Growing Renal Mass: Lessons Learned on the Road From an Atypical Presentation to Successful Therapy.

A 25 4/7 week boy was born with a prenatal diagnosis of polyhydramnios and enlarged left kidney. Over the next 2 months serial ultrasounds demonstrated abnormal growth of the kidney, with 28.9% split function. At gestational age 39 4/7, he underwent a left radical nephrectomy. Pathology revealed congenital mesoblastic nephroma with mixed classic and cellular features. This case was puzzling due to prenatally diagnosed renal enlargement in a premature infant and inconclusive post-natal ultrasonographic imaging. Although the patient had paraneoplastic signs of polyhydramnios and hypertension, the mass did not have a classic appearance of CMN; possibly due to severe prematurity.