During development in the womb, the ureters grow up from the bladder, forming connections with the kidneys. However, in this condition, one of the ureters fails to connect with the kidney. Because that kidney cannot work, a number of cysts form; hence the term ‘multicystic’. Most usually, one kidney is affected while the other is normal. MCDK is a developmental problem and is not the same as polycystic kidneys, an inherited condition.