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

Since the mid-1980s, unilateral agenesis of the diaphragm (DA) has attracte d the attention of paediatric surgeons as more babies affected by this extr eme form of congenital diaphragmatic hernia (CDH) survive. Some authors bel ieve that it represents a separate clinical entity. We undertook a retrospe ctive analysis of all babies with CDH treated in the South-West Regional Pa ediatric Surgical Centre in Bristol between 1981 and 1995. Of 108 babies 16 (14.8%) were identified as having DA. All presented with severe respirator y 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 w ere subjected to operation and all required diaphragmatic replacement. Only 3 survived; thus, mortality in the DA group was 81.25%, and among those wh o underwent surgery 66.6% The same data for babies with postero-lateral her nia were 15.2% and 7.2%, respectively. Our results indicate that DA is asso ciated with high morbidity and mortality, but we have not found any evidenc e that this anomaly is a distinct entity. In addition, we reviewed all post -mortem reports of fetuses with diaphragmatic defects available for the sam e period. Of 19 fetuses, 10 (52.5%) had DA. The morphological details of th e diaphragmatic defect and the presence of associated anomalies were analys ed. Our observations support the hypothesis that DA occurs in the very earl y stages of embryonic life and may be attributed to developmental arrest of the septum transversum.