The axial location of structural regions in the urethra: a magnetic resonance study in nulliparous women*1

Abstract

OBJECTIVE-To define and quantify the appearance and location of distinct regions of the bladder neck and urethra by using axial magnetic resonance images from healthy, continent, nulliparous women.METHODS-Seventy-eight asymptomatic, healthy, nulliparous women (mean age 29.2 ± 5.4 years) volunteered for this study. All women were proven continent on urodynamic examination. Axial proton density magnetic resonance images of the pelvic floor were analyzed at 5-mm intervals. A geometric origin was established at the internal urethral meatus. The presence or absence of each of six structural regions-the bladder base, bladder neck, striated urethral sphincter, compressor urethrae and urethrovaginal sphincter, perineal membrane, and distal urethra-was then noted in each more distal image. The proportion of women in whom a structural region was seen at each 5-mm interval was recorded.RESULTS-The striated urogenital sphincter was observed at 5-25 mm distal to the bladder base. It was observed 10 and 15 mm below the bladder base in 91% (95% confidence interval [CI] 85%, 98%) and 99% (95% CI 97%, 100%), respectively, of all women. The perineal membrane, marking the distal end of the muscular urethra, was located 20-35 mm distal to the bladder base. The length of the muscular region of the urethra ranged from 20 to 35 mm (mean 24 mm, 95% CI 24, 25 mm).CONCLUSION-Magnetic resonance images allow the normal appearance and location of urethral and bladder neck structures to be quantified in healthy, continent, nulliparous women.To identify the anatomic changes that might be associated with impaired urethral function, it is important first to describe the normal variation in urethral morphology in healthy, continent individuals.Histologic studies have been used to describe this variation in vitro 1-5 ; however, interpretation of the results is complicated by the unknown continence status of the donors. When ultrasound, 6-8 computed tomography, 9 and magnetic resonance 10 are used to study urethral morphology in vivo, along with urodynamic studies of the same individuals, they offer the possibility of correlating structure-function relationships in a way that is not usually possible with in-vitro studies.

Urethral Sphincter Morphology and Function With and Without Stress Incontinence

“…Axial MRI scansin each individual were reviewed to determine slices containingthe bladder base, the vesical neck and SUS, includingCU/UVS (Figure 1). 7 Figure 2 shows an exampleusing MRI. Each slice was considered to have a single predominant region, that is each slice was identified as the bladder base, vesical neck or SUS but not 2 designations.The length of the vesical neck, SUS and total urethral length were calculated by multiplying the number of slices in which these structures were seen by the 5 mm interval between each slice.…”

“…Strohbehn et al established the histologicaland radiological identification of its layers 3. Several studies of normal asymptomatic women showed that urethral anatomy can be visualized with MRI 4–7. However, to our knowledge differences in women with and without pelvic floor dysfunction have been not been directly compared and analyzed.…”

Vaginal Birth and De Novo Stress Incontinence

“…Structure of the urethra and striated urogenital sphincter muscle-The length of the muscular urethra was measured as the distance from the internal urinary meatus to the distal end of the perineal membrane where the urethra becomes fibrous (23,24), and the length of the striated urogenital sphincter was assessed from this landmark to the top of the visible sphincter. Examiners were blinded to the continence status and parity of subjects.…”

Is there a correlation between levator ani and urethral sphincter complex status on 3D ultrasonography?

“…In the same way, the urethral sphincter musculature can also be easily visualized and readily measured using endovaginal ultrasonography (EVUS) [15,16], intraurethral ultrasonography [17,18] and MRI [19][20][21]. The levator ani muscle and the urethral rhabdomyosphincter are both skeletal muscles.…”