Congenital valve of the posterior urethra

The posterior urethral valve was first described by Giovanni Morgagni in 1717, and then the description was published in a series of books published in 1769 and devoted to anatomical abnormalities. Later in 1802, he was described by Langenbek as a result of an autopsy as valve-like folds. Nikolai Tolmachev in 1870 made a comprehensive description ^[4] and suggested that the valves are too strong development of folds and ridges of the urethra wall ^{[6] [7]} . Finally, in 1919, an up-to-date description of Hugh Young appeared in ^{[8] [9]} clinical presentation and anatomical features ^[4] . In particular, Young gave a classification of 4 types of valve and described a rudimentary urethroscope for removal through the urethra ^[9] . However, in 1992, Young's classification was simplified to two types of valve and explained more precisely by Paddy Dewan and colleagues ^{[10] [11]} .

Under normal conditions, the fetal bladder is cyclically filled and emptied, under low pressure. If the valve of the posterior urethra prevents the emptying, then to empty the bladder it is necessary to create additional force, and the pressure inside it increases. As a result, the walls of the bladder usually become thinner, which impairs its function, and the upper parts of the urethra expand under increased pressure. Ultimately, too much pressure damages the layer of renal parenchyma necessary for their functioning ^[12] .

The exact causes of the formation of the posterior valve of the urethra are unknown, but they are multifactorial, not inherited, and belong to embryopathy ^{[4] [5]} .

The valve is formed, presumably, between the 4th and 6th weeks of embryo development. The Wolf duct , from which the ureter is subsequently formed, is introduced into the posterior wall of the resulting urinary tract, resulting in two folds, but if the Wolf duct is introduced more by its front part than along, then folds and bumps are formed, similar to valves that interfere normal outflow of urine ^{[5] [10]} .

The valve of the posterior urethra interferes with normal urination, is an infravesical obstruction, and can lead to hydronephrosis , megacystis , vesicoureteral reflux , bladder dysfunction, pyelonephritis, and chronic kidney disease . About half of the patients have vesicoureteral reflux ^[4] . Bladder dysfunction can be expressed in three main ways ^[2] :

• hyperreflective bladder ,
• hypertensive bladder with reduced volume and controllability,
• bladder with myogenic dilatation.

At the age of 5-6 years, bladder dysfunction can pass from one form to another ^[2] .

In almost a third of children with a posterior urethral valve, bladder dysfunction can be neurogenic , leading to progressive chronic kidney disease ^[2] .

Also, children with this diagnosis are prone to recurrent urinary tract infections, and, accordingly, pyelonephritis, which is facilitated by a number of factors ^[4] :

• increased pressure inside the bladder,
• stagnation of urine due to too much residual urine after emptying,
• dilated ureter ( megaureter ),
• vesicoureteral reflux .

A preliminary diagnosis can be made in utero, but an accurate diagnosis can only be made after birth. The presence of a posterior urethral valve in the fetus may be indicated by signs of infravesical obstruction ^[5] :

• expansion of the pyelocaliceal system ( hydronephrosis );
• expansion of the ureters ( megaureter );
• large bladder size ( megacystis );
• lack of emptying of the fetus within 30-40 minutes during the study;
• expansion of the posterior urethra.

However, infravesicular obstruction may also occur in other diseases, including serious illnesses such as Potter’s syndrome and plum belly syndrome ^[5] .

In the presence of a posterior urethral valve, urination may be too frequent, intermittent, difficult or with a weak flow ^[3] . Enlarged kidneys and bladder can also be felt .

The presence of a posterior urethral valve is diagnosed using mycystic cystourethrography , which requires filling the bladder through a catheter with a contrast agent. In the presence of a posterior urethral valve, cystourethrography may show expansion of the posterior urethra ^{[5] [3]} . Functional visualization of the upper part of the urethra is done no earlier than one month of age to enable the developing kidneys to mature a little ^[4] .

Cystoscopy of the bladder through the urethra can also be used, in which imaging occurs using a miniature camera. Initially, an assessment of the urethra and visualization of the valves is performed. Valves can be pressed against the walls of the urethra, so a slight pressure on the bladder can be applied to inflate its valves, creating antegrade pressure on the valve. After visualization of the valve, the condition of the bladder is evaluated ^[9] .

The valve of the posterior urethra can be accompanied by other causes of infravesical obstruction, such as: meatal stenosis of the urethra, stenosis of the stem of the urethra, dysplasia of the stem of the urethra, stenosis of the penoscrotal angle of the urethra, stenosis of the urethral bulbous region, stenosis of the membranous urethra, anterior stenosis of the bladder urethra, posterior urethral diverticulum ^[13] .

Intrauterine treatment reduces to the same methods as in the treatment of fetal megacystis to normalize the pressure inside the bladder, and carries certain risks associated with surgical intervention.

Treatment is by ablation of the posterior urethral valve, which usually leads to the restoration of the independent functioning of the urethra, as well as to an improvement in urodynamics. In case of obstruction of the upper part of the urethra and the presence of complications before removal, long drainage-free methods of urine removal are performed ^[2] , including vesicostomy ^[3] . It should be noted that valve removal during the neonatal period leads to the formation of an overactive bladder in almost half of children aged 5-6 years, due to which urodynamics worsen and the need for pathogenetic treatment arises. Children with a remote posterior urethral valve should be monitored until adolescence ^[2] .

In the past, a hypertrophied bladder neck was sometimes removed along with the valve, but now this procedure must be avoided, since it leads to constant urinary incontinence ^[9] .

In case of complication of urinary tract infection in children up to 3 months old, they require mandatory hospitalization, and treatment is carried out with intravenous antibiotics ^[14] .

• Hydronephrosis
• Megacystis
• Chronic kidney disease