Magnetic resonance-based female pelvic anatomy as relevant for maternal childbirth injury simulations

Abstract

The objectives of the study are to review the female pelvic floor anatomy relevant to childbirth simulations, to discuss available methods for clinical evaluation of female pelvic floor function, and to review the variation in pelvic floor changes after vaginal childbirth. A high-resolution magnetic resonance (MR) data set from an asymptomatic nullipara was used to illustrate the MR anatomy of the female pelvic floor. Manual segmentation was performed and three-dimensional reconstructions of the pelvic floor structures were generated, which were used to illustrate the 3D anatomy of the pelvic floor. Variation in the post partum appearance of the levator ani muscles is illustrated using other 2D MR data sets, which depict unilateral and bilateral disruptions in the puborectalis portion of levator ani, as well as shape variations, which may be seen in the post partum levator. The clinical evaluation of the pelvic floor is then reviewed. The female pelvis is composed of a bony scaffold, from which the pelvic floor muscles (obturator internus, levator ani) are suspended. The rectum fits in a midline groove in the levator ani. The vagina is suspended across the midline, attaching bilaterally to the obturator and levator ani. The vagina supports the bladder and urethra. MR studies have demonstrated disruptions in levator ani attachments after vaginal childbirth. Such disruptions are rare in women who have not given birth vaginally. Changes to the neuromuscular apparatus of the pelvic floor can also be demonstrated after vaginal delivery. The combination of childbirth-related anatomic and neurological injury to the pelvic floor may be associated with pelvic floor dysfunction (PFD). These changes are difficult to study in vivo but may be studied through simulations. Appropriate consideration of clinical anatomy is important in these simulations.