Formation of floating ball thrombus at left atrium during anticoagulation in a case of cerebral embolism

A 69-year-old woman with mitral stenosis showing chronic atrial fibrillation abruptly began to present left hemiplegia and disturbances of consciousness. Computed tomography showed an extensive hypodense area in the territory of right middle cerebral artery. The patient was diagnosed as having experienced cerebral embolism of cardiac origin. Anticoagulation was started one month after the onset. However, on the sixteenth day of anticoagulation a large peduncular thrombus at the left atrial wall was found by two-dimensional echocardiography. Moreover, on the twenty-second day of the treatment a floating large ball thrombus measuring 20 mm in diameter and showing undulating motion with heart beats was found by echocardiography in the left atrium. An emergent thrombectomy was done on the same day. A ball thrombus of 24 mm in diameter and several fragments of wall thrombi at appendage were found in the left atrium at surgery. The result indicates that anticoagulation to patients with mitral stenosis showing chronic atrial fibrillation should be started carefully while examining the left atrial thrombi by means of two-dimensional echocardiography.