How accurate is the endoscopist's assessment of visualization of the left colon seen at flexible sigmoidoscopy?

There are concerns that the left colon may be incompletely examined by the standard 60-cm flexible sigmoidoscope. Our objective was to compare the endoscopist's assessment of the length of colon seen with the actual length visualized.

During flexible sigmoidoscopy, endoscopists were asked to state how far they had reached. This was compared with the length of colon actually seen, assessed by a novel electromagnetic imaging (EMI) device that records the three-dimensional position of the scope within a magnetic field pervading the patient's abdomen. If EMI showed that the splenic flexure had not been reached, the endoscopist was asked to use the imager to see if it helped advance the scope further.

In 94 patients, the endoscopist's assessment of position reached was correct in only 47 cases (50%), with an overestimate of length of colon visualized in 24 (25.5%) and an underestimate in 23 (24.5%). EMI showed the splenic flexure had not been reached in 56 patients (59.6%). Using information from the EMI system, further progress was subsequently made in 45/56 (80.4%).

Caution is required in the diagnosis of rectal bleeding using flexible sigmoidoscopy alone. This has implications for the use of the 60-cm flexible sigmoidoscope as a screening tool.