Anomalous mitral arcade in twin-twin transfusion syndrome

Echocardiography has documented acquired pulmonary stenosis and cardiomyopathy in recipient fetuses in twin-twin transfusion syndrome. At autopsy, we also have identified anomalous mitral arcade, a rare valve deformity associated with mitral regurgitation.

To identify a profile for anomalous mitral arcade, we compared clinicopathological data from 11 sets of autopsied twin-twin transfusion syndrome fetuses, including 4 twin pairs in whom the recipient had anomalous mitral arcade (affected) and 7 pairs in whom both had structurally normal mitral valves (unaffected). Anomalous mitral arcade was characterized by a thick fibrous band at the free margin of the leaflets tethering papillary muscles and absent/short tendinous cords. One affected recipient also had pulmonary stenosis and tricuspid valve dysplasia. In all 11 sets, recipient hearts were larger than paired donor hearts. All 11 recipients had moderate to severe cardiac dysfunction by echocardiography. Echocardiography disclosed left atrial enlargement in all affected recipients but none of the unaffected recipients. Mitral regurgitation was present before demise in all affected recipients evaluated with color Doppler. Progressive decrease in mitral leaflet mobility was noted in those affected recipients with serial echocardiography.

Previously unreported in twin-twin transfusion syndrome, anomalous mitral arcade was identified in 4 of 11 recipient fetuses (36%) in this autopsy series. Ultrasound or echocardiographic evidence of left atrial dilation, mitral regurgitation, and decreased leaflet mobility in recipients should raise suspicion for anomalous mitral arcade. Development of anomalous mitral arcade in twin-twin transfusion syndrome recipients suggests that the lesion is an acquired valve deformity in this setting, not a malformation.