Unilateral agenesis of the diaphragm: a separate entity or an extremely large defect?

Since the mid-1980s, unilateral agenesis of the diaphragm (DA) has attracted the attention of paediatric surgeons as more babies affected by this extreme form of congenital diaphragmatic hernia (CDH) survive. Some authors believe that it represents a separate clinical entity. We undertook a retrospective analysis of all babies with CDH treated in the South-West Regional Paediatric Surgical Centre in Bristol between 1981 and 1995. Of 108 babies 16 (14.8%) were identified as having DA. All presented with severe respiratory distress from birth. In comparison to the group of patients with postero-lateral hernia, neonates with DA had lower Apgar scores and required longer preoperative stabilisation with inotropic support and vasodilators. Nine were subjected to operation and all required diaphragmatic replacement. Only 3 survived; thus, mortality in the DA group was 81.25%, and among those who underwent surgery 66.6% The same data for babies with postero-lateral hernia were 15.2% and 7.2%, respectively. Our results indicate that DA is associated with high morbidity and mortality, but we have not found any evidence that this anomaly is a distinct entity. In addition, we reviewed all post-mortem reports of fetuses with diaphragmatic defects available for the same period. Of 19 fetuses, 10 (52.6%) had DA. The morphological details of the diaphragmatic defect and the presence of associated anomalies were analysed. Our observations support the hypothesis that DA occurs in the very early stages of embryonic life and may be attributed to developmental arrest of the septum transversum.