Comparison of rigid vs flexible sigmoidoscopy in detection of significant anorectal lesions

Sigmoidoscopy is an essential tool in colorectal clinics in the detection of anorectal lesions including rectosigmoid adenomas and carcinomas. However, rigid sigmoidoscope (RS) is still more widely used than flexible sigmoidoscope (FS) as the primary investigation, despite the fact that the latter is more comfortable to the patient and has greater diagnostic yield. Hence we wanted to compare the two modalities in terms of diagnostic use for picking up significant anorectal lesions.

A retrospective review of all patients referred to the colorectal clinic who had undergone both rigid and flexible sigmoidoscopy for investigation of colorectal symptoms in 2001 was done. Findings recorded during rigid and flexible sigmoidoscopy including depth of insertion, site of lesion and complications were analysed.

152 patients underwent both rigid and flexible sigmoidoscopy as part of investigation of colorectal symptoms. Of the 115 (75.6%) declared normal by RS, 39 (33.9%) had significant lesions including 7 polyps and 4 malignant lesions within 20 cm of the anal verge during FS. Of the 31 patients (20.4%) in whom RS was not helpful due to faecal loading, 15 (48.4%) had significant lesions including 4 malignancies and 1 polyp --all within 20 cm of the anal verge during FS. Only 2 polyps and 1 malignant lesion were picked up by both flexible and rigid sigmoidoscopy. There were no complications in both procedures.

Since flexible sigmoidoscopy is superior to rigid sigmoidoscopy in terms of patient comfort, diagnostic value and ease of doing procedures like biopsy and polypectomy; it can be used as a front line investigation to exclude colorectal pathology in out patient clinics. The utility of rigid sigmoidoscope is in question and in view of obvious shortcomings, may be replaced by flexible sigmoidoscopy, though obvious resource constraints need to be considered.