Sphincter: properties, types and application

Behavioral and functional abnormalities often are not considered in protocols for evaluation of recurrent UTIs; dysfunctional voiding is an abnormality of bladder emptying in neurologically normal individuals in whom there is increased external sphincter activity during voluntary voiding. It is thought to be a learned behavior, often evolving from attempt to suppress impending or active bladder contractions by inappropriately contracting the pelvic floor muscles, thereby tightening the urinary sphincter complex; it must be differentiated from true detrusor-external sphincter dyssynergia, which occurs as a result of neurological disease or injury. There are many reports of this condition in children; in adults however much less has been written. In addition to recurrent UTIs dysfunctional voiding may result in storage symptoms (frequency, urgency and urge incontinence) and emptying symptoms (decreased force of stream, hesitancy, need to strain and a feeling of incomplete bladder emptying); it may also be responsible for acute or chronic urinary retention. To date, standard urodynamic investigation is an important tool in the assessment of lower urinary tract symptoms; recent enhancement in imaging has allowed the use of ultrasound to investigate the main anatomic and functional alterations of the perineum, i.e. to evaluate the anatomy of the urethro-vesical junction, urethral sphincter volume and bladder wall thickness. We have studied the role of perineal ultrasound in the assessment of women with recurrent UTIs, to evaluate whether it can be recommended in the diagnostic work up of female patients with recurrent UTIs. Multichannel video urodynamic investigation was then performed in all the patients, according to ICS criteria. The sonographic examination (ESAOTE, model. Technos MP, Genova, Italy) was performed in all subjects, with the patients supine, using both the translabial approach (3.5 MHz sector probe) and the introital approach (6.5 MHz end fire endovaginal probe); the latter was used to allow proper location of the end extremity of the probe close to mid urethra and, due to its superior spatial resolution, to provide a more detailed depiction of minute structure when examining the echogenic texture of the urethra. The posterior urethro-vesical angle, the proximal pubo-urethral distance and the angle of urethral inclination were calculated. The thickness of the bladder detrusor wall was measured at the dome of the bladder. Visualization of the four-rings different echo texture of the urethra was performed in the same scan plane. Urethral sphincter volume was assessed by measurements of 3 dimensions; they were first determined in the axial plane by measuring the transverse and antero-posterior dimension at the estimated point of widest transverse dimension; the longitudinal dimension was measured in the sagittal plane just off the midline; the ellipsoid volume formula was then applied as follows: volume = height x width x length x 0.52. In adults functional obstruction at the level of the membranous urethra has been recognized for many years, although it is not as well described as in children; it has been referred to by various terms, including pseudo-dyssynergia, external sphincter spasticity and non-relaxing external urethral sphincter. There are several theories of why dysfunctional voiding occurs in adults: it could be a learned behavior in response to an adverse pelvic condition (infection, inflammation, trauma); it could be the result from voluntary withholding of urination in individuals who are out of home long hours; it could be a primary abnormality of detrusor instability with the dyssynergic sphincter response developing as a result of sudden unanticipated detrusor contractility. The diagnosis of dysfunctional voiding is made when there is increased external urethral sphincter activity during a sustained voluntary detrusor contraction, noted as an increase in electromyography activity and/or dilated proximal urethra, often with intermittent sphincteric activity on voiding cysto-urethrography and usually associated with decreased or intermittent urinary flow. The association of dysfunctional voiding with recurrent UTIs is documented. It has been observed that videourodynamic study is able the define the anatomic and functional characteristics of bladder outlet obstruction in women, and patients with urethral sphincter obstruction have high rates of detrusor overactivity associated with chronic spasm of the sphincter, not relaxing during the voiding phase. Recently ultrasound has gained importance to evaluate urethral or bladder neck morphology and dynamics, bladder wall thickness and urethral sphincter volume. On axial US images the normal urethra has a characteristic target-like appearance and is seen as composed by four concentric rings of different echogenicity. It has been observed that abnormal findings in patients with increased urethral functional length include (a) thickening of individual rings; (b) haziness of contours; and (c) change in the echogenic texture with loss of the characteristic four-rings appearance. Morphologic changes in the sphincter echo-texture can occur as result of a variety of factors; but while an intrinsic sphincter deficiency can easily be suggested on axial US images by loss of its normal characteristic target-like appearance, the coexistence of abnormal urethral rings and increased detrusor wall thickness might be due to functional compressive urethral obstruction from sphincter overactivity, both idiopathic or neurological in origin. Perineal ultrasonography provides serial non-invasive examinations for assessing the condition of the bladder wall; the normal bladder wall is 3 to 6 mm thick, although it may vary with intravesical volume; it may be thickened secondary to chronic infection, inflammation after surgery, or radiation; measurement of bladder wall thickness may be helpful for detecting detrusor overactivity. Urethral sphincter volume can be the cause of functional obstruction, as a consequence of a dysfunctional voiding. In patients with detrusor overactivity a positive correlation was observed between rhabdosphincter thickness and detrusor contraction pressure, and between rhabdosphincter thickness and urethral resistance, as measured by maximal urethral closure pressure. We think that a first line approach in female patients with recurrent UTIs can be done by flow electromyography, with recording of urine flow and perineal activity during voiding, and by perineal ultrasound, with the evaluation of sphincter volume and detrusor wall thickness; these investigation in our experience are able to select patients with dysfunctional voiding. Multichannel video urodynamics can therefore represent a second line diagnostic approach.