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Chapter 8
Ultrasound assessment of the extracranial cerebral circulation
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CHAPTER CONTENTS
Introduction 85 Anatomy 86
Collateral pathways and anatomical variants 86
Possible symptoms of carotid and vertebral artery disease 88
Scanning 88
Objectives and preparation 88
Technique 89
B-mode imaging 93
Normal appearance 93
Abnormal appearance 93
Color imaging 95
Normal appearance 95
Abnormal appearance 95
Spectral Doppler waveforms 96
Normal appearance 96
Abnormal appearance 96
Grading the disease 97
Imaging 98
Spectral Doppler 100
Combining B-mode, color imaging and spectral Doppler information 102
Normal and abnormal appearances of vertebral artery flow 103
Problems encountered in imaging carotid artery flow 103
Calcified atheroma 103
Vessel tortuosity 104
Postoperative and post-angioplasty carotid artery appearance on ultrasound 105
Nonatheromatous carotid artery diseases 105 Transcranial Doppler ultrasound 106 Reporting 107
INTRODUCTION
Ultrasound can be used to evaluate the extracranial cerebral circulation in order to investigate patients who may be at risk of suffering a stroke or who have already suffered a stroke. Stroke is the third most common cause of death in the United Kingdom, with the stroke rate being approximately 2 in 1000 of the population per year. Approximately 80% of strokes are ischemic (i.e., thrombotic or embolic or both) as opposed to hemorrhagic. Up to 80% of ischemic strokes occur in the carotid territory, the area of the brain supplied by the carotid arteries. Recent trials have shown that patients with signifi- cant carotid artery disease and relevant symptoms may benefit from surgery in order to prevent a stroke. The majority of carotid artery disease devel- ops at the carotid bifurcation, and in the presence of a significant stenosis, carotid endarterectomy can be performed. In this procedure, the diseased inner wall of the artery, the plaque, is removed, thus elim- inating a potential source of emboli or flow-limiting stenosis. Carotid ultrasound examinations can be used to screen patients for carotid artery disease before further investigation with angiography. Alter- natively, many centers now use ultrasound examina- tion to select patients directly for surgery, without preoperative angiography, as angiography is known to carry its own risks of transient and permanent neurological deficit. Developments in magnetic resonance angiography (MRA) may make this a safer alternative to x-ray angiography for confirming ultrasound findings prior to surgery or for further investigations, when ultrasound has provided only limited results.