A fetus was found to have a large left thoracic cyst on routine prenatal ultrasound at 23 weeks of gestation. This lesion caused compression of the normal left lung tissue and contralateral mediastinal shift. At 23 weeks of gestation the cyst was percutaneously aspirated without subsequent reaccumulation of fluid. Serial ultrasounds showed decrease in the size of the cyst. The clinical diagnosis of congenital cystic adenomatoid malformation was made. At birth, the child had no respiratory distress, and a CT scan confirmed the finding of a fluid-filled cyst in the left chest. At the time of resection, a nonaerated extralobar bronchopulmonary sequestration (with a systemic arterial blood supply and separate pleural investment) was found. The dominant cyst had ciliated respiratory epithelium with cartilage, indicative of a bronchogenic cyst, and the remainder of the specimen had the histologic hallmarks of a congenital cystic adenomatoid malformation. The coexistence of three separate anomalies in one lesion suggests a common embryological link for these malformations.

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