ABSTRACT
CDH is diagnosed on antenatal ultrasound scan in approximately 50 per cent cases. The diagnosis should prompt a detailed scan for associated anomalies. Although in the majority of cases CDH is an isolated defect, genetic associations include trisomies 13 and 18 and syndromes including Fryn (MIM229850), Coffin-Siris (MIM135900) and DenysDrash (MIM194070). The presence of associated anomalies has been shown to have a detrimental impact on outcome: up to 93 per cent of cases perish antenatally. Technological improvements in antenatal diagnosis have stimulated considerable interest in determining reliable prognostic indicators for isolated CDH. Many prognostic indices have been suggested, including gestational age at diagnosis, the site and size of the defect, polyhydramnios, and the presence of the liver in the thoracic cavity (‘liver-up’ cases). Determining the extent of pulmonary hypoplasia in the antenatal period has been an area of extensive research. Measurements such as the lung-to-head ratio (LHR) and the lung-to-thoracic ratio (LTR) have been suggested as ultrasound predictors of the degree of lung hypoplasia. The LHR calculates the ratio between the circumference of the skull (to normalize for fetal size) and the diameter of the lung contralateral to the diaphragmatic defect. An increasing number of reports have defined limits for this variable to correlate with outcome. An LHR below one is almost universally fatal, and a value greater than 1.4 is likely to imply a favourable outcome. Although promising as a useful tool to assess the adequacy of lung development in the fetus, all studies to date have been retrospective. A large prospective trial is warranted to confirm the validity of this measure as a prognostic marker. Fetal magnetic resonance imaging (MRI) lung volumetry also has been reported, but at present its use remains largely experimental.
