Agenesis of the right lung was diagnosed prenatally in two neonates born at 36 and 37 weeks, respectively. Computed tomographic scans and magnetic resonance imaging indicated that both cases had a Type 2 pulmonary agenesis, which was confirmed later by bronchoscopy. Both patients were clinically stable during the neonatal period. Serial pulmonary function tests revealed a decrease in specific respiratory system compliance (sCrs) in both neonates and a marked discrepancy between functional residual capacity measured by the nitrogen washout technique (FRCN2) and by plethysmography (FRCpleth) on follow‐up. Early decrease of respiratory system compliance (Crs) and increase of respiratory system resistance (Rrs) in one infant preceded the onset of tracheal stenosis, which remained asymptomatic until the age of 8 weeks, when the infant developed acute respiratory failure requiring intubation and mechanical ventilation with high airway pressures. Aortopexy, implantation of a tissue expander into the right hemithorax, and laser ablation of fibrotic tissue at the site of tracheal stenosis were performed to achieve successful extubation. The second infant remained asymptomatic. Values for lung mechanics and volumes for both infants with pulmonary aplasia were as follows: Crs, 3.43 and 10.60 mL · kPa−1 · kg−1; sCrs, 0.23 and 1.28 kpa−1; Rrs, 11.1 and 7.4 kpa · s · L−1; FRCN2, 14.9 and 10.2 mL · kg−1; FRCpleth, 28.2 and 25.8 mL · kg−; FRCN2: FRCpleth ratio, 0.56 and 0.54 for patients 1 and 2, respectively. These values differed considerably from results of a control group of nine term healthy neonates (Crs, 10.0 ± 1.8 mL · kPa−1 · kg−1; sCrs, 0.43 ± 0.08 kpa−1; Rrs, 5.10 ± 0.55 kpa · s · L−1; FRCN2, 24.0 ± 2.5 mL · kg−1; FRCpleth, 31.1 ± 6.0 mL · kg−1; FRCN2:FRCpleth ratio, 0.78 ± 0.10). In conclusion, serial assessment of lung mechanics and pulmonary gas volumes detects airway obstruction early in neonates with unilateral lung agenesis. Bronchoscopy is recommended. Along with conventional surgical procedures, an expandable implant may improve management or prevent respiratory failure in selected cases. Pediatr Pulmonol. 1998; 26:138–144. © 1998 Wiley‐Liss, Inc.
