The anal cross-sectional area on 2D introital ultrasonography (IUS) represents a new sensitive index capable of providing both superior anatomic details and clear depiction of anorectal prolapse in women. The parameter is calculated at rest and on straining by outlining the inner and the outer margin of the hypoechoic internal anal sphincter (IAS) and measuring the included area at the level of the middle anal canal in the axial plane. Average values of the inner area (1.08 ± 0.25 cm2 vs 3.02 ± 0.73 cm 2), as well as the inner-to-outer ratio (49.6 ± 8.2 % vs 81.3 ± 2.9 %) and percentage increase on straining (Δ-0.007 vs +0.42) have been found by us to differ significantly (p <0.01) in control groups (n = 10) and patients with rectal prolapse (n = 20). Further differentiation is made possible at sonography between those patients with rectal prolapse and obstructed defecation as their main presenting symptom from those with staining episodes and/or fecal incontinence by noting whether or not the integrity of the anal sphincter is preserved. Thanks to rapid advances in technology and recent refinements in interpretation, IUS can be considered, especially in young female patients, the best imaging modality to start with in assessing rectal prolapse in a safe and noninvasive manner.
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