Prenatal Diagnosis of Isolated Congenitally Corrected Transposition of the Great Arteries.

Congenitally corrected transposition of the great arteries (ccTGA) is an uncommon congenital heart defect characterized by atrioventricular and ventriculo-arterial discordance resulting from abnormal leftward looping of the primitive cardiac tube. Although this double discordance produces a physiologically corrected circulation, the morphologic right ventricle functions as the systemic ventricle, and the tricuspid valve serves as the systemic atrioventricular valve, predisposing affected individuals to late complications. Prenatal diagnosis of ccTGA is often challenging, particularly in isolated cases without associated cardiac anomalies, as the four-chamber view may appear deceptively normal on routine obstetric ultrasound. In current prenatal cohorts reported in the literature, isolated ccTGA without additional structural cardiac anomalies is uncommon. In several series of prenatally diagnosed ccTGA, only about 13-15% of cases were isolated when postnatal findings were also considered. We report a case of isolated ccTGA diagnosed at 24 weeks and 4 days of gestation through detailed fetal echocardiographic evaluation and confirmed postnatally. Compared with the routine anomaly scan, which assesses only basic cardiac views (situs, four-chamber, and outflow tracts), a dedicated fetal echocardiography was performed. A sequential segmental approach was used, including confirmation of situs, detailed four-chamber morphology, atrioventricular and ventriculo-arterial connections, outflow tract and three-vessel views, aortic and ductal arches, and cranio-caudal sweeps from abdomen to mediastinum were used to track chamber continuity, great artery relationships, and color Doppler evaluation of flow across the valves and great vessels. Systematic assessment demonstrated ventricular inversion, with the systemic ventricle showing coarse trabeculations and a moderator band, along with apical displacement of the systemic atrioventricular valve consistent with tricuspid morphology. Atrioventricular discordance was clearly identified, and the great arteries were observed to run in a parallel orientation with abnormal ventriculo-arterial connections, key echocardiographic features that enabled accurate prenatal diagnosis. Importantly, no additional intracardiac anomalies were detected. The neonate remained clinically stable after birth, with a normal sinus rhythm and no evidence of immediate hemodynamic compromise. This case highlights the importance of a structured fetal cardiac evaluation extending beyond the standard four-chamber view. Careful attention to ventricular morphology, atrioventricular valve offsetting, and the spatial relationship of the great arteries is essential for identifying isolated ccTGA. Early prenatal diagnosis facilitates appropriate parental counseling, optimized perinatal planning, and structured long-term follow-up. Children with congenitally corrected transposition of the great arteries require lifelong surveillance because of the risk of progressive systemic right ventricular dysfunction, tricuspid valve regurgitation, arrhythmias, and conduction abnormalities, and early recognition allows timely intervention and improved functional outcomes into adolescence and adulthood.