Effect of immediate versus slow intrauterine reduction of congenital diaphragmatic hernia on lung development in the sheep: a morphometric analysis of term pulmonary structure and maturity.

The incidence of congenital diaphragmatic hernia (CDH) is 1:1,200-5, 000, and the condition is associated with high mortality and morbidity attributed principally to associated pulmonary hypoplasia. One treatment approach has been for intrauterine intervention to induce lung growth to a sufficient level to allow survival at birth. Repair of the hernia in utero has been attempted, using a method of immediate reduction and repair of the hernia (patch) compared to a slow reduction method using a silastic "silo" sewn over the diaphragm defect to contain the hernial contents. In animal studies, this second method has been associated with lower fetal morbidity and mortality. This study, utilizing the sheep model of CDH, focuses on analysis of lung structural development and maturation, comparing the efficacy of the immediate vs. slow methods of hernial repair in preventing/reversing pulmonary hypoplasia. We hypothesized that: a) Both the immediate (patch) and slow (silo) methods of hernia repair performed in the lamb model of CDH will stimulate lung growth and structural development and restore lung structure and maturity towards normal levels by term gestation; b) Effects will be detectable by morphometric measurement of the following parameters: lung volume; parenchyma to nonparenchyma tissue ratio; volume density of connective tissue in nonparenchyma; gas exchange tissue to airspace ratio; gas exchange surface area; capillary loading; alveolar/airspace density; and alveolar perimeter; c) Effects will be seen in all lobes of the lung; and d) There will be no significant difference in lung size or structural parameters between the two groups. Forty-four pregnant ewes were allocated randomly to one of four groups. Fetal lambs in three groups (n = 36) underwent CDH creation at days 72-74 of gestation. Of surviving lambs showing an adequate hernia, 9 were not operated on further, 11 underwent "repair" using a silastic chimney around the hernial contents (slow reduction), and 11 underwent "repair" by a silastic patch over the diaphragmatic defect (immediate reduction). The fourth group were normal controls. All surviving lambs (n = 8 in each group) were delivered by Cesarian section at 141-143 days (term = 145-149 days). Lungs were obtained at autopsy, inflation-fixed, divided into lobes, and sampled, and morphometric analysis was performed. Comparisons were made between these groups and with matched normal controls and CDH untreated animals prepared in conjunction and previously reported. The lungs from the CDH animals treated by both methods of fetal hernia repair showed significant lung growth and structural development and maturation, although they remained significantly hypoplastic compared to normal. There were minor differences in the lung parameters between these two groups, with a tendency for the slow method to provide more normal parameter values. An exception was the increase in lung volume that was greater for the immediate (patch) method, particularly in the left lower lobe. In conclusion, intrauterine hernia repair by both methods is capable of partially reversing total lung and lobar structural hypoplasia and immaturity. The slow reduction method, with reduced potential for mortality and morbidity, is at least as good at reversing pulmonary hypoplasia as the immediate method. Alternative intrauterine interventions to prevent or reverse pulmonary hypoplasia are discussed and compared with the hernia repair methods used in this study.

Morphometric analysis of pulmonary development in the sheep following creation of fetal diaphragmatic hernia.

Congenital diaphragmatic hernia (CDH) in humans is relatively common and associated with high mortality attributed mainly to pulmonary hypoplasia. Previous animal models have induced CDH late in gestation, in contrast to the human situation, and only limited morphometric analyses have been reported. We undertook early surgical creation of CDH in fetal lambs, days 72-74 of gestation (n = 8), with unoperated lambs (n = 8) as controls. At 143 days (term = 145-149) a cesarean section was performed and the lungs were obtained, inflation fixed, divided into lobes, and processed for morphometry. In the CDH group the total lung volumes (51.3 mL compared to 223.8 mL) and gas exchange surface areas (5.85 m2 versus 26.43 m2) were less than one quarter of control values. Capillary loading was reduced from 0.3 mL/m2 in controls to 0.12 mL/m2 in CDH and parenchymal volume reduced from 77% in controls to 57% in CDH. Within parenchyma, gas exchange tissue volume was increased in CDH (66%) compared with controls (50%). CDH lungs had primitive air sacs/alveoli that were smaller (perimeter 83 microns) and more numerous (1321 per mm2) than in controls (perimeter 132 microns, 504 per mm2). The left lung and left upper lobe were affected most. Induction of CDH in the lamb at this early age results in quantifiable, reproducible pulmonary hypoplasia from which comparisons can be made with the human condition.