Cystic Kidney

Paula J. Woodward, MD

DIFFERENTIAL DIAGNOSIS

Common

Rare but Important

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Do the “cysts” connect?
- Real-time evaluation is essential for differentiating an obstructed system from true renal cystic disease

Helpful Clues for Common Diagnoses

Multicystic Dysplastic Kidney (MCDK)
- Multiple, variable-sized cysts in renal fossa
- Reniform shape is lost
- Often large, distorting normal abdominal anatomy
- Variable in-utero course; some involute and others increase in size
Hydronephrosis (Mimic)
- Distended calyces may appear “cyst-like”
- Must show that calyces connect with renal pelvis (longitudinal views best)
- Causes: Ureteropelvic junction (UPJ) or bladder outlet obstruction
Obstructive Cystic Dysplasia
- Cystic parenchymal change from chronic obstruction
  - Hydronephrosis → cortical cysts
  - Reflects nephron damage and decreased renal function
- Cysts are often cortical
  - Form in subcapsular nephrogenic zone
- Kidneys become echogenic
- Reniform shape generally retained
- Rarely can appear identical to MCDK
Duplicated Collecting System with Obstruction (Mimic)
- Upper and lower pole moieties separated by band of renal parenchyma
- Upper pole prone to obstruction and can appear as cystic mass
- Look for ureterocele in bladder

Helpful Clues for Rare Diagnoses

Simple Cyst
- Isolated, unilocular renal cyst
- Vast majority resolve during pregnancy
  - 4% progress to MCDK
Meckel-Gruber Syndrome
- Triad of classic findings (2 findings required for diagnosis)
- Renal cystic dysplasia most consistent finding, present in 95-100%
  - Grossly enlarged, echogenic kidneys most common, but may present with bilateral, large cysts
- Encephalocele in 60-80%
- Post-axial polydactyly in 55-75%