4 | DISCUSSION
This study was a larger-scale study of prenatal CAT diagnosis, with a particular focus on the diagnostic accuracy of two-dimensional ultrasonography compared with STIC images for anatomical subtypes and to assess the effect of intra-cardiac and extra-cardiac structural abnormalities associated with CAT on pregnancy outcomes. According to the anatomical classification proposed by Van Praagh, CAT is classified following the anatomical origin of the pulmonary artery and the spatial relationship between the vessels. Among the 108 foetuses with CAT in this study, the incidence of the A1 and A2 types was higher (90.7%), which was consistent with a previous study2. Among them, 22 cases (20.4%) were isolated CAT, and the remainder were combined with complex intra-cardiac and extra-cardiac structural deformities.
As an accurate prenatal assessment of CAT is extremely challenging, many cases may be misdiagnosed during prenatal ultrasonography screening.5 A large proportion of foetuses in this study had complex intra-cardiac and extra-cardiac malformations, with prevalence rates of 51.8% and 27.8%, respectively, and only 20.4% of the foetuses were isolated. In contrast, the incidence of CAT complicated with intra-cardiac malformations was higher (51.8%), and the incidence of extra-cardiac malformations was consistent with that reported by Gomez et al.6 However, Abel et al. reported that the incidence of extra-cardiac malformations was 58.8%.7 This difference may be because most of the studies focused on examining the foetal cardiac structure and ignored the extra-cardiac structural malformations. A total of 55 systemic abnormalities were found in 30 cases of combined extra-cardiac structural malformations, of which facial and physical abnormalities were the most common (40.0%), followed by the urinary and nervous systems. Previous studies only reported the incidence of combined extra-cardiac malformations, and the incidence in each system was not specified. Thus, detailed facial and body scans should be routinely performed after a CAT diagnosis.
The prognosis of CAT is closely related to the type of combined deformity. Complex intra-cardiac structural abnormalities complicate the surgery, leading to higher postpartum mortality and morbidity and may affect the decision of the parents to continue or terminate the pregnancy.3 In previous studies, the incidence of pregnancy termination varied widely at 24%,840%9 and 75%,10 respectively. In our study, 61.1% of pregnant women and their families chose to terminate the pregnancy after consulting a prenatal diagnostician. Duke et al. reported a lower incidence of pregnancy termination,8 possibly due to the first detection during the third trimester. In contrast, up to 75% of foetal terminations in Gomez’s cohort may have included only 8 cases, and the accuracy of prenatal diagnosis was only 67%.10
Previous studies have shown that foetal echocardiography and STIC images are useful in improving the differential diagnosis of CAT.6, 11 In our series, 61.1% of the parents chose to terminate the pregnancy due to complicated intra-cardiac and extra-cardiac malformations. We retrospectively analysed 108 cases of traditional two-dimensional echocardiography and STIC images.12 STIC images can be used to evaluate the anatomical structure of the CAT and pulmonary artery stereoscopically and intuitively, which is of great value in determining the CAT classification and differential diagnosis.13 STIC completely displays the aortic arch, which is a better display rate than IAA.14 In our study, prenatal STIC images were obtained for 88 cases, of which 1 case of A4 type STIC image intuitively showed IAA. The prenatal diagnosis was consistent with the autopsy results. The STIC image quality of the other 20 cases was poor, so satisfactory STIC volume images could not be obtained, possibly due to shorter or longer gestational age, along with other influencing factors such as maternal obesity. Therefore, STIC can be used as an auxiliary diagnostic method to increase the accuracy of CAT diagnosis.
The prenatal diagnosis of CAT has been mainly differentiated from other malformations of the conus arteriosus, such as tetralogy of Fallot (TOF) and pulmonary atresia with ventricular septal defect (PA-VSD). In the case of TOF, the finer branches of the pulmonary artery arise from the right ventricular outflow tract with two sets of semilunar valves.15 In PA-VSD, the pulmonary artery is not connected to the ventricle or the ascending aorta. The majority of the aortopulmonary collateral arteries or retrograde ductus arteriosus supply blood, and most of them are associated with the right aortic arch (RAA).16 Only 22 foetuses (20.4%) had an RAA in our study. This study shows that the STIC images were more accurate for differential diagnosis and with the types between PTA, TOF and PA-VSD.
In summary, prenatal echocardiography combined with STIC images was useful for accurately diagnosing CAT and identifying its subtypes. This study included intra-cardiac and extra-cardiac anomalies associated with CAT; therefore, it can be used as an important basis for clinical decisions.
Ethical approval
This study was granted an exemption from the Medical Ethics Committee of Gansu Provincial Maternity and Child-care Hospital. The participants provided their written informed consent to publish their cases (including publication of images).