Ultrasonic detection of thrombus at the origin of the internal carotid artery

Abstract

Cerebral emboli frequently arise from extracranial carotid artery lesions. Ultrasound and Doppler techniques have been demonstrated to provide accurate and reproducible information about the degree of stenotic lesions in the region of the carotid bifurcation.' Little information is available regarding the detection of thrombus in vivo in the carotid system. We present a case in which a small mobile thrombus a t the carotid bifurcation was detected preoperatively by ultrasound and briefly describe its ultrasonic and Doppler characteristics. CASE REPORTA 67-year-old white man had sudden onset of numbness of the left hand and inability to move his fingers, which lasted about 1 h. He had no visual symptoms, and only mild tingling persisted in his fingertips for several days. When seen by his family physician several days after the initial event, no bruit was audible, but he was referred for ultrasoundlDoppler examination of his carotid system. Real-time imaging using a 7.5-MHz mechanical scanhead disclosed a small (3 mm) mobile echogenic area in the carotid bulb just at the origin of the right internal carotid artery. In real time, this structure could be seen to move into the origin of the internal carotid system. Its appearance was highly suggestive of thrombus, and it appeared to be in contact with a calcified plaque (Fig. 1). The Doppler signal from the internal carotid artery above this clot appeared normal, but as the sample volume of the pulsed system was placed just above the origin of the internal carotid artery near the thrombus, late systolic-early diastolic flow was noted to approach zero. This finding is considered abnormal but might not have been recognized if the clot had not been visualized in real time (Fig. 2). To exclude artifact as a cause of this filling defect, the sample volume of the Doppler instrument was placed adjacent to the thrombus, and a characteristic low-frequency sound was generated as the thrombus moved into the sample volume, a sound not unlike the sound produced by wall artifact in Doppler echocardiography . A t angiography, a shallow, broad-based plaque was noted a t the origin of the internal carotid artery associated with an eccentric, lobular filling defect extending into the lumen (Fig. 3). At operation, a 3-mm pedunculated thrombus was seen to be adherent to a plaque at the origin of the internal carotid artery.The patient made an uneventful recovery.