What is the classic prenatal signature of Transposition of the Great Arteries (TGA)?

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Ventriculoarterial discordance is the hallmark of Transposition of the Great Arteries. In this condition, the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle, so the great arteries run in parallel rather than cross over each other. Prenatally, this is best seen in the three-vessel and trachea views where the great arteries appear side by side instead of forming the normal spiraling/overlapping pattern. The aorta typically is anterior and to the right of the pulmonary artery, reflecting the abnormal connections.

This is distinct from a normal heart, where the aorta arises from the left ventricle and the pulmonary artery from the right ventricle; from a heart with dextrocardia and situs inversus, which is a different visceral arrangement; and from truncus arteriosus, where a single great artery arises from the heart. Therefore, the classic prenatal signature of TGA is the aorta arising from the right ventricle and the pulmonary artery arising from the left ventricle with parallel great arteries on imaging.