Ahmad H. Bani-Hani, MD, FAAP, FACS
BASICS
DESCRIPTION
• Refers to dilatation of any part of the collecting system, single or combined:
– Pelviectasis (renal pelvis)
– Caliectasis (calyces)
– Pelvocaliectasis (both renal pelvis and calyces)
– Ureterectasis (ureter)
– Hydroureteronephrosis (entire collecting system is dilated)
• Society of Fet al Urology (SFU) grading of infant hydronephrosis (1)[A]:
EPIDEMIOLOGY
• Prenatal hydronephrosis is detected in about 1.4% of total prenatal ultrasound performed in US
• The true incidence is difficult to determine secondary to many asymptomatic, undetected cases
RISK FACTORS
• Family history of hydronephrosis, maternal type I diabetes mellitus (associated with infant sacral agenesis)
• Genetic syndromes: Downs, trisomy 13, trisomy 18, CHARGE, Ehlers–Danlos, Menkes, Prune belly, etc
• Horseshoe kidney/pelvic kidney
• Duplication renal anomalies
• Neurogenic bladder secondary to tethered spinal cord, myelodysplasia, sacral agenesis
Genetics
No specific genetic abnormalities except if associated with specific genetic syndromes as outlined above
ALERT
Hydronephrosis is not a specific diagnosis but a finding or sign. The cause of the hydronephrosis is the diagnosis and indicates the appropriate treatment.
PATHOPHYSIOLOGY
• Physiologic hydronephrosis: Unclear etiology but typically improves with serial renal ultrasound monitoring
• Pathologic hydronephrosis
– Vesicoureteral reflux: Reflux can be primary or secondary to conditions that raises the intravesical pressures (eg, bladder outlet obstruction and neurogenic bladder)
– Ureteropelvic junction (UPJ) obstruction (2)[A]:
Defined as obstruction to the flow of urine from the renal pelvis to the proximal ureter
Considered to be the commonest cause of prenatal hydronephrosis
Obstruction can be caused by an intrinsic narrowing at the UPJ or by an extrinsic compression by a lower pole anteriorly crossing vessel
Examples of intrinsic obstruction can include: Narrow segment with muscular discontinuity, ureteral valves, mucosal folds, or ureteral polyps
– Ureterovesical junction (UVJ) obstruction:
Primary: Called primary obstructive megaureter. The most common finding is a distal adynamic ureteral segment that affects the free efflux of urine resulting in a functional obstruction
Secondary: Distal stone, hypertrophy of the distal ureter and trigone in neurogenic bladder or posterior urethral valves
– Ureterocele:
Defines as cystic dilatation of the distal ureteral segment
More common in females and can cause obstruction to the distal urine flow
Often associated with duplication anomalies of the kidneys particularly involving the upper pole moiety
– Ectopic ureter:
Occurs when the distal opening of the ureter is not in the normal location at the corner of the trigone
Ureter can enter the bladder neck, urethra, and, in female, the vestibule, vagina, and rarely the uterus
Ectopic ureters opening outside the bladder or urethra tend to be obstructed and often associated with nonfunctioning renal moiety
Commonly involves the upper pole moiety in duplicated renal anomalies
– Posterior urethral valves:
The most common cause of congenital lower urinary tract obstruction in males (1/4,000 to 1/7,500 births)
Varies in severity and can result in deterioration of fet al renal function, and progressive oligohydramnios, which may lead to pulmonary hypoplasia with a high risk of perinatal morbidity and mortality
– Other causes:
Anterior urethral valves
Urethral atresia
Nonneurogenic neurogenic bladder (Hinman syndrome)
ASSOCIATED CONDITIONS
Hydronephrosis can by physiologic or pathologic associated with many condition as noted above
DIAGNOSIS
HISTORY
• Detailed prenatal history of:
– Timing of 1st detection of hydronephrosis in relation to gestational age
– Unilateral vs. bilateral
– Gender of the baby
– Maternal diabetes mellitus, particularly type I (associated with fet al sacral agenesis)
– Family history of renal anomalies
– Amniotic fluid volume
– Paternal allergy to penicillin
• Detailed postnatal history:
– Circumcision status
– Birth weight
– Jaundice
– Urinary tract infections
– Progression with potty training
– Incontinence
– Hypertension, failure to thrive
PHYSICAL EXAM
• Vital signs, particularly blood pressure
• Weight
• Jaundice
• Abdominal masses
• Is bladder palpable?
• Cutaneous manifestations of spina bifida occulta (hairy patch, sacral dimple, lipoma, asymmetric or short gluteal fold)
• Genital/anorectal exam
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Basic metabolic panel
• Urine analysis and culture if indicated
Imaging
• Renal and bladder ultrasound (RUS):
– Should be 1st-line imaging study
– Will give excellent idea about the laterality and severity of hydronephrosis, associated bladder pathology such as ureterocele, are ureters dilated too?
– Bladder pathology such as abnormal bladder wall thickness, key hole sign in posterior urethral valves
– Indirect way to assess overall renal function by looking at echogenicity and thickness of renal parenchyma
• Abdominal kidney-ureter-bladder (KUB) x-ray:
– Displaced bowel pattern from hydronephrosis or bladder distension
– Stool load and distribution to help in management
• Voiding cystourethrogram:
– Assess presence of reflux
– During early filling, a ureterocele can be identified
– Assess the entire urethra for evidence of posterior or anterior urethral valves
• Diuretic renal scan (MAG-3 with Lasix):
– Evaluates differential renal function and drainage curves from each kidney.
– Very useful for the diagnosis and evaluation of possible UPJ/UVJ obstruction
• MR urogram:
– Can provide useful information such as renal function and anatomic details when evaluating conditions such as ectopic ureter location
Diagnostic Procedures/Surgery
• Usually reserved for treatment of certain conditions such as posterior urethral valve ablation
• Cystoscopy and retrograde pyelogram can be used to define the anatomy of the collecting system and placement of a drainage stent
Pathologic Findings
Depends on the underlying pathology responsible for the hydronephrosis
DIFFERENTIAL DIAGNOSIS
• Prominent extrarenal pelvis
• Multicystic dysplastic kidney
• Polycystic renal disease
• Renal cysts
TREATMENT
GENERAL MEASURES
Depends on underlying pathology responsible for the hydronephrosis
MEDICATION
First Line
• Antibiotic prophylaxis may be needed in severe cases of hydronephrosis and/or presence of reflux
– Prophylactic daily antibiotics to keep urine sterile, preferentially given at bedtime to maximize urinary retention
<2 mo age: Amoxicillin 20 mg/kg/d
≥2 mo of age: Trimethoprim–sulfamethoxazole 2 mg/kg/d (concentrates in urine); nitrofurantoin is an alternative, but liquid is expensive and bad-tasting
Second Line
• Anticholinergics in cases of an overactive bladder and/or raised intravesical pressures
• β-blockers in some cases of bladder outlet obstruction
SURGERY/OTHER PROCEDURES
• Vesicoureteral reflux: Antibiotic prophylaxis vs. surgical correction
• UPJ obstruction: Pyeloplasty
• UVJ obstruction: Distal ureterectomy and ureteral reimplant
• Ureterocele: Several options available including observation, intravesical puncture, ureteroureterostomy, and partial nephrectomy
• Ectopic ureter: Several options available including heminephrectomy and ureteroureterostomy
• Posterior urethral valves: Endoscopic ablation
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
• Clean intermittent catheterization in cases of neurogenic bladder
• Biofeedback in some patients with voiding dysfunction
Complementary & Alternative Therapies
N/A
ONGOING CARE
PROGNOSIS
Varies and depends on underlying pathology and its severity (3)[A]
COMPLICATIONS
• Hypertension
• Kidney/bladder stones
• Multiple UTIs
• Reflux
• Renal insufficiency
• Renal scarring
• Urinary incontinence
FOLLOW-UP
Patient Monitoring
• Patients need meticulous follow-up once hydronephrosis is diagnosed before and after treatment
• Referral to pediatric urology/nephrology for full assessment and treatment
Patient Resources
National Kidney Foundation. http://www.kidney.org/atoz/content/hydronephrosis.cfm
REFERENCES
1. Fernbach SK, Maizels M, Conway JJ. Ultrasound grading of hydronephrosis: Introduction to the system used by the Society for Fet al Urology. Pediatr Radiol. 1993;23(6):478–480.
2. Koff SA. Pathophysiology of ureteropelvic junction obstruction. Clinical and experimental observations. Urol Clin North Am. 1990;17:263–272.
3. Liu HY, Dhillon HK, Yeung CK, et al. Clinical outcome and management of prenatally diagnosed primary megaureters. J Urol. 1994;152:614–617.
ADDITIONAL READING
Mesrobian HG, Mirza SP. Hydronephrosis: A view from the inside. Pediatr Clin North Am. 2012;59(4):839–851.
See Also (Topic, Algorithm, Media)
• Hydronephrosis/Hydroureteronephrosis, (Dilated Ureter/Renal Pelvis), Adult
• Hydronephrosis/Hydroureteronephrosis, (Dilated Ureter/Renal Pelvis), Prenatal
• Hydronephrosis/Hydroureteronephrosis, (Dilated Ureter/Renal Pelvis), Pediatric Images 
• Megaureter
• Posterior urethral valves
• Ureterocele
• Ureteropelvic junction obstruction
CODES
ICD9
• 591 Hydronephrosis
• 596.54 Neurogenic bladder NOS
• 753.3 Other specified anomalies of kidney
ICD10
• N13.30 Unspecified hydronephrosis
• N31.9 Neuromuscular dysfunction of bladder, unspecified
• Q63.1 Lobulated, fused and horseshoe kidney
CLINICAL/SURGICAL PEARLS
• Hydronephrosis is not a diagnosis but a sign.
• Renal ultrasound, VCUG, and diuretic renal scan can establish the underlying etiology of hydronephrosis.