Introduction

What is a sigmoidoscopy?

A sigmoidoscopy is an examination (similar to a colonoscopy) that is used to examine the colon. Unlike a colonoscopy, however, the 'range' of a sigmoidoscopy is not as good; whilst a colonoscopy can visualise the entire large bowel, a sigmoidoscopy can only visualise as far as the sigmoid colon (it is therefore primarily used to visualise the rectum and parts of the sigmoid colon). As large numbers of lower GI tumours occur in this region, this is a very useful investigation, that is less invasive than a full colonoscopy. In addition to the 'flexible' sigmoidoscopy (that utilises an instrument similar to a short colonoscope), a 'rigid' sigmoidoscopy can also be performed in the outpatient clinic. This uses a smaller clear plastic instrument, that is similar in appearance to a proctoscope.

• Rigid = 25cm (examination to just above the recto-sigmoid junction - 25-30% of colorectal cancers occur here)
• 'Short' flexible = 35cm (visualises 50-75% of the sigmoid colon and can detect about 50-55% of polyps) • 'Long' flexible = 60cm (reaches the proximal end of the sigmoid colon in 80% of examinations, and detects 65-75% of polyps and 40-65% of colorectal cancers)

NB: 'depth of insertion' into the bowel is usually 5-10cm less than the length of the instrument.

Indications

Sigmoidoscopy can be performed for a number of reasons:

• In the screening of healthy (and asymptomatic) patients for colorectal cancers.
• For the management of lower GI tract bleeding (this can be used, however colonoscopy is often performed as well as/instead of sigmoidoscopy - this all depends upon the patient's symptoms, age and history. Sigmoidoscopy can therefore sometimes be more of a 'first-line' investigation)
• In evaluating patients with suspected inflammatory bowel disease and sigmoid diverticulae.

When exactly to perform a sigmoidoscopy first (vs a colonoscopy), is a matter of debate. It is worth asking the lower GI surgeons near you, as they may be the ones examining you (it never does any harm to recall to the examiner their own preferences in how to manage patients!).

How is it performed?

In a clinical scenario, always remember to do the basics first: introduce yourself, check the patient's identity and explain what you are going to talk to them about.

Preparation: Before the examination, an enema (laxative suppository) is used to soften the stools and empty the bowel in order to help improve visualisation of the bowel). The patient lies down on their left side with their knees brought up to their elbows (the 'left lateral' position).

The procedure: After a digital rectal examination has been performed, the sigmoidoscope (flexible or rigid tube) is inserted into the back passage. Air is blown through the tube to gently inflate the bowel, in order to improve the view. The device is also fitted with a light source and (in the case of the flexible device), a small camera. The sigmoidoscope is pushed very slowly into the lower bowel, and is then then gently pulled back out whilst the lining of the bowel is inspected for any abnormalities (such as ulceration, inflammation or masses). The examination can cause some discomfort, but is not usually too painful. The inflation with air can sometimes cause a feeling of 'wanting to go to the toilet', or some wind/colicky pain. This resolves soon. Biopsy samples of suspicious-looking tissue masses can also be taken and inspected in the laboratory.

A smaller (around 10cm) similar 'rigid' device called a proctoscope may also be used after this, in order to get a better view of the more distal parts of the rectum.

The entire investigation is usually performed without anaesthetic (as an outpatient) and lasts around 10 minutes at the most. The patient can go home immediately, as sedation is not usually used.

After your explanation, always ask the patient if they have any further questions or concerns. Don't forget to discuss the complications.

Complications

As with most 'invasive' procedures, patients in the UK will be required to sign a standardised consent form prior to the procedure. In order to do this, the patient must be competent, the consent must be based upon comprehensive information, and must be free from coercion (should not be forced). Bear in mind though, that despite this (and rather bizarrely), a consent form is not a legally valid document! In any case, you should discuss the significant risks of the procedure with patients. The main two of note, are perforation and bleeding. The chance of these occurring are very low, and sigmoidoscopy is considered to be a safe procedure. Proctoscopy is more of a 'clinic' procedure, and tends to only require verbal consent rather than written consent. Always check what the local policy is at your hospital.