Figure 5a. Medullary sponge kidney and an obstructing calculus in the right distal ureter in a 62-year-old woman. (a) Axial unenhanced CT scan demonstrates right hydronephrosis (arrowheads) with a nonobstructing calculus (arrow). (b) Axial unenhanced CT scan demonstrates a calculus in the distal right ureter (arrow). (c, d) Axial excretory-phase CT scan (c) and post-CT radiograph (d) demonstrate a paintbrush appearance in the papillae of the left kidney (arrows). Right hydronephrosis is again noted (arrowheads in c).