Computerised 3-dimensional vector volume analysis--the role of a new method for assessing anal sphincter competence

The results of manometric assessment (using conventional parameters) in idiopathic faecal incontinence overlap with normals, especially if the impairment is not severe. Computerised three-dimensional vector volume analysis is a recently introduced method of integrating the pressure profile along the anal canal in multiple radial directions, which may detect minor sphincter weaknesses more accurately. We compared the two methods in 47 subjects (normals = 25, patients with idiopathic faecal incontinence = 22), to analyse the same data derived from a station pull-through manometric technique. The conventional parameters of mean resting and maximum voluntary contraction pressures did not differ significantly between normal and incontinent subjects. The anal canal length in incontinent patients was significantly shorter (mean 2.9 SEM 0.2 cm in normals and 2.0 SEM 0.3 cm in incontinent; p less than 0.5). The computer calculated vector volumes and pressure symmetries (both at rest and during contraction) were not significantly different between the two groups. Although local areas of weaknesses may be identified on computerised vector diagrams, the vector volume calculations gave little additional objective information to the conventional indices to discriminate milder degrees of idiopathic faecal incontinence.