Reliability of pleural fluid lymphocyte counts in the antenatal diagnosis of congenital chylothorax

Two cases are presented in which fetal thoracentesis was performed to evaluate pleural effusions. In the first, a fetus with nonimmune hydrops had pleural effusions with lymphocyte counts consistent with congenital chylothorax. However, amniotic fluid cultures grew cytomegalovirus and the diagnosis of congenital cytomegalovirus infection was confirmed at autopsy. In the second, the pleural fluid lymphocyte count was lower than that considered to be diagnostic of congenital chylothorax. Nevertheless, the clinical course in this case and the patient's history of two previous infants who were presumed to have that disease suggest that this was the most likely diagnosis. These cases emphasize that pleural fluid lymphocyte counts alone are not reliable in establishing the cause of hydrothorax before birth.