APCU25CR5 Elongated right coronary cusp prolapse plugging an unrepaired perimembranous ventricular septal defect in a 68-year-old: a rare natural history

Introduction PMVSD is the most common ventricular septal defect and is usually repaired in childhood to prevent complications such as cusp prolapse and progressive aortic regurgitation (AR). While RCC prolapse into a VSD is well documented in younger cohorts, untreated cases persisting into late adulthood are exceptionally rare. Here, we describe a 68-year-old with unoperated PMVSD complicated by aneurysmal RCC prolapse mimicking pseudoaneurysm, providing insights into the long-term haemodynamic evolution of congenital shunts.Case Presentation A 68-year-old with a childhood diagnosis of PMVSD, never surgically repaired, presented with progressive exertional dyspnoea. There was no history of infective endocarditis or prior cardiac surgery. TTE was done, showing a conspicuous “double-ring sign” adjacent to the aortic valve suggested pseudoaneurysm. His TOE demonstrated elongated aneurysmal RCC along the margin exposed to the high-velocity jet. The prolapsed cusp intermittently occluded the VSD, most prominently during diastole. No true pseudoaneurysm or paravalvular abscess was detected. AR was mild.Despite the anatomical distortion, the patient remained haemodynamically stable with mild limitation. Multidisciplinary review favoured conservative management with close surveillance over immediate repair.Discussion This case highlights the unusual persistence of unrepaired PMVSD with cusp prolapse into late adulthood. Unlike classical downward displacement, the cusp exhibited progressive elongation and aneurysmal change, probably induced by chronic jet impact. This dynamic cusp prolapse mimicked pseudoaneurysm on TTE, highlighting the importance of multimodality imaging in complex adult congenital lesions. Notably, despite marked distortion, AR severity remained mild. A plausible explanation is that the prolapsed cusp acted as a natural “plug,” reducing shunt flow and limiting regurgitant burden. This paradoxical protective mechanism contrasts with the typical progression of cusp prolapse leading to worsening AR.Conclusion This report illustrates a unique natural history of unoperated PMVSD with aneurysmal RCC prolapse presenting in late adulthood. It emphasizes the value of comprehensive imaging in avoiding misdiagnosis and expands current understanding of VSD-related complications. Documenting such rare presentations raises important questions regarding the long-term adaptive and paradoxically protective roles of cusp prolapse in congenital heart disease.