Unilateral Large Kidney

Sara M. O’Hara, MD, FAAP

DIFFERENTIAL DIAGNOSIS

Common

Hydronephrosis
Duplication
Crossed Fused Ectopia
Compensatory Hypertrophy
Multicystic Dysplastic Kidney (MCDK)
Pyelonephritis
Wilms Tumor

Less Common

Multilocular Cystic Nephroma
Mesoblastic Nephroma
Renal Vein Thrombosis, Acute Phase
Trauma

Rare but Important

Infarction
Venolymphatic Malformations
Renal Medullary Carcinoma
Unusual Renal Tumors

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Comparison to contralateral kidney is key
Look up renal length when side of abnormality is not apparent
Assess
- Renal contour
- Corticomedullary differentiation
- Contrast enhancement pattern
- Presence of cysts or masses
- Vascular compromise: Abnormal supply, compression, tumor thrombus
- Adjacent spaces and nodes

Helpful Clues for Common Diagnoses

Duplication
- Look for band of cortex separating upper and lower poles
- Look for 2nd renal pelvis and ureter
Crossed Fused Ectopia
- Contralateral kidney will be absent
- Occasionally lower renal tissue lies in midline, “J” shape
- Part of spectrum of renal ascent and rotation abnormalities
- Lower renal moiety ureter will cross to contralateral trigone
Compensatory Hypertrophy
- Seen most commonly with contralateral aplasia or MCDK
- Also seen following early surgical removal of kidney
- Less common with hypoplasia/dysplasia
Multicystic Dysplastic Kidney (MCDK)
- Classic type: Conglomerate cysts without discernible renal pelvis
- Hydronephrotic type: Central cyst thought to be remnant of obstructed pelvis
- High incidence of contralateral renal abnormalities
  - Ureteropelvic junction obstruction
  - Vesicoureteral reflux
- MCDK initially large, but vast majority shrink over course of years
- 1/2 of all MCDK have involuted by age 5
- 12 reported cases of Wilms and renal cell carcinoma occurring in MCDK
  - National MCDK Registry tracks incidence and behavior
- Imaging: Ultrasound and nuclear scan to confirm nonfunction
Pyelonephritis
- May have normal echotexture on ultrasound
- Look for
  - Altered corticomedullary interface
  - Focal hypoechoic area
  - Decreased perfusion on Doppler exam
  - Bulge in cortex from focal swelling
  - Striated nephrogram on CT, MR, or IVP
  - Poorly enhancing areas on contrast studies
  - Wedge-shaped photopenic area on DMSA
- Imaging
  - DMSA most sensitive exam
  - CT & MR next most sensitive
  - Ultrasound least sensitive but does exclude complications of abscess, perinephric collection, obstruction
Wilms Tumor
- Malignant tumor of primitive metanephric blastema
- Most common renal tumor in children
- Peak incidence ages 2-5
- Typically heterogeneous soft tissue
- Vascular extension and tumor thrombus common
- 5-10% are bilateral, associated with nephroblastomatosis
- Large tumors grow into perinephric space, periaortic nodes
- Metastasize to lung
- Cure rate is 90% or better with chemotherapy
- Imaging: Ultrasound, CT, MR, nucs (per treatment protocol)

Helpful Clues for Less Common Diagnoses

Multilocular Cystic Nephroma
- a.k.a. cystic nephroma
- Rare, benign tumor
- Bimodal age distribution
  - Childhood: M:F = 2:1, 3 months to 2 years
  - Adulthood: M:F = 1:8, 30 years or older
- Can mimic cystic Wilms tumor; always removed
- Imaging: Ultrasound, CT, MR, nucs (per treatment protocol)
Mesoblastic Nephroma
- Most common renal tumor in neonate
- Peak age 3 months
- Typically solid but can also be cystic
- Predominantly benign but can be locally invasive or recur
- Imaging: Ultrasound, CT, MR, nucs (per treatment protocol)
Renal Vein Thrombosis, Acute Phase
- Obstruction to venous outflow causes renal engorgement, ischemia, and eventually infarction if not relieved
- Chronically, kidney scars and atrophies
- Imaging: Ultrasound with Doppler, CT angiography, conventional angiography (rarely)
Trauma
- Contusion of kidney with global swelling
- Perinephric hematomas, urinomas, subcapsular hematomas, etc. can all mimic enlarged kidney
- Imaging: CT best in acute setting, ultrasound to follow-up

Helpful Clues for Rare Diagnoses

Infarction
- Arterial compromise, particularly from emboli, can cause renal enlargement
Venolymphatic Malformations
- Rarely retroperitoneal vascular malformation may involve kidney
Renal Medullary Carcinoma
- Rare tumor
- Young patients with sickle cell trait
- Highly aggressive tumor
- Central, infiltrating tumor with caliectasis and regional adenopathy
- Metastases often seen at presentation
- Poor prognosis
Unusual Renal Tumors
- Clear cell carcinoma
- Rhabdoid tumor
- Primitive neuroectoderm tumor (PNET)
- Renal cell carcinoma