Sigmoidoscopy: rigid and flexible

Sigmoidoscopy is the minimally invasive medical examination of the large intestine from the rectum through the last part of the colon. There are two types of sigmoidoscopy, rigid sigmoidoscopy, which uses a rigid endoscope, and flexible sigmoidoscopy, which uses a flexible device. Flexible sigmoidoscopy is today generally the preferred procedure.

Anatomy (Van Dam J, Wong RCK, 2004)

• The terminal portion of the large intestine consists of two parts: the sigmoid colon and the rectum. The rectum is continuous with the anus. A network of striated muscle that forms both the internal and the external anal sphincters regulates the anal outlet.
• Dentate line, located approximately 2 cm proximal to the anal verge, marks the transition between columnar epithelium proximally (innervated by the autonomic nervous system) and squamous epithelium distally (innervated by the somatic nervous system) The patient can experience painful somatic sensation distal to the dentate line.
• Rectum, located proximal to the anal canal, contains three semicircular valves (valves of Houston or transverse folds of the rectum).
• Rectosigmoid junction is a sharp bend which begins approximately 15 cm proximal to the anal verge.
• Sigmoid colon, located proximal to the rectosigmoid junction, is approximately 40 cm in length in adults in Western countries.
• Descending colon, is a relatively straight tubular portion of the colon approximately 20 cm in length. It connects the sigmoid colon to the splenic flexure.
• Splenic flexure, where the colon takes a sharp bend to form the transverse colon (characterized by triangular-appearing folds). The splenic flexure is reached in approximately 22% of cases at full insertion using a 60 cm long, 16 mm diameter flexible sigmoidoscope. The vascular supply to the colon includes the so-called “watershed” areas (splenic flexure and rectosigmoid junction) which are particularly susceptible to ischemic injury.

A.

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B.

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Fig. 1.Anatomy of the lower GI tract (A), with details of the small and large intestines (B)

Rigid sigmoidoscopy

It may be still useful in anorectal diseases such as bleeding per rectum or inflammatory rectal disease, particularly in the general practice and paediatrics.

Indications for rigid sigmoidoscopy (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000)

1. Rectal bleeding
2. Lower abdominal and pelvic trauma
3. Extraction of foreign bodies
4. Stool cultures
5. Evaluation and biopsy of ileal pouch

Contraindications to rigid sigmoidoscopy (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000)

1. Massive lower GI bleeding
2. Anal stricture
3. Acute perirectal abscess
4. Acutely thrombosed haemorrhoids

Technique

For performing this examination, the patient should lie on the left side with his/her left leg extended and right leg flexed (in the so-called ‘Sim’s position’); lithotomy or prone jackknife position is also useful. The distal colon should previously be emptied with a suppository or enema (tap water or saline may be used), and a digital rectal examination (DRE) is first performed to assess for masses.

The rigid sigmoidoscope (see Fig. 2) is lubricated with water soluble lubricant and inserted with obturator in general direction of the navel. The direction is then changed and the obturator is removed so that the physician may penetrate further with direct vision. A bellows is used to insufflate air in order to distend the rectum. Lateral movements of the instrument’s tip negotiate the Houston valve and the recto-sigmoid junction. Further advancement of the sigmoidoscope is made (under direct vision) as far as it is tolerated by the patient, usually 20-25 cm (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000) . The mucosa should be inspected closely and systematically while the instrument is slowly withdrawn.

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Fig. 2.An example of a Seward Thackray single-use rigid sigmoidoscope (Sigmaster proctoscope)

To minimize the risk of perforation of the bowel, the sigmoidoscope should be advanced only when its lumen is clearly visualized. To biopsy a mass or polyp, the instrument should be advanced until part of the mass is within the barrel of the scope. After inserting the biopsy forceps into the barrel, a specimen of tissue can be grasped (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000) .

Complications

1. Bleeding – usually self-limited (e.g. following biopsy); if it is haemodynamically significant, endoscopic treatment may be necessary.
2. Intestinal perforation – usually manifested by abdominal pain, distention, and loss of hepatic dullness to percussion; free air under the diaphragm on upright chest X-ray confirms the diagnosis. The patient should be treated surgically.

Flexible sigmoidoscopy

Flexible sigmoidoscopy (FS) employs a flexible instrument to examine the rectum, sigmoid, and a variable length of more proximal colon (American Society for Gastrointestinal Endoscopy, 2000) . It is preferred over colonoscopy (i.e. a technique that uses a video camera mounted in the end of the scope to render recordable images and colour photographs of the colonic mucosa; it also allows for surgical intervention, e.g. polypectomy or tumour removal), because it can be done without sedation (Wrightson WR (ed), 2006) . FS is also preferred over rigid sigmoidoscopy because it provides a working channel for additional procedures.

Flexible sigmoidoscopy has been recommended by many national health organizations as a screening tool for colon cancer. This procedure is also an integral part of the evaluation of a variety of disorders including unexplained abdominal pain, rectal bleeding, alteration in bowel habits, and stools positive for occult blood.

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Fig. 3.Flexible sigmoidoscopy

A thin, lighted tube is inserted through the anus and rectum into the sigmoid colon to look for abnormal areas. Inset shows patient on table having a sigmoidoscopy. [Colour drawing by Terese Winslow. Source: NCI Visuals Online, 2005]

Specific indications for diagnostic FS (American Society for Gastrointestinal Endoscopy, 2000)

• Screening of asymptomatic, average risk patients at risk for colonic neoplasia (Fig. 4)
• Evaluation of suspected distal colonic disease when there is NO indication for colonoscopy
• Evaluation of the colon in conjunction with barium enema
• Evaluation for anastomotic recurrence in rectosigmoid carcinoma
• Patients with a family history of familial adenomatous polyposis:
  • Annual FS from age 10-12 years with colectomy when polyps develop
  • Annually to age 40 years if no polyps found, then every 3-5 years thereafter

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Fig. 4. Endoscopic image of colon adenocarcinoma in the sigmoid colon. (Permission obtained from patient to post in public domain).

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Fig. 5. Endoscopic image of haemorrhoids seen on retroflexion of the flexible sigmoidoscope at the ano-rectal junction. (Released into public domain on permission of patient).

FS is generally contraindicated for (American Society for Gastrointestinal Endoscopy, 2000) , (Davis PW, Stanfield CB, 1999) :

• Contraindications listed above in ‘General contraindications to GI endoscopy’
• Documented acute diverticulitis

And also, when the patient presents with:

• Dissecting aortic aneurysm
• Acute peritonitis
• Paralytic ileus

Relative contraindications to FS (Davis PW, Stanfield CB, 1999)

• Severe cardiac or pulmonary disease
• Acute inflammatory bowel disease
• Suspected ischemic bowel necrosis
• Toxic megacolon
• Recent colon surgery
• Pelvic adhesions
• Coagulation disorders
• Inadequate bowel preparation
• Operator inexperience

Specific indications for therapeutic FS (American Society for Gastrointestinal Endoscopy, 2000)

• All colonoscopic procedures under special circumstances, e.g.:
  • polypectomy in patient with subtotal colectomy
  • laser photocoagulation of a rectal carcinoma

NOTE: For therapeutic colonic procedures (e.g. polypectomy), colonoscopy and not FS is generally indicated

Patient preparation

The patient preparation consists of an enema the night before the procedure and a second enema the morning of the sigmoidoscopy.

Technical remarks

The goal of FS is to evaluate a full 60 cm to 70 cm of the descending and rectosigmoid colon, and the average procedure time is 16-20 minutes (performance of a biopsy increases this time markedly) (Holman JR, Marshall RC, Jordan B, Vogelman L, 2001) .The capacity to detect lesions in FS, however, is dependent both on the depth of insertion of the instrument and the maximum reach, and routine insertion to below the splenic flexure would result in an unacceptable degree of missed lesions. In many instances, at 50 to 60 cm of insertion the looping of the instrument causes the scope to reach only the upper sigmoid or descending colon, which should be considered an incomplete examination. The routine use of various manoeuvres to shorten the colon during the examination will result in the examiner traversing a greater length of the bowel. It has also been shown that women often have a more acute angle at the junction of the rectum and sigmoid colon that can make passage more difficult; also in women with a history of pelvic surgery an overall insertion depth of the sigmoidoscope can be decreased (Holman JR, Marshall RC, Jordan B, Vogelman L, 2001) .

Glossary

HES

Hemalun Eosine Safran (histology, French: Cell components revelation method)