Cor triatriatum sinister versus bowed septum primum in an infant with total anomalous pulmonary venous connection: a difficult imaging distinction.

In cor triatriatum sinister, a membrane divides the left atrium into a posterior chamber that receives the pulmonary veins and an anterior chamber that communicates with the mitral valve. With right-side chamber overload, the septum primum can separate from the muscular septum and bow toward the left atrial cavity, leading to a thin membrane within the left atrium and imaging findings that may mimic cor triatriatum. We report the multidetector CT findings of a 3-month-old infant with a supracardiac total anomalous pulmonary venous connection with a bowed septum primum. A description of the imaging findings that distinguish cor triatriatum and bowed septum primum will be discussed. This case demonstrates the usefulness of MDCT in the assessment of supracardiac vascular anomalies and intracardiac anatomy.