Congenital ureteropelvic junction obstruction in children

　　1. Etiology

　　Although extensive research has been conducted in embryology, histology, and anatomy, the exact cause of UPJO is still unclear. Currently, it is generally believed that it is due to developmental stagnation at the renal pelvis and ureter junction or a process of substantiation and recanalization of the ureter during fetal stage. If recanalization is incomplete, it can cause endogenous obstruction of the renal pelvis and ureter junction:

　　1. Endogenous Obstruction

　　(1) Stagnation of Circular Muscle Development at the Renal Pelvis and Ureter Junction: In 1958, Murnaghan discovered the phenomenon of stagnation of circular muscle development at the renal pelvis and ureter junction. This phenomenon destroys the funnel-like structure of the junction, causing poor urine drainage. Renal hydronephrosis can exacerbate the destruction of the funnel-like structure.

　　(2) Excessive Collagen Fiber Content: In 1968, Nutley and in 1976, Hanna et al., found under the electron microscope that the arrangement of muscle cells at the UPJO is normal, but the content of collagen fibers is greatly exceeded, which leads to increased spacing between muscle fibers, and many muscle cells even atrophy. This results in the destruction of the contractile function of the renal pelvis and ureter junction muscle, causing the urine in the renal pelvis to be unable to be emptied.

　　(3) Ureteral Valve: Congenital mucosal plicae of the ureter are a type of ureteral valve. It is a very common phenomenon in the upper segment of the fetal ureter after 4 months. These mucosal plicae can even extend to the neonatal period. Generally, mucosal plicae do not cause obstruction and can disappear with growth and development. They are rarely seen in older children or adults.

　　(4) Other Causes: Other causes of endogenous obstruction within the renal pelvis and ureter junction include:

　　① Valvular Mucosal Plicae: Valvular mucosal plicae are a type of ureteral valve, which is a very common phenomenon in the upper segment of the fetal ureter after 4 months. These mucosal plicae can even extend to the neonatal period. Generally, mucosal plicae do not cause obstruction and can disappear with growth and development. They are rarely seen in older children or adults.

　　② Persistent Tortuosity and Folding of the Ureter in Fetal Stage: The tortuosity and folding of the ureter during fetal stage can persist.

　　③ Ureteral Papilloma at the Starting Segment: Papillomas are generally small and often located at the junction of the renal pelvis and ureter or in the upper segment of the ureter. They can cause incomplete obstruction, leading to hematuria in children or intermittent abdominal pain. The ratio of its detection in UPJO is increasing, and postoperative recurrence is rare according to follow-up.

　　2. External obstruction

　　The most common external obstruction is the compression of the renal pelvis and ureteral junction by the vagus or accessory branch vessels that innervate the renal cortex of the lower pole. This vessel often passes in front of the renal pelvis and ureteral junction or the upper end of the ureter. The incidence of UPJO caused by the vagus vessel is between 15% and 52%, and it is more common in adults than in children. The vagus vessel causes the ureter to fold at an angle, and when the pelvis is filled, it can form obstructions at two places: the renal pelvis ureteral junction and the ureter where the vessel passes through. The ureter, pulled and folded upwards by the vagus vessel, can form fascial adhesions with the pelvis. Long-term compression of the ureter can lead to ischemia, fibrosis, and stricture. Therefore, although some people believe that detaching the adhesions and freeing the vessel can resolve UPJO, it is still better to excise the obstructed ureter.

　　3. Secondary obstruction

　　UPJO can be caused by severe vesicoureteral reflux, accounting for about 10% of the total cases. Reflux can cause the ureter to twist, thicken, and elongate, while the relative fixed position of the renal pelvis and ureteral junction can produce folds, leading to obstruction. Similarly, UPJO can also be caused by obstruction at the bladder ureteral junction. The incidence of UPJO in children with renal malformation is quite high, including other congenital malformations. The reported incidence of contralateral UPJO is 10% to 40%, and other conditions can be renal hypoplasia, polycystic kidney disease, etc. UPJO can also occur in the upper or lower pole of a duplicated kidney, or in a horseshoe kidney or ectopic kidney. The incidence of mild vesicoureteral reflux in UPJO patients can reach about 40%, and it is more likely to be caused by urinary tract infection, which can disappear spontaneously. The incidence of UPJO in the Vater syndrome is 21%.

　　II. Pathogenesis

　　Obstruction of urine flow caused by many internal and external urinary tract lesions ultimately leads to increased intrarenal pressure, obstruction of the urine excretion from the renal calyces and pelvis, prolonged retention of urine within the pelvis, expansion of the pelvis, gradual increase in pressure within the renal curvature tubules, expansion of the tubules affecting urine secretion, and at the same time, compression of nearby blood vessels causing anemic atrophy of the renal parenchyma. Due to the expansion of the pelvis and calyces, atrophy of the renal parenchyma, renal dysfunction, is called hydronephrosis (hydronephrosis). The progression of hydronephrosis can be divided into:

　　1. The renal pelvis expands, and the renal pelvis wall becomes thin.

　　2. The renal papillae atrophy (at this time, the renal pelvis angiography shows the cup-shaped renal calyces gradually flattening until they finally bulge outward).

　　3. The renal parenchyma progressively atrophies and becomes thin. When the pelvis is of the intrarenal type, the atrophy of the renal parenchyma appears earlier and more severely. Urinary tract obstruction occurs when the urine from the pelvis and calyces is obstructed, and some of the fluid can enter the lymphatic and venous systems (pelvic lymphatic reflux, pelvic venous reflux), which slightly reduces the pressure within the pelvis and renal tubules, yet still retains the ability to continue secreting urine. When both ureters are blocked, uremia often occurs within 3 days. If the obstruction is resolved within 8 days, renal function can usually be restored. Partial obstruction or intermittent obstruction can cause hydronephrosis, which can reach a very large volume.

　　Congenital ureteropelvic junction obstruction in children often complicated with recurrent urinary tract infections, hydronephrosis, hypertension, and growth and development delay. The disease severely affects the health of children, so timely treatment is essential after diagnosis.

　　1. The urinary tract obstruction caused by UPJO is incomplete, the progression of the disease is slow, and there are no clear symptoms. Sometimes, due to poor drainage, abdominal pain may occur when the urine volume is large, resulting in contraction of the renal pelvis. However, it is difficult to point out the specific location, and it can be accompanied by nausea and vomiting. In newborns or infants, UPJO can cause asymptomatic abdominal masses, which may be discovered incidentally during physical examination. In the days before ultrasound, about 50% of cases were discovered in this way. With the routine use of prenatal ultrasound in recent years, many cases of UPJO-induced hydronephrosis have been diagnosed during the fetal stage. Other manifestations include growth and development delay, feeding difficulties, recurrent urinary tract infections, and hematuria, etc. It has been reported that the incidence of urinary tract infections can reach 30% after the neonatal period. For many years, among the 304 cases of UPJO-induced hydronephrosis, only 6 cases were reported to have urinary tract infection as the initial symptom, among those caused by wandering blood vessels.

　　2. Due to intermittent obstruction, children may experience intermittent abdominal pain, sometimes accompanied by vomiting. Hematuria is often caused by the rupture of blood vessels in the mucosa of the dilated renal pelvis. In adolescents, it is common for them to experience abdominal pain after drinking a large amount of water. Elderly patients may develop hypertension, which is due to the expansion of the collecting system, a decrease in renal blood flow, functional renal ischemia, and the production of renin and angiotensin-mediated, which requires re-examination for children with renal hydrops diagnosed during fetal stage, preferably within a few weeks after birth (usually 4 weeks). Within about 3 months after birth, the kidneys are still developing, and the renal pyramids and medulla are translucent, which can produce the false appearance of hydronephrosis. Therefore, regular ultrasound examination after birth is very necessary. At present, it is still difficult to estimate the degree of hydronephrosis in fetuses and newborns. From the existing reports, most of the mild to moderate hydronephrosis (in most children with renal pelvis dilation of 2 cm) can be spontaneously resolved within 2 years. The isotope renal imaging curve of these children shows normal uptake of radioactive isotopes but significantly delayed excretion. Laboratory tests for UPJO-induced hydronephrosis do not show characteristic changes.

　　Congenital ureteropelvic junction obstruction in children is a congenital disease, the etiology of which is not yet clear, and there is no specific preventive measure. After clear diagnosis, obstruction should be removed as soon as possible and active prevention and treatment of urinary tract infection should be carried out.

　　1. Urine routine examination:The urine routine of most children is normal. When urinary tract infection occurs, there may be white blood cells; some children may also show hematuria.

　　2. Routine blood test:Anemia, decreased red blood cell count, and decreased hemoglobin may occur when the kidney is damaged.

　　3. Renal function examination:In general, the renal function of children with hydronephrosis is within the normal range, unless there is progressive renal failure in very severe bilateral hydronephrosis. B-ultrasound can show hydronephrosis, and X-ray examination is the main diagnostic method. Plain film and pyelovenography can understand the condition of both kidneys and ureters, and can also perform radionuclide renal imaging.

　　4. Ultrasound examination:It is the most commonly used and effective non-invasive examination method, which can detect dilated and separated renal pelvis and calyces, and can also measure the thickness of the renal cortex. Generally, in UPJO causing hydronephrosis, the diameter of the ureter is basically normal. Ultrasound can show hydronephrosis, and X-ray examination is the main diagnostic method. Plain film and pyelovenography can understand the condition of both kidneys and ureters, and can also perform radionuclide renal imaging. However, unless it is a very severe case of massive hydronephrosis, the data from ultrasound cannot reflect the severity of hydronephrosis and the actual renal function, but it is still the preferred method.

　　5. Excretory venous urography:(IVU) shows renal pelvis dilatation, calyces dilatation, interruption of the renal pelvis-ureteric junction, non-display of the ureter. Children commonly use 60% or 76% iohexol, neonates 8-10ml, <6 months 10-12ml, 6-12 months 12-15ml, and in cases of poor renal function, blood urea nitrogen up to 50mg/dl, rather than at the time of urinary retention, the dose can be increased to 2.2ml/kg, with an equal amount of glucose solution administered rapidly, delayed radiography, full urinary tract imaging at 60-120min, where the renal pelvis shadow can often be seen, and if necessary, renal puncture angiography can be performed to understand the obstruction site, but it must be performed separately on both sides to avoid renal failure. We commonly use 76% iohexol 2.2ml/kg administered rapidly intravenously, the length of time for renal imaging to start and the degree of contrast agent display can reflect the changes in renal function, from the size of the kidney, the degree of dilatation of the renal pelvis and calyces, and the time of contrast agent excretion, the severity of hydronephrosis can be reflected. Depending on the severity of hydronephrosis, the appearance of the calyces can range from a slightly blunt, flattened cup-like shape to severe outward bulging, prominence, and fullness. Sometimes, contrast agent may remain in the dilated calyces without entering the renal pelvis, resembling a palette used for painting. In cases of severe renal dysfunction, delayed radiography may be necessary, such as 240min, 360min, or even imaging the next day to ascertaining the renal shape as clearly as possible. However, when the kidney does not show up due to severe hydronephrosis, MRU is often used instead. UPJO generally does not show the ureter, but even if the distal ureter at the renal pelvis-ureteric junction can be visualized, there may still be severe obstruction at the renal pelvis-ureteric junction. Retrograde ureteral catheterization with cystoscopy can clearly define the entire ureter. It is generally recommended to perform this on the day of surgery. Voiding cystourethrography is commonly used in diagnosing lower urinary tract obstruction in children, where the contrast agent can enter the bladder through three methods.

　　6, Diuretic renal scan hydronephrosis:Another important diagnostic method for hydronephrosis is the diuretic renal scan, which uses isotope technology to measure the blood perfusion, renal function, and tracer excretion of the kidneys. Generally, the isotope uptake phase of the renal scan curve is used to evaluate renal function, and the excretion phase after furosemide injection can determine the severity of obstruction. For children with intermittent renal pelvis ureteral junction obstruction, diuretic renal scans are particularly valuable. These children can only detect the presence of PUJO when they have abdominal pain, and their excretory urography can be completely normal when asymptomatic. This situation is often seen in hydronephrosis caused by vagal vessel compression. After furosemide injection, the urine output increases, and the renal pelvis cannot be emptied in time, leading to the appearance of symptoms of hydronephrosis. Of course, some children may experience abdominal pain during the diuretic renal scan. The diuretic renal scan avoids the radioactive hazards of conventional造影 methods, has high sensitivity, and can display even in kidneys with poor function if there is isotope tracer entering. It can provide indicators of individual renal function, thereby allowing for comparison of pre- and postoperative conditions. According to the speed of tracer excretion in the renal pelvis, the severity of obstruction can be inferred. From our experience, a renal scan review after surgery is best performed at 6 months postoperatively. If a diuretic renal scan is performed before 3 months, it may be affected by anastomotic edema, which can still present as a mechanical obstruction sign.

　　7. Magnetic Resonance Urography:(MRU) Due to urinary tract obstruction, hydronephrosis and dilation can be displayed on the T2 phase of magnetic resonance imaging, especially in cases with poor renal function where IVU and radionuclide renal scans cannot show the situation. Through MRU, the anatomical morphology of the urinary tract can be displayed, indicating the site of obstruction. Magnetic Resonance Urography (MRU) can clearly show the location of upper urinary tract obstruction. The combination of urodynamic studies and X-ray examination is very important for detecting some problems in lower urinary tract obstruction, such as bladder compliance and coordination between the detrusor muscle and the urethral sphincter muscle.

　　8. Voiding cystourethrography:All children with hydronephrosis must undergo voiding cystourethrography to exclude hydronephrosis caused by vesicoureteral reflux.

　　Children with congenital ureteropelvic junction obstruction need timely treatment. After treatment, patients should eat more nutritious foods and pay more attention to the details of life, diet habits, and a reasonable diet structure.

　　1. Treatment

　　1. With less hydronephrosis and normal renal function, children with good growth and development can be followed up and observed. Decisions should be made based on the progression of hydronephrosis. For children with clear diagnosis and renal damage, or those with recurrent abdominal pain, hematuria, and urinary tract infections, surgical treatment is recommended. The surgical method is mature, involving the creation of a ureteropelvic junction anastomosis. In the past 5 years, the affiliated Xinhua Hospital of the Second Military Medical University of Shanghai has performed 300 surgeries, with only 3 cases of postoperative stricture at the anastomosis. Regarding the need for a stent, there is still debate. Reports from the United States often do not use a stent, only leaving a wound drain. In China, some use double 'J' stents, but the problem is that they need to be removed under anesthesia through cystoscopy 3 to 4 months later. If it is a small infant, cystoscopy may not be possible, and the bladder may need to be incised. In summary, anesthesia is required. The routine method is to use an 8Fr gastric tube, inserting it from the pelvis into the ureter, with the other end passing through the renal cortex and fixed to the skin incision. The stent has lateral holes in the pelvis, so in addition to supporting the anastomosis, it also serves as a drain. The Department of Pediatrics at Fudan University generally leaves the stent in place for about 10 days, flushing it with 2 to 3 days before removal. If necessary, pressure measurement and contrast studies can also be performed through the stent. Tube removal is very simple, requiring no anesthesia or pain. In the past 10 years, endoscopic technology has developed rapidly, and laparoscopic ureteropelvic junction reconstruction has also been reported.

　　2. The United States, France, and Hong Kong have accumulated a considerable number of cases, and the surgery time has been significantly shortened, and the success rate has increased significantly, but there is still a gap compared to open surgery. Due to the high difficulty of mini-laparoscopic pyeloplasty, the operation success rate has reached over 99%, and the operation time is generally about 1 hour. Most opinions believe that the widespread implementation of laparoscopic pyeloplasty is still waiting for the right time, especially relying on the further development of robotic laparoscopic technology. In 2002, Boston Children's Hospital reported at the American Pediatric Conference that robotic laparoscopic pyeloplasty had received great attention. The main problem at present is that the instruments and their use costs are too high, making it difficult to popularize. Severe giant hydronephrosis cases are now rare. Since children's kidneys often have considerable compensatory function, it is necessary to be cautious in handling kidneys with massive hydronephrosis and not to make hasty decisions to remove the kidneys. Fudan Children's Hospital first performs nephrostomy on such children to observe the recovery of renal function, and the results are as follows:

　　3. After 6 to 9 months of observation, 32 of the 36 cases of stented kidneys showed renal function recovery, IVU showed renal imaging from non-imaging to imaging, renal function imaging by isotope renal scans increased, all underwent pyeloplasty, and follow-up showed that renal function was maintained in a good state, only 4 cases underwent nephrectomy in the end. The timing of surgery for UPJO-induced hydronephrosis, especially for fetal and neonatal hydronephrosis, has always been controversial. In the early 1980s, there were reports of fetal renal decompression to protect renal function. Now, it is only necessary to use it when there is progressive reduction of amniotic fluid in the case of bilateral fetal hydronephrosis. However, the extent of renal function and pulmonary function recovery after fetal hydronephrosis decompression has not been proven yet. The timing of surgery for children with hydronephrosis after birth is also controversial. Many people believe that early surgery can restore renal function and that the surgery itself is safe and reliable with few complications. On the other hand, many physicians, especially pediatric urologists in the United States, have followed up on children with hydronephrosis for a long time and found that even in newborns with severe hydronephrosis and renal pelvis dilation, renal function has not deteriorated.

　　II. Prognosis

　　Mild cases, those who can be successfully treated, have a good prognosis. Recurrent urinary tract infections, massive renal hydrops leading to progressive renal failure, can affect the prognosis.