Anal vector volume analysis: an effective tool in the management of pelvic floor disorders

Different trials have investigated the role of conventional anal manometry in the diagnosis of pelvic floor disorders. The aim of the present study is to define the role and the effectiveness of vector anal manometry and vector asymmetry index scoring in the assessment of pelvic floor disorders i.e. fecal incontinence and obstructed defecation.

Between 2005 and 2007, 387 patients underwent clinical and manometric evaluation in the Department of Surgery, University Hospital Tor Vergata, Rome, Italy, and were included in the present prospective cohort study. All the patients underwent clinical examination, Wexner incontinence scoring, and anal vector manometry and were classified into three groups. Group I included patients with normal resting anal pressure values (195 patients). Groups II and III consisted of patients with resting anal pressure higher and lower than normal values, respectively (90 and 102 patients, respectively). All patients were classified into asymmetric and non-asymmetric according to the vector asymmetry index using a cut-off of 20%. We investigated the correlation between anal asymmetry and pelvic floor disorders, i.e. fecal incontinence due to sphincter injury, rectal prolapse, and obstructed defecation.

In Group III, the number of asymmetric patients was significantly higher than non-asymmetric ones (P < 0.0001). Asymmetry values were significantly higher in group III than in groups I and II considering squeeze (P < 0.0001) or resting pressures (P < 0.0001). Furthermore, there was a statistically significant association between anal asymmetry and both anal incontinence (P < 0.0001) and rectal prolapse (P = 0.0270). No such association was found between anal asymmetry and obstructed defecation.

Anal vector manometry using vector analysis of resting and squeeze pressures is complementary to endoanal ultrasonography, as it provides information on anal sphincter function and integrity. The vector asymmetry index >20% correlates with fecal incontinence due to anal sphincter lesions. Therefore, anal vector manometry may be useful as an independent method of screening for pregnant women at risk of sphincter injury and for patients undergoing anorectal surgery with risk factors for incontinence, like previous anorectal surgery or a history of two or more previous vaginal deliveries.