Late Diagnosis of Unroofed Coronary Sinus Associated with Persistent Left Superior Vena Cava in Patient with Repaired Tetralogy of Fallot: Case Report

<b>Background:</b> An unroofed coronary sinus (UCS) is a rare congenital cardiac anomaly, accounting for less than 1% of atrial septal defects and frequently associated with a persistent left superior vena cava (PLSVC). Its coexistence with Tetralogy of Fallot (TOF) is exceptionally uncommon and has been reported almost exclusively in isolated case reports. <b>Case Presentation:</b> We report the case of a 20-year-old woman with a history of surgically corrected TOF in infancy, who presented with progressive exertional dyspnea. Multimodality imaging, including transthoracic echocardiography and cardiac magnetic resonance imaging, revealed a large atrial-level shunt caused by a type I unroofed coronary sinus associated with a persistent left superior vena cava, leading to significant right-sided chamber dilation and pulmonary hypertension. Notably, this anomaly had not been identified at the time of the initial TOF repair. The patient underwent a successful surgical correction with interatrial compartmentation and tricuspid annuloplasty, with an uneventful postoperative course. <b>Conclusions:</b> This case underscores the extreme rarity of the UCS-TOF association and highlights the potential for UCSs with PLSVC to remain clinically silent for years after complex congenital heart surgery. A comprehensive reassessment of the systemic venous and atrial anatomy using advanced multimodality imaging is essential in symptomatic adults with repaired TOF, as late-presenting venous anomalies may have significant hemodynamic and clinical implications.