The vanishing fetal intrathoracic mass: consider an obstructing mucous plug.

An intrathoracic homogeneous hyperechogenic mass diagnosed in the second trimester of pregnancy represents a challenge to the sonographer. A disappearance of such a finding is an enigma. We have recently encountered such a case in which a mucous plug obstructing a main bronchus was the causative factor. To the best of our knowledge, this is the first report of such an etiology in cases of vanishing fetal intrathoracic masses diagnosed by ultrasonography.