Vascular lesions in Chinese patients with transient ischemic attacks

The prevalence of intracranial occlusive cerebrovascular disease is thought to be higher in the Chinese and Japanese than in whites, ^[1] but there have been few systematic studies to assess the frequency of intracranial stenosis in symptomatic individuals. Using noninvasive Doppler methods, we performed a prospective evaluation of the prevalence of arterial lesions in Chinese patients presenting to us with TIAs.

Methods.

Patients referred to the Department of Neurology of the Peking Union Medical College Hospital (Beijing, China) with symptoms of TIA during the preceding month were recruited for this study. They were divided into three groups based on their presenting symptomatology: amaurosis fugax, carotid territory TIA, or vertebrobasilar territory TIA. Patients who had involvement of more than one territory were classified according to their most dominant symptoms. Those who complained of symptoms without localizing value, such as vertigo and syncope, were excluded. CT of the brain was performed for all patients who entered the study.

Transcranial Doppler examination was carried out using an EME TC2000 ultrasonograph (Eden Medizinische Elektronik GmbH, Uberlingen, Germany) with a 2-MHz pulsed wave transducer. Examination of the extracranial arteries was performed with a 4-MHz transducer. Duplex ultrasonography was also done. The temporal window was used for insonating the middle cerebral artery (MCA), terminal internal carotid artery (TICA), anterior cerebral artery (ACA), and posterior cerebral artery (PCA); the orbital approach for the ophthalmic artery (OPA) and siphon of the internal carotid artery; and the occipital approach for the vertebral artery and basilar artery. Compression of common carotid arteries (CCA) was performed in patients with low MCA blood velocities to evaluate the collateral circulation. Patients with abnormally high velocities had their examinations repeated after 1 month to ascertain reproducibility and to exclude the possibility of transient vasospasm.

An intracranial artery was considered to be stenotic if the mean blood velocity was greater than 120 cm/s. Intracranial arterial occlusion was diagnosed if all basal arteries except the artery in question were detectable or if there was a greater than 21% reduction of its mean velocity compared with that of the contralateral vessel. ^[2] Stenosis or occlusion of the extracranial carotid artery was suggested by low ipsilateral MCA or siphon velocity; evidence of intracranial collateral circulation, such as increased velocity in the posterior or contralateral circulation, decreased velocity while the opposite CCA was compressed, and flow reversal of the ipsilateral ACA or OPA; and systolic ratio of ICA/CCA higher than 1.8 and peak systolic velocity greater than 120 cm/s. ^[3]

Results.

Ninety-six patients were studied. Their ages ranged from 12 to 81 years (mean 49.3), and 50 were men. Twenty-nine patients (30%) had a history of hypertension and 11 patients (11%) had diabetes mellitus. There were 7 cases of amaurosis fugax, 71 cases of carotid TIA, and 18 cases of vertebrobasilar TIA. The CT was abnormal in 29 cases (30%), showing mainly lacunar infarctions, ventricular dilatation, or cortical atrophy. Sixty-two patients (65%) showed one or more vascular lesions, with evidence of extracranial disease in 18 (19%) and intracranial disease in 49 (51%) (Table 1). The distribution of arterial lesions is shown in Table 2. The most frequently encountered extracranial lesion was stenosis of the carotid bifurcation, whereas the most frequently encountered intracranial lesion was stenosis of the TICA or proximal MCA. In the vertebrobasilar group, three of seven patients with intracranial lesions had occlusion of the TICA, suggesting "steal" of blood from the posterior circulation.

Discussion.

The frequency of symptomatic intracranial stenosis is unknown, even among Chinese patients in whom the disease is generally regarded as common. Previous studies were usually small and subject to selection bias, as only patients referred for angiography were studied. In an earlier study from Taiwan of patients with carotid TIA, intracranial stenosis was present in 15% of 47 patients. ^[4] A later study, also from Taiwan, of patients with capsular infarcts and prior ipsilateral TIA showed intracranial stenosis in 67% of 21 patients. ^[5] At the New England Medical Center located near Boston's Chinatown, 43% of 24 Chinese patients with TIA or stroke had MCA stem stenosis, whereas the same lesion was present in only 14% of 24 age- and sexmatched white patients. ^[6] In contrast, 50% of white patients had severe stenosis of the extracranial ICA, whereas only 9% of the Chinese patients had a similar lesion. In an autopsy study from Hong Kong, atherosclerosis of at least one intracranial artery was present in 31% of 114 consecutive patients who died from a variety of causes. ^[7]

Transcranial Doppler is a noninvasive method of measuring blood velocities in the intracranial basal arteries. Combined with color-coded duplex ultrasonography, it offers a reliable method of detecting stenosis or occlusion of vessels supplying the brain. This study showed a high rate of intracranial arterial lesions among Chinese patients referred for the investigation of TIA. The rate of intracranial disease was approximately three times that of extracranial disease. Our data suggest that lesions of the intracranial ICA and MCA are common among Chinese patients. Artery-to-artery embolism or hypoperfusion in the presence of intracranial stenosis may be important factors causing TIA in our population.