The appearance is compatible with renal tubular ectasia. This "paintbrush" appearance overlaps with medullary sponge kidney, and the difference between the two is really one of degree and symptoms.

• renal tubular ectasia
  • less pronounced than medullary sponge kidney
  • asymptomatic, incidental
  • no calcifications
• medullary sponge kidney
  • more pronounced than renal tubular ectasia
  • predisposes to medullary nephrocalcinosis and renal stone formation