A rare kidney tumor, often congenital and known by a variety of names (mesoblastic nephroma,1 leiomyomatous hamartoma,2 fetal renal hamartoma,3 mesenchymal hamartoma of infancy4), has been confused with Wilms' tumor. On occasion, inappropriately aggressive therapy has been instituted.
An autopsy was recently performed on an infant with this tumor. Wilms' tumor was the primary diagnosis before death. The need to convey the benign nature of this mimic of Wilms' tumor prompted this case report.
Report of a Case.—A premature boy was delivered vaginally following 36 weeks gestation. Polyhydramnios complicated the otherwise uneventful pregnancy. Amniotic fluid, 5,000 ml, escaped when the membranes ruptured during an attempted amniocentesis, followed promptly by labor and delivery.
The infant's cry and grasp were good, but the initial Apgar score of 3 rose only to 5 after three minutes. Apnea occurred a few minutes later. Oxygen therapy and resuscitation restored spontaneous breathing, but the infant