Inspection and digital rectal examination tell the doctor a great deal. But they cannot show the inside of the anal canal or the lower rectum. For that, an instrument is needed. This chapter covers two simple instruments used every day in outpatient practice: the proctoscope and the rigid sigmoidoscope. Both are quick and inexpensive. Both can be used in the clinic, without anaesthesia, in almost every patient.
6.1 Why This Step Follows the Digital Rectal Examination
The finger can feel more than the eye can see. But the proctoscope can show even more than the finger can feel. A finger reaches only the lower part of the anal canal, and the very lowest part of the rectum. A proctoscope shows the anal canal and lower rectum directly, under good light. A rigid sigmoidoscope goes further still. It often reaches 20 to 25 centimetres from the anal verge. It can show growths, inflammation, or bleeding points. These often lie beyond the reach of the finger.
Proctoscopy and sigmoidoscopy always come after a proper history and a careful digital rectal examination. They must never replace these steps. Each step in the examination builds on the one before it.
6.2 Equipment and Preparation
A proctoscope, with its obturator. It should be disposable, or freshly sterilised.
A rigid sigmoidoscope, with its own obturator and insufflation bulb. Use this after the proctoscope, if a longer view is needed.
A good light source. This may be attached to the instrument, or worn as a separate headlight.
Water-based lubricant.
Gauze swabs, and sponge-holding forceps, to clean the field if needed.
A suction device, in case blood or mucus blocks the view.
No bowel preparation is needed for simple proctoscopy. For sigmoidoscopy, give one phosphate enema shortly before the procedure. This clears the rectum and lower sigmoid colon well enough for a clear view in most patients.
6.3 Patient Position
Use the left lateral position for proctoscopy and sigmoidoscopy. This is the same position used for inspection and digital rectal examination. The patient lies on the left side. The hips and knees are drawn up toward the chest. The buttocks are brought to the edge of the examination table. This position gives easy access. Most patients also find it more comfortable, and less exposing, than the knee-chest position.
6.4 Performing Proctoscopy
Warm the proctoscope if possible. Lubricate it well, including the obturator. Explain each step to the patient before you do it.
Keep the obturator in place. Gently insert the closed proctoscope through the anal canal. Direct it toward the umbilicus at first, following the natural curve of the canal.
Once the proctoscope is fully inserted, remove the obturator.
Attach the light source. Slowly withdraw the outer sleeve. Examine the mucosa as it comes into view.
Ask the patient to strain gently, as if passing stool. Do this while you withdraw the proctoscope a short distance. Straining often brings a prolapsing pile, or a mucosal prolapse, clearly into view. This may not be seen if the proctoscope is held still.
Done gently, the whole procedure takes only a minute or two. Most patients feel little discomfort.
6.5 What to Assess on Proctoscopy
The anal canal mucosa. Note its colour, and any ulceration. Look for a fissure, usually seen as a linear tear, most often in the posterior midline.
The haemorrhoidal cushions. Note their size, number, and position on the clock face. Note whether they prolapse into view on straining.
Any fistula opening. This is seen as a small pit, or as granulation tissue, on the canal wall.
Any growth. Note its size and surface. Note whether it bleeds when the instrument touches it gently.
The lower rectal mucosa, as far as the instrument allows it to be seen.
6.6 Performing Rigid Sigmoidoscopy
Rigid sigmoidoscopy follows proctoscopy. Use it when a view of the rectum and lower sigmoid colon is needed. It is not needed in every patient. Use it mainly when there is rectal bleeding, a change in bowel habit, or another finding that raises suspicion of disease higher up.
Lubricate the sigmoidoscope well. Insert it with its obturator through the anus. Direct it toward the umbilicus at first, exactly as with the proctoscope.
Once past the anal canal, remove the obturator. Attach the eyepiece and light source.
Advance the instrument only under direct vision. Never advance it blindly. Follow the visible lumen of the bowel at all times.
Use the attached bulb to gently blow a small amount of air into the bowel. This opens the bowel wall ahead, and makes the lumen easier to follow.
Advance slowly, as far as the instrument comfortably allows. Then withdraw slowly. Examine the mucosa in a circular sweep as the instrument comes out.
If the patient reports sharp pain, stop advancing. If the lumen cannot be seen clearly, stop advancing. Never force the instrument forward. A clear view on withdrawal is just as valuable as one on insertion. It is also far safer.
6.7 What to Assess on Sigmoidoscopy
Mucosal colour and surface. A healthy mucosa is pink and glistening, with a fine visible pattern of blood vessels.
Any inflammation, ulceration, or bleeding on contact. These may point toward inflammatory bowel disease, or infective proctitis.
Any growth, polyp, or stricture. Note its distance from the anal verge, its size, and its surface.
Any blood, mucus, or pus in the lumen. Note whether it looks fresh or old.
Diverticular openings, if present. Full assessment of diverticular disease still needs colonoscopy or imaging.
6.8 Complications and How to Avoid Them
Proctoscopy and sigmoidoscopy are very safe when done gently, and under direct vision. The main risks are pain, from a hurried or forceful technique, and minor mucosal bleeding, from contact with the instrument. Very rarely, blind or forceful advancement can perforate the bowel wall.
One simple rule prevents almost every complication. Advance only what you can see. Stop at once if there is pain or resistance. Blind advancement, past a bend that cannot be seen, is the single most common cause of injury during sigmoidoscopy.
6.9 Common Mistakes to Avoid
Skipping the digital rectal examination, and going straight to instrumentation.
Inserting the proctoscope or sigmoidoscope without enough lubrication.
Advancing the sigmoidoscope without a clear view of the lumen ahead.
Forcing the instrument past resistance or pain.
Withdrawing the proctoscope too quickly. A prolapsing pile, or a mucosal prolapse, is often seen only when the patient strains.
Assuming that a normal proctoscopy and sigmoidoscopy rule out disease higher in the colon. Any patient with red flag symptoms, or with bleeding that is not explained, needs colonoscopy or further imaging.
6.10 Recording the Findings
Record proctoscopy and sigmoidoscopy findings clearly. State the instrument used. State the position of any abnormal finding on the clock face. State its distance from the anal verge in centimetres, where relevant. For example: "Proctoscopy: second-degree haemorrhoids at 3, 7, and 11 o'clock, prolapsing on straining. No fissure or fistula seen." A clear record lets any other doctor follow the findings, without repeating the examination.
6.11 Why This Chapter Matters
Proctoscopy and sigmoidoscopy complete the local examination. This began with inspection, and continued with digital rectal examination. Together, these steps let a doctor see and feel almost the whole anal canal, and a good part of the rectum. They need nothing more than simple instruments, and a careful, unhurried technique. The next chapter brings these findings together. It shows how they are used to reach a provisional diagnosis.