How to perform 2D and 3D transperineal ultrasound, looking at how TPUS can be used to demonstrate pelvic floor dysfunctions or abnormalities during maximal Valsalva manoeuvre.
Dynamic perineal ultrasound demonstrated
Conventional convex transducers (frequencies between 3 and 6 MHz and field of view at least 70°) provide 2D imaging of the pelvic floor. Transperineal ultrasound is performed with the patient placed in the dorsal lithotomy position, with the hips flexed and abducted. If necessary, the patient can be examined standing, to maximise descent of pelvic organs, especially if the patient finds it difficult to produce an effective Valsalva maneuver. No rectal or vaginal contrast is used. Perineal ultrasound provides sagittal, coronal and oblique sectional imaging, with the mid-sagittal plane being the most commonly used as this gives an overall assessment of all anatomical structures (bladder, urethra, vaginal walls, anal canal and rectum) between the posterior surface of the symphysis pubis and the posterior part of the levator ani (LA) (Figures 1a-1b). The imaging is usually performed at rest, on maximal Valsalva maneuver and on pelvic floor muscle contraction (PFMC). The access to the mid-sagittal plane allows the following evaluations:
- Integrity of the perineal body: appearing as a triangular shaped, slightly hyperechoic structure anterior to the anal sphincter;
- Measurement of the anorectal angle (ARA): formed by the longitudinal axis of the anal canal and the posterior rectal wall;
- Dynamic assessment of the posterior compartment. During Valsalva it is possible to visualize descent of an enterocele, to assess the movement of the anterior rectal wall to detect a rectocele, and to evaluate movement of the PR and ARA to diagnose pelvic floor dyssynergy (Figure 1c).
3D perineal ultrasound imaging may be performed with volumetric probes (electronic curved array of 4–8 MHz). An advantage of this technique, compared to 2D mode, is the opportunity to obtain tomographic or multislice imaging, e.g. in the axial plane, in order to assess the entire PR and its attachment to the pubic rami (Figure 2). It is also possible to measure the diameter and area of the levator hiatus (LH) and determine the degree of hiatal distension on Valsalva. Four dimensional (4D) imaging indicates real-time acquisition of volume ultrasound data.
Obstructed defecation syndrome (ODS)
The term obstructed defecation syndrome (synonyme: 'outlet obstruction') encompasses all pelvic floor dysfunctions or abnormalities, which are responsible for an incomplete evacuation of fecal contents from the rectum, straining at stool and vaginal digitations. During maximal Valsalva manoeuvre, dynamic TPUS may be used to demonstrate:
- Rectocele: herniation of a depth of over 10mm of the anterior rectal wall (Figure 3);
- Rectal intussusception: invagination of the rectal wall into the rectal lumen, into the anal canal or exteriorized beyond the anal canal (rectal prolapse);
- Enterocele: herniation of bowel loops into the vagina (Figure 4). It can be graded as small, when the most distal part descends into the upper third of the vagina, moderate, when it descends into the middle third of the vagina, or large, when it descends into the lower third of the vagina;
- Dyssynergic defecation: the ARA becomes narrower, the LH is shortened in the anteroposterior dimension, and the PR muscle thickens as a result of contraction.
