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However, there is no evidence of their congenital origin Elongation of papillary muscles can be found at birth in the mitral or tricuspid apparatus, but the muscles usually have an ischemic, beige aspect Sometimes the ischemic origin is demonstrated by acute rupture at or shortly after birth Isolated dilation of the annulus is not found at birth Both dilation of the annulus and elongation of the suspension apparatus are usually associated with significant volume loading of the left ventricle (e.g., with a large ventricular septal defect [VSD] or large patent ductus arteriosus) The pathophysiology is of initial dilation of the posterior annulus under the effect of the volume loading, followed by elongation of the marginal cords and prolapse of the free edge of the anterior leaflet In rare cases minor anomalies of the valvar tissue or the papillary muscles indicate a true congenital origin Mitral Valve Disease With Excess of Leaflet Tissue and Mitral Valve Prolapse It is debatable whether the mitral valve prolapse syndrome in its most common form―limited to the middle scallop of the posterior defect—is congenital In a large population of neonates22 and using strict criteria, the incidence of mild bulging of the anterior leaflet was negligible and no prolapses were detected This tends to prove that mitral valve prolapse is an acquired disease In its common form, it is rarely encountered in neonates and infants In adults, the histologic anomalies are limited to the middle scallop of the posterior leaflet, with predominant elastic fiber alteration and myxomatous tissue proliferation.23 The more extensive form of mitral valve prolapse, however, can be seen in neonates and infants In that case, an excess of tissue is distributed to both the anterior and posterior leaflets and histologic examination reveals extensive infiltration of the spongiosa with myxomatous tissue The histologic anomalies are identical to those found in patients with Marfan syndrome,23,24 EhlersDanlos syndrome, and osteogenesis imperfecta Marfan syndrome is an autosomal dominant disorder with varying penetrance The mutation is found on the fibrillin gene Ehlers-Danlos syndrome is represented by a constellation of mutations linked to different subtypes.25 The extensive form of the mitral valve prolapse syndrome is encountered in sporadic cases or in familial forms demonstrating autosomal dominant and X-linked inheritance Different loci on chromosomes 16, 11, and 13 have been found to be linked to the disease.26 Recently, mutations in the dachsous cadherin-related 1 gene (DCHS-1) have been identified as a cause of mitral valve prolapse.27 Anomalies of the Mitral Valve in the Setting of Anomaly of the Ventricular Arterial Connection and Ventricular Septal Defect Essentially Double-Outlet Ventriculoarterial Connections Together With Anterosuperior Interventricular Muscular Communication Often the heart has unbalanced ventricles and the anatomy does not affect the surgical treatment Straddling, when one papillary muscle (usually the anterosuperior one or a lesser head of the latter), is located in the morphologic right ventricle is more common than overriding, where part of the mitral valve annulus is located beyond the morphologic right side of the interventricular septum and above an outlet VSD (Fig 34.16) FIG 34.16 Heart with double-outlet right ventricle and subpulmonary interventricular communication, the so-called Taussig-Bing malformation There is straddling and overriding of the superoanterior end of the zone of apposition between the aortic and mural leaflets In this instance, the leaflets retain their location within the left ventricle, with straddling of the tendinous cords to attach to a papillary muscle located in the right ventricle Stenosis Versus Incompetence It is often difficult for the morphologist to predict from a specimen whether the observed pathology would have produced stenosis or incompetence A much better appreciation is obtained by the surgeon, as described later in this chapter.6,28,29 When insufficiency is the primary lesion, this is most frequently the consequence of problems with the leaflets, exacerbated by dilation of the annulus Alternatively, insufficiency as a primary feature can be caused by subvalvar problems, such as chordal retraction or elongation, or hypoplasia or agenesis of the papillary muscles Prolapse is obviously the major substrate for many patients with mitral valvar problems When stenosis is the major problem, this is likely to be a result of fusion along the ends of the zone of apposition between the leaflets of a dysplastic valve, a hammock lesion, a parachute deformity, or a funnel-shaped valve Combined stenosis and insufficiency are related to fusion of the ends of the zone of apposition between the leaflets, a hammock valve, a parachute deformity, or papillary muscular hypertrophy Effect on the Heart Valvar pathology always affects the cardiac pump and, despite compensatory mechanisms, may lead to serious side effects in the myocardium and endocardium It should always be remembered that valvar pathology can also affect the pulmonary vascular bed, with pulmonary hypertension as a possible consequence.30
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