Renal agenesis: an acquired condition?

Renal agenesis is a relatively common congenital anomaly, although its etiology is unknown. It is clear that some solitary kidneys are the result of postnatal involution of multicystic dysplastic kidneys. The authors present a series of nine neonates with abnormal prenatal renal ultrasound findings; subsequent postnatal investigations showed an absent kidney. Five children had a prenatal diagnosis of multicystic dysplastic kidney (MDK) and two of hydronephrosis. In five cases (56%) there was a contralateral renal unit anomaly. It appears that MDK, and occasionally hydronephrosis, can involute prenatally, producing the postnatal appearance of renal agenesis.