Pediatric posterior urethral valve

　　1. Etiology

　　Urethral valves are divided into two types: anterior urethral valves and posterior urethral valves. The anterior urethral valves are often located at the junction of the penis and scrotum, with two mucosal valves protruding into the urethra, with a cleft in the middle, resembling vocal cords and affecting urination.

　　1. The classification of posterior urethral valves is generally divided into 3 types: Type I: The most common type, the valve originates from the distal end of the acrosome and ends at the upper part of the urethra. The valve is usually two, starting from the acrosome and extending outward to connect with the posterior and lateral walls of the urethra, with a crack in the middle. Some valves first fuse at the distal end of the acrosome and then divide into two, ending at the lateral wall of the urethra; some have only one valve, and a single valve rarely causes urethral obstruction. Others have more than two valves, and some originate from the middle segment of the acrosome, all of which belong to Type I. Type II: The valve originates from the proximal end of the acrosome, extends upward and outward, and ends at the neck of the bladder. It is currently believed that this type does not exist clinically. These valve-like substances originate from superficial muscle hyperplasia and hypertrophy from the ureteral orifice to the acrosome, which is secondary to increased urinary resistance and appears in mechanical and functional obstructions such as neurogenic bladder, detrusor-sphincter dyssynergia. Type III: The valve is at the level of the distal membranous urethra of the acrosome,呈membranous shape, with only a tiny hole the size of a needle in the center, resembling an iris. During urination, the long elastic mucosal folds can prolapse into the urethra to form a typical windsock-shaped valve, accounting for about 5% of posterior urethral valves. In our cases, we have only seen one case.

　　The IV type: In addition to the aforementioned 3 types, in 1983, Stephens reported the existence of the fourth type of posterior urethral valve in the obturator hernia syndrome, which is caused by the relaxation and unsupported prostate mucosal folds folding into the urethra, forming a relative outflow obstruction. It has not been universally recognized yet, and there are also three types of posterior urethral valves.

　　2. Etiology The true cause of type Ⅰ posterior urethral valves is not yet fully understood, but it is generally believed to be due to abnormal insertion of the mesonephric duct into the primitive cloaca. Normally, the mesonephric duct enters the cloaca from the side. When the cloaca folds and separates the anal-rectal canal and the urogenital sinus, the opening of the mesonephric duct moves backward to the median and finally opens at the seminal vesicle. In patients with type Ⅰ posterior urethral valves, the mesonephric duct enters the cloaca at a more anterior position. When it folds, the mesonephric duct is obstructed and fuses in front of the median line to form a valve. The formation of type Ⅲ posterior urethral valves is related to incomplete absorption of the urogenital membrane, and its manifestations can vary depending on the elasticity of the membrane and the position of the small holes.

　　Second, pathogenesis

　　Posterior urethral valves form in the early embryonic stage and can cause developmental abnormalities and dysfunction of the urinary system and other systems. Fetal urine is the main source of amniotic fluid in the middle and late stages of pregnancy. Fetal urine from posterior urethral valves, due to urethral obstruction, has less urination, leading to reduced amniotic fluid. Insufficient amniotic fluid hinders the normal movement of the fetal chest and the expansion of the lungs in the uterus, causing underdeveloped lungs. The newborns often have respiratory difficulties, cyanosis, respiratory distress syndrome, pneumothorax, and mediastinal emphysema, and may die from respiratory failure. Due to urinary tract obstruction, increased bladder pressure causes dysregulation of the antireflux mechanism of the ureter, leading to bladder-ureteral reflux and hydronephrosis of the kidney and ureter, increasing the pressure in the renal papilla and causing abnormal renal development. Increased upper urinary tract pressure can damage the collecting duct system of the kidney, causing dysfunction of renal tubular concentration, i.e., acquired polyuria or diabetic nephropathy, increased urine output, which further aggravates ureteral dilation, and also increases bladder capacity, forming a vicious cycle. To overcome the resistance of urination, the detrusor muscle contracts and thickens, followed by the deposition of collagen fibers, which further reduces the contractile function of the detrusor muscle, causing abnormal bladder function.

　　Bladder-ureteral reflux, ureteral hydronephrosis, renal hydronephrosis, chronic renal insufficiency, acquired polyuria or diabetic nephropathy, associated with urinary tract infection and sepsis; may be associated with other malformations, such as seminal vesicle hypertrophy, cryptorchidism, abdominal wall defects, etc.

　　Due to the difference in age and the degree of obstruction by posterior urethral valves, the clinical manifestations vary:

　　1. Neonatal period

　　There may be symptoms such as difficult urination, crying and dribbling, and even acute urinary retention. An enlarged bladder, with thick walls, can often be felt in the lower abdomen. Respiratory difficulties and cyanosis may also occur due to underdeveloped lungs. Some children may have urinary ascites. Urine can leak from the renal parenchyma or renal sinus and渗入腹腔 through permeable peritoneum. Urinary ascites can cause disorders of water and electrolyte balance, even posing a threat to life. However, the分流 of urine to the peritoneal cavity reduces the pressure on the kidneys, and the peritoneum can absorb the ascites, which is beneficial for the prognosis of the child. Newborns with severe urinary tract obstruction due to posterior urethral valves may have severe urinary tract infections, uremia, dehydration, and electrolyte disorders.

　　2, Infancy

　　Children with posterior urethral valve during infancy may have growth and development delay and urinary tract infection, even sepsis. Because of vomiting and malnutrition, it can be suspected as a gastrointestinal disease.

　　3, School age

　　The main manifestation is prolonged urination time, thin urinary line, difficult urination, often with residual urine leading to urinary incontinence and enuresis. Ultrasound examination should be performed in male children with abnormal urination, difficult urination, and recurrent urinary tract infections, such as the presence of bilateral hydronephrosis, bladder dilation, and small trabeculae and cysts, followed by transperineal posterior urethral ultrasound, experienced physicians can find the valve. Considering that the posterior urethral valve should be performed voiding cystourethrogram (VCUG), VCUG can see the expansion of the prostatic urethra, the distal urethra is extremely thin, the bladder margin is not smooth, with the formation of trabeculae and cysts, and there may be varying degrees of vesicoureteral reflux. The fetus with posterior urethral valve is first manifested as hydronephrosis, but it has its characteristics, often bilateral hydronephrosis and ureteral hydronephrosis, bladder wall thickening, and amniotic fluid reduction. In the fetus, the reduction of amniotic fluid is an important signal of obstruction in the lower urinary tract. Newborns with bilateral hydronephrosis at birth should be further examined by ultrasound and VCUG as soon as possible to diagnose posterior urethral valve early.

　　How to prevent posterior urethral valve in children:

　　Currently, there is no specific preventive method. Active prevention and treatment of urinary tract infections, active prevention and treatment of complications, active treatment, to improve the prognosis, preventive measures can be referred to other congenital defects, should be from pre-pregnancy to prenatal, pre-marital physical examination mainly includes serological examination (such as hepatitis B virus, syphilis spirochete, HIV), reproductive system examination (such as screening of cervical inflammation), general physical examination (such as blood pressure, electrocardiogram) and inquiry of family history of disease, personal past medical history, etc., to do well genetic disease consultation work, pregnant women should try to avoid harmful factors, including staying away from smoke, alcohol, drugs, radiation, pesticides, noise, volatile harmful gases, toxic and harmful heavy metals, etc., during the process of prenatal care in pregnancy, it is necessary to carry out systematic screening for birth defects, including regular ultrasound examination, serological screening, etc., and chromosomal examination is necessary if necessary; once there are abnormal results, it is necessary to determine whether to terminate the pregnancy; the safety of the fetus in the uterus; whether there are sequelae after birth, whether they can be treated, and how the prognosis is, etc., take practical and feasible diagnostic and treatment measures, the fetus with posterior urethral valve is first manifested as hydronephrosis, its characteristics are often bilateral hydronephrosis and ureteral hydronephrosis, bladder wall thickening, amniotic fluid reduction, in the fetus, the reduction of amniotic fluid is an important signal of obstruction in the lower urinary tract. The issue of performing intrauterine cystostomy to decompress the fetus with posterior urethral valve is currently very controversial, the impact on the mother and fetus, the achievable effects, and the occurrence of complications are all under observation.

　　One, laboratory examination

　　When there is an infection, the urine examination shows white blood cells and pus cells. The blood creatinine level 5 to 7 days after urine drainage and anti-inflammatory treatment for 5 to 7 days after the newborn is born can serve as a baseline value for the renal function index of the child, but the blood creatinine value of the newborn immediately after birth reflects the renal function level of the mother. In addition to the elevated creatinine level, there is a reduction in renal concentrating function, with low and fixed urine specific gravity, which is related to the development and dysfunction of the distal part of the renal unit caused by obstruction. Renal concentrating dysfunction leads to two consequences:

　　1. The reduced water-regulating ability of the kidneys makes children more prone to dehydration and electrolyte disorders when water loss occurs (such as vomiting, diarrhea, high fever, etc.).

　　2. High urine flow leads to further abnormalities in the function of the ureter and bladder, and some blood urea nitrogen and creatinine levels may increase, and there is often hypokalemia, hyponatremia, and decreased carbon dioxide binding capacity.

　　Radioisotope renal

　　Ultrasonography of the kidneys and intravenous urography can reveal bilateral hydronephrosis, the degree of which may be inconsistent on both sides, or it may be unilateral. After renal function failure, intravenous pyelography may not show any contrast, but normal pelviureteral anatomy does not necessarily exclude urethral valves. Bilateral hydronephrosis, hydroureter, thick-walled bladder, and dilated posterior urethra highly suggest posterior urethral valves. Clear renal cortex-medulla boundaries on ultrasound are a good prognostic sign. If bilateral hydronephrosis and persistent bladder distension are found during fetal ultrasound, this disease should be suspected, and an ultrasound examination or cystourethrography should be performed within 24 hours after birth. There have been reports of fetal cystoscopy recently. Radionuclide renal scans can be used to observe total and differential renal function, and for newborns, it should be delayed until one month after birth to facilitate renal maturation. Initial renal scan tests can serve as an evaluation indicator of treatment effect.

　　Third, Urethrogram

　　Urethrogram is of great help in diagnosis, and voiding cystourethrogram is more valuable. Owing to the wide application of this examination, the diagnosis rate of this disease is increasing year by year. The most common type I can show a very thin filling defect at the valve location, with the bladder showing the appearance of trabeculation. The proximal part of the posterior urethra is dilated, with the neck muscle protruding, resembling a stricture. When the posterior urethra is extremely dilated, it is connected with the bladder neck, resembling a gourd. The anterior urethra has a thin or no urine flow. In type II and type III (with septum near the acrosyringe) the posterior urethra is not dilated. In type III, when retrograde urethrogram is performed, the contrast medium is blocked at the septum, and the contrast medium stays in the posterior urethra, pushing the septum into the bladder, forming a spherical shape. Retrograde urethrogram and voiding cystourethrogram have a greater diagnostic value when compared.

　　Fourth, Urethroscope Examination

　　The valve can be directly seen, which is suitable for all patients and can exclude other coexisting diseases, such as duplicated urethra, megourethra, anterior urethral diverticulum, and cystic spinal cord herniation, etc. In addition, in two cases of children with urinary retention who underwent suprapubic cystostomy, urethral probe was used for posterior urethral convergence examination. One probe goes outwards through the bladder neck, and the other goes inwards from the urethral orifice into the posterior urethra. The two probes meet at the valve location. Although the two probes can touch each other, there is a sense of diaphragm. Subsequent cystourethrography confirmed the presence of posterior urethral valves, so probe detection can also be used as a diagnostic method.

　　Fifth, Urodynamic Examination

　　Urodynamic examination is of great value in the diagnosis of lower urinary tract obstruction of the bladder, but it is limited due to the non-cooperation of infants and young children. Cystometry shows a decompensated bladder with much residual urine, a large bladder capacity, a low compliance bladder. If the bladder pressure is too high due to low compliance, it is not possible to perform ureteral reimplantation. Urethral pressure profile measurement is of great significance for localization diagnosis. The normal urodynamic pressure profile of infants and young children is in the form of a slope. In cases of congenital posterior urethral valves, the pressure can suddenly rise at the valve location, forming a saddle-shaped curve. Pressure/flow rate examination, cystourethrography-pressure-flow rate examination is the most accurate diagnosis, but it is often not possible to perform due to the non-cooperation of children. Ureteral dynamics examination also has certain significance. When the obstruction of the posterior urethral valve is treated and the hydronephrosis of the upper urinary tract does not relieve, this examination must be performed to clarify the cause of the hydronephrosis. Percutaneous upper urinary tract pressure-flow test (Whitaker test) helps to differentiate between mechanical or dynamic obstruction in the upper urinary tract. Studies have shown that the incidence of true vesicoureteral junction obstruction is extremely low.

　　Dietary recommendations for children with posterior urethral valves mainly include the following aspects: 1. Eat light foods mainly and pay attention to dietary regularity. 2. Eat rationally according to the doctor's advice. 3. Avoid spicy and刺激性 foods.

　　I. Treatment

　　Once a posterior urethral valve is diagnosed, a catheter should be retained to relieve lower urinary tract obstruction, correct water and electrolyte imbalances, control infection, and then perform transurethral bladderoscopic valve electrocautery. In areas that are remote, poorly accessible, and without electrocision equipment, or when the child is small and the bladderoscope cannot enter, bladder cystostomy can be performed, but a bladder skin ostomy without an indwelling catheter should be used. The care is simple, and some children, due to severe damage to bladder function, may still be unable to urinate after valve resection; or if renal and metabolic functions have not improved, bladder cystostomy can also be performed. For children who cannot have an endoscope inserted through the urethra, it can be inserted through the bladder cystostomy site, and electrocautery of the valve is required. For fetal posterior urethral valve surgery, the main issue is the controversy over bladder cystostomy for decompression, the impact on the mother and fetus, the achievable effects, and the occurrence of complications are all under observation.

　　II. Prognosis

　　The prognosis of posterior urethral valves is not optimistic, especially for children who exhibit symptoms at birth. In clinical practice, we often see that after electrocautery of the valve, urinary tract obstruction is relieved, but there is always residual urine in the bladder, and renal pelvis and ureteral hydronephrosis does not improve or even worsens, leading to renal function failure. Therefore, regular follow-up should be conducted after valve electrocautery, observing bladder emptying, whether there are recurrent urinary tract infections, and the recovery of renal function. For vesicoureteral reflux, it is generally considered for surgical treatment more than 6 to 12 months after electrocautery of the valve. For abnormal bladder function, such as difficulty in urination or incontinence, it should be treated based on the muscle contraction status of the bladder, bladder capacity, and compliance. Anticholinergic drugs, intermittent catheterization, or bladder augmentation surgery can be used to improve symptoms.