Prenatal ultrasound has been invaluable in furthering our understanding of the natural history of congenital malformations and in identifying pathophysiological features that affect prognosis.We describe a case, diagnosed prenatally at 24 weeks' gestation, of congenital cystic adenomatoid malformation of the left lung with massive mediastinal shift and compression of the right lung. Serial ultrasound examinations showed gradual reduction in the size of the mass relative to the thorax, with return of the mediastinum to the midline and normal development of the right lung. To our knowledge, this is the first time that such an observation has been reported.
CASE REPORTA 29-yearA old woman, gravida 1, para a was admitted at 24 weeks· ' gestation in premature labor. Ultrasound examination of the fetus demonstrated massive mediastinal shift to the right side. The left lung was enlarged and extremely echo· genic. Cystic and tubular structures were noted at the base close to the left hemidiaphragm ( Fig. 1). Our diagnosis was congenital cystic adenomatoid malformation involving the en-