Normal and hypoplastic fetal lungs: volumetric assessment with prenatal single-shot rapid acquisition with relaxation enhancement MR imaging.

Purpose: To determine which parameters are most closely correlated with normal fetal total lung volume and to investigate the use of these parameters in the evaluation of fetal pulmonary hypoplasia.
Materials and Methods: Single-shot rapid acquisition with relaxation enhancement (RARE) magnetic resonance (MR) imaging was used to perform planimetric measurement of total lung volume in 46 fetuses at 18-32 weeks gestation. Total lung volume was correlated with gestational age, and biometric parameters in fetuses were correlated with normal chest findings at ultrasonography (US) (n = 24). This analysis was used to evaluate relative lung volume in fetuses suspected of having pulmonary hypoplasia (n = 22).
Results: Normal fetal total lung volume was strongly correlated with liver volume measured at MR imaging (r = 0.94), fetal weight estimated at US (r = 0.93), head circumference measured at US (r = 0.90), and gestational age (r = 0.87). In fetuses suspected of having pulmonary hypoplasia, the relative lung volume varied from 4.6% to 81.6% when the observed total lung volume was expressed as a percentage of the predicted total lung volume.
Conclusion: Normal fetal total lung volume is strongly correlated with biometric measurements. Relative fetal lung volume can be calculated by expressing the observed volume as a percentage of the predicted volume calculated from biometric measurements; knowledge of the relative fetal lung volume assists in the confirmation and quantification of fetal pulmonary hypoplasia.