Flexible Sigmoidoscopy

Flexible sigmoidoscopy is a procedure wherein a sigmoidoscope is inserted through the anus, the distal colonic mucosa (up to 60 cm from the anal verge) is examined, and any diagnostic or therapeutic maneuvers performed, as needed.

Intracolonic visualization with an endoscope dates back to 1958, when Matsunaga used a gastroscope for this purpose in Japan. ^[1] The next step was the incorporation of the fiberoptic bundles into the gastroscopes, which in turn led to the development of the first fiberoptic flexible sigmoidoscope by Overholt and its successful use in 1963. ^[1] Continuing development through the years has led to the modern sigmoidoscope, which uses a charge–coupled device connected to a video processor. 

Alternatives to flexible sigmoidoscopy include the following:

• Colonoscopy, which examines the whole colon
• Fecal occult blood testing for colorectal cancer screening ^[2]
• Barium enema for visualization of large polyps or cancerous lesions (no longer recommended as a screening test for colorectal cancer screening)
• Computed tomography (CT) colonography, which examines the whole colon but is less invasive than colonoscopy ^{[3, 4]}
• Rigid sigmoidoscopy (not commonly performed)
• Colon capsule endoscopy ^[5]

The following are the usual indications for flexible sigmoidoscopy ^[6] :

• Screening for colorectal cancer (CRC) ^{[7, 8, 9, 10, 11, 12, 13]}  - Although sigmoidoscopy is a preferred and cost-effective screening measure for CRC, it tends to be less widely employed than colonoscopy in current practice
• Preoperative evaluation before anorectal surgery
• Surveillance of a previously diagnosed (treated or untreated) malignancy (or polyp with high-grade dysplasia) in the rectum or the sigmoid colon
• Local treatment of ailments such as radiation proctitis
• Removal of rectal foreign bodies
• Biopsy of the gastrointestinal (GI) pathology in the rectum and the sigmoid colon
• Performance of therapeutic procedures such as endoluminal stent placement for strictures, balloon dilation, and decompression with placement of a decompression tube, however a conventional colonoscopy is often commonly used
• Hematochezia necessitating hemostasis

Intraoperative flexible sigmoidoscopy may also prove useful for assessing a colorectal anastomosis, as an alternative to the conventional air-leak test. ^[14]  

Evidence-based screening strategies for CRC are recommended in order to reduce morbidity and mortality. ^[15] Screening tools available include high-sensitivity guaiac fecal occult blood testing (HSgFOBT), fecal immunochemical testing (FIT), multitarget stool DNA (mt-sDNA) testing, CT colonography (virtual colonoscopy), flexible sigmoidoscopy, flexible sigmoidoscopy with FIT, and traditional colonoscopy. Apart from the conventional screening tools, novel techniques such as liquid biopsy, colon capsule endoscopy, urinary metabolomics, and stool-based microbiome testing are being studied.

Although flexible sigmoidoscopy and fecal occult blood testing are comparable when applied as screening tools to reduce mortality due to colorectal cancer, there has been little evidence to indicate that screening with either approach reduces colorectal cancer deaths more than the other. ^[16] A systematic review and meta-analysis by Zhang et al (four randomized controlled trials [RCTs]; N = 457,871) found that flexible sigmoidoscopy–based screening was significantly associated with a 20% relative risk reduction in CRC incidence and a 24% reduction in CRC mortality, though this benefit did not translate to proximal colon cancer specifically. ^[17]

In a systematic review of 25 studies that analyzed the cost-effectiveness of sigmoidoscopy for CRC screening, Diedrich et al found that the combination of annual stool testing and sigmoidoscopy at 5-year intervals was a more cost-effective screening option than either strategy alone. ^[18]

In a systematic review on the recommended number of flexible sigmoidoscopy or colonoscopy biopsies for the diagnosis of microscopic colitis, Malik et al reported that a total of six biopsies should be taken from the ascending and descending colon for better diagnostic accuracy. ^[19]

Colonoscopy following an acute sigmoid diverticulitis is routinely recommended as part of colorectal cancer screening. Hannan et al described a possible alternative in the form of flexible sigmoidoscopy and reported lesser rates of detection of polyp in the sigmoid colon (5.9%) as well as beyond it (1.1%). ^[20] Hence, restricting the use of full-length colonoscopy to those patients with significant findings on flexible sigmoidoscopy offers numerous advantages with respect to time consumption, safety, cost, avoidance of bowel preparation, and intravenous (IV) sedation.

Absolute contraindications for flexible sigmoidoscopy include the following:

• Bowel perforation
• Acute diverticulitis
• Active peritonitis
• Fulminant colitis
• Cardiopulmonary instability

Relative contraindications for flexible sigmoidoscopy include the following:

• Lack of informed consent - This is a contraindication except in emergencies, during which two physicians must document the life-threatening nature of the condition before treatment can continue
• Lack of patient cooperation
• Lack of good bowel preparation

Anatomy

The rectum lies in the sacrococcygeal hollow and changes to the anal canal at the puborectal sling formed by the innermost fibers of the levator ani. The rectum has a dilated middle part called the ampulla. The rectum is related anteriorly to the urinary bladder, prostate, seminal vesicles, and urethra in males and to the uterus, cervix, and vagina in females. Anterior to the rectum is the rectovesical pouch in males and the rectouterine pouch in females. The anal canal is related to the perineal body in front and the anococcygeal body behind; both of these are fibromuscular structures.

For more information about the relevant anatomy, see Large Intestine Anatomy, Colon Anatomy, and Anal Canal Anatomy.

Best practices

The following measures are recommended for improving the performance of flexible sigmoidoscopy:

• Never push against resistance
• Always keep the lumen in view
• When in doubt, pull back, insufflate, and advance once the lumen is in view
• Learn how to use torque effectively to control the instrument tip
• Use air (as much as needed but as little as possible); too much distention can lead to patient discomfort and kinking of the colon
• When encountering many large diverticula, take the necessary time to determine the direction of the true lumen
• Know when to abandon the procedure