Congenitally corrected transposition of the great arteries: clues for prenatal diagnosis.

Congenitally corrected transposition of the great arteries (ccTGA) is an uncommon cardiac defect characterized by the atria connecting with the anatomically discordant ventricles and the ventricles connecting with discordant and transposed great arteries. Parallel vessels are evident in corrected TGA, but as this sign is also present in complete TGA, a heart anomaly requiring major cardiac surgery in the postnatal period, it is important to differentiate between the entities prenatally. Most cases of ccTGA have associated anomalies but isolated forms or those with a mild associated cardiac anomaly are infrequently detected prenatally. We report on three cases detected between 21 and 25 weeks' gestation on screening ultrasound with associated mild findings. One fetus had an isolated ventricular septal defect (VSD) first detected at 34 weeks. The child developed heart block at 4 years of age. The second case was associated with a small VSD, a tiny pulmonary trunk and a persistent right umbilical vein. After birth, mild pulmonary stenosis was found as an additional cardiac finding at 4 months of age. The third fetus had no additional cardiac anomalies prenatally, but after birth a bicuspid aortic valve was detected. The first case needed pacemaker implantation but the other two children required no cardiac surgery. Two of the cases were referred because abnormal vessel anatomy was detected on screening ultrasound. As prenatal detection of TGA is becoming a more frequent occurrence, this paper aims to present clues aiding in the prenatal diagnosis of atrioventricular and ventriculoarterial discordance, especially in its differentiation from complete transposition. These details are crucial for counseling and perinatal management.