Echocardiographic evaluation of fetal hydrothorax: the effusion ratio as a diagnostic tool

Fetal hydrothorax may lead to hydrops and is associated with mortality as high as 50%. The objective of this study was to define the pathophysiology of fetal hydrothorax and its relation to hydrops.

Measurements from echocardiograms of 33 fetuses diagnosed with hydrothorax were made, and included diameters of the thorax, heart, inferior vena cava, right ventricle (RV), left ventricle (LV) and aortic and pulmonary valves. Doppler-derived velocities were measured in the aorta and pulmonary artery just above the aortic and pulmonary valves. The ratio of the area of the effusion to the area of the thorax (effusion ratio) was calculated. Variables were converted into Z-scores from regression equations based on normal data. Features of fetuses with and without hydrops were compared.

Higher effusion ratios were noted in hydropic versus non-hydropic fetuses. Compared to a normal population, study subjects had smaller dimensions of LV, RV and aortic and pulmonary valves. They also had higher pulmonary artery peak velocities. The comparison between non-hydropic and hydropic fetuses revealed lower values for LV and pulmonary valve dimensions, and peak aortic velocity in hydropic fetuses. The severity of LV compression correlated significantly with effusion ratio.

Fetal hydrothorax is accompanied by compression of the cardiac structures, resulting in altered cardiac hemodynamics. Echocardiographic assessment, including the measurement of effusion ratio, may be a useful tool in guiding fetal therapy.