Focal xanthogranulomatous pyelonephritis in a young child.

An 18-month-old female child presented with fever and an abdominal mass, which, after ultrasonography, computed tomography, and magnetic resonance imaging was considered to be an atypical cystic renal neoplasm. Nephrectomy was performed. Histopathological examination demonstrated the mass to be focal xanthogranulomatous pyelonephritis. This lesion should be considered in the differential diagnosis of renal neoplasms in childhood, particularly cystic Wilms' tumor or Wilms' tumor with significant intratumoral hemorrhage.