Common atrioventricular canal in a newborn foal--case report and review of the literature.

This paper presents the embryological and pathological features as well as the terminology and classification of common atrioventricular canal, a type of endocardial cushion defect. The authors give a complete description of an extremely rare congenital cardiac malformation in an equine neonate. The diagnosis of a complete, balanced common atrioventricular canal of type C in Rastelli's classification scheme was based on two-dimensional, contrast and colour Doppler echocardiography and subsequent postmortem gross pathology. To support our diagnosis and study the pathophysiological effect of the alteration, physical examination, blood gas analysis and other laboratory tests, electrocardiography and thoracic radiography were also performed. Our search of the literature suggests that this type of developmental anomaly might account for a higher percentage of equine congenital cardiac defects than was thought earlier. We suppose that some previously described congenital heart abnormalities were misinterpreted: these anomalies could have actually represented some type of atrioventricular canal defect, resulting from the failure of the endocardial cushions to undergo complete and proper fusion.