Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University
Cerebral ischemia from severe, flow-limiting stenosis caused by atherosclerotic disease involving the extracranial carotid arteries is found in 20-30％ of stroke patients. And around 80％ of cerebrovascular accident （CVA） are thromboembolic in origin, often with plaque in carotid system as the embolic source. Carotid atherosclerotic plaque with resultant stenosis usually involves the internal carotid artery （ICA） within 2 cm of the carotid bifurcation. This location is readily amenable to examination by sonography. Accurate diagnosis of carotid stenosis clearly is critical to identify patients who would benefit from surgical intervention. Color Doppler ultrasound （CDU） plays an important role in the detection and quantification the degree of stenosis in symptomatic patients who have a history of stroke either complete or transient attacks. CDU study could establish both the degree of stenosis and the length of affected segment. In addition, ultrasound can assess plaque morphology, such as determining homogeneous or heterogeneous plaque and also ulcerative plaque, which known to be a risk factor for CVA. Recently, carotid sonography has largely replaced angiography as the principle screening method for suspected extracranial carotid atherosclerotic disease. Gray-scale examination, color Doppler, power Doppler, and pulsed Doppler imaging techniques are routinely used in the evaluation of patients with neurologic symptoms and suspected extracranial cerebral disease including the evaluation of patients with carotid bruits and amaurosis fugax. Other carotid ultrasound applications are preoperative screening prior to major vascular surgery and workup of pulsatile neck masses for excluding carotid body tumors. Ultrasound is an inexpensive, noninvasive, and highly accurate modality of diagnosing carotid stenosis. Magnetic resonance angiography （MRA） and computed tomography angiography （CTA） are additional noninvasive screening tools for the identification of carotid bifurcation and also intracranial disease as well as for clarification of ultrasound imagings. Angiography is often now reserved for those patients for whom the ultrasound or MRA was equivocal or inadequate. An accurate study requires a knowledge of cerebrovascular anatomy and normal findings then pathology affecting the carotid system.