Selecting patients for flexible sigmoidoscopy. Determinants of incomplete depth of insertion

Flexible sigmoidoscopy (FS) is an effective method to prevent and reduce mortality from colorectal carcinoma (CRC). Incomplete depth of insertion (IDI) during FS may result in missed polyps and carcinomas. To determine whether it is possible to predict IDI, the authors analyzed factors that affected the depth of insertion in FS.

For the current study, FS results were recorded prospectively over a 5-year period. A questionnaire was administered to the patient by the investigator prior to FS to collect data, including age, gender, weight, comorbid illnesses, history of prior abdominal and pelvic surgeries, family history of colon carcinoma or polyps, and prior FS or colonoscopies. The depth of insertion of the flexible sigmoidoscope from the anal verge, which was defined as the reading on the outside of the instrument at its maximal insertion, was measured in centimeters. IDI was defined as a depth of insertion < 50 cm. Classification and regression tree analysis was used to develop a model that included variables predictive of IDI.

The best classification tree included gender, age < 69 years (in women), and a history of hysterectomy. Men had a < 5% risk of an IDI and women age < 69 years without a hysterectomy fared as well (6.6%). Older women and younger women who underwent hysterectomy had higher rates of IDI (29.2% and 22.3%, respectively.)

The authors developed a model based on age, gender, and hysterectomy status that, after further validation, may be useful for predicting which patients likely will have an incomplete examination. In those patients who have a high probability of IDI, the choice can be made to offer colonoscopy or perform FS under sedation, with analgesia, or with the help of distraction techniques.