Fetal lung interstitial tumor: a cause of late gestation fetal hydrops.

Most fetal lung masses present by mid gestation, grow during the canalicular phase of lung development (18-26 weeks of gestation), and plateau in growth or shrink after 26 weeks of gestation. We describe the unique case of a fetal lung mass presenting at 37 weeks of gestation with hydrops and fetal heart failure. The late growth of this lesion and resultant hydrops prompted resection as part of the ex utero intrapartum treatment. Histopathology revealed a rare, recently described fetal lung interstitial tumor. This case demonstrates that a subset of fetal lung masses may continue to grow later in gestation and emphasizes the need for late gestation imaging and close follow-up in this patient cohort.