Mild eccentric aortic regurgitation in bicuspid aortic valve causing anterior mitral leaflet perforation.

Type 0 bicuspid aortic valve (BAV) with mild aortic regurgitation (AR) is generally considered a benign lesion. We report two pediatric cases of type 0 BAV with mild eccentric AR causing a previously undescribed complication: anterior mitral leaflet (AML) aneurysm and perforation through a novel "jet lesion" mechanism. A 13-year-old girl and an 8-year-old boy presented with palpitations and exertional dyspnea. Both had type 0 BAV with posteriorly or inferiorly directed mild eccentric AR. Transthoracic echocardiography identified a localized AML aneurysm with perforation resulting in severe secondary mitral regurgitation (MR). Inflammatory markers and blood cultures were negative, excluding infective endocarditis. Surgical exploration in one case confirmed a circular defect in the AML at the exact site where the AR jet impacted the leaflet. Pericardial patch repair was performed with successful restoration of mitral valve competence at 3-month follow-up. We propose that chronic low-velocity eccentric AR jets striking the AML induce endothelial denudation and localized myxomatous degeneration. Cyclic mechanical stress from regurgitant flow promotes progressive structural weakening, leading to aneurysm formation and eventual perforation with hemodynamically significant secondary MR. This observation challenges the assumption that mild AR in BAV is inconsequential. The temporal clustering of these cases suggests an underrecognized complication warranting heightened surveillance in BAV patients with posteriorly directed AR jets, regardless of AR severity. Systematic evaluation in larger cohorts is needed to clarify the prevalence, risk stratification, and optimal management strategies for this novel jet lesion complication in type 0 BAV disease.