Pediatric urinary tract obstruction

　　One, etiology

　　1. The common causes of urethral obstruction include stricture, which can occur at the prepuce orifice, urethral orifice, or urethra. Urethral stricture is often caused by trauma or inflammation, while congenital anterior and posterior urethral valves, and anterior urethral diverticula are important causes of urinary tract obstruction in children. In addition, urethral stones and pelvic or perineal tumors can also cause obstruction.

　　2. The common causes of bladder and bladder neck neurological dysfunction include obstruction, in addition to bladder malformations (such as bladder diverticula, duplicated bladder), stones, and both intravesical and extravesical tumors.

　　3. Ectopic ureteral orifice stenosis, ureteral cyst causing ureteral obstruction, vesicoureteral reflux is more common in children than in adults, while calculi and pelvic tumors infiltrating and compressing are also causes of obstruction.

　　4. The most common renal and renal pelvis lesions are congenital narrowing at the junction of the renal pelvis and ureter, which can also be caused by valve or ectopic blood vessel compression at this site. Poor urine drainage due to renal malformation (such as horseshoe kidney) and renal ectopia can also cause obstruction. Stones and tumors can also lead to obstruction.

　　Second, pathogenesis

　　1. Renal pelvis enlargement and thinning of the renal pelvis wall.

　　2. Renal papillary atrophy (at this time, renal pelvis angiography shows the cup-shaped renal calyces gradually flattening and finally bulging outward).

　　3. The renal parenchyma progressively atrophies and becomes thin. When the renal pelvis is of the intrarenal type, the atrophy of the renal parenchyma appears earlier and is more severe.

　　4. In urinary tract obstruction, when the urine from the renal pelvis and calyces is blocked, part of the fluid may enter the lymphatic vessels and veins (renal pelvis lymphatic reflux, renal pelvis venous reflux), which slightly reduces the pressure within the renal 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 often be restored. Partial obstruction or intermittent obstruction may cause hydronephrosis to reach a very large volume.

　　5. The consequences of urinary tract obstruction vary depending on the location and nature of the obstruction. Upper urinary tract obstruction (obstruction above the kidney and ureter) occurs because the obstruction site is close to the kidney, leading to rapid development of hydronephrosis. However, only the affected side is involved, while the contralateral kidney often presents with compensatory hypertrophy. Therefore, the total renal function remains normal. When there is lower urinary tract obstruction, due to the thickening of the bladder muscle to strengthen the force of urination to overcome the obstruction, the bladder muscle bundles are interlaced. If the duration is long, the bladder mucosa may bulge from the muscle bundles, forming small trabecular pseudo-diverticula. Due to compensatory detrusor overactivity, and hypertrophy and bulging of the bladder neck and trigone tissue, inflammation may further aggravate the bladder neck obstruction. When the enhanced force of urination still cannot overcome the obstruction, residual urine remains after each urination. Generally, the amount of residual urine is proportional to the degree of bladder dysfunction. Subsequently, hydronephrosis and hydroureter may occur, the muscular wall of the ureter thickens, the ureter dilates and extends, forming bends, adhesions, fixation, aggravating the obstruction and the development of hydronephrosis. In lower urinary tract obstruction, although the bladder acts as a buffer area, the development of hydronephrosis is slow, both kidneys are involved, and the total renal function is low. The above describes the process of lower urinary tract obstruction.

　　Acute or chronic urinary retention or pseudo-incontinence may occur, which may be accompanied by hydronephrosis, urinary tract infection, kidney stones, and renal dysfunction. Renal insufficiency may develop after renal dysfunction, manifested as oliguria, even anuria, anemia, hypertension, and so on. In severe urethral infection, periurethral abscess may occur, and abscess rupture may easily form a urethral fistula, resulting in large amounts of urinary salt loss. This may lead to hyperosmotic dehydration, hyperkalemia, hyperchloric acidosis, renal tumor, renal cyst, polycystic kidney, or hydronephrosis. Patients with red cell增多症, spontaneous urinary leakage into the peritoneal cavity, may cause urinary ascites.

　　1, Lower urinary tract symptoms:Urethral stricture, benign prostatic hyperplasia, neurogenic bladder, or bladder tumor invasion into the bladder neck, often manifested as difficulty in urination, frequent urination, thin urinary stream. Depending on the duration and severity of obstruction, acute or chronic urinary retention or pseudo-incontinence may occur.

　　2, Upper urinary tract symptoms:Ureteral stricture, calculus movement, manifested as typical renal colic and hematuria. When hydronephrosis occurs, an abdominal mass can be palpated.

　　3, Manifestations of renal tubular dysfunction:Polyuria, nocturia, thirst; renal tubular reabsorption is impaired, and a large amount of urinary salt is lost, which can cause hyperosmotic dehydration and hyperkalemia-high chloride acidosis.

　　4, Renal insufficiency:Bilateral obstructive lesions can cause renal insufficiency, manifested as oliguria, even anuria, loss of appetite, nausea, vomiting, and weight loss.

　　5, Urinary tract infection:Upper urinary tract infection is manifested as chills, fever, costovertebral angle pain or tenderness, urinary burning, cloudy urine. Lower urinary tract infection is manifested as frequent urination, urgency, and dysuria.

　　6, Renal calculus:Both the cause of obstruction and a complication of urinary tract obstruction, most of the calculi are of guano type (ammonium magnesium phosphate-magnesium carbonate). This is because of the poor flow of urine, easy for bacteria to stay and grow, bacteria containing urease to decompose urea to produce ammonia, neutralize hydrogen ions in urine, increase pH, and cause the precipitation of ammonium magnesium phosphate-magnesium carbonate, forming calculi.

　　7, Hypertension:The pathogenesis of hypertension in obstructive nephropathy is the same as that of other renal实质 hypertension, caused by factors such as the expansion of extracellular fluid volume, the activity of the renin-angiotensin system, and the reduction of vasodilator substances. After the unilateral or bilateral obstruction is relieved, hypertension can be self-resolved.

　　8, True erythrocytosis:Erythrocytosis can be seen in patients with renal tumor, renal cyst, polycystic kidney, or hydronephrosis. The erythrocytosis in obstructive nephropathy is related to the increased synthesis and release of erythropoietin.

　　9, Urinary ascites:In cases of obstructive nephropathy in neonates or infants, spontaneous leakage of urine into the abdominal cavity may occasionally occur, causing urinary ascites. At this time, the creatinine/serum creatinine ratio of ascites becomes 3:1, while the ratio of non-urinary ascites is 1:1, which can be used for differentiation.

　　It is necessary to eliminate lower urinary tract obstruction and infection, such as surgical treatment for urethral stricture and other diseases, to cure urinary tract infection, especially those that decompose urea bacteria, avoid bladder foreign bodies, reduce the occurrence of calculus, and prevent the occurrence of upper urinary tract calculus. It is necessary to eliminate urinary tract obstruction factors, such as actively treating congenital urinary tract anomalies, such as early detection of phimosis and urethral stricture, and timely relief. In cases of trauma and inflammation, inflammation should be controlled in time, and urinary tract infection should be treated thoroughly to prevent the occurrence of urinary tract obstruction. For patients with urinary tract calculus, the following preventive measures should be taken:

　　1. Review once every six months, increase exercise, and those who have been lying in bed for a long time should often turn over.

　　2. Increase water intake for patients with urinary stones. If the urine volume is increased by 50%, the incidence of urinary stones will decrease by 86%, especially before going to bed, more water should be drunk, and the habit of drinking water should be cultivated to keep the daily urine volume not less than 2000-2500ml.

　　3. For patients with calcium oxalate stones, they should eat less spinach, reed, tofu, chocolate, and other foods containing a lot of oxalate or calcium; for patients with calcium urate stones, they should avoid eating meat crabs, spinach, animal internal organs such as liver, brain, and kidney.

　　4. Actively treat various infectious diseases.

　　5. It is not advisable to take sulfonamides and acetazolamide, which are easy to cause urinary crystallization, for a long time.

　　One. Abdominal Plain Film (KUB)

　　Abdominal plain film can see the outline or calcification shadow of the kidney, which can help find positive stones in the kidney and ureter, and understand the size of the kidney.

　　Two. Intravenous Pyelography (IVP)

　　Intravenous pyelography can understand the condition of both kidneys and ureters. This examination reflects not only the anatomical structure of the kidneys, renal calyces, renal pelvis, and ureters, but also roughly reflects renal function. Children commonly use 60% or 76% diatrizoate meglumine, newborns 8-10ml, <6 months 10-12ml, 6-12 months 12-15ml, and in cases of poor renal function, with blood urea nitrogen up to 50mg/dl, not in the case of anuria, the dose can be increased to 2.2ml/kg, with an equal amount of glucose solution infused rapidly, delayed filming, and full urinary tract films taken 60-120 minutes later, which can achieve satisfactory results in most cases. In cases of hydronephrosis, the contrast agent can be seen to remain in the dilated renal pelvis, but when the serum creatinine level is greater than 442μmol/L, the contrast is usually poor, and this examination should not be chosen. If necessary, renal puncture造影 can be used to understand the site of obstruction, but it must be performed on both sides separately to avoid renal failure.

　　Three. Voiding cystourethrogram

　　1. Method: Contrast agent can enter the bladder through three methods:

　　(1) Administer medication intravenously.

　　(2) Insert a catheter into the bladder through the urethra, remove the catheter after medication, and perform voiding cystourethrogram. In infants, the bladder must be pressed by hand to perform voiding cystourethrogram.

　　(3) Inject medication through puncture above the pubic bone.

　　2. Points to note: Pay attention to the following points in any method:

　　(1) Take multiple photographs during urination to observe whether there is vesicoureteral reflux, because vesicoureteral reflux is not always visible during each examination and oblique films should be taken.

　　(2) Fill the bladder to its capacity to estimate whether there are trabeculae, 5-13 years old bladder capacity (ml) = 146ml + 6.1 × age, newborns are 75ml, and children can reach 300ml.

　　(3) After bladder emptying, pay attention to the problem of residual urine. The local film of the urethra is best taken in oblique position, which has the advantage of being able to see the full length of the urethra during urination, and the least radiation dose is received by the scrotum in oblique position.

　　(4) Pay attention to the normal filling defects in cystourethrogram, which are more obvious at the end of urination, and normal seminal colliculus may also have filling defects.

　　4. Ultrasound examination

　　Since this examination is non-invasive and does not depend on renal function, it is the first choice for determining whether there is hydronephrosis in the renal pelvis and calyces. The accuracy is greater than 90%, but the false positive rate of B-ultrasound examination is 8%-26%, and it cannot also determine the location and etiology of obstructive renal disease, which is its disadvantage. B-ultrasound examination can assist in the localization of urinary tract obstruction, such as proximal ureteral obstruction, where the ureter is not dilated, and lower urinary tract obstruction or distal ureteral obstruction with reflux, the ureter appears dilated.

　　5. Radionuclide examination

　　Renal scanning is a good method to understand unilateral renal function. In addition to assisting in the diagnosis of obstruction location, it can also understand the function of each kidney. However, it is not good for the location of obstruction. Urodynamic imaging is less valuable for the diagnosis of obstruction than IVP, but this technique only uses a small amount of radioactive nuclide, without the systemic reaction of contrast agent, and can sensitively show the residual renal function, which is very helpful for understanding whether the patient's renal function can recover or whether the kidney can be preserved. During the renal scan and urodynamic imaging examination, intravenous injection of furosemide 0.3-0.5mg/kg helps to determine whether there is mechanical obstruction.

　　6. CT

　　Especially useful for determining the location and etiology of obstructive renal disease, there is a trend to replace invasive retrograde pyelography. However, due to the high cost of CT and the use of a large amount of contrast agent, it is not the first choice.

　　7. Magnetic Resonance Imaging (MRI)

　　Advantages and disadvantages are similar to CT, magnetic resonance urography (MRU) can clearly show the location of upper urinary tract obstruction. Urodynamic studies combined with X-ray examinations are very important for detecting some problems in lower urinary tract obstruction, such as bladder compliance and coordination between bladder detrusor muscle and urethral sphincter muscle.

　　8. Ureteropelvic urography

　　It is divided into antegrade and retrograde two types. Antegrade urography is used for cases where the above examinations cannot clearly show pathological anatomical changes or poor renal excretion of contrast agent. It is usually performed under the guidance of ultrasound or CT, by percutaneous puncture into the dilated renal pelvis, injection of contrast agent for examination. This technique is not only used for diagnosis but also for treatment. Retrograde ureteropyelography needs to be performed under cystoscopy. Cystoscopy has unique advantages in observing posterior urethral and bladder lesions. Under cystoscopy, retrograde ureteral catheterization is performed, urine is collected from the unilateral or bilateral ureters for analysis, and then contrast agent is injected to show ureteral or ureteropelvic obstruction.

　　Dietary注意事项 for pediatric urinary tract obstruction patients mainly include the following points: 1. Patients should mainly eat light foods and pay attention to dietary regularity. 2. Patients need to eat a balanced diet according to the doctor's advice.

　　1. Treatment

　　1. Treatment principles

　　(1) Aggressive treatment of life-threatening complications: When severe partial or complete urinary tract obstruction occurs, accompanied by pyelonephritis and subsequent gram-negative sepsis, blood and urine bacterial cultures are required, and antibiotics are administered non-enterically; acute renal papillary necrosis secondary to pyelonephritis or obstruction requires emergency surgical treatment, relief of obstruction, such as cystostomy tube insertion or percutaneous nephropyelotomy; dialysis treatment should be started immediately in cases of acute or chronic renal failure with hyperkalemia, acidosis, delirium, coma, or pericarditis.

　　(2) Relief of obstruction and protection of renal function: Timely measures should be taken to reduce intrarenal pressure and prevent further deterioration of renal function.

　　(3) Determine the cause of obstruction and provide special treatment: such as removing the obstructive lesion and reconstructing the continuity of the urinary tract. When obstructive lesions cannot be removed, urinary diversion is performed, such as bladder stenting, nephrotomy, pyelotomy, percutaneous ureterotomy, suprapubic cystotomy, percutaneous ureterointestinal anastomosis, etc.

　　2. Surgical treatment

　　Before surgical treatment of obstructive lesions, a comprehensive evaluation of the etiology, severity, and duration of the obstruction is required. Generally, if obstruction occurs for only a few weeks, renal glomerular filtration rate can gradually recover within 1-4 weeks after surgical treatment. If obstruction has occurred for several months or years, renal function will be irreversibly lost. Appropriate measures should be taken for obstructive lesions at different locations.

　　(1) Renal pelvis obstruction: Patients with costal pain, mass, recurrent infection, and progressive renal damage require renal pelvisoplasty. The postoperative radiological changes in the renal pelvis are not significant, but they can alleviate renal function deterioration and recurrent infection. For patients with renal pelvis dilation, mild ureteropelvic obstruction, and stable renal function, surgery is generally not required.

　　(2) Renal calculi: Stones at the ureteropelvic junction that cause obstruction for more than a few days require surgical stone removal. Large renal pelvis stones with a horn-like shape may not require surgery if there is no obstruction; surgical stone removal is necessary if there is obstruction. During surgery, it is essential to completely remove the stones, and postoperative infection prevention is necessary to avoid recurrence of stones.

　　(3) Ureteral obstruction: Stones are the most common cause of adult ureteral obstruction. Stones less than 5-7mm in diameter can be spontaneously excreted within a few days or weeks. Stones measuring 7-15mm in diameter can be treated with extracorporeal shock wave lithotripsy. 90% of the stones can be shattered, and the fragments can be excreted within 3 months. Ureteral stricture caused by tuberculosis, external compression due to tumor or retroperitoneal fibrosis, requires more extensive surgical treatment, including urinary diversion. Vesicoureteral reflux is a functional obstructive kidney disease, and children require early surgical treatment to correct the reflux. If proteinuria, renal insufficiency, and hypertension are present, surgical treatment is ineffective. Adult vesicoureteral reflux does not require surgical treatment, and surgery is only considered when the patient experiences severe lower back pain during bladder filling or voiding.

　　(4) Lower urinary tract obstruction: Patients with severe urinary difficulty, renal function impairment, and recurrent urinary tract infections may undergo surgical treatment for bladder neck or urethral obstruction. For neurogenic bladder, urinary diversion is required, usually with an ileal conduit.

　　(5) Nephrectomy: Indicated for the treatment of unilateral obstruction. Indications for unilateral nephrectomy include severe obstruction, irreversible damage, and recurrent, difficult-to-treat infections.

　　3. Medical Treatment

　　Maintaining water and electrolyte balance Chronic partial urinary tract obstruction, complete or severe partial bilateral obstruction, postoperative obstruction after surgery can occur, with daily urine output reaching several to tens of liters, with large amounts of sodium, potassium, and bicarbonate lost in the urine. Therefore, it is necessary to increase the intake of sodium and water, and supplement potassium and bicarbonate. 0.45% sodium chloride solution is a relatively suitable replenishing fluid for post-obstructive diuresis. Post-obstructive diuresis must be distinguished from fluid retention, physiological diuresis, and iatrogenic diuresis caused by excessive intravenous fluid replacement.

　　(1) Urinary tract infection: Under urinary tract obstruction, bacteriuria is difficult or impossible to clear, resulting in acute urinary tract infection, accompanied or not accompanied by pyelonephritis, requiring bacterial culture and drug sensitivity testing. Appropriate antibiotics are selected based on the results of drug sensitivity testing. However, it is usually necessary to select antibiotics with high concentrations in the kidneys and urine for treatment before the results of the drug sensitivity test are available, and the course of treatment should be long, usually 3 to 4 weeks. For patients with obstructive kidney disease, the administration of parenteral antibiotics 1 hour before and a few hours after urological instrument examination can reduce the incidence of infection. Long-term prophylactic use of antibiotics for several months or years can reduce the recurrence of infection in patients with chronic obstruction and (or) infectious calculi.

　　(2) Hypertension: Hypertension associated with obstructive kidney disease needs to be treated with antihypertensive drugs, such as calcium channel blockers or angiotensin-converting enzyme inhibitors. If hypertension cannot be controlled by medication, surgery to correct unilateral obstruction can reduce blood pressure.

　　(3) Renal failure: Dialysis treatment is required when chronic renal failure or end-stage renal failure is caused by urinary tract obstruction. End-stage renal failure caused by obstruction is also suitable for kidney transplantation, but it is usually necessary to perform bilateral nephrectomy before surgery to remove the focus of infection.

　　(4) Long-term follow-up: Patients with chronic obstruction or obstruction after surgery need long-term follow-up, including clinical evaluation, urine analysis, clean middle urine bacterial culture, renal function testing, and regular radiographic examination evaluation.

　　II. Prognosis

　　The prognosis is related to the location of the obstruction, the cause of the obstruction, and the speed of occurrence. If the obstruction can be resolved in time and smoothly, the prognosis is good. If the obstruction cannot be resolved through internal and external medical treatment, it often requires long-term drainage.