Depth of insertion at flexible sigmoidoscopy: implications for colorectal cancer screening and instrument design

The depth of insertion at flexible sigmoidoscopy is variable, depending upon bowel preparation, patient tolerance and distal colonic anatomy. Many endoscopists routinely aim to insert the 60 cm flexible sigmoidoscope to the splenic flexure; however internal endoscopic markers are unreliable, making the true anatomical extent of the examination difficult to assess. The aim of this study was to assess the depth of insertion at flexible sigmoidoscopy.

Two separate studies were done. In the first (study 1), magnetic endoscopic imaging was used to determine the final depth of insertion at non-sedated, screening flexible sigmoidoscopy. In the second (study 2), "real-time" imaging was utilized to determine sigmoid looping and the anatomical location of the endoscope tip after 60 cm of instrument had been inserted during total or limited colonoscopy. A total of 117 consecutive average-risk patients, aged 55-65 years participated in study 1, and 136 patients underwent either limited, (33) or attempted total colonoscopy (103) in study 2.

In study 1 the median insertion distance was 52 cm, range 20-58. In 61 % of patients the imaging system showed that the descending colon had not been visualized by the end of the procedure. Failure to reach the sigmoid/descending junction occurred in 29 (24%) patients. Reasons for failure included poor tolerance of the procedure due to pain (23 patients) inadequate preparation (3 patients) and, excessive looping (3 patients). In study 2, after 60 cm of instrument had been inserted, the splenic flexure or beyond was reached in 29% and the descending colon in 9%, whilst in 62 % the endoscope tip had not passed beyond the sigmoid/descending colon junction. A sigmoid loop formed in 70% of patients, and unusual loops such as the alpha, reverse alpha and reverse sigmoid spiral loop occurred more frequently in women compared to men (P = 0.0249). In those 104 patients where the splenic flexure was reached the mean maximum length of instrument inserted prior to reaching the flexure was 75.4 cm, (SD = 21.9).

Examination of the entire sigmoid was not achieved in approximately one-quarter of patients undergoing screening flexible sigmoidoscopy, mainly because of discomfort. The descending colon is intubated in a minority of cases (using standard instruments), even after 60 cm has been inserted. Alternative instruments with different shaft characteristics (floppy, narrow calibre, 80-100 cm in length) may be necessary to ensure deeper routine intubation in nonsedated patients.