Anal Sphincter Morphology & Function Assessed with Novel MR Imaging Techniques

描述（申请人提供）：内肛门括约肌（IAS）、外肛门括约肌（EAS）和耻骨直肠肌（PRM）是三种括约肌机制，为肛门失禁提供三重安全机制。EAS是大便失禁患者最常受影响的肌肉，原因是它在阴道分娩时经常受伤。高达35%的女性在第一次阴道分娩后会出现EAS肌肉缺陷，这是通过超声成像检测到的。重叠括约肌成形术是大便失禁患者中最常见的手术，因为肛门括约肌的超声图像显示出主要的解剖缺陷。然而，重叠括约肌成形术5年的成功率不足50%。重叠括约肌成形术失败的原因可能有几个；我们认为其中一个原因是对EAS肌形态的错误理解。目前认为，EAS是环形或甜甜圈状肌肉，EAS肌产生的圆周挤压是导致EAS收缩相关肛管压力增加的原因。我们的初步数据表明，EAS不是一个圆形的肌肉；相反，该肌肉具有独特的“8字形”形态，EAS的收缩作用是由于目前已知的EAS和会阴横肌的“打结”作用。事实上，会阴横部实际上是外发肌的延伸。我们使用最先进的磁共振成像技术，即扩散张量成像来确定EAS肌肉的真实形态。此外，我们使用速度编码的动态磁共振成像来确定EAS肌肉纤维的动态运动，以证明EAS肌肉收缩作用的性质。我们认为，正确认识EAS形态学对于预防损伤和修复重叠括约肌成形术中的EAS肌肉至关重要。与外阴中线切开术相比，外阴外侧切开术切开会阴横肌，被认为可以省去外阴肌。我们认为会阴横向确实是EAS肌，外阴外侧切开术并不是保留括约肌的手术。我们的研究还表明，PRM不仅负责肛肠角的形成；它实际上会导致肛管近端关闭。对于这些研究，我们利用最先进的3D-US成像和高清压力计来证明我们的假设。我们相信，我们的研究将为肛管的解剖和功能提供新的认识，并在预防和治疗大便失禁方面取得重大进展。

DESCRIPTION (provided by applicant): Internal anal sphincter (IAS), external anal sphincter (EAS) and puborectalis muscle (PRM) are 3 sphincter mechanisms that provide triple security mechanism for the anal continence. EAS is most commonly affected muscle in patient with fecal incontinence, the reason being that it gets injured fairly frequently during vaginal child birth. Up to 35% of women have defects of the EAS muscle after the first vaginal delivery, as detected by US imaging. Overlapping sphincteroplasty is the most commonly performed surgery in patients with fecal incontinence when US images of the anal sphincter muscle show major anatomical defects. However, the success rate of the overlapping sphincteroplasty is less than 50% at 5 years. There are probably several reasons for the failure of overlapping sphincteroplasty; we propose that one of the reasons is incorrect understanding of the morphology of the EAS muscle. Current thinking is that the EAS is a ring or a donut shaped muscle and circumferential squeeze generated by the EAS muscle is responsible for the genesis of EAS contraction related increase in the anal canal pressure. Our preliminary data show that that the EAS is not a circular muscle; instead the muscle has the unique "figure of 8" type of morphology and the constricting action of the EAS is due to the "tying of knot" like action of what is currently known as the EAS and transverse perinea muscles. In fact, transverse perinea are actually extension of the EAS muscles. We use state of the art magnetic resonance imaging techniques, i.e., diffusion tensor imaging to determine the true morphology of EAS muscle. Furthermore, we use velocity encoded dynamic MR imaging to determine the dynamic motion of EAS muscle fibers to prove the nature of constricting action of EAS muscle. We believe that correct understanding of the EAS morphology is of paramount importance in prevention of injury in the first place and repair of EAS muscle during overlapping sphincteroplasty. Lateral episiotomy, which incises transverse perinea muscle, is thought to spare the EAS muscle, as compared to midline episiotomy in which the incision extends to the EAS muscle. We propose that the transverse perinea are indeed the EAS muscle and lateral episiotomy is not a sphincter sparing procedure. Our studies also show that the PRM is not only responsible for the formation of anorectal angle; it actually causes closure of the proximal half of the anal canal. For these studies, we utilize state of the art, 3D-US imaging and high definition manometery to prove our hypothesis. We are confident that our studies will provide a new understanding of the anatomy and function of anal canal and with this new understanding a significant stride can be made in the prevention and treatment of fecal incontinence. PUBLIC HEALTH RELEVANCE: Our studies show that the true morphology of the EAS muscle is different from our current understanding of a donut shaped muscle. Our studies use state of the art magnetic resonance imaging techniques to determine the true morphology and function of the EAS muscle. The proposed new EAS muscle morphology will, 1; prevent injury to the EAS muscle during vaginal delivery and 2; allow better surgical repair of the muscle to treat symptoms of fecal incontinence.