The causes of pediatric hydronephrosis are divided into primary and secondary. Secondary refers to obstruction secondary to severe vesicoureteral reflux, lower urinary tract obstruction, inflammation, traumatic stricture, etc. Primary refers to primary congenital ureteropelvic junction obstruction (UPJO), which is a common cause of pediatric hydronephrosis.
Congenital ureteropelvic junction obstruction can be seen in all age groups, with about 25% seen within the first year of life and more than 80% of fetal dilatation of the renal collecting system being ureteropelvic junction obstruction. The ratio of males to females is 5:1, with the left side being more common. Beijing Children’s Hospital reported a group of 497 cases, 21% were diagnosed within 1 year of age, 10% were diagnosed above 10 years of age, 293 cases on the left side, 112 cases on the right side, and 92 cases bilaterally.
[Etiology
The etiology of renal pelvic ureteral junction obstruction is commonly as follows.
1, pelvic ureteral junction stenosis More than 90% of pelvic ureteral junction obstruction is pelvic ureteral junction stenosis, the stenotic segment is about 2 cm long, part of it is 3-4 cm long, sometimes multiple stenoses are seen, individual stenoses are only a few millimeters long, and full-length stenosis has also been reported.
2.High ureteral opening High ureteral opening leads to poor drainage of the renal pelvis, sometimes combined with ureteral stenosis or tortuosity.
3.Pelvic ureteral junction flap There is a fold in the pelvic junction containing muscle to form a flap causing obstruction.
4.Polyps in the pelvic ureteral junction Polyps are sea anemone like and cause obstruction in the junction.
5.Pelvic ureteral junction compression The vagus vessels or collateral vessels from the renal artery trunk or directly from the abdominal aorta supplying the lower pole of the kidney cross the ureter and cause it to be compressed.
6.Primary ureteral power obstruction Due to abnormal ureteral or renal pelvis peristaltic function.
Pathology and pathogenesis
In recent years, ultrastructural observation of the pelvic ureteral junction by electron microscopy revealed abnormal smooth muscle cells in the pelvic ureteral junction. The smooth muscle cells of the normal pelvic ureter were arranged in bundles and closely connected. In the proximal part of the pelvic calyx, there is a special type of smooth muscle cell that is capable of receiving urine stimulation and generating electrical activity called pacemaker cells. The electrical activity generated by the pacemaker cells is transmitted from top to bottom, causing peristalsis of the renal pelvis and ureter to send urine downward. In stenosis of the ureteropelvic junction, the smooth muscle cells are surrounded by an abnormally large number of collagen fibers and stroma and lose their normal alignment, blocking intercellular electrical activity and impairing peristalsis. Such pathological changes are also present in the dilated renal pelvic wall. It has also been suggested that the lack of myofilaments and dense bodies within the smooth muscle cells of the stenotic segment leads to contractile dysfunction of the smooth muscle cells. In addition, the cause of stenosis may be related to local developmental arrest due to fetal vascular compression, incomplete ureteral tubularization, and interruption of circumferential muscle development in the stenotic segment.
Clinical manifestations
The early appearance of symptoms of congenital obstructive hydronephrosis of the ureteropelvic junction is related to the degree of obstruction, and the more severe the obstruction, the earlier the symptoms appear. The main manifestations are
1, abdominal masses More than half of newborns and infants are seen with asymptomatic masses, and 75% of children can find the masses. The mass is smooth, non-pressure, moderately tense, occasionally fluctuating, and in some cases there is a change in the size of the mass, such as sudden onset of abdominal pain with abdominal mass, and after a lot of urination the mass shrinks until it disappears, which is an important diagnostic basis.
2. Intermittent pain in the lower back and abdomen The vast majority of children can state epigastric or periumbilical pain. Older children can clearly point out that the pain comes from the affected lumbar region. With nausea and vomiting, it is often misdiagnosed as gastrointestinal disease.
Hematuria is caused by rupture of the renal medullary vessels due to high pressure in the renal pelvis or by minor abdominal trauma or urinary tract infection or stones. The incidence is 10%-30%, and it is visual or microscopic hematuria.
4, urinary tract infection The incidence is less than 5%, once it occurs, it often has high fever, chills and sepsis and other symptoms of systemic toxicity.
5.Hypertension The dilated collecting system compresses the blood vessels in the kidney, leading to renal ischemia, which reflexively causes an increase in renin secretion, causing an increase in blood pressure.
6, renal rupture The dilated renal pelvis is ruptured by external force, manifesting as acute abdomen.
7.Uremia Bilateral hydronephrosis or unilateral hydronephrosis may have renal insufficiency in the late stage. The child has slow growth, growth retardation, feeding difficulties or anorexia.
【Diagnosis
Ultrasound and intravenous pyelogram (IVP) are the preferred diagnostic methods.
IVP can show dilated pelvis and calyces, and the contrast agent abruptly terminates at the pelvic-ureteral junction, and the ureter is not visualized. Delayed radiographs delayed to 60, 120 or even 180 minutes can improve the diagnostic rate. ultrasonography showing a dilated renal pelvis but not a dilated ureter is diagnostic. Combining with IVP can improve the confirmation rate. IVP and ultrasound are sometimes difficult to diagnose due to severely impaired renal function and intestinal pneumatization in children. Shandong Provincial Hospital uses 3D CT urography (CTU), which can clearly show the dilated pelvis and calyces and the site of obstruction, with a 100% diagnostic compliance rate. Isotope kidney scan can understand the impaired renal function and provide a basis for surgical treatment.
【Treatment
Fetal ultrasonography detects hydronephrosis and should be reviewed 1-3 weeks after birth. Mild dilatation of the renal pelvis and calyces can be followed up by ultrasound. Progressive dilatation or comorbidities such as abdominal pain, infection, and stones should be operated promptly.
Disconnected pyeloureteroplasty (Anderson-Hynes proccedure) is the most commonly used surgical procedure. It has the best outcome because the abnormal development of the myocytes is removed, and the success rate is over 95%. The anastomosis should be wide, low, funnel-shaped, with tight and tension-free sutures, and the anastomosis should be smooth and free of folding and distortion.
If there is no leakage 3-5 days after surgery, the renal fossa drainage tube can be removed and the ureteral stent tube can be removed 7-10 days after surgery. If the urine stains blue within 1 hour and gradually becomes lighter to clear within 24 hours, the anastomosis is shown to be patent, and if there is no fever or abdominal pain after 48-72 hours of continuous clamping, the renal or pyelostomy tube can be removed. After removal of the stent tube, pelvic urography through the nephrostomy tube is more helpful to understand whether the anastomosis is patent and whether there is urinary extravasation. Ultrasound, IVP or renal nucleus scan is feasible for review 3-6 months after surgery to understand the morphology and function of the kidney.
Regarding nephrectomy, through postoperative renal nuclear scan and ultrasound follow-up observation, it is generally believed that the function of the affected kidney should be preserved when it is above 30%. Because the renal function can be expected to improve after the obstruction is lifted, the function and morphology of the affected kidney improved significantly in 6 months after surgery, and the thickness and area of the renal parenchyma gradually recovered and grew after surgery, with the most obvious increase in 3-6 months and slow growth afterwards. Nephrectomy should be considered only when the thickness of renal parenchyma is below 2 mm, the specimen seen by pathology has no kidney unit, and the kidney function is below 10%. A large hydronephrosis, IVP without visualization, and a significant decrease in renal function on nuclear scan are not absolute indications for nephrectomy, especially if the hydronephrosis is bilateral. Bilateral hydronephrosis is often one light and one heavy. Generally, pyeloplasty is performed first on the side with better renal function, or pyeloplasty can be performed at the same time, and nephrectomy should not be performed easily to avoid acute renal insufficiency.