Posterior urethral valve is the most common disease in congenital lower urinary tract obstruction in male children. It only occurs in males. The literature reports that it accounts for 9% of neonatal urinary tract obstruction. Early diagnosis and treatment are particularly important because they can cause dysplasia and dysfunction in the urinary system and other systems. This study retrospectively analyzed the clinical data of children's posterior urethral valve ultrasound, bladder urethroscopic findings and urethral valve resection records, in order to improve the accuracy of preoperative ultrasound diagnosis.

1.1 Research object
Twenty patients with urethral valve diagnosed by transurethral cystoscopy and urethral valvuloplasty were enrolled in our hospital from 2010 to 2018. The age of children was 1 day to 9 years old, including <1 year old. 17 cases, and > 1 year old  3 cases. Clinical symptoms: 12 cases of urinary dysplasia (hyperhydration, ureteral dilatation, abnormal urethral echo mass), 4 cases of urinary tract infection, 2 cases of dysuria, 1 case of urinary tract, and 1 case of urinary incontinence.
1.2 Instruments and methods
Application MINDRAY DC-8 and GE Voluson E8 color Doppler ultrasound diagnostic equipment, convex array probe (frequency is 6~8MHz) and high-frequency linear array probe (frequency 8~12MHz) combined scanning.
Follow-up and image analysis: Retrospective study was performed on all the clinical data of sonograms, excretory urography (VCU) and surgical records of children with urethral valve diagnosed by urethral urethra microscopy.

2 results
2.1 Ultrasound findings 
Ultrasound diagnosis results: 20 cases of posterior urethral valve were diagnosed by preoperative ultrasound and urinary catheter test 14 cases of urethral valve; suggesting double hydronephrosis and bilateral ureteral dilatation, considering the possibility of lower urinary tract obstruction in 4 cases; misdiagnosis of neurogenic source 2 cases of sexual bladder.
2.2 Follow-up results of clinical and surgical data 
The results of urethral urethroscopic microscopy and intraoperative findings, surgical methods: 20 cases were diagnosed by cystoscopic urethroscopic examination, and at the same time undergoing cystoscopy urethral valve resection and catheterization.18 cases of type I valve were diagnosed during operation，the posterior urethral fine distal white valve structure, from the ventral side to the dorsal side confluence, the local urethra narrowed, forming an obstruction; 
and 2 cases of type III valve were diagnosed during operation, the posterior urethra fine distal white valve structure, ring-shaped, diaphragm-like structure There is a hole in the center, and the local urethral lumen is narrowed to form an obstruction.

1.In this group of patients, 13 cases of urinary dysplasia were diagnosed by prenatal ultrasound after 24 weeks of gestation. Most of them showed only renal pelvis dilatation and ureteral dilatation in the second trimester, and hydronephrosis in late pregnancy (28 weeks later). Aggravated growth rate, immediately recommended by experts in obstetrics and gynecology to our hospital urology specialist consultation and follow-up, 9 of which were diagnosed and treated in advance by pediatric urology and obstetrics and gynaecologists. All the 13 children with prenatal ultrasound diagnosis were hospitalized within 1 day after birth, and all survived, suggesting that early diagnosis and treatment are of great significance for the prognosis of children.
2.According to the age group and the degree of obstruction, the clinical manifestations of children vary. Most of the neonates in the perinatal period are diagnosed by urinary dysplasia because of prenatal ultrasound diagnosis. Some neonates have reduced urination and insufficient amniotic fluid due to urinary tract obstruction in the fetus, which causes the amount of amniotic fluid and lung developmental stimulation of the fetus. Insufficient thoracic activity leads to lung dysplasia and even post-natal respiratory failure. Children may present with post-natal paralysis and difficulty breathing . Infants and children of school age and school-age children often due to abnormal urination, can be manifested as dysuria, small urine line, urine drip, urinary tract infection, and even acute urinary retention, abdominal mass and so on. One patient in this group who had prenatal diagnosis of hydronephrosis was admitted to the hospital more than 6 hours after birth, suggesting a combination of lung dysplasia.
3.The kidney, ureter and bladder were observed by abdominal ultrasound. The sonogram and ureterospasm were different according to the degree of obstruction. Most cases were bilateral and a few were unilateral; the ureter showed dilatation throughout the whole process; the bladder was overfilled. The bladder wall is thickened and the inner wall is not smooth, not smooth, and the urinary wall or diverticulum is formed in the bladder wall. The above changes are highly suspected of the presence of lower urinary tract obstruction. At this time, the urethra should be further observed through the perineum. In the urinary state, the proximal urethra and the urethral bladder entrance are widened. Only a small amount of fluid is filled at the distal end. Some children can clearly observe the strong echogenic membrane structure from the urethra side. The wall bulges into the cavity and oscillates slightly as the urethral sphincter contracts. This sonogram is highly suggestive of posterior urethral obstruction and urethral valve.
4.The posterior urethral valve sonogram mainly needs to be differentiated from the neurogenic bladder and bilateral primary vesicoureteral reflux. The identification points are as follows: 1. Neurogenic bladder: The children have a clear history of spinal cord lesions and spinal cord surgery. For children with unclear history of spinal cord, observation of urethral dilatation and stenosis is the key point for identification. In the experiment, the two sides have difficulty in differential diagnosis. 2. Primary vesicoureteral reflux: children have no posterior urethral dilatation. Dynamic observation can show changes in the degree of hydronephrosis in some kidneys, and some children are caused by reflux and repeated urinary tract infections. Renal parenchymal injury and scarring of the kidney. The sonogram shows the difference in size of the kidneys and the dysplasia of the affected side. The posterior urethral valve is often characterized by hydronephrosis. Because about 50% of cases in the posterior urethral valve combined with vesicoureteral reflux, when ultrasound is difficult to identify, further cystography, excretory urography (VCU) combined with imaging diagnosis.

Ultrasound examination of the urethra is simple and non-radioactive. It not only displays the urethra of the child in real time, but also visualizes the valve structure. It can also assess the structure and function of the kidney, ureter and bladder without interventional procedures such as catheterization. Suitable for any age group, especially for neonatal examination, it can be used as the first choice for imaging diagnosis of posterior urethral valve in children. Posterior urethral dilatation and urination experiments identify valve-like structures, irregular thickening of the bladder wall, trabecular formation, hydronephrosis and ureteral dilatation are the main points of ultrasound diagnosis of posterior urethral valve.

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