What specific imaging is performed for fetal pleural effusions?
Fetal pleural effusions are divided into two main groups: hydropic and nonhydropic. Hydropic pleural effusions result from conditions causing the hydrops itself and are often evident from the history or presence of anomalies known to be associated with hydrops. Nonhydropic pleural effusions can be associated with:
- • Congenital heart defects not causing fetal congestive failure.
- • Lung lesions.
- • CDH.
- • Chromosomal abnormalities (trisomy 18, trisomy 21, and Turner syndrome).
- • Pulmonary lymphangiectasia (which may also result in hydrops).
- • Pulmonary venous atresia.
- • Thoracic wall hamartoma.
- • High output failure due to fetal mass (e.g., SCT) or other noncardiac etiology.
US for pleural effusions is directed at determining whether or not hydrops is present and in determining the underlying etiology. For nonhydropic effusions, it may be difficult to determine an etiology if the cause is not from an associated cardiac abnormality, lung lesion, or chromosomal abnormality.
For both treatment decision making and follow-up, estimation of the pleural effusion volume is helpful. Though 3D US has been advocated for such measurements, particularly for follow-up, we have used a simpler measurement. We measure the internal (pleural surface to pleural surface) dimensions of each hemithorax. We then measure the lung on each side and calculate the volumes of each hemithorax and lung using the prolate ellipsoid formula (volume = L × W × D × 0.523). Subtraction of the lung volume from the hemithorax volume gives an estimate of the pleural effusion volume for that side