Spontaneous regression of a large intrathoracic fetal lesion before birth.

All fetal intrapulmonary lesions diagnosed antenatally reported in the literature to date have persisted as an ultrasound finding for the remainder of the pregnancy, although spontaneous improvement in utero has been reported recently. We describe a case of a large intrathoracic lesion diagnosed at 24 weeks' gestation by ultrasound that became indistinguishable from the rest of the lungs as the pregnancy approached term. Although the frequency with which this process occurs cannot yet be assessed, the possibility of significant spontaneous regression must now be considered when counseling the parents on an affected fetus.