Distal Urethral Stenosis in Infancy and Childhood (Spasm of the External Urinary Sphincter) and Dysfunctional Voiding
There has been considerable confusion about the site of lower tract obstruction in young girls who have enuresis, a slow and interrupted urinary stream, recurrent cystitis, and pyelonephritis and who, on thorough examination, often exhibit vesicoureteral reflux. Treatment has been directed largely to the bladder neck on rather empiric grounds. Most of these children, however, have congenital distal urethral stenosis with secondary spasm of the striated external sphincter rather than bladder neck obstruction.
Lyon and Tanagho (1965) found that the distal urethral ring calibrates at 14F at age 2 and at 16F between the ages of 4 and 10. Even though from the hydrodynamic standpoint, such a stenotic area should not be obstructive, almost all observers agree that dilatation of the ring does relieve symptoms in these children and that it results in cure or amelioration of persistent infection or vesical dysfunction in 80% of cases (Kondo et al, 1994). Tanagho et al (1971) measured pressures in the bladder and in the proximal and mid urethra simultaneously in symptomatic girls and found high resting pressures, some as high as 200 cm of water (normal, 100 cm of water) in the midurethral segment. Attempts at voiding caused intravesical pressures as high as 225 cm of water (normal, 30–40 cm of water) to develop. Under curare, the urethral closing pressures dropped to normal (40–50 cm of water), proving that these obstructing pressures were caused by spasm of the striated sphincter muscle. If the distal urethral ring was treated and symptoms abated, repeat pressure studies showed normal midurethral and intravesical voiding pressures. It seems clear, therefore, that the likely cause of urinary problems in young girls is spasm of the external sphincter and not vesical neck stenosis (Smith, 1969).
In addition to recurrent urinary tract infections, these patients have hesitancy in initiating micturition and a slow, hesitant, or interrupted urinary stream. Enuresis and involuntary loss of urine during the day are common complaints. Abdominal straining may be required in order to void. Small amounts of residual urine are found, which impair the vesical defense mechanism. A voiding cystourethrogram may reveal an open bladder neck and ballooning of the proximal urethra secondary to spasm of the external sphincter (Figure 42–1).
Distal urethral stenosis with reflux spasm of voluntary urethral sphincter. Left: Voiding cystourethrogram showing bilateral vesicoureteral reflux, a wide-open vesical neck, and severe spasm of the striated urethral sphincter in the mid portion of the urethra (arrow) secondary to distal urethral stenosis. Right: Postvoiding film. The bladder is empty and the vesical neck open, but the dilated urethra contains radiopaque fluid proximal to the stenotic zone. Bacteria in the urethra thus can flow back into the bladder. (Courtesy of AD Amar.)