Perineal body anatomy in living women: 3-dimensional analysis using thin-slice magnetic resonance imaging

Abstract

Objective To describe a framework for visualizing the perineal body's complex anatomy using thin-slice MR imaging. Study Design Two mm-thick MR images were acquired in 11 women with normal pelvic support and no incontinence/prolapse symptoms. Anatomic structures were analyzed in axial, sagittal and coronal slices. 3-D models were generated from these images. Results Three distinct perineal body regions are visible on MRI: (1) a superficial region at the level of the vestibular bulb, (2) a mid region at the proximal end of the superficial transverse perineal muscle, and (3) a deep region at the level of the midurethra and puborectalis muscle. Structures are best visualized on axial scans while cranio-caudal relationships are appreciated on sagittal scans. The 3-D model further clarifies inter-relationships. Conclusion Advances in MR technology allow visualization of perineal body anatomy in living women and development of 3D models which enhance our understanding of its three different regions: superficial, mid and deep.

Mobility of the perineal body and anorectal junction before and after childbirth

“…Advanced dynamic imaging is needed to assess movement and function of this structure in live women. While MRI can define the perineal body, the low resolution of dynamic MR limits its usefulness in this regard [5,9].…”

“…This is also evident in the highly significant association we observed between levator hiatal distensibility and perineal and anorectal junction mobility. This is plausible, since the perineal body is attached and partly suspended by the levator ani muscles, especially the puboperineal fibers of the pubovisceral component of the levator ani [5]. Sample size of each group in parenthesis C/S cesarean section, NVD normal vaginal delivery a Paired t test between antepartum and postpartum mobility in millimeters …”

“…In the axial plane, it appears as a pyramid-shaped area between the vagina and rectum [5]. It consists of three distinct levels, including a superficial, central, and deep region [5]. The superficial transverse perineal muscle and external anal sphincter traverse the superficial region.…”

“…A component of the levator ani inserts into the lateral margin of the perineal body. The deep region is said to be at the level of the puborectalis muscle [5].…”

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

“…Interestingly, that is not the case with the EAS muscle; it has been suggested that the anterior/ventral ends of EAS muscle fibers are inserted into the midline fibroaponeurotic structure of the perineal body (PB) (35). Separate sets of muscles, transverse perineal (TP) and bulbospongiosus [BS, also called bulbocavernosus (17)] that originate from the pubic rami are also inserted into the PB (35) (see supplemental material for this article available online at the Journal website). Crossover of EAS muscle fibers in the midline of the PB, from one side to the other, which has been suggested by several investigators (21,22,35), raises the possibility that perhaps the muscle fibers of the EAS cross in the midline structure of the PB to continue as contralateral TP/BS muscles.…”