(a) Transvaginal US. Anatomical elements: a pubic arcuate ligament, C bladder neck, U urethra, and Ve bladder. (b) Transrectal US. Anatomical elements: A pubic arcuate ligament, Ve bladder, and Va vagina. (c) Perineal US. Anatomical elements: A pubic arcuate ligament, C bladder neck, U urethra, and Ve bladder
37.1 Anatomical Elements
In basal conditions the urethra has a virtual lumen and is seen at US as a thin echogenic line surrounded by a hypointense; the course of the urethra basically runs parallel to the vagina and is slightly downward arched.
37.1.2 Bladder Neck
The bladder neck is an important element in both static and dynamic measurements; it presents as a small groove at the level of the bladder base, continuing up from the urethra. Generally, whatever the US technique used, the urethra and the bladder neck can easily be seen. Only rarely is it necessary to apply a catheter to show up the course of the urethra and the position of the bladder neck.
37.1.3 Bladder Base
The bladder base is rounded and situated, in normal conditions, above the inferior margin of the pubic symphysis. The bladder neck and urethra-trigonal junction are closed in basal conditions and located about 2 cm above the pubic symphysis.
37.1.4 Pubic Symphysis
At US the pubic symphysis appears as an intensely echo-reflecting meniscus-like image, located vertically underneath the median third of the urethra. An important reference point when making an assessment of dynamic modifications of the bladder base is the pubic arcuate ligament. This appears as a weakly echogenic zone above the inferior margin of the pubic symphysis, on the median line. Anatomically, it consists of a cartilage that binds the two pubic bones.
When making quantitative assessments of cervico-urethral static conditions, the measurement of some angles is extremely important:
The angle of mobility of the bladder neck is included between the line perpendicular to the puborectal line, at the level of the arcuate ligament, and the slightly downward arched bladder neck line.
The angle of the urethral axis lies between the urethral axis and the puborectal line.
The angle of mobility of the bladder base lies between the puborectal line and the line that joins the arcuate ligament to the lowest point of the bladder base.
In normal subjects the bladder base and neck lie near to, and slightly below, the line running perpendicular to the puborectal line (distance <2 cm).
The distance between the bladder neck and the puborectal line must be >2 cm, the mobility angle of the bladder base >30°, the mobility angle of the bladder neck <45°, the urethral axis angle about 50°, and the posterior urethrovesical angle >110°.
An important point when assessing any prolapse of the bladder neck and base is to carry out a stress test in the dynamic phase and during micturition.
The patient is asked to cough repeatedly and undergo a prolonged Valsalva maneuver (not less than 5 s), repeated several times, at least three, in order to obtain a more pronounced descensus. This will make it possible to obtain an objective evaluation of an abnormal mobility of the bladder base, the urethra, and the bladder neck. It is extremely important to note any abnormal opening of the bladder neck under stress, and any urine leakage is a sign of a probable rhabdosphincter deficit that should be confirmed by a urodynamics test. In normal subjects, the position and shape of the urethra and bladder neck under stress are not much different from those in basal conditions .
It is essential to keep the same orientation of the images in all the examinations. As regards qualitative parameters, it is important to note any funneling of the bladder neck, the position (high or low) and mobility (fixed or hypermobile) of the urethra, and the mobility of the bladder base (vertical, rotational shift, descensus).
Among the quantitative measurements mentioned above, the most important are undoubtedly the distance between the bladder neck and the puborectal line that indicates the degree of an anterior defect (urethrocele) (Fig. 37.2) and the hypermobility angle of the bladder base that defines the degree of a posterior defect (cystocele) (Fig. 37.3).
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