Anatomy of the Pelvic Floor, Perineum and Anal Sphincter

The anatomy of the pelvic floor, perineum, and anal sphincter is a complex and surprisingly dynamic field with new insights, discoveries, and controversies. The controversies arise as new and innovative tools are used to study anatomy for varying purposes. Anatomists, with insight from cadaveric dissections, have proposed structures that may differ from a surgeon’s depiction or understanding of the structure/function relationships of the pelvis as seen in the operating room. This controversy is best seen in describing the external anal sphincter (EAS) and the puborectalis muscle. Is the puborectalis a part of the EAS? Is the EAS comprised of one, two, or three loops of striated muscle? Perhaps all descriptions are correct, depending on the point of view and purpose of evaluation. The goal of this chapter is not to solve these controversies, but to describe the functional and structural anatomy as it is known from cadaveric dissections, radiological imaging, and surgical repairs to improve the management of our patients. An understanding of this anatomy is essential for health care providers to care for patients during and after vaginal delivery.