A. CAKUT Definition and Epidemiology

Definition: Congenital Anomalies of the Kidney and Urinary Tract encompass a spectrum of structural malformations affecting the kidney, ureter, bladder, or urethra, resulting from disruption of nephrogenesis or urogenital development.

Incidence and Prevalence: - Overall incidence: 1 in 300-500 live births (approximately 200,000 cases per year in the United States) - Represents 30-40% of all congenital anomalies detected prenatally - Leading cause of ESRD in children (40-50% of pediatric ESRD due to congenital anomalies) - Accounts for $1.2 billion in annual healthcare expenditures in pediatric nephrology

Genetic Contributions: - Monogenic mutations (PAX8, GDNF, RET, ROBO2) account for 10-15% of cases - Chromosomal abnormalities (Down, Turner, Potter syndromes) associated with CAKUT in 30-40% - Multifactorial inheritance with environmental factors - Familial clustering in 5-10% of cases (autosomal dominant inheritance pattern common)

B. Developmental Embryology

Timeline: - Week 5: Ureteric bud (Wolffian duct) emerges from mesonephric duct caudal to mesonephros - Weeks 5-13: Ureteric bud undergoes branching morphogenesis, forming ureter, renal pelvis, major calyces, minor calyces, collecting ducts - Weeks 5-35: Mesenchymal-epithelial transition (MET) in metanephric mesenchyme; condensation around collecting duct tips - Weeks 8-34: Nephron formation occurs as collecting ducts branch and induce nephron formation in adjacent mesenchyme - Week 34-36: Nephrogenesis completes; approximately 1 million nephrons per kidney

Key Signaling Molecules: - GDNF (Glial-derived neurotrophic factor): Secreted by metanephric mesenchyme; signals to ureteric bud via RET tyrosine kinase receptor - RET (REarranged during Transfection): Proto-oncogene; receptor for GDNF; essential for ureteric bud outgrowth - PAX8 (Paired box gene 8): Transcription factor; regulates development of both kidney and thyroid - SIX1/SIX2: Control mesenchymal progenitor maintenance and differentiation - WNT signaling: Regulates both nephrogenesis and ureteric bud development - FGF signaling: Regulates ureteric bud branching and mesenchyme differentiation

Disruption of Development Leads to CAKUT: - Reduced/absent GDNF or RET signaling → oligonephronia, dysplasia, agenesis - Misdirection of ureteric bud → ectopic kidney, duplex collecting system, VUR - Obstruction of ureteric outflow → hydronephrosis, hydroureter, secondary dysplasia

C. CAKUT Classification (International Nomenclature, ISN 2014)

Major Categories:

A. Renal Agenesis

Unilateral Renal Agenesis (ULRA)

Epidemiology: - Incidence: 1 in 1,000-2,000 live births - Often incidental finding on imaging for other indications - No significant impact on renal function; single kidney can achieve normal adult GFR through compensatory hypertrophy

Pathophysiology: - Complete failure of ureteric bud induction or early regression - Ipsilateral ureteral agenesis (typically) - Contralateral kidney often normal or with increased size due to compensatory growth

Clinical Presentation: - Majority asymptomatic; incidental imaging finding - May be detected on prenatal ultrasound - No renal dysfunction (serum creatinine and GFR normal) - Risk: Increased proteinuria over time from hyperfiltration; slightly increased risk of hypertension in adulthood

Diagnosis: - Ultrasound: Absent kidney; normal contralateral kidney (often enlarged) - Renal scintigraphy: No uptake ipsilateral; normal function contralateral - CT or MRI: Confirms absent renal tissue; no ectopic kidney

Management: - No treatment required; normal renal function expected - Counseling: Avoid contact sports, NSAIDs if possible; avoid dehydration - Monitor: Annual blood pressure, urinalysis, serum creatinine - Avoid nephrotoxic drugs - Genetic counseling: 5-10% risk of CAKUT in siblings; 4-5% risk in offspring - Prenatal counseling for future pregnancies: Ultrasound screening at 20 weeks

Bilateral Renal Agenesis (BLRA)

Epidemiology: - Incidence: 1 in 4,000-7,000 live births - Incompatible with postnatal life; lethal in utero if severe

Pathophysiology: - Complete bilateral failure of ureteric bud induction - Associated with severe bilateral oligohydramnios (due to absent fetal urine production) - Potter sequence: Characteristic facial features (low-set ears, micrognathia, beak nose), limb deformities, severe pulmonary hypoplasia

Prenatal Diagnosis: - Maternal ultrasound: Absent amniotic fluid (severe oligohydramnios) + bilateral absent kidneys - Fetal imaging: No bladder filling (no fetal urine production)

Management: - Antenatal counseling regarding poor prognosis - Perinatal palliative care discussions with family - Birth planning: Expected neonatal death from pulmonary hypoplasia - Offers of comfort care, organ donation (in selected cases)

B. Renal Hypoplasia and Dysplasia

Definitions:

Hypoplasia: - Structurally normal kidney with reduced number of nephrons (oligonephronia) - Normal calyceal architecture; normal echogenicity on ultrasound - Usually detected only through functional studies (reduced GFR for kidney size)

Dysplasia: - Abnormal kidney development with primitive metanephric tissue, disorganized calyces, fibrosis, and often cystic dilation - Histologic findings: Smooth muscle hyperplasia, disorganized glomeruli, primitive ducts - May be diffuse or segmental

Hypodysplasia (Combined Hypoplasia + Dysplasia): - Most common form of renal underdevelopment - Reduced nephron number with abnormal development - Accounts for 30-40% of congenital renal insufficiency in children

Epidemiology: - Combined incidence: 1 in 800-1,000 live births - Accounts for 10-15% of pediatric ESRD cases

Etiology: - Genetic: Mutations in GDNF, RET, PAX8, SIX1/SIX2, ROBO2 - Maternal teratogens: ACE inhibitors/ARBs (especially 2nd/3rd trimester), NSAIDs, cocaine, maternal diabetes - Obstructive: Secondary dysplasia from chronic prenatal obstruction (e.g., PUV, severe UPJ obstruction) - Syndromic: Associated with chromosomal abnormalities or genetic syndromes

Clinical Presentation: - Often asymptomatic; detected on prenatal ultrasound or during workup for renal insufficiency - Some present with acute kidney injury if bilateral involvement - Progressive renal failure if bilateral or if single kidney severely affected - May have growth failure, hypertension, anemia (if significant renal disease)

Diagnosis:

Imaging Findings: - Ultrasound: Small kidney(s) with increased echogenicity; irregular contour; may have cystic spaces - Renal scintigraphy (DMSA): Reduced tracer uptake; segmental areas of photopenia if dysplastic - MRI: Better defines cystic vs. non-cystic dysplasia; assesses for associated VUR or upper tract obstruction

Renal Biopsy (if diagnosis uncertain): - Histology shows: Primitive tubules, smooth muscle proliferation, fibrosis, disorganized architecture - Immunofluorescence: Nonspecific (no immune deposits)

Progression: - Bilateral symmetric hypodysplasia: Progressive loss of renal function; may reach ESRD by adulthood - Unilateral: Generally benign if contralateral kidney normal

Management: - Conservative: Serial renal function monitoring; management of complications (hypertension, anemia, growth failure) - Nutritional: Adequate calories and protein for growth; may require nutritionist support - Pharmacologic: ACE inhibitor or ARB to reduce proteinuria and slow progression - Monitoring: Blood pressure, urinalysis, serum creatinine every 3-6 months - RRT: Dialysis or transplantation if ESRD develops

A. Horseshoe Kidney

Epidemiology: - Incidence: 1 in 400-600 live births - Most common renal fusion anomaly - No gender predominance - Associated with Turner syndrome (5-10%), Down syndrome, and other chromosomal abnormalities

Embryology: - Kidneys undergo normal ascent from pelvis but fuse at lower poles during ascent (typically at L5 level) - Isthmus of renal parenchyma or fibrous tissue connects the two kidneys - Anomalous blood supply common (multiple renal arteries and veins) - Ureteropelvic junction often malpositioned anteriorly

Pathophysiology: - Usually asymptomatic and incidental finding - Risk of obstruction at UPJ (from anomalous vessels, fibrous tissue, or abnormal ureteral course) - Increased risk of UTI (urinary stasis in lower-pole calyces) - Increased risk of trauma (lower, more anterior position) - Slightly elevated risk of renal malignancy (increased with other CAKUT)

Clinical Presentation: - Often asymptomatic; discovered incidentally on imaging - May present with flank pain (if obstruction develops) - May present with fever (UTI) - Recurrent UTI in some cases

Diagnosis: - Ultrasound: Isthmus connecting lower poles; abnormal kidney shape - CT or MRI: Excellent anatomic detail; shows vascular anatomy - Renal scintigraphy: Reduced function if obstruction present - IVU (less commonly used): Shows characteristic “tent-like” appearance with medial deviation of ureters

Management: - No treatment if asymptomatic (majority of cases) - Conservative: Periodic imaging (ultrasound or renal scintigraphy) to assess for obstruction - Surgical: Pyeloplasty for symptomatic UPJ obstruction - Avoid: Contact sports, excessive abdominal trauma (relative contraindication given anterior position) - Imaging for evaluation: If recurrent UTI, use renal scintigraphy to assess for obstruction - Anesthesia consideration: Abnormal vascular anatomy; communicate with anesthesia if surgery needed

B. Ectopic Kidney

Epidemiology: - Incidence: 1 in 900 live births - Kidneys fail to migrate normally from sacral region

Classification:

Thoracic Ectopia (rare): - Kidney ascends above diaphragm - Usually discovered incidentally on chest imaging - No functional impairment; no treatment needed - Risk: Retroperitoneal masses can compress lung tissue or cause cardiac compromise if large

Lumbar Ectopia: - Kidney remains lateral to normal position on iliac wing - Usually asymptomatic; incidental finding - May have anomalous blood supply and ureter - No specific treatment needed unless obstruction develops

Pelvic Ectopia: - Kidney remains in pelvis; does not ascend - May have anomalous blood supply (hypogastric artery) - Increased risk of obstruction, UTI, and trauma - May cause urinary retention or dysmenorrhea if large

Crossed Fused Ectopia: - Both kidneys on same side; fused at mid-pole - Three patterns: Type I (inferior fused), Type II (superior fused), Type III (side-by-side) - Increased risk of obstruction and UTI

Clinical Presentation: - Usually asymptomatic - May present with flank pain, recurrent UTI, hematuria - Rarely: acute abdomen from torsion of ectopic kidney

Diagnosis: - Ultrasound or CT: Shows ectopic location; assess for hydronephrosis - Renal scintigraphy: Confirms functional tissue; assesses differential renal function - IVU or MRI: Detailed anatomy; important if surgery planned

Management: - Asymptomatic: Observation; periodic imaging (ultrasound q 1-2 years) - Symptomatic obstruction: Pyeloplasty or nephrostomy if severe - Recurrent UTI: Consider prophylactic antibiotics; imaging to assess for obstruction - Surgical planning: Communicate anomalous vascular anatomy to surgeon

A. Duplex Collecting System (Duplicated Ureter)

Epidemiology: - Incidence: 1 in 125-600 live births (unilateral duplications more common) - Bilateral in 5-10% of cases - Female predominance (2:1 ratio)

Classification:

Partial Duplications: - Y-shaped ureter: Divergence occurs below pelvic brim; single ureter continues distally - Most common form (60-70% of duplications) - Usually asymptomatic; discovered incidentally

Complete Duplications: - Two separate ureters drain respective renal halves; both reach bladder - Classic teaching: Superior pole ureter has abnormally low bladder insertion (Weigert-Meyer rule in 85% of cases) and is at risk for ectopic insertion and obstruction - Inferior pole ureter has higher (more normal) insertion but predisposed to VUR - Differential function: Usually preserved; 50% of renal function to each collecting system in most cases

Ectopic Ureter: - Ureteral orifice drains outside the bladder (below internal urethral sphincter) - More common in females; may lead to continuous urinary leakage - In males: May insert into posterior urethra or prostate (usually dry, but may cause symptoms)

Clinical Presentation:

Asymptomatic (Majority): - Discovered incidentally on prenatal ultrasound - Detected during imaging for other indications

Symptomatic: - Recurrent UTI: Particularly if upper pole ureter obstructed - Vesicoureteral reflux: Lower pole ureter more susceptible to VUR (50% of cases) - Flank pain: From hydronephrosis of obstructed moiety - Continuous urinary incontinence (females): If ectopic insertion below sphincter - Urinary leakage in males: If ectopic insertion in posterior urethra or prostate

Diagnosis: - Ultrasound: Two separate ureters on longitudinal scan; may see hydronephrosis of one moiety - VCUG: Demonstrates VUR if present; assesses bladder; may show ectopic ureteral orifice - Renal scintigraphy (DMSA or MAG3): Assesses differential function; MAG3 shows differential clearance - CT or MRI: Excellent anatomic detail; shows ectopic insertion if present; vascular anatomy - Cystoscopy: Direct visualization of ectopic orifice if location uncertain

Management:

Asymptomatic, No Obstruction or VUR: - Observation; periodic imaging (ultrasound q 1-2 years) - Standard infection precautions; good perineal hygiene

Symptomatic Upper Pole Obstruction: - Partial nephrectomy (heminephrectomy): Upper pole nephrectomy indicated if <20% differential function - Pyeloplasty: If >20% function and obstruction symptomatic - Success rate for heminephrectomy >95%

Symptomatic Lower Pole VUR: - Conservative: Prophylactic antibiotics; periodic VCUG - Surgical: Ureteral reimplantation if high-grade reflux, recurrent UTI, or noncompliance with prophylaxis

Ectopic Ureter: - Conservative: Prophylactic antibiotics; use pads if leakage - Surgical: Ureteroureterostomy (anastomosis to normal moiety collecting system) or nephrectomy if nonfunctional

B. Ureteropelvic Junction (UPJ) Obstruction

Previously detailed in pediatric kidney disease handout; highlighted here as important CAKUT component:

Key Points: - Most common intrauterine urinary tract anomaly - Functional or anatomic narrowing at UPJ - Differential function >20% typically managed conservatively with monitoring - Pyeloplasty success rate >95% for symptomatic or worsening cases

A. Autosomal Recessive Polycystic Kidney Disease (ARPKD)

Epidemiology: - Incidence: 1 in 20,000 live births - Gene: PKHD1 (chromosome 6q21) encodes fibrocystin - Homozygous mutations required for disease expression

Pathophysiology: - Cilia dysfunction in collecting ducts and bile ducts - Abnormal cell-cell signaling; cyst formation - Associated with congenital hepatic fibrosis (biliary dysgenesis) - Progressive bilateral disease; differs from ADPKD

Clinical Presentation by Age:

Prenatal (Identified on Ultrasound): - Symmetric, diffuse bilateral kidney enlargement with “echogenic” appearance - Severe oligohydramnios (decreased fetal urine output) - Potter sequence features (if severe bilateral disease) - Hepatomegaly may be present

Perinatal/Neonatal (Most Severe Form, ~40% of cases): - Bilateral massive kidney enlargement - Severe respiratory distress from pulmonary hypoplasia and massive abdominal distension - Renal insufficiency (elevated creatinine; often oliguria) - Hypertension (severe, difficult to control) - Failure to thrive - Mortality: 50% in first month without aggressive support; early ESRD development

Infantile Form (~40% of cases): - Slower progression - Mild-to-moderate kidney enlargement - Hypertension (95% of cases) - Progresses to ESRD by age 5-10 years - May develop esophageal varices from portal hypertension

Juvenile/Adolescent Form (~20% of cases): - Minimal renal symptoms initially - Progresses slowly; ESRD by adolescence - Clinically apparent hepatic fibrosis with portal hypertension - Increased morbidity from liver disease

Diagnosis: - Prenatal ultrasound: Echogenic, enlarged kidneys; oligohydramnios - Postnatal ultrasound: Bilaterally enlarged kidneys with “striated” echogenic appearance (collecting ducts dilated) - Renal biopsy: Not typically needed; recognizable histology if performed - Genetic testing: PKHD1 gene sequencing for confirmation and family planning - Liver imaging: Ultrasound or MRI to assess for congenital hepatic fibrosis

Management:

Neonatal Period: - Respiratory support (may require mechanical ventilation from pulmonary hypoplasia) - Aggressive blood pressure control (ACE inhibitor or ARB first-line) - Fluid and electrolyte management - Nutritional support; early feeding attempts - Renal function monitoring; prepare for dialysis if needed

Ongoing: - Blood pressure control: ACE inhibitor/ARB + additional agents as needed - Renal function monitoring; CKD staging - Growth monitoring; nutritional support - Screening for hepatic complications: Ultrasound q 1-2 years; if evidence of portal hypertension, upper endoscopy for varices - Management of renal osteodystrophy (secondary hyperparathyroidism, phosphate binders, calcitriol) - Anemia management with EPO-stimulating agents - Dialysis and transplantation when ESRD reached

Prognosis: - Highly variable; perinatal form has poorest prognosis - Progressive renal disease inevitable - Median age at ESRD: 10-15 years (varies by presentation) - Survival to age 20 years: ~80% with intensive management

B. Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Epidemiology: - Incidence: 1 in 400-1,000 live births - Genes: PKD1 (chromosome 16p13, 85% of cases) and PKD2 (chromosome 4q21, 15% of cases) - Heterozygous mutation (one normal allele sufficient for disease); high penetrance

Presentation in Childhood: - Often asymptomatic; discovered on family screening or prenatal ultrasound - Renal cysts present at birth but slowly progressive - Majority of children have normal renal function for many years - Hypertension may develop (10-30% of children)

PKD1 vs PKD2 Genetics:

Clinical Features in Children: - Usually asymptomatic - Hypertension (develops in minority; monitor blood pressure) - Renal cysts on imaging (symmetric, bilateral) - Normal renal function typically maintained through childhood and early adulthood - Extrarenal manifestations: Liver cysts (60-75%), cardiac valve abnormalities (25%), cerebral aneurysms (8-10%, higher if family history)

Diagnosis: - Renal ultrasound: Bilateral, diffuse renal cysts; preserved renal parenchyma - Genetic testing: PKD1/PKD2 sequencing; confirms diagnosis and allows for family counseling - Family screening: Ultrasound for at-risk relatives; genetic counseling if confirmed

Management in Children: - Blood pressure control: Target <50th percentile for age/height; ACE inhibitor or ARB if hypertension develops - Monitoring: Annual BP checks; serum creatinine; urinalysis - Avoidance of NSAIDs (increased cyst growth and renal decline) - Cardiac evaluation: Echocardiography if cardiac symptoms or family history of cardiomyopathy - Neuroimaging: Screening for cerebral aneurysm considered if family history of SAH; controversial in asymptomatic children - Genetic counseling: 50% risk to offspring - Lifestyle: Avoid trauma; avoid contact sports with uncertain renal function - Long-term follow-up: Transition to adult nephrology; continue monitoring for complications

A. Concept of Nephron Endowment

Definition: Total number of nephrons present at birth; represents maximum renal functional potential throughout life.

Normal Nephron Number: - Term infant: 0.8-1.2 million nephrons per kidney - Nephrogenesis complete by 34-36 weeks gestation - Subsequent kidney growth results from nephron hypertrophy, not new nephron formation

Determinants of Nephron Endowment: 1. Genetic factors: Mutations in GDNF, RET, PAX8, SIX genes affect maximum nephrogenesis 2. Intrauterine growth: Low birth weight associated with reduced nephrogenesis 3. Maternal factors: Gestational diabetes, hypertension, proteinuria, malnutrition affect fetal kidney development 4. Gestational age: Premature infants (<34 weeks) have incomplete nephrogenesis; continued development postnatally (limited) 5. Environmental exposures: Maternal ACE inhibitor/ARB use (2nd/3rd trimester), cocaine, NSAIDs, maternal smoking

Clinical Significance: - Low nephron endowment = reduced renal reserve - Predisposes to earlier CKD development with superimposed renal insults - Increases lifetime hypertension risk - Increases proteinuria risk - Increases ESRD risk with age

B. Low Birth Weight and Renal Outcomes

Epidemiology: - Low birth weight (LBW, <2,500 g): Incidence 8-10% of live births in developed countries - Very low birth weight (VLBW, <1,500 g): ~1-2% of live births - Extremely low birth weight (ELBW, <1,000 g): ~0.5-1% of live births

Mechanisms of Reduced Nephron Endowment in LBW:

Intrauterine Growth Restriction (IUGR): - Placental insufficiency reduces nutrient and oxygen delivery to developing fetus - Altered GDNF-RET signaling in response to hypoxia - Results in oligonephronia (reduced nephron number)

Prematurity: - Birth before 34 weeks gestation results in incomplete nephrogenesis - Extrauterine development cannot compensate; only ~2-5% additional nephrons form postnatally - Risk of abnormal renal development from immature regulatory mechanisms - Exposure to nephrotoxic medications (aminoglycosides, ACE inhibitors, NSAIDs)

Associated Risk Factors for Worse Outcomes: - Maternal hypertension, diabetes, smoking - Placental abnormalities (placental hypoplasia, infarction) - Maternal infections (congenital cytomegalovirus, toxoplasmosis) - Maternal nutritional deficiencies

Long-Term Renal Outcomes in LBW Infants:

Management Strategies:

1. Early Screening:
   • Renal ultrasound at discharge (assess for CAKUT, renal size)
   • Serum creatinine at discharge; follow serially during neonatal period
   • Monitor growth; identify failure to thrive (indicator of worsening CKD)
2. Prevention of Secondary Renal Insults:
   • Avoid nephrotoxic medications (aminoglycosides, contrast agents, NSAIDs)
   • Minimize volume depletion (aggressive hydration before contrast)
   • Strict infection control; prompt treatment of UTI
   • Optimize nutrition; avoid dehydration
3. Blood Pressure Control:
   • Screen at 3-4 months postnatal age; then at routine visits
   • Treat if >95th percentile for age/height
   • ACE inhibitor or ARB preferred for renoprotection
4. Monitoring:
   • Annual BP measurement through childhood
   • Annual serum creatinine; calculate eGFR
   • Annual urinalysis; screen for proteinuria
   • Parental counseling: Increased risk of future CKD; lifestyle modifications (salt restriction, exercise, avoid NSAIDs)
5. Transition Planning:
   • Early nephrology referral if GFR <90 mL/min/1.73 m² or other CKD evidence
   • Establish continuity of care with adult nephrology

A. Classification and Differential Diagnosis

Grading Systems (Prenatal): - Mild: Pelvic anteroposterior diameter (APD) 7-10 mm (15-20 weeks) or 10-15 mm (after 20 weeks) - Moderate: APD 15-25 mm - Severe: APD >25 mm

Differential Diagnosis of Antenatal Hydronephrosis:

B. Antenatal Surveillance and Counseling

Surveillance Protocol:

1. Initial Detection (Anomaly Scan, 18-22 weeks):
   • Measure pelvic APD; assess for bilateral involvement
   • Assess bladder size and emptying
   • Assess amniotic fluid volume
   • Assess for other congenital anomalies
2. Follow-up Ultrasounds (Interval Scanning):
   • Mild hydronephrosis (7-10 mm): Repeat ultrasound at 28 weeks and 36 weeks
   • Moderate hydronephrosis (10-15 mm): Repeat at 24 weeks and 36 weeks
   • Severe hydronephrosis (>15 mm): Repeat at 24 weeks and 32 weeks; consider MRI
   • Assess progression: Increasing APD suggests obstruction; stable or decreasing suggests non-obstructive
3. Antenatal MRI (Selected Cases):
   • Severe bilateral dilation (>15 mm)
   • Suspected obstructive lesion
   • Unclear diagnosis on ultrasound
   • Assess renal parenchymal thickness and echogenicity

C. Postnatal Management

Timing of First Postnatal Imaging: - Term infants: Renal ultrasound within first 48-72 hours of life (captures important early data; may see improvement if non-obstructive) - Preterm infants: Often deferred until approaching term-equivalent age (allows for ongoing postnatal nephrogenesis)

Postnatal Imaging Sequence:

Stage 1: Ultrasound (Initial): - Confirm pelvicalyceal dilation; measure APD - Assess corticomedullary differentiation (preserved = better function) - Assess for features suggesting obstruction (calyceal dilation, renal parenchymal thinning) - Assess contralateral kidney - Antibiotic Prophylaxis Consideration: Controversial; some clinicians initiate prophylaxis pending diagnostic workup; others reserve for high-risk cases or confirmed VUR/obstruction

Stage 2: Renal Scintigraphy (MAG3 or DTPA; timing 4-6 weeks): - Assess differential renal function (normal >45% to affected kidney) - Assess for obstruction: Delayed clearance from collecting system - MAG3 preferred over DTPA (better extraction rate; superior images in low-function kidneys)

Stage 3: VCUG (4-6 weeks, after infection ruled out): - Assess for vesicoureteral reflux (predicts need for prophylaxis/management) - Assess bladder size and emptying - Assess for posterior urethral valves or other lower tract abnormality

Assessment of Obstruction: - Clinical obstruction: Reduced differential renal function (<40%) + delayed drainage on scintigraphy + progressive dilation on ultrasound - Functional obstruction: Normal function but delayed drainage; no clear anatomic obstruction - Non-obstructive: Normal drainage kinetics despite persistent dilation

D. Management Decisions

Conservative Management (Majority): - Indications: >45% differential function, non-obstructive pattern on imaging, no VUR or low-grade VUR - Prophylactic antibiotics: Controversy exists; some data suggest prophylaxis reduces symptomatic UTI risk; other studies show no benefit on scarring - Regimen if used: Nitrofurantoin 1-2 mg/kg daily or TMP-SMX 1 mg/kg TMP daily - Monitoring: Serial ultrasounds (3-6 month intervals) and repeat scintigraphy at 1 year - Expected outcome: 40-60% resolution over first 2 years

Surgical Management (Selected Cases): - Pyeloplasty indications: - Differential function 20-45% - Symptomatic obstruction (recurrent UTI, pain) - Progressive dilation or deteriorating function - Parental anxiety/preference - Non-compliance with follow-up - Success rate: >95% for pyeloplasty; low morbidity - Timing: Typically after 6 weeks of age (stabilized from delivery stressors); some perform as early as 2-4 weeks if critical obstruction

Percutaneous Nephrostomy (Urgent Cases): - Indications: Bilateral obstruction with renal dysfunction; infected obstructed system (pyonephrosis) - Allows decompression and recovery of renal function before definitive surgical repair