Hypothesis / aims of study
The perineal body is a fibromuscular pyramidal structure located between the vagina and the anus. There is a question about whether damage to the perineal body is associated with vaginal prolapse. The genital hiatus (POP-Q GH) measured clinically during the POP-Q examination is known to be associated with vaginal prolapse and the recurrence of vaginal prolapse after surgery. Using 2D transperineal ultrasound to measure the perineal body, this study attempts to determine whether there is an association with vaginal prolapse.
Study design, materials and methods
Women were recruited from clinics in hospital. All women underwent examination in the left lateral position and vaginal prolapse was assessed using the POP-Q system. The women were divided into prolapse patients and healthy nulliparous volunteers (control group).
Clinical assessment, including POP-Q and trans-perineal 2D ultrasound measurement of the perineal body. A curved 7MHz 2D probe (AB27D) was used with the GE Voluson TM E8 scanner. The scan was performed with the patient supine and legs hip distance apart. The prolapse was manually reduced and post-void. The images were obtained in the mid-sagittal plane. The scanning angle was opened to 107 degrees. In the mid-sagittal plane the urethra, perineal body and anal canal were aligned. Once in alignment, the perineal body was zoomed in for accurate measurement assessment. The perineal body height, length, perimeter, and area were measured. The perimeter was obtained by manually tracing the perineal body on the screen during live scanning. The angles at the base of the perineal body were assessed.
The data was tested for normality with the Shapiro-Wilk test and was found to be normally distributed. Parametric tests were used, as the data was normally distributed. Results are reported as mean and 95% Confidence Intervals (95% CI). The data was tested for normality with the Shapiro-Wilk test.
101 subjects were recruited. Seventy-nine women with vaginal prolapse were recruited and twenty-two were nulliparous healthy non-pregnant volunteers were the control group. Mean perineal body measurements in controls: height 22.50mm 3.34, length 17.36mm 2.74, perimeter 7.55mm 0.92, and area 2.85 cm2 0.38.
Amongst the prolapse patients, 49 had a rectocele. Perineal body measurements in 79 prolapse patients: height 16.90mm 1.75, length 15.97mm 1.41, perimeter 6.50mm 0.47 and area 8.1cm2 0.47.
In the control group, the perineal body appeared to be like an upright right-angled triangle in the mid-sagittal plane. In prolapse patients, the perineal body appearance varied from a scalene triangle, to a rounded deformed small structure. The angles of the base of the perineal body triangle was not measurable in 48/79 (60%) of prolapse patients. Perineal body angles were significantly less measurable when the perineal body was smaller than 1.87cm2 (paired t-test, p=0.0004). Perineal bodies with unmeasurable angles had an area of 1.65cm2 (95 CI 0.37), compared with perineal bodies with measurable angles that had an area of 2.09cm2 (95 CI 0.62).
A small perineal body (less than 1.87cm2) was strongly associated with posterior compartment prolapse (paired t-test, p<0.0001) and wider POP-Q GH (paired t-test, p=0.007). The POP-Q PB was not significantly different between the two groups.
Interpretation of results
It is possible to measure the perineal body on 2D ultrasound scanning. An increased POP-Q GH has been associated with prolapse in previous studies. In this study a perineal body mid-sagittal area has been shown to be associated strongly with prolapse.
The perineal body is the confluence of three pelvic floor muscles on either side (levator ani, transverse perineal and bulbospongiosus muscles). These data shows that this structure is damaged in patients with posterior compartment prolapse.
This study can not prove the temporality of events of causality: Does perineal body damage cause prolapse or does the perineal body get damaged because of the prolapse?
This data supports the traditional thinking to prolapse, as described by Emmet in 1880s and Kelly in 1910s (1, 2). In their teaching and approach they emphasised the importance of the perineal body reconstruction in prolapse surgery.
More recent theories of prolapse, authors have emphasised the importance of levator ani injury, the hammock hypothesis, paravaginal defects, the importance of collagen within the vaginal walls, arcus tendinous fascia pelvis and the role of adipose tissue within the ischorectal fossa (3).