Unilateral Hydronephrosis

Sara M. O’Hara, MD, FAAP

DIFFERENTIAL DIAGNOSIS

Common

Ureteropelvic Junction (UPJ) Obstruction
Ureterovesical Junction (UVJ) Obstruction
Ureterocele
Posterior Urethral Valves
Urolithiasis (Stones)
Vesicoureteral Reflux

Less Common

Megaureter
Bladder Mass
Iatrogenic
- VUR Post Ureterocele Incision
- Deflux Complications
- Ureteral Re-Implant Complications
- Stent Misplacement or Blockage
- Ureteral Ligation During Pelvic Surgery

Rare but Important

Ureteral Fibroepithelial Polyp

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Many cases are found prenatally and precisely diagnosed in newborn period
Determining extent or level of dilation is key to narrowing differential
Dilated calyces and disproportionately enlarged renal pelvis often indicate UPJ obstruction
Dilation from top to bottom points to problems at UVJ
- Intrinsic UVJ obstruction
- UVJ stone
- Ureterocele
- Megaureter
- Bladder mass
- Compression from other pelvic mass
Mid-ureteral transitions to normal caliber are unusual; if present, consider
- Urolithiasis
- Aberrant anatomy: Crossing vessel
- Stricture: Postsurgical or radiation related
- Compression by adjacent mass
- Ureteral mass or polyp is very uncommon

Helpful Clues for Common Diagnoses

Ureteropelvic Junction (UPJ) Obstruction
- Most common cause of hydronephrosis in children
- Focal narrowing at junction of renal pelvis and ureter
- Degree of UPJ obstruction
  - Varies from mild to severely obstructed
  - May change with age and hydration state
- Obstruction may be intrinsic or extrinsic
  - Intrinsic likely starts in fetal life
  - Fibrosis, abnormal innervation, failure of canalization are all suspected etiologies
  - By the time narrowing is resected, pathologically cannot determine cause
  - Extrinsic causes are typically crossing vessels, adenopathy, or mass
- Imaging of UPJ obstruction
  - Ultrasound and diuretic renography are mainstays for degree of obstruction, scarring, renal growth, superimposed infection
- Treatment of UPJ obstruction
  - Dismembered pyeloplasty
Ureterovesical Junction (UVJ) Obstruction
- 2nd most common cause of hydronephrosis in children
- Megaureter is specific subtype of UVJ obstruction
  - Caused by distal adynamic segment
- Other causes of UVJ obstruction
  - Stricture, fibrosis, aberrant anatomy
  - Compressed distal ureter: Bladder wall hypertrophy, mass, adenopathy, etc.
- Imaging: Diuretic renogram, ultrasound, RUG, VCUG, MR urogram
Ureterocele
- Congenital cystic dilation of distal submucosal ureter
- Location: Intra- or extravesical
- Insertion site
  - Orthotopic at trigone (“simple”)
  - Ectopic insertion anywhere else, typically medial and distal to trigone
- Kidney being drained
  - Single system; typically simple, intravesicle variety
  - Duplex system; typically ectopic &/or extravesical
- Imaging: VCUG, US, MR urography
Posterior Urethral Valves
- Congenital condition
- Seen only in boys
- Persistent tissue just distal to verumontanum partially obstructs urethra
- Unilateral VUR or urinoma protective to contralateral kidney
  - Better long-term prognosis
- Degree of obstruction varies
  - Severe obstruction seen in fetus and newborn
  - Secondary oligohydramnios, respiratory and renal insufficiency
  - Mild obstruction may go undetected for several years
  - Can present late with renal failure, bladder dysfunction
- Imaging: VCUG
  - Shows valve tissue &/or urethral caliber change
- Treatment: Endoscopic valve ablation
Urolithiasis (Stones)
- Much less common problem in pediatrics than in adults
- Stone types in decreasing frequency
  - Calcium phosphate or oxalate
  - Struvite
  - Uric acid
  - Cystine
  - Mixed
- Degree of obstruction varies with stone size and location
- Imaging: Ultrasound, CT, IVP (rare)
- Treatment: Hydration, diuretics, endoscopic basketing, lithotripsy
Vesicoureteral Reflux
- Retrograde flow of urine from bladder toward kidneys
- Graded from 1 (mild) to 5 (severe)
- 80% of children outgrow reflux by puberty
- Associated infection and renal scarring
- Imaging: VCUG, nuclear cystogram, sonocystogram (where ultrasound contrast is available)

Helpful Clues for Less Common Diagnoses

Megaureter
- Focal concentric narrowing of extravesical distal ureter 1-3 cm in length
- Unknown etiology; theorized causes include
  - Paucity of ganglion cells
  - Hypoplasia/atrophy of muscle fibers in distal ureteral segment
- Refluxing and nonrefluxing varieties
- Imaging: Diuretic renogram, ultrasound, VCUG, MR urography
- Treatment: Resection of narrowed segment and re-implantation
Bladder Mass
- Rhabdomyosarcoma most common
- Inflammatory pseudotumor
- Neuroblastoma and transitional cell rare
- Imaging: Ultrasound, VCUG, CT, or MR for local extent
- Treatment: Resection and ureteral re-implant or diversion
Iatrogenic
- Consider whenever there has been recent surgery or invasive procedure