A comparison of the usage of anal verge and dentate line in measuring distances within the rectum

Introduction: The anal verge is key in determining measurement-based suitability for neoadjuvant radiotherapy in rectal cancer. The dentate line is a distinct anatomic landmark and may permit more accurate measurement for rectal lesions. This study aimed to establish measurative ranges for distances of the rectal valves from the dentate line and the anal verge and to compare variability between the two. Methods: Patients (n = 104) undergoing colonoscopy and sigmoidoscopy were prospectively accrued. The distances of rectal valves were measured from the anal verge and the dentate line respectively by using a vector subtraction-based approach. Distances were correlated with gender, age and body mass index. Standard deviation was the measure of variability. Results: The gross topography of the rectum was remarkably consistent with three valves identifiable in the majority (99 of 104) of patients. The median distance between the dentate line and the anal verge was 2.0 cm. The distances of each rectal valve (proximal to distal) to the anal verge and dentate line were 11.4 ± 2.0 cm, 8.6 ± 2.0 cm, 6.0 ± 1.7 cm and 9.1 ± 1.6 cm, 6.3 ± 1.6 cm, 3.7 ± 1.5 cm, respectively. Betweengroup variability was minimally reduced when using the dentate line as a reference point. Obesity was associated with an increased distance of the proximal rectal valve from the anal verge and the dentate line (p = 0.004 and 0.015 respectively). Conclusions: Rectal valve anatomy is remarkably consistent. Both dentate line and anal verge are reliable landmarks from which distances can be measured within the rectum.