Chapter 540 ◆ Obstruction of the Urinary Tract 2567 Table 540-1 Types and Causes of Urinary Tract Obstruction LOCATION CAUSE Infundibula Congenital Calculi Inflammatory (tuberculosis) Traumatic Postsurgical Neoplastic Renal pelvis Congenital (infundibulopelvic stenosis) Inflammatory (tuberculosis) Calculi Neoplasia (Wilms tumor, neuroblastoma) Ureteropelvic junction Congenital stenosis Chapter 540 Calculi Neoplasia Inflammatory Obstruction of the Postsurgical Traumatic Ureter Congenital obstructive megaureter Urinary Tract Midureteral structure Jack S. Elder Ureteral ectopia Ureterocele Retrocaval ureter Ureteral fibroepithelial polyps Most childhood obstructive lesions are congenital, although urinary Ureteral valves tract obstruction can be caused by trauma, neoplasia, calculi, inflam- Calculi matory processes, or surgical procedures. Obstructive lesions occur at Postsurgical any level from the urethral meatus to the calyceal infundibula (Table Extrinsic compression 540-1). The pathophysiologic effects of obstruction depend on its level, Neoplasia (neuroblastoma, lymphoma, and other retroperitoneal or pelvic the extent of involvement, the child’s age at onset, and whether it is tumors) acute or chronic. Inflammatory (Crohn disease, chronic granulomatous disease) ETIOLOGY Hematoma, urinoma Ureteral obstruction occurring early in fetal life results in renal dys- Lymphocele plasia, ranging from multicystic kidney, which is associated with ure- Retroperitoneal fibrosis teral or pelvic atresia (see Fig. 537-2 in Chapter 537), to various Bladder outlet and Neurogenic bladder dysfunction degrees of histologic renal cortical dysplasia that are seen with less- urethra (functional obstruction) severe obstruction. Chronic ureteral obstruction in late fetal life or Posterior urethral valves after birth results in dilation of the ureter, renal pelvis, and calyces, Anterior urethral valves with alterations of renal parenchyma ranging from minimal tubular Diverticula changes to dilation of Bowman’s space, glomerular fibrosis, and inter- Urethral strictures (congenital, traumatic, stitial fibrosis. After birth, infections often complicate obstruction and or iatrogenic) can increase renal damage. Urethral atresia Ectopic ureterocele Prenatal screening with ultrasonography may detect antenatal Meatal stenosis (males) hydronephrosis, which is graded by the trimester and the anterior- Calculi posterior diameter of the renal pelvis (Table 540-2); most are mild. Foreign bodies Table 540-3 notes the eventual etiology. Phimosis Extrinsic compression by tumors CLINICAL MANIFESTATIONS Urogenital sinus anomalies Obstruction of the urinary tract generally causes hydronephrosis, which typically is asymptomatic in its early phases. An obstructed kidney secondary to a ureteropelvic junction (UPJ) or ureterovesical junction obstruction can manifest as a unilateral mass or cause upper abdominal or flank pain on the affected side. Pyelonephritis can occur because of urinary stasis. An upper urinary tract stone can occur, Table 540-2 Definition of Antenatal Hydronephrosis by causing abdominal and flank pain and hematuria. With bladder outlet Anterior-Posterior Diameter obstruction, the urinary stream may be weak; urinary tract infection (UTI; see Chapter 538) is common. Many of these lesions are identified DEGREE OF by antenatal ultrasonography; an abnormality involving the genitouri- ANTENATAL SECOND THIRD nary tract is suspected in as many as 1 in 100 fetuses. HYDRONEPHROSIS TRIMESTER TRIMESTER Obstructive renal insufficiency can manifest itself by failure to Mild 4 to <7 mm 7 to <9 mm thrive, vomiting, diarrhea, or other nonspecific signs and symptoms. Moderate 7 to ≤10 mm 9 to ≤15 mm In older children, infravesical obstruction can be associated with over- flow urinary incontinence or a poor urine stream. Acute ureteral Severe >10 mm >15 mm obstruction causes flank or abdominal pain; there may be nausea and From Nguyen HT, Herndon CDA, Cooper C, et al: The society for fetal urology vomiting. Chronic ureteral obstruction can be silent or can cause vague consensus statement on the evaluation and management of antenatal abdominal or typical flank pain with increased fluid intake. hydronephrosis. J Pediatr Urol 6:212–231, 2010, Table 2, p. 215. 2568 Part XXIV ◆ Urologic Disorders in Infants and Children parenchymal thickness, and presence or absence of ureteral dilation DIAGNOSIS should be assessed. Most pediatric urologists grade the severity of Urinary tract obstruction may be diagnosed prenatally by ultrasonog- hydronephrosis from 1-4 using the Society for Fetal Urology grading raphy, which typically shows hydronephrosis and occasionally a dis- scale (Table 540-4), whereas pediatric radiologists generally utilize the tended bladder. More complete evaluation, including imaging studies, adjectives mild, moderate, and severe. The clinician should ascertain should be undertaken in these children in the neonatal period. that the contralateral kidney is normal, and the bladder should be Urinary tract obstruction is often silent. In the newborn infant, a imaged to see whether the bladder wall is thickened, the lower ureter palpable abdominal mass most commonly is a hydronephrotic or mul- is dilated, and bladder emptying is complete. In acute or intermittent ticystic dysplastic kidney. With posterior urethral valves, which is an obstruction, the dilation of the collecting system may be minimal and infravesical obstructive lesion in boys, a walnut-sized mass represent- ultrasonography may be misleading. ing the bladder is palpable just above the pubic symphysis. A patent draining urachus also can suggest urethral obstruction. Urinary Voiding Cystourethrogram ascites in the newborn usually is caused by renal or bladder urinary In neonates and infants with congenital grade 3 or 4 hydronephrosis extravasation secondary to posterior urethral valves. Infection and and in any child with ureteral dilation, a contrast voiding cystoure- sepsis may be the first indications of an obstructive lesion of the throgram (VCUG) should be obtained, because the dilation is second- urinary tract. The combination of infection and obstruction poses a ary to vesicoureteral reflux in 15% of cases. In boys, the VCUG also is serious threat to infants and children and generally requires parenteral performed to rule out urethral obstruction, particularly in cases of administration of antibiotics and drainage of the obstructed kidney. suspected posterior urethral valves. In older children, the urinary flow Renal ultrasonography should be performed in all children during the rate can be measured noninvasively with a urinary flowmeter; decreased acute stage of an initial febrile UTI. flow with a normal bladder contraction suggests infravesical obstruc- tion (e.g., posterior urethral valves, urethral stricture). When the Imaging Studies urethra cannot be catheterized to obtain a VCUG, the clinician should Renal Ultrasonography suspect a urethral stricture or an obstructive urethral lesion. Retro- Hydronephrosis is the most common characteristic of obstruction grade urethrography with contrast medium injected into the urethral (Fig. 540-1). Upper urinary tract dilation is not diagnostic of obstruc- meatus helps delineate the anatomy of the urethral obstruction. tion and often persists after surgical correction of a significant obstruc- tive lesion. Dilation can result from vesicoureteral reflux, or it may be Radioisotope Studies a manifestation of abnormal development of the urinary tract, even Renal scintigraphy is used to assess renal anatomy and function. The when there is no obstruction. Renal length, degree of caliectasis and 2 most commonly used radiopharmaceuticals are mercaptoacetyl tri- glycine (MAG-3) and technetium-99m-labeled dimercaptosuccinic acid. MAG-3, which is excreted by renal tubular secretion, is used to Table 540-3 The Etiology of Antenatal Hydronephrosis assess differential renal function, and when furosemide is adminis- tered, drainage also can be measured. An alternative to MAG-3 is ETIOLOGY INCIDENCE diethylene tetrapentaacetic acid, which is cleared by glomerular filtra- Transient hydronephrosis 41-88% tion. The background activity of diethylene tetrapentaacetic acid is much higher than that of MAG-3. Dimercaptosuccinic acid is a renal Ureteropelvic junction obstruction 10-30% cortical imaging agent and is used to assess differential renal function Vesicoureteral reflux 10-20% and to demonstrate whether renal scarring is present. It is used infre- Ureterovesical junction obstruction/megaureters 5-10% quently in children with obstructive uropathy. In a MAG-3 diuretic renogram, a small dose of technetium-labeled Multicystic dysplastic kidney 4-6% MAG-3 is injected intravenously (Figs. 540-2 and 540-3). During the Posterior urethral valve/urethral atresia 1-2% 1st 2-3 min, renal parenchymal uptake is analyzed and compared, allowing computation of differential renal function. Subsequently, Ureterocele/ectopic ureter/duplex system 5-7% Others: prune belly syndrome, cystic kidney disease, Uncommon congenital ureteric strictures, and megalourethra Table 540-4 Society for Fetal Urology Grading System From Nguyen HT, Herndon CDA, Cooper C, et al: The society for fetal urology for Hydronephrosis consensus statement on the evaluation and management of antenatal hydronephrosis. J Pediatr Urol 6:212–231, 2010, Table 5, p. 217. Renal Image RENAL GRADE OF CENTRAL RENAL PARENCHYMAL HYDRONEPHROSIS COMPLEX THICKNESS 0 Intact Normal 1 Slight splitting Normal 2 Evident splitting, Normal