The clinical morphology of mitral atresia. Atresia of the left atrioventricular valve.
In this paper we have reviewed the salient features of the anatomy of mitral atresia which should be of interest to the clinician. In the preceding paper, we reviewed the comparable features of tricuspid atresia, defined as lack of exit from the systemic venous atrium, even though some of the lesions may have affected a morphologically mitral valve. In this paper, we consider lesions producing lack of exit from the pulmonary venous atrium even though some of them may affect a morphologically tricuspid valve. Left atrioventricular valve atresia is a more accurate term, but mitral atresia is used because of its clinical applications. As with tricuspid atresia, mitral atresia may be due to either absence of an atrioventricular connexion or to presence of an imperforate valve membrane. In the setting of mitral atresia, the distinction is rarely if ever of practical clinical significance but understanding of the difference is essential for correct interpretation of the anatomy. When the left connexion is absent, the atrioventricular sulcus tissue completely separates the muscular floor of the left atrium from the underlying ventricular myocardium. When an imperforate valve membrane is present, it separates the cavity of the left atrium from an underlying ventricular cavity. Either of these lesions can be found with all the various forms of mitral atresia. The major anatomical subdivision is into groups with co-existing aortic atresia and with a patent aortic root. With aortic atresia, almost invariably the right atrium is connected to a right ventricular chamber. When there is a patent aortic root, the right atrium can be connected to a right ventricular chamber, a left ventricular chamber or rarely an indeterminate ventricular chamber, and these forms can all be found with various ventriculo-arterial connexions. The anatomical features are illustrated with diagrams and with hearts sectioned so as to simulate diagnostic planes used during two-dimensional echocardiographic examination. The convention used for categorizing these hearts as either biventricular or univentricular is discussed, emphasizing how disagreements about such nosological matters should be subordinate to accurate description of the underlying anatomy.
D001021:Aortic Valve / Q000002:abnormalities; D004452:Echocardiography; D014644:Genetic Variation; D006801:Humans; D008943:Mitral Valve / Q000002:abnormalities* / Q000473:pathology; D009206:Myocardium / Q000473:pathology