Congenital left atrial enlargement. A case report with special reference to myocardial fine structure.

A case of intrapericardial congenital left atrial enlargement was reported. The patient is an asymptomatic 3 year-old girl with abnormal cardiac silhouette seen on a chest roentgenogram. Angiography showed marked left atrial enlargement, and the diagnosis of intrapericardial congenital left atrial enlargement was confirmed on operation. Specimens of the atria were electron microscopically examined. Myocardiocytes of the left atrium showed marked increase of the mitochondria and decrease of myofibrils. Abnormal Z bands and disarrangement of myofibrils were often observed. Atrial specific granules in the left atrium were increased in size and number. The right atrium also showed same changes. The pathogenesis of this condition was discussed.