Background: The precise etiology of hypoplasia of the posterior mitral valve leaflet (PMVL) remains incompletely elucidated; however, it has been hypothesized to stem from genetic mutations occurring during fetal development. Herein, we present the anatomical characteristics of the mitral valve and associated cardiac pathologies in patients with hypoplastic PMVL.

Methods: This single-center retrospective study involved patients who presented between 2015 and 2021 at a tertiary healthcare facility. Among the cohort, 44 individuals had hypoplastic PMVL and were divided into 2 groups: those with severe mitral regurgitation (MR) and those with non-severe MR.

Results: Among the patients, 11 (25%) had severe MR. The median lengths for the PMVL was 5 mm (5-6). Moreover, 10 patients had concomitant muscular formation. We found that 13 patients had bicuspid aortic valve (BAV), while the second most common concomitant cardiac congenital pathology was secundum atrial septal defect (ASD) in 7 patients. The anterior mitral leaflet (AML) length (P = .007), AML prolapse (P < .001), and A2P2 distance (P = .008) were higher in the group with severe MR. In addition, muscular formation was more common in patients with hypoplastic PMVL with severe MR (P < .001).

Conclusion: Hypoplastic PMVL is a rare but significant anomaly that causes MR. While it can coexist with numerous congenital conditions, the most frequent associations include BAV and, secondly, ASD. Severe MR is particularly observed in cases accompanied by dilated mitral annulus, AML prolapse, and muscular formation.