other equipments used for the test may include an obturator and bellows.

Sigmoidoscopy Preparation

Like many other diagnostic tests, both flexible and rigid sigmoidoscopy requires patients to take some preparation beforehand. The advance preparation is more important in case of flexi sig than rigid sig.

Flexible Sigmoidoscopy Preparation

It is necessary to empty the colon of an affected individual by following a low residue diet before the examination. Otherwise, it may be difficult to view the rectum and colon during the test. A doctor generally asks a patient to follow some or all of the guidelines given below:

  1. Following diet on the day preceding the exam. Usually, a patient is not allowed to eat any solid food the whole day before the examination. The individual may be allowed to drink clear liquids like water, carbonated beverages and broth. He or she may also drink coffee and tea without cream or milk.
  2. Taking a laxative on the preceding night of the exam. The doctor may recommend taking a laxative in the pill or the liquid form.
  3. Using an enema kit. Sometimes, a patient may need to use an OTC enema kit on the preceding night or a couple of hours before the test for the purpose of emptying the colon.
  4. Adjusting the medications. The doctor may adjust the dosages of certain medications such as diabetes medicines, aspirin or health supplements (containing iron and blood thinners). A patient may be asked to stop taking drugs or modify their dosages temporarily.

Rigid Sigmoidoscopy Preparation

The exam requires very little preparation from the patient. A phosphate enema can be very helpful for allowing a better view. However, its availability is limited in outpatient clinics. Anticoagulation reversal is needed if biopsies need to be collected during the test. However, a physician may apply flexi sig for biopsy collection after the rigid sig. It is naturally advisable that patients prepare for that in advance.

Individuals under some long-term medication and those who take iron supplements should inform their doctor about it prior to the test. The doctor may adjust or discontinue the dosage temporarily.

Abnormal Sigmoidoscopy Results

This examination may yield abnormal results if one or more of the following conditions are present:

  • Anorectal abscess
  • Colorectal polyps
  • Anal fissures
  • Hemorrhoids
  • Bowel obstruction
  • Inflammatory bowel disease
  • Diverticulosis (abnormal bulges on the intestine lining)
  • Hirschsprung’s disease
  • Infection or inflammation (proctitis)

After the Sigmoidoscopy Procedure

A patient generally feels mild discomfort following the examination. A doctor may ask the patient to remain in the lying position for some time as the process is a little tiring. One may feel bloated for a few hours and pass the gas left in the colon from the test. The patient may be allowed to walk slowly in his or her room to relieve the bloating. The doctor checks the patient after some time. If everything is normal, the patient is allowed to go home. In some cases, however, the time for recovery may be longer and the individual may have to stay in the hospital overnight.

If the results are normal, the individual is allowed to return to the usual diet and take part in all daily activities after the examination. However, it is not advisable for a patient to drive immediately after the procedure. Naturally, doctors recommend a patient to bring someone along who will be able to drive him or her home.

It is normal to pass a little blood with urine and stool for a few days after the exam. However, it is advisable to consult a doctor if a patient experiences serious side effects like considerable amounts of blood or blood clots in the urine and bowel movement, severe abdominal pain and fever (100°F or higher).

Sigmoidoscopy Vs Colonoscopy

People often confuse sigmoidoscopy with the diagnostic test named colonoscopy which is performed in the similar manner. The main difference between these two procedures lies in the different parts of the colon that can be evaluated using these tests. For a very long time, the colonoscopy has been considered to be the best screening test for detecting a colon cancer risk in adults. It is basically an endoscopic evaluation of the large intestine and the distal part of the small intestine of an individual. However, recent studies show that sigmoidoscopy is often being regarded as the best screening test among the two at present. The flexible form of the test is the most preferred examination for detecting colon cancer in individuals of various ages.

The process is far more minimally invasive compared to colonoscopy making it much easier for an individual to go through the test. Being relatively minimally invasive makes it less uncomfortable for the patient. Sigmoidoscopy examines the large intestine of an individual. The sigmoidoscope is inserted into the rectum and is navigated to the terminal part of the colon. Both the forms of this exam are useful for evaluating the entire colon and determining the risk of development of colon cancer in a sufferer.

A sigmoidoscopy examination takes a shorter time to complete than colonoscopy and smaller amount of air is inserted into the patient’s colon making it easier to endure.

Sigmoidoscopy Risks and Complications

One may experience the following after-effects of the procedure:

Rupture in the bowel

It is a very rare complication. A tear may occur during the process, especially if a doctor performs a biopsy or removes a polyp. This condition may lead to infection and requires prompt medical attention.

Severe Bleeding

A little bleeding is normal after the exam. In some cases, however, a patient may experience serious blood loss. This is more likely if a polyp has been removed or a biopsy has been performed during the test.

Other Complications

If sedatives have been used during the procedure, it can lead to some health problems regarding the rate of breathing, heart rate and blood pressure of a patient.

Sigmoidoscopy Limitations

There are a few limitations of this test including the following:

  • It cannot be used for detecting cancer and polyps in the transverse colon
  • It can detect only 40% to 50% of colon cancers
  • It is inadequate for the purpose of colon cancer screening

Sigmoidoscopy Alternatives

There are various tests that can be used as substitute for Sigmoidoscopy. These include:

  • Barium enema
  • Colonoscopy
  • CT colonography and virtual colonoscopy
  • FOB test
  • Proctoscopy

Sigmoidoscopy is counted among the most useful modern diagnostic tests for identifying various colon abnormalities and assessing the chances of colon cancer. Recent studies show that individuals who undergo this examination are less likely to develop a colon cancer in the future as compared to those who did not.

Sigmoidoscopy Pictures

Here are some pictures displaying the sigmoidoscope.

Picture of Sigmoidoscope

Picture 1 – Sigmoidoscopy

Image of Sigmoidoscope

Picture 2 – Sigmoidoscopy Image


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