Right‐sided congenital diaphragmatic hernia: the challenge remains

Fetal surgery is without a doubt one of the greatest achievements in fetal medicine over the last three decades, addressing a number of lethal or otherwise debilitating congenital conditions and pregnancy complications. Fetal endotracheal occlusion (FETO) for the treatment of pulmonary hypoplasia secondary to congenital diaphragmatic hernia (CDH), although always ‘high on the fetal surgery agenda’, has seen many waves of ‘hope and despair’ (Deprest JA et al., Fetal surgery for congenital diaphragmatic hernia is back from never gone, Fetal Diagn Ther 2011;29:6–17). Indeed, despite sound physiological theories and animal experiments suggesting its potential benefits, randomised controlled trials comparing FETO to expectant management have not consistently shown the expected success (Harrison MR et al., A randomized trial of fetal endoscopic tracheal occlusion for severe fetal congenital diaphragmatic hernia, N Engl J Med 2003;349:1916–24). Notwithstanding the low incidence of CDH, a continued challenge surrounding FETO has been the difficulty in accurately determining fetal prognostic factors which may prompt intervention. These concerns appear to be greater in right-sided CDH (RCDH), given that its incidence is 70–80% lower than left-sided defects, and that liver herniation, a major prognostic factor in contralateral cases, is almost universally present (Hedrick HL et al., Right congenital diaphragmatic hernia: prenatal assessment and outcome, J Pediatr Surg 2004;39:319–23). In their study, DeKoninck et al. correctly point out that most CDH studies address isolated left-sided defects, and that perhaps RCDH may be a different pathology altogether, worthy of its own evaluation. To describe the specific characteristics and outcomes of RCDH, they conducted a retrospective review of cases with isolated RCDH and liver herniation subjected to FETO at two centres over 10 years, and find that fetuses with a lung-to-head ratio ≤45% have a tendency towards increased survival at 42% relative to 17% among expectantly managed cases (P = 0.09), without a significant increase in preterm birth. Akin to left-sided defects, they re-iterate that initial lung size predicts survival following FETO in right-sided defects. These results, although not statistically significant, point to the value that FETO may have in severe RCDH. Or do they? The issue with retrospectively analysing rare pathologies using observational data that is collected outside the realm of a controlled trial, in addition to not offering a power calculation, is that facing non-statistically significant results such as those provided in this study, one cannot attribute the differences, or lack thereof, between subjects and controls either to a lack of statistical power or to the absence of a true relationship between intervention and outcome. The nuanced interpretation in conclusions such as ‘Though the current data do not show benefit, in poor prognosis cases FETO may seem to be justifiable’ needs to be therefore regarded with the utmost caution. Indeed, the same way in which a trend towards positive outcomes, such as increased survival, may prompt intervention, the risk of rendering a non-statistically significant negative outcome such as preterm birth significant, increases. All in all, it would seem from these results that at best, FETO increases survival in fetuses with RCDH O/E LHR between 30 and 45%, to a rate similar in those with an O/E LHR between 46 and 55% who are expectantly managed. These are promising results and important findings that add substance to the literature, but which need to be prospectively and formally studied in the context of FETO-based trials. The author reports no conflict of interest.

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