This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
Paint brush appearance is a feature of 
Select and explain. 
A. Hydronephrosis, B. PCKD, C. Medullary sponge kidney, D. Papillary necrosis
C: Medullary sponge kidney
Answer: C: Medullary sponge kidney 
Explanation: Paint brush appearance - Medullary sponge kidney.
Egg in CUP appearance  - Papillary necrosis.