Cause: Embryologic anomaly that appears related to developmental anomaly of ureteric bud (Development 1996;122:1919). Generally thought to result from failure of the ureteral bud to come into contact with the metanephric blastema. May also be related to regression of multicystic dysplastic kidney (MCDK) (J Urol 1993;150:793) (see 8.4).

Epidem: Most common congenital urinary malformation (Am J Kidney Dis 2002;39:689). Bilateral renal agenesis is rare and occurs in 1 in 4000 births. Unilateral renal agenesis occurs in 1 in 1000-1500 births (Am J Dis Child 1974;127:17; Mayo Clin Proc 1966;41:538). Males more than females.

Pathophys: For nl renal development a nl ureteral bud must penetrate a nl metanephric blastema. Associated genital anomalies more common in females and include uterus didelphys and vaginal agenesis. In males, hypospadias, undescended testicles (UDTs), vasal anomalies, and cysts of seminal vesicle and prostate have been noted (Int Urol Nephrol 1988;20:29). Other associated anomalies include chromosomal syndromes (trisomy 10) and cardiac, skeletal, gi, and respiratory (Obstet Gynecol 1997;90:26; Pediatr Nephrol 1996; 10: 498; Adv Pediatr 1995;42:575; J Med Genet 1995;21:153; Am J Dis Child 1974; 127: 17). Gu anomalies seen in up to 48% and include
vesicoureteral reflux (VUR) (28%), ureterovesical junction (UVJ) obstruction (11%), and ureteropelvic junction obstruction (UPJO) (7%) (J Urol 1999; 162: 1081). Increased association between maternal diabetes and renal agenesis; prevalence odds ratio of 14.8, 95% CI, 3.5-62.1 (Diabetic Med 2005;22:693). Unilateral renal agenesis noted in 28% pts with Mayer-Rokitansky-Kuster-Hauser syndrome (Am J Med Genet 2005;135:314).

Sx: Asx if unilateral. If bilateral, virtually fatal from respiratory compromise.

Si: Ipsilateral nonpalpable vas deferens and other associated genital anomalies

Crs: Renal failure and respiratory distress if bilateral. With unilateral renal agenesis, may be at increased risk of proteinuria, HT, renal insufficiency in the long term (Ped Nephrol 1992;6:412).

Cmplc: Unilateral renal agenesis predisposes women with uterine abnormalities to preeclampsia (Eur J Obstet Gynecol Reprod Biol 2004;114:39). Approximately 2/3 of seminal vesicle cysts are associated with ipsilateral renal agenesis because both the ureteral bud and the seminal vesicles originate from the mesonephric (Wolffian) duct (Urology 1986;28:313).

Diff Dx: Ectopic kidney (see 8.2) and involuted MCDK.

Lab: UA

Xray: DMSA scan to r/o ectopic kidney and VCUG to r/o contralateral VUR

Rx: Rx associated congenital anomalies. With unilateral renal agenesis, f/u of BP, UA, and renal function indicated over the long term.

Cause: Failure of kidney to reach nl location. Crossed ectopia thought to be related to overbending and rotation of the caudal end of the developing embryo (Birth Defects 1977;13:327).

Epidem: Incidence is 1 in 100 autopsies (J Urol 1994;151:1660); in screening studies, incidence is 1 in 500 pts (Pediatrics 1989; 84:1086); L more than R; may be ectopic to pelvic, iliac, abdominal, thoracic, contralateral, or crossed locations. Bilateral in 10% (Mayo Clin Proc 1971;46:461). Most (90%) crossed ectopic kidneys are fused to ipsilateral kidney; solitary crossed ectopia usually involves L kidney migrating to R side with absence of R kidney. Males more than females.

Pathophys: Ureter enters into nl side of the bladder. Most ectopic kidneys lie inferior to nl position. Familial inheritance of crossed fused renal ectopia reported (Pediatr Nephrol 2001; 16:269).

Crs: Increased incidence of hydronephrosis and calculi (J Urol 1994;151:1660). May be at increased risk for injury from blunt trauma.

Cmplc: High incidence of associated urologic anomalies including VUR (most common), renal dysplasia, cryptorchidism, hypospadias, and other genital anomalies (J Urol 2004;172:1757). Skeletal anomalies present in 50% with solitary crossed renal ectopia and 40% with genital anomalies (Urology 1991;38:556). Rarely, adrenal gland is absent or abnormally located.

Si/Sx: Asx; if obstructed, may have pain atypical for renal colic

Xray: Often identified during radiographic evaluation for other medical problems or on prenatal ultrasound

Rx: Not necessary unless obstruction or calculus

Cause: Most common renal fusion abnormality

Epidem: Incidence is 1 in 400 (N Engl J Med 1959;261:684). Male-to-female ratio is 2:1; > 90% cases lower poles of two kidneys connected by a parenchymatous or fibrous isthmus (J Ultrasound Med
2000;19:27). Seen in 20% pts with trisomy and up to 60% females with Turner’s syndrome (Pediatrics 1988;82:852).

Pathophys: Originates at 2- to 6- wk gestation when inferior portion of metanephric blastema fuses before ascent and rotation of the kidneys. The isthmus encroaches on the inferior mesenteric artery, which prevents further migration. Pelvis and ureters usually anteriorly located, crossing ventral to the isthmus.

Sx: One-third asx; may present with vague abdominal pain

Si: Rarely a palpable midline mass

Crs: High-incidence congenital anomalies include skeletal, CV, CNS, VUR, or UPJO in > 50% (J Urol 2002;167:2566). About 24% have UPJO (J Urol 2002;167:2566).

Cmplc: Hydronephrosis, infection, calculus; increased incidence of Wilms’ tumor (2 X) (J Urol 1985;133:1002)

Lab: If sx, obtain UA and c + s to r/o UTI.

Xray: Typical radiographic features include caudal renal position, malrotation with reversed longitudinal axis of each kidney, and anterior extrarenal pelvis. Isthmus usually identified on CT (AJR 1998;171:829).

Cause: Exact cause unknown. Proposed etiologies include atresia of the ureter or renal pelvis, which leads to severe hydronephrosis (Semin Roentgenol 1975;10:113) and failure of union of ureteric bud and metanephric blastema, leading to cystic dilation (Arch Klin Chir 1894;48:343).

Epidem: Incidence of 1:4300 live newborns (J Urol 1988;140:1231). L more than R. One of the most common causes of abdominal mass in infants. Contralateral UPJO in 3-12% infants with MCDK. Contralateral VUR in 18-43% (J Pediatr 1992;121:65). More commonly identified in utero on prenatal US. May be bilateral in
19-34% (Radiology 1986;161:27). Increased risk of MCDK in infants of mothers with gestational or pregestational diabetes (Eur J Pediatr 2002;161:634).

Pathophys: Ureteral and/or pelvic atresia leads to severe hydronephrosis. Renal vessels small or absent. Kidney typically has little (≤ 10%) or no function on functional renal scan (DMSA).

Sx: Often asx. If kidney markedly enlarged, may cause respiratory compromise.

Si: Abdominal mass. HT in 0-20% (Eur J Pediatr 2001;160:78).

Crs: Typically involutes over time, with complete involution in 20-37% and partial involution in 49-67% (Ren Fail 2005;27:189); BJU Int 2005;95:868). Rarely, renal size will increase. Rare potential for malignant degeneration (Wilms’ tumor, embryonal cell tumor, renal cell carcinoma) in MCDKs.

Cmplc: HT, respiratory insufficiency, malignancy

Diff Dx: UPJO

Lab: If both sides appear to be affected, check serum BUN and creatinine.

Xray: US shows collection of renal cysts of various sizes, no dominant central or medial cyst, little if any identifiable renal parenchyma. US usually dx (Pediatr Nephrol 2000;14:1098). DMSA scan shows little if any ipsilateral renal function. VCUG should be obtained to r/o contralateral VUR.

Rx: In absence of respiratory compromise or HT, follow with serial US studies until kidney has completely involuted. If contralateral, VUR, routine management of VUR.

Cause: May be primary or secondary, related to intrinsic or extrinsic pathology. Exact cause not fully understood but may be related
to incomplete canalization of ureter during development. Histopathologic evaluation of UPJ reveals increased collagen and decreased smooth muscle. Smooth muscle is disoriented, and there are more circular smooth muscle fibers than longitudinal fibers (J Urol 1976;116:725). Less common intrinsic causes include valvular mucosal folds (J Urol 1980;123:742), persistent fetal convolutions (J Urol 1979;122:251), and proximal ureteral polyps (J Urol 1981;126:796). Extrinsic obstruction may be secondary to aberrant lower pole vessels. Secondary UPJO may occur with high-grade VUR (AJR 1983;140:231).

Epidem: Incidence is 5 per 100,000. Male-to-female ratio: 3-4:1. Sporadic occurrence but familial tendency described (BJU 1985;57:365). L more than R. About 10% coexisting VUR (Urol Clin North Am 1998;25:173). Bilateral UPJOs diagnosed in 21-36% of cases of neonatally detected UPJOs (J Urol 1988;140:1216). Half of children have other urologic anomalies (Radiol Clin North Am 1977;15:49).

Pathophys: Histopathologic alterations at UPJ result in inefficient propulsion of urine through UPJ and dilation of the renal pelvis and calyces. Ureter may have a high insertion on renal pelvis, whether a primary abnormality or secondary to the pelvic dilation or there may be a crossing lower pole vessel.

Sx: Intermittent abdominal/flank pain in older children and adults; often asx in infants

Si: Palpable flank mass that transilluminates in children and infants; hematuria, failure to thrive, feeding difficulties, UTI, HT

Crs: If obstruction is significant and remains untreated, may lead to decreased renal function, increased risk of stone formation and infection, renin-mediated HT

Diff Dx: Obstruction due to other causes such as a retroperitoneal mass, UVJ obstruction, nonobstructive dilation, and MCDK

Lab: UA, c + s. If bilateral, serum BUN and creatinine.