Clinical significance of the lung/thorax transverse-area ratio in fetuses with cystic lung disease.

We examined the clinical significance of the lung-thorax transverse-area ratio (L/T) in fetuses with cystic lung disease (CLD). The transverse section of the thorax was analyzed at the level of the 4-chamber view of the heart. L/T was calculated as the bilateral normal lung area divided by the thoracic area. Within a 9-year period, ultrasonography was performed in 15 fetuses with CLD, 13 of which were histologically diagnosed: congenital cystic adenomatoid malformation of the lung (CAM; n = 8), pulmonary sequestration (n = 4), and bronchial atresia (n = 1). Although the initial L/T measurement (29.6 +/- 4.2 weeks) showed significantly lower values than in the controls, the final measurement (36.4 +/- 1. 6 weeks) indicated that the L/T in CLD excluding CAM was significantly higher than that in CAM. Six patients with a final L/T of less than 0.21 required mechanical ventilation immediately after birth. Two of these patients died, and the autopsy findings indicated pulmonary hypoplasia. In these cases, a significant correlation was observed between the maximal value of L/T and preductal alveolar-arterial oxygen difference (A-aDO(2)), although the final L/T was not correlated to A-aDO(2). These results indicate that serial measurements of L/T may be useful in the diagnosis of CLD and may help to predict postnatal respiratory conditions.