Hypothesis / aims of study
To investigate incontinence, imaging can be used to target diagnosis and interventions. However, the process of voiding is not usually imaged as part of these investigations. Urodynamic investigation provides information about pressure changes during filling and voiding but not visual information. A micturating cystourethrogram acquired under fluoroscopy is the current method to visualise voiding. However, this involves ionising radiation, bladder catheterisation and contrast administered to acquire the voiding images. Realtime ultrasound is now commonly used to image pelvic structures though has not been used to visualise voiding. A transabdominal approach does not visualise the urethra or periurethral structures, and the transperineal approach would inhibit voiding due to position of the transducer. A transpubic approach has been suggested.
The first aim of this study was to investigate the feasibility of transpubic ultrasound imaging to visualise the process of voiding and assess the dynamics of the vesicourethral sphincter, the urethra and pelvic floor muscles during initiation, duration and cessation of micturition. The second aim was to document voiding patterns at different stages throughout a single adult female subject's reproductive years and postpartum recovery, to provide a visual template of physiological changes during pre-, peri- and post-partum period.
Study design, materials and methods
This is a descriptive study exploring the feasibility of, and methodology for, using transpubic ultrasound imaging to image the process of voiding. A pre-scanning bladder filling protocol was used to ensure a moderately full bladder. Scanning was undertaken with the subject seated in a voiding posture on an over-toilet seat and the sonographer seated to her side. A curved array transducer of 2-5 MHz. was placed in the mid-sagittal plane over the pubic symphysis to image through the hypoechoic cartilage. The curved footprint of the transducer was large enough to visualise the entire cranio-caudal length of the fibrocartilaginous symphysis pubis (LFSP) as the only fixed reproducible landmark and to ensure a midline plane; the entire length of the urethra, the full bladder, anterior and posterior vaginal walls, lower uterine segment and the ano-rectal angle. Adequate transducer contact pressure was placed on the symphysis pubis without obstruction to urine flow. The videos were recorded and viewed in the radiological convention cranio-caudal inverted presentation. The subject gave informed consent at each time point. She was requested to void and the initiation, duration and cessation of voiding was imaged, including a pelvic floor muscle contraction at the end of the void. A single subject was used to reduce anatomical variation, and over eleven years to document micturition during the pre-, peri- and post-partum period. Visual changes were noted and documented descriptively. Measurements were taken of the angle between the LFSP and the bladder neck to measure urethral mobility. The subject self-reported any pelvic floor dysfunction at each scan. After her final scan, the subject had an objective pelvic floor assessment by a qualified physiotherapist.
A single female subject with no urinary symptoms was recruited and scanned from age 36 to age 46. The subject’s BMI was 23.9 at the start of pregnancy one and at the end of this study was BMI of 25.7.
This longitudinal study showed that the methodology of the transpubic approach was reproducible, and that it was feasible to visualise the voiding patterns at multiple physiologic time points (Table 1). The transpubic approach was shown to allow voiding to occur during scanning with the subject in a standard voiding position. The critical criterion for reproducibility was to use the midline sagittal plane. This was gained by visualising the full LFSP at each scan. Before the first pregnancy, after the Caesarean section and after the third childbirth, the urethra was stable during the void. At all other timepoints, the urethra was mobile, with maximum mobility seen after the second childbirth, when the subject reported stress urinary incontinence. The larger angles throughout the void indicate urethral mobility (Table 1).
Interpretation of results
This study shows that the transpubic scanning technique is feasible, reproducible, can document dynamic and measurable data, demonstrates consistency in data over time, and that image criteria are reproducible on different ultrasound machines.