Case Report: Fenestration-free non-obstructive left atrial membrane overlapping with the cor triatriatum spectrum: multimodality imaging and three-year follow-up.

Non-obstructive left atrial membranous anomalies may overlap anatomically with the cor triatriatum spectrum while lacking the classical hemodynamic features of functional left atrial compartmentalization. We report a 23-year-old woman referred for echocardiographic evaluation, in whom a left atrial membrane was characterized by multimodality imaging. Transesophageal echocardiography demonstrated a membrane originating adjacent to the left atrial appendage ostium and attaching to the interatrial septum at the aortic rim, without detectable transmembranous flow. Mitral inflow and pulmonary venous Doppler patterns were normal, and left atrial appendage emptying velocity was preserved (58 cm/s). Contrast-enhanced cardiac computed tomography confirmed the membrane's anatomical configuration, its spatial relationship to the left atrial appendage and interatrial septum, and the superior localization of pulmonary venous inflow relative to the membrane. Conservative management was adopted, and three-year follow-up remained entirely event-free, with no arrhythmia, thromboembolic event, or hemodynamic progression. This case illustrates that apparent anatomical continuity does not necessarily imply physiological obstruction in left atrial membranous anomalies and underscores the role of integrated multimodality assessment in guiding long-term management.