Flexible Sigmoidoscopy

Updated: Oct 27, 2020
  • Author: Gaurav Arora, MD, MS; Chief Editor: Vikram Kate, FRCS, MS, MBBS, PhD, FACS, FACG, FRCS(Edin), FRCS(Glasg), FIMSA, MAMS, MASCRS, FFST(Ed)  more...
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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)


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

  • Screening for colorectal cancer [7, 8, 9, 10, 11, 12]  - Although flexible sigmoidoscopy and fecal occult blood testing are comparable when applied as screening tools to reduce mortality due to colorectal cancer, there is little evidence to indicate that screening with either approach reduces colorectal cancer deaths more than the other [13]
  • 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]  



Absolute contraindications for flexible sigmoidoscopy include the following:

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

Technical Considerations


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