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Purse-string morphology of external anal sphincter revealed by novel imaging techniques.

ABSTRACT: The external anal sphincter (EAS) may be injured in 25-35% of women during the first and subsequent vaginal childbirths and is likely the most common cause of anal incontinence. Since its first description almost 300 years ago, the EAS was believed to be a circular or a "donut-shaped" structure. Using three-dimensional transperineal ultrasound imaging, MRI, diffusion tensor imaging, and muscle fiber tracking, we delineated various components of the EAS and their muscle fiber directions. These novel imaging techniques suggest "purse-string" morphology, with "EAS muscles" crossing contralaterally in the perineal body to the contralateral transverse perineal (TP) and bulbospongiosus (BS) muscles, thus attaching the EAS to the pubic rami. Spin-tag MRI demonstrated purse-string action of the EAS muscle. Electromyography of TP/BS and EAS muscles revealed their simultaneous contraction and relaxation. Lidocaine injection into the TP/BS muscle significantly reduced anal canal pressure. These studies support purse-string morphology of the EAS to constrict/close the anal canal opening. Our findings have implications for the effect of episiotomy on anal closure function and the currently used surgical technique (overlapping sphincteroplasty) for EAS reconstructive surgery to treat anal incontinence.

SUBMITTER: Mittal RK

PROVIDER: S-EPMC3949029 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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Purse-string morphology of external anal sphincter revealed by novel imaging techniques.

Mittal Ravinder K RK Bhargava Valmik V Sheean Geoff G Ledgerwood Melissa M Sinha Shantanu S

American journal of physiology. Gastrointestinal and liver physiology 20140123 6

The external anal sphincter (EAS) may be injured in 25-35% of women during the first and subsequent vaginal childbirths and is likely the most common cause of anal incontinence. Since its first description almost 300 years ago, the EAS was believed to be a circular or a "donut-shaped" structure. Using three-dimensional transperineal ultrasound imaging, MRI, diffusion tensor imaging, and muscle fiber tracking, we delineated various components of the EAS and their muscle fiber directions. These no ...[more]

PMID: 24458022

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Project description:Background & aimsThe anal sphincters and puborectalis are imaged routinely with an endoanal magnetic resonance imaging (MRI) coil, which does not assess co-aptation of the anal canal at rest. By using a MRI torso coil, we identified a patulous anal canal in some patients with anorectal disorders. We aimed to evaluate the relationship between anal sphincter and puborectalis injury, a patulous anal canal, and anal pressures.MethodsWe performed a retrospective analysis of data from 119 patients who underwent MRI and manometry analysis of anal anatomy and pressures, respectively, from February 2011 through March 2013 at the Mayo Clinic. Anal pressures were determined by high-resolution manometry, anal sphincter and puborectalis injury was determined by endoanal MRI, and anal canal integrity was determined by torso MRI. Associations between manometric and anatomic parameters were evaluated with univariate and multivariate analyses.ResultsFecal incontinence (55 patients; 46%) and constipation (36 patients; 30%) were the main indications for testing; 49 patients (41%) had a patulous anal canal, which was associated with injury to more than 1 muscle (all P ≤ .001), and internal sphincter (P < .01), but not puborectalis (P = .09) or external sphincter (P = .06), injury. Internal (P < .01) and external sphincter injury (P = .02) and a patulous canal (P < .001), but not puborectalis injury, predicted anal resting pressure. A patulous anal canal was the only significant predictor (P < .01) of the anal squeeze pressure increment.ConclusionsPatients with anorectal disorders commonly have a patulous anal canal, which is associated with more severe anal injury and independently predicted anal resting pressure and squeeze pressure increment. It therefore is important to identify a patulous anal canal because it appears to be a marker of not only anal sphincter injury but disturbances beyond sphincter injury, such as damage to the anal cushions or anal denervation.

Dataset Information

Purse-string morphology of external anal sphincter revealed by novel imaging techniques.

Publications

Purse-string morphology of external anal sphincter revealed by novel imaging techniques.

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