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

Abstract

Objective: The objective of the study was to describe a framework for visualizing the perineal body's complex anatomy using thin-slice magnetic resonance (MR) imaging.

Study design: Two millimeter 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. Three-dimensional (3-D) models were generated from these images.

Results: Three distinct perineal body regions are visible on MR imaging: (1) a superficial region at the level of the vestibular bulb, (2) a midregion 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, whereas craniocaudal relationships are appreciated on sagittal scans. The 3-D model further clarifies interrelationships.

Conclusion: Advances in MR technology allow visualization of perineal body anatomy in living women and development of 3-D models that enhance our understanding of its 3 different regions: superficial, mid, and deep.

Copyright © 2010 Mosby, Inc. All rights reserved.

Figures

Figure 1. Building 3-D Model

Top: axial image at level of vestibular bulb (VB). Middle: Outlines of structures including pelvic bones (white), VB (turquoise), bulbo-sponsiosus (BS, green), superficial transverse perineal (SPT, blue), external anal sphincter (EAS, red), internal anal sphincter (IAS, pink), and rectum (R, yellow). Bottom: 3-D model on MRI. © DeLancey 2010.

Figure 2. Axial MR images showing perineal body (PB) anatomy

Arcuate pubic ligament (APL) as reference slice. (-) numbers are caudal and (+) numbers cephalad to APL. Abbreviations list: PB-perineal body, B-bladder, U-urethra, V-vagina, R-rectum, PS-pubic symphysis, IC-iliococcygeous, VB-vestibular bulb, PuR-pubic rami, Ba-Bartholins, IAS-internal anal sphincter, PR-puborectalis. Table 2 lists PB component abbreviations. © DeLancey 2010.

Figure 3. Sagittal MR images showing perineal body (PB) anatomy

Midsagittal slice as reference slice with “R” to the right. PB outlined in turquoise. Abbreviations list: PB-perineal body, B-bladder, U-urethra, V-vagina, R-rectum, PS-pubic symphysis, IC-iliococcygeous, VB-vestibular bulb, PuR-pubic rami, IAS-internal anal sphincter, PR-puborectalis. Table 2 lists PB component abbreviations. The region that corresponds to the images shown in Figure 2 is indicated, however, please note, this is a different subject than shown in Figure 2 so that minor variations in spatial relationships exist. © DeLancey 2010.

Figure 4. 3D Model of perineal body (PB)

(A) Dorsal lithotomy view and (B) left lateral aspect of same image. With removal of pelvic bones able to better appreciate superficial region (C) with BS, STP and EAS. (D) Lateral view with BS removed to illustrate mid region at proximal STP with PP, PM and PA. With removal of EAS, STP, PP, and PM can visualize deep region (E) with LR, PVa, PA. IAS visible with EAS removed. PVa muscle is barely visible lateral to the vagina in this image. PR-puborectalis, B-bladder, U-urethra, V-vagina, G-GI tract; all other abbreviations in Table 2. © DeLancey 2010.