[A case of bioprosthetic mitral valvular dysfunction due to pannus-formation].

A case of bioprosthetic mitral valvular dysfunction accompanied by mitral stenosis due to pannus is reported. A 69-year-old woman, whose mitral valve had been replaced with a Hancock bioprosthetic valve in June 1979, underwent the second mitral valve replacement in September 1988 because of valvular dysfunction. The ring and cusps of this Hancock valve was partially covered with hard and milky white pannus which resulted in mitral stenosis. The tear of cusp was observed at the point of contact with pannus, which resulted in mitral regurgitation. Histologically, pannus was consisted of two-layered structure, fibrin and collagen fiber, which demonstrated this over-growth was based on thrombus. Main causes of bioprosthetic valve dysfunction are calcification and tear of cusps. But, valvular dysfunction due to pannus-formation described in this case has been experienced very rarely.