Anomalous papillary muscle insertion beyond hypertrophic cardiomyopathy: insights from reported cases

Anomalous insertion of the papillary muscle (APM) into the mitral valve leaflet is a rare congenital abnormality of the subvalvular apparatus. Most published reports describe direct papillary muscle insertion in association with obstructive physiology, particularly in hypertrophic cardiomyopathy (HCM), where it contributes to left ventricular outflow tract (LVOT) obstruction and systolic anterior motion (SAM)-related mitral regurgitation. However, similar papillary muscle-leaflet continuity may also serve as a primary mechanical determinant of valve dysfunction in patients without a clinical diagnosis of HCM. This review synthesizes published reports of APM insertion across different clinical contexts and interprets them within a mechanism-oriented framework based on LVOT dynamics and functional role of the papillary muscle rather than disease labels. Available reports indicate a heterogeneous clinical spectrum in which hemodynamic manifestations reflect interactions among papillary muscle anatomy, mitral valve mechanics, and ventricular geometry. Although LVOT obstruction remains an important presentation, many cases show predominant mitral regurgitation due to leaflet tethering or, less commonly, functional mitral stenosis from impaired diastolic leaflet opening. These phenotypes arise from subvalvular mechanical restriction rather than primary leaflet pathology. Echocardiography plays a central role in diagnosis, yet APM insertion may be overlooked if assessment focuses primarily on leaflet morphology or Doppler findings. Transesophageal echocardiography, cardiac computed tomography, and cardiac magnetic resonance imaging provide complementary anatomical detail for accurate characterization and surgical planning. Greater awareness of this geometry-based interaction and adoption of a structured imaging approach may reduce diagnostic oversight and improve decision-making in patients with atypical mitral valve dysfunction.