Functional and Anatomical Significance of Patulous Anus

A patulous anus is often associated with prior anal sphincter injury and fecal incontinence (FI). We aimed to understand the clinical and functional significance of a patulous anus as identified on MRI defecography (MRD).

We conducted a retrospective review of the clinical characteristics, high-definition anorectal manometry, MRD, and symptom severity scores from a prospectively maintained registry of patients with or without patulous anus.

Of the 161 patients (86.3% women), who presented with various anorectal symptoms, 47 (29%) exhibited a patulous anus. Ninety-five percent of patients with a patulous anus were women (p = 0.018), older (66 ± 12.7 vs. 56 ± 15.1 y, p = 0.0003), and had a history of pelvic surgery (39% vs. 22%, p = 0.038). Patients with a patulous anus were more likely to report FI with higher Wexner scores (p < 0.05), associated with a shorter anal high-pressure zone, reduced resting tone and squeeze pressures (p < 0.01), independent of age, gender, and previous surgeries. MRD revealed higher Oxford grades of rectal intussusception (p < 0.0001), longer levator hiatus length (p = 0.002), greater perineal descent (p = 0.006), and a wider anorectal angle at rest (p < 0.001). After adjusting for age, gender, and history of previous pelvic surgeries, such differences remained significant. Stepwise logistic regression identified higher Oxford grade, lower resting tone, and wider anorectal angle at rest as independent predictors of a patulous anus.

A patulous anus on MRD indicates clinically important underlying anorectal anatomical and functional abnormalities and warrants screening for FI and/or advanced rectal intussusception.