Cystic dilatations of the upper urinary tract: a radiologist's developmental model.

The ureteral bud in the embryonic kidney grows and branches dichotomously for 15 generations. This branching tree is modified by a series of narrowings and expansions and becomes the ureter, the renal pelvis, the calyces, and the collecting tubules. Simultaneously, the ureteral bud induces the formation of nephrons. If many of the renal cystic diseases and congenital dilatations of the renal pelvis and ureter are viewed as a series of growth disturbances along the branching ureteral bud, their morphology and pathophysiology become clarified even though their etiology is often not known.