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).