Flexible Sigmoidoscopy

Updated: Mar 30, 2022
Author: Gaurav Arora, MD, MS; Chief Editor: Vikram Kate, MBBS, PhD, MS, FACS, FACG, FRCS, FRCS(Edin), FRCS(Glasg), FIMSA, FFST(Ed), MAMS, MASCRS 



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]  

Evidence-based screening strategies for colorectal cancer 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.

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.[16]

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%).[17] 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:

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

Periprocedural Care

Preprocedural Planning

Typically, a sigmoidoscopy does not require a full colon preparation. A clear liquid diet on the day before the examination, along with overnight fasting, is usually sufficient; one or two tap-water enemas may also be given on the morning of the examination.

For patients with chronic or severe constipation, administration of a pegylated balanced electrolyte solution (eg, GoLYTELY, Miralax, HalfLYTELY) on the night before the procedure may be considered.

Free fatty acid suppositories have been reported to be well tolerated, with no significant side effects and good bowel-emptying effect and rectal cleansing. The height of scope insertion was also found to be similar to that with the conventional enema bowel preparation.[18]


A flexible video sigmoidoscope is used for the procedure. However, other instruments, such as a standard upper endoscope or a colonoscope (limited insertion), can also be used. Some centers commonly use pediatric colonoscopes for flexible sigmoidoscopy.

The scope contains a shaft, a control head, and an umbilical (which is connected to the video processor). The control head contains the up/down and left/right dials, the suction valve, the air/water valve, and a working channel through which a biopsy forceps or other accessories can be inserted. This channel can also be used to hook a large syringe for pushing water inside the colon.

The images from the camera are projected on a video monitor.

Patient Preparation

Typically, no sedation is required for flexible sigmoidoscopy. If sedation is needed, fentanyl (or meperidine) and midazolam may be given intravenously. The preferred position for the patient is the left lateral position, with the hip and knee joints partially flexed.



Flexible Sigmoidoscopy

In advance of the procedure, check to make sure that all the required equipment is functional, especially the air/water and suction valves. Check the quality of the image on the video monitor, and use the controls on the processor to ensure correct white balance on the display.

Put on gloves and a protective apron. Perform a perianal inspection and a digital rectal examination (DRE) using a water-based lubricant. The DRE should include evaluation for any masses or hemorrhoids, as well as evaluation of the prostate in men.

Lubricate the distal 10-20 cm of the shaft of the sigmoidoscope, taking care not to smear the lubricant on the lens at the distal end, and insert the scope gently into the anus under direct vision. Once the shaft's end is inside, shift attention to the video monitor. Insufflate air, and bring the lumen of the rectum into view, using the control knobs on the handle.

The three semilunar valves are visible in the rectum (see the image below). Advance the endoscope gently, keeping the lumen in view; to navigate, apply torque (by twisting the shaft) and use the up/down knob.

Rectum as shown by flexible sigmoidoscopy. Rectum as shown by flexible sigmoidoscopy.

Approximately 20 cm from the anal verge, the rectosigmoid junction comes into view. Negotiate it carefully, taking care not to apply any undue pressure. The sigmoid colon is then entered (see the image below). This structure contains multiple turns; take your time in passing through them. Try to minimize air insufflation. Water infusion from a foot-controlled pedal may be used.

Sigmoid colon as shown by flexible sigmoidoscopy. Sigmoid colon as shown by flexible sigmoidoscopy.

Because of the way in which the colon curves, the endoscope tends to form a loop as it passes through the sigmoid colon toward the descending colon. Excessive loop formation may result in pain or discomfort for the patient and may increase the risk of perforation. To reduce a loop, pull back the shaft of the endoscope while simultaneously suctioning the air from the lumen. Torquing toward the right while pulling back may also help straighten the sigmoid colon.

The descending colon appears as a straight tube with a circular lumen (see the image below). Keep advancing.

Descending colon as shown by flexible sigmoidoscop Descending colon as shown by flexible sigmoidoscopy.

The splenic flexure (see the image below) may have a slightly dark appearance because of the adjacent spleen. It may also contain a small pool of fluid (with the patient in the left lateral position). Beyond the flexure, the triangular appearance of the transverse colon is visible. The splenic flexure marks the distal limit of a sigmoidoscopic examination.

Splenic flexure as shown by flexible sigmoidoscopy Splenic flexure as shown by flexible sigmoidoscopy.

Begin to withdraw the endoscope, taking care to examine the colonic mucosa carefully as you do so. Any abnormalities (eg, polyps, erythema, ulceration, masses, or diverticula) should be noted. Depending on the skills of the endoscopist, biopsies or polypectomies may be undertaken; otherwise, these patients may be referred to a gastroenterologist for a full colonoscopy, as well as for therapeutic maneuvers such as polypectomy.

Once the scope is back in the rectum, undertake retroflexion to ensure that no distal rectal lesions have been missed and to look for any internal hemorrhoids. Withdraw the endoscope to the anal canal, which is distinguished from the rectum by the change in the color of the mucosa and the narrowing of the lumen, and take the following three actions simultaneously:

  • Turn the big knob all the way to the up position
  • Torque the shaft to the right
  • Push the shaft in

When these actions have been taken, a retroflexed view should become available as the endoscope's shaft becomes visible on the screen (see the image below). Insufflation of air insufflation and adjustment of the left/right knob can further improve the view.

Rectum (retroflexed view) as shown by flexible sig Rectum (retroflexed view) as shown by flexible sigmoidoscopy.

Next, turn the knobs back to the neutral position; the view should be forward before the endoscope is extracted. In addition, suction as much air as possible before removing the endoscope.

Throughout the examination, take photographs of any abnormal findings. If everything looks normal, take photographs of the most distal extent of the examination, as well as of the retroflexed view in the rectum, for documentation purposes.

The endoscopy report should include details on any abnormalities found. It should also include the indication for the procedure, the medications administered (if any), the extent of the examination, any intraprocedural complications that develop, the details of any diagnostic or therapeutic maneuvers performed, and the follow-up plan.

The videos below depict various disease states visualized via flexible sigmoidoscopy.

Flexible sigmoidoscopy: inflammation due to diverticulitis in sigmoid colon. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Flexible sigmoidoscopy: inflammation of rectum (proctitis) in patient who had surgery with J pouch created. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Flexible sigmoidoscopy: pseudopolyps in colon. This is common in inflammatory bowel disease (eg, Crohn disease or ulcerative colitis). Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.
Flexible sigmoidoscopy: segmental colitis associated with diverticulosis (SCAD). Inflammation is apparent in setting of diverticulosis in sigmoid colon. Video courtesy of Dawn Sears, MD, and Dan C Cohen, MD, Division of Gastroenterology, Scott & White Healthcare.


Complications related to sedation (if used) include the following[19] :

Potential complications of flexible sigmoidoscopy include the following[19, 20] :

  • Pain
  • Bleeding
  • Perforation
  • Infection