MRI prediction of fetal lung volumes and the impact on counselling

AIM To assess whether lung volume percentages in congenital diaphragmatic hernia (CDH) differ depending on which formula is used to calculate the expected volume for gestation and any potential impact this may have on perinatal counselling. MATERIALS AND METHODS Forty-seven patients with left-sided CDH who had undergone fetal magnetic resonance imaging (MRI) at Sheffield Teaching Hospitals were reviewed. The lung volumes were measured on MRI and compared with the volumes that would be expected at the given gestation for each patient. Expected values were calculated using four formulae from the literature and the authors’ in-house method. These measurements were used to calculate the percentage total lung volume observed compared with the expected lung volume in a healthy fetus of the same gestation. The differences in percentage lung volumes using these five methods were then compared with how they relate to predicted rates of survival. How predicted survival would change depending on which formula was used to calculate the percentage lung volume was investigated with a view to how this may change the counselling given to a family. RESULTS In 10/47 (21%) patients, there was no change in the predicted percentage chance of survival depending on which formula was used to calculate the predicted lung volume. In 37/47 (79%), the predicted chance of survival changed depending on which formula was used to calculate the expected lung volume at the given gestation. In 20 (47%) of these cases, the change in predicted survival depending on which formula used was 45% (i.e., from 25% to 70% survival in four and from 50% to 95% survival in 16) and in two cases (4%) this difference was 70% (i.e., from 25% predicted survival to 95% predicted survival). CONCLUSION There are several different methods for calculating expected lung volumes for any given gestation. When used to estimate the percentage lung volume in patients with CDH, there is a large difference in values depending on which method is used. This in turn leads to a large variation in predicted survival with some patients in this study having either a 25% or 95% chance of survival depending on which method is used. This has a huge impact on perinatal counselling and the difficult decisions made by families.