Imaging description

Cor triatriatum, also known as cor triatriatum sinister, is a congenital abnormality of the left atrium in which a fibromuscular membrane separates the atrium into anterior and posterior chambers (Figure 21.1). The membrane appears as a low-attenuation structure on cardiac CT extending from the atrial septum medially to the ridge of tissue between left pulmonary vein ostia and the left atrial appendage laterally. Cor triatriatum is the result of incomplete fusion of a common pulmonary vein chamber posteriorly with the anterior mitral valve and left atrial appendage during fetal life. The result is a fibromuscular membrane within the left atrium which usually contains one or multiple openings that allow communication between anterior and posterior chambers. Depending on the size of the opening(s) of the membrane, there may be obstruction of pulmonary venous outflow, resulting in symptoms similar to mitral stenosis. Cor triatriatum with larger defects may present with symptoms late in adulthood or can be entirely asymptomatic (Figures 21.1, 21.2).

Importance

Cor triatriatum is an uncommon abnormality, which in adults is frequently misdiagnosed at initial presentation as mitral valve disease or pulmonary hypertension. If identified, it is important to draw attention to the abnormality and recommend further non-invasive evaluation with echocardiography to assess for any functionally significant obstruction that might require surgical treatment.

Typical clinical scenario

Cor triatriatum is a rare abnormality, accounting for less than 1% of all congenital cardiac malformations. The majority of patients with cor triatriatum present in infancy; however, a minority of patients will present in adulthood.

Differential diagnosis

Cor triatriatum should be differentiated from a complete total anomalous pulmonary venous return, in which pulmonary veins connect to a common venous chamber that drains separately into the heart. Chronic left atrial clot can sometimes have angular or web-like appearances that may simulate cor triatriatum; however, it will often be associated with a masslike thrombus or calcifications.