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Mitral valve prolapse: an atypical variation of the anatomy.

BACKGROUND
The mitral valve apparatus is a complex structure composed of an annulus, mitral leaflets, chordae tendinae, papillary muscles and left ventricular, atrial and aortic walls. Deficiency or degeneration of one or more of these structures may result in dysfunction of the valvular apparatus leading to mitral valve prolapse during systole.


OBJECTIVE
To review the chordal attachment of surgically resected mitral valve tissue from cases of mitral valve incompetence.


METHODS
The clinical and morphological features of 135 surgically resected posterior mitral valve leaflet specimens were reviewed for mitral valve prolapse from January 1999 to June 1999. Four mitral leaflets removed either surgically or at autopsy served as controls.


RESULTS
Excised posterior mitral leaflets from two patients had segments containing free margin and rough zone chordae that lacked attachment to larger 'strut' or 'stem' chordae or to either papillary muscle. These chordae were observed in otherwise normal mitral valves with adjacent areas that had normal chordal arrangements. Such chordae of the posterior leaflet were termed 'atypical chordae tendinae'. There was no good gross or histological evidence of chordal rupture, and this atypical arrangement appears to be congenital in origin. Grossly and histologically, these atypical variants otherwise exhibited characteristics similar to those of leaflet tissue from typical cases of mitral valve prolapse, with shiny, grey-white and "edematous" tissue that contained increased mucopolysaccharides in the zona spongiosa and chordae tendinae.


CONCLUSIONS
This review found atypical attachment of mitral valve chordae tendinae such that isolated segments of the posterior leaflet congenitally lack chordal support, likely leading to mitral valve prolapse. Review of the literature suggests that this is a heretofore unreported cause of mitral valve incompetence.