Comparison of transanal and external perineal ultrasonography

Anal endosonography with rotating endoprobes provides state-of-the-art imaging of sphincter integrity; however, the technique is not widely available and requires expensive equipment. Since pelvic anatomy permits the use of standard external ultrasound probes, we tested the feasibility, tolerance and reproducibility of uniplanar perineal sonography, with respect to visualisation of the anal sphincter, using both convex and linear 3.5- to 7.5-MHz and 360 degree rotating 7-MHz probes. Twenty healthy nulliparus female volunteers were investigated. Two operators performed endosonography and perineal sonography in duplicate, each blinded to the findings of the other. We then used this technique to examine 20 postpartum primiparus patients. The examination was well tolerated by all subjects. The internal anal sphincter appeared in perineal sonography as a hypoechogenic ring surrounded by an echogenic ring representing the external anal sphincter. Endosonography revealed six sphincter tears, four external and internal sphincter tears, one isolated external tear and one isolated internal tear. Perineal sonography recognised in all cases external sphincter tears. In one case the internal sphincter defect was missed. Perineal sonography appears to be a feasible alternative to anal endosonography in female patients and provides good information on external sphincter defects suggesting that this procedure might be particularly useful in incontinence screening. Perineal sonography gives a good image of internal sphincter. The lack of an isolated internal defect cannot be considered as relevant to our study.