3D ultrasonography has a potential major role in urogynecology because of its wide availability in daily ob-gyn practice. However, most of the studies in pelvic floor US have been done with high-end large-size systems (1), so the usability of a middle level US apparatuses for this purpose is not clear. 
Our aim was to determine the result of US imaging of pelvic organ prolapse cases with a popular small-size US system that are commonly used in a  gynecological clinic by the examination table and discuss the usefulness of exploiting 3D introital ultrasonography as a first-line tool for pelvic floor evaluation.

Six of our patients who came to seek surgical treatment of POP that had occurred soon after delivery, aged 38 to 45 years, were selected as they had serious likelihood of major obstetric pelvic floor injuries. We reviewed their 3D whole pelvic floor US and 3D anal sphincter US volume data.
The data had been obtained by GE Voluson I manufactured in 2008 equipped with a 3D transvaginal probe RIC5-9W-RS. In the whole pelvic floor US, volume data were recorded using real time scanning mode, after adjusting the probe head in a sagittal plain at the opening of vagina with help of the 3-dimensional acquisition screen. In the anal sphincter US, volume data were recorded using single scanning mode with the probe head on the perineo-introital area toward the anus in a transverse plane. We used GE ViewPal v 6.6.1 for analysis of the volume data.

In the whole pelvic floor US, avulsion injury of the puborectalis (PR) muscle and inhomogeneous internal echo were clearly depicted in all of the 6 patients (Fig 1). In the anal sphincter US, the longitudinal muscle and the puboanalis (PA) muscle could be identified in 4 of them. The anterior gap of the external sphincter (EAS) was clearly demarcated in all cases and the average combined length of gap and injury in the EAS was 12.2mm (SD 3.5mm). In some cases, distorted contour of the anus was noted close to the gap, indicating enhanced traction by the longitudinal and the PA muscles. The distortion and/or the gap in the anterior part of the EAS were often closely located to the attachment of PA muscles (Fig2). The distal end of the PR muscle was not clearly depicted in these cases.

Thanks to its high resolution, 3D transvaginal probe gave detailed images of the pelvic floor muscles and the anal sphincter in introital US. 3D introital US enabled close observation of the peri-anal structures that are located laterally and anteriorly to the anal canal.
The high anterior gap of the EAS, which we encounter often in a woman with or without birth experience (2), has been considered to be a natural variation. However, any intra-abdominal pressure increase augments traction by the PA muscle to the latero-anterior part of the EAS and,  the images obtained  in our study indicate that this traction may act as an acute or chronic mechanism of generating the high anterior gap of the EAS.

It was found that introital US by 3D transvaginal probe is very useful as a first-line tool for taking a view of injuries in the pelvic floor and the anal/peri-anal structure.  3D convex probes are not essential to ultrasonographic pelvic floor evaluation.

Dietz HP, et al. Levator trauma after vaginal delivery. Obstet Gynecol. 2005; 106: 707-12.
Bollard RC, et al. Normal female anal sphincter: difficulties in interpretation explained. Dis Colon Rectum. 2002; 45: 171-5.