Redundancy of the foramen ovale flap may mimic aortic coarctation in the fetus.

Objective: Aim of this study is to assess the relationships between a redundant foramen ovale flap (RFOF) - in the absence of a clearly restrictive foramen ovale - and ventricular disproportion in three group of foetuses: 1) foetuses with a final diagnosis of aortic coarctation (CoA); 2) foetuses referred for a suspicion of ventricular disproportion and/or CoA who did not develop CoA postnatally; 3) normal foetuses. Methods: This is a retrospective study including 73 fetuses, allotted to three groups: 1) foetuses with a final diagnosis of isolated CoA (12 cases); 2) foetuses referred for a suspicion of ventricular disproportion and/or CoA who did not develop CoA postnatally (30 cases); 3) normal foetuses (31 cases). Four-dimensional volume datasets and clips were assessed offline. Diameters of the flap valve, left and right atrium, left and right ventricle and, where available, aortic isthmus and arterial duct were measured; areas of the flap valve, left and right atria and ventricles were measured, too. The left/right ratios for all segments of the heart as well as the ratio between flap diameter / left atrium diameter (FOFD/LAD ratio) and flap area / left atrium area were calculated. Regression analysis was performed to assess the relationships between FOF redundancy and ventricular disproportion. Means were compared with the ANOVA test. Results: Repeatability was fair, with all variables showing an ICC > 83%. In the pooled group of of normals or ventricular disproportion (61 cases), there was a linear correlation between prominence of the FOF and degree of ventricular disproportion (p < 0.01 and p < 0.05 for diameters' and areas' ratios, respectively). Categorising the FOF prominence, cases with FOFd/LAd ratio ≥ 0.65 were highly associated with ventricular disproportion (p = 0.006) Based on the degree of FOF prominence, 4 categories were described, ranging from no prominence/no ventricular disproportion (Stage 0) to severe prominence/ventricular disproportion + transient obstruction of the foramen ovale or mitral orifice. Then, comparing cases with FOFd/LAd ratio ≥ 0.65 vs those with neonatal evidence of coarctation, there was no statistically significant difference in degree of ventricular disproportion nor in the z-score of the aortic isthmus. Conclusions: This study demonstrates that: 1) there is an association between RFOF and ventricular disproportion, independently of the association with a restrictive foramen ovale, and 2) the presence of a RFOF may fully simulate CoA. In fact, it determines both ventricular disproportion and a significant reduction in the diameter of the aortic isthmus, associated in some cases also with reverse isthmic flow. Future prospective studies are needed to evaluate whether focusing the sonologist's attention on the aspect of the FOV may reduce the rate of false positive diagnoses for CoA.