There are two variants of valvular defects: stenosis (narrowing) and atresia (absent connection).
Heart chambers proximal to the site of obstruction show marked hypertrophy (increased preload) and there is congestion proximal to obstruction. Right sided obstructions produce decreased pulmonary flow, left sided obstrucions produce decreased systemic blood flow. In addition heart chambers distal to atresia are hypoplastic (insufficiently developed because of absent blood flow).
Dysplastic valves: anomalies of shape and insertion anomalies
Polyvalvular dysplasia: atriventricular and seminular valves are dysplastic in 90% of the cases of trisomy 18, less often in the other aneuploidias (trisomy 13 etc.) The leaflets and cusps are redudant, myxomatously thickened or nodular not infrequently with minute blood cysts at the valve margins. Aortic and pulmonary valves are often bicuspid. The most severe changes are present in mitral and tricuspid valves.
Bicuspid pulmonary valve, trisomy 18, fetus: Bicuspidal pulmonary artery, Macro, autopsy (72047)
Atresia of the tricuspid valve with aortopulmonary transposition and coarctation of the aorta: Atresia of the tricuspid valve, transposition, Macro, autopsy (73176) Atresia of the tricuspid valve, transposition, Macro, autopsy (73177) Atresia of the tricuspid valve, transposition, Macro, autopsy (73178) Atresia of the tricuspid valve, transposition, Macro, autopsy (73179) Atresia of the tricuspid valve, transposition, Macro, autopsy (73180) Atresia of the tricuspid valve, transposition, Macro, autopsy (73181)
Polyvalvular dysplasia: Polyvalvular dysplasia, heart, Macro, autopsy (73717) Polyvalvular dysplasia, heart, Macro, autopsy (73718) Polyvalvular dysplasia, heart, Macro, autopsy (73719) Polyvalvular dysplasia, heart, Macro, autopsy (73720)