A fifth of all transient ischemic attacks (TIAs) and ischemic strokes are in the territory of the vertebrobasilar circulation. The atherosclerotic plaque of vertebrobasilar artery is the main reason leading to recurrent posterior circulation symptoms [
Conventional vascular imaging diagnostic approaches such as MR angiography (MRA), digital subtraction angiography (DSA), and CT angiography (CTA) were commonly used to assess extracranial and intracranial artery stenosis in the past few decades. However, these imaging techniques have the limitations that they only show luminal narrowing and occlusion without providing information of the vascular wall.
High-resolution MR imaging (HRMRI) is a fast growing imaging technique for assessing vessel wall characteristics with suppression of arterial blood and cerebrospinal fluid (CSF) signals. With such technique, high-resolution intracranial vessel wall images are usually acquired using 1.5 or 3.0 T MRI scanners [
Using HRMRI, researchers found more atherosclerotic lesions on the BA which were not visualized by the conventional MRA method [
The aims of this study were to compare plaque’s morphological characteristics and distribution pattern between the symptomatic and asymptomatic groups using 3.0 T HRMRI and to investigate risk factors of posterior ischemic events in patients with BA stenosis > 50%.
This study was approved by the institutional ethics committee of our hospital. Between June 2014 and July 2016, consecutive patients with confirmed BA stenosis were recruited. The inclusion criteria were as follows: (a) symptomatic patients who had posterior ischemic stroke confirmed by clinical MRI examination within four weeks (acute stroke: 0–7 days; subacute stroke: 7–28 days) and asymptomatic patients who were diagnosed with other diseases without history of cerebrovascular event but had BA stenosis confirmed on image screening as well as patients who had a previous stroke event that occurred outside of the BA territory. All enrolled subjects had moderate (stenosis: 50%–69%) or severe (stenosis: 70%–99%) BA stenosis based on the findings of preceding CTA and/or DSA [
All patients signed an informed consent before the HRMRI examinations. All subjects were scanned on a 3.0 T MR scanner (MAGNETOM Verio; Siemens, Erlangen, Germany) equipped with a 32-channel head coil. HRMRI was performed using precontrast and postcontrast 3D T1-weighted imaging-SPACE (3D T1WI-SPACE) sequence [
HRMRI has good blood suppression properties and high sampling efficiency [
The following sequence parameters were selected: 3D T1WI-SPACE MR imaging sequence: TR/TE = 900/15 ms, field of view (FOV) = 170 × 170 mm2, slice thickness = 0.53 mm, and voxel size = 0.5 × 0.5 × 0.5 mm3; the 3D TOF MRA sequence: TR/TE = 20/3.6 ms, FOV = 220 × 220 mm2, slice thickness = 0.7 mm, and voxel size = 0.7 × 0.7 × 0.7 mm3.
A commercial workstation (syngo.via; Siemens, Erlangen, Germany) was used for MR image analysis by two neuroradiologists; both were blinded to the final diagnosis. Discrepancies between the two neuroradiologists were solved by visual consensus. MR vessel wall images were blinded to clinical information and other MR images. Precontrast and postcontrast 3D T1WI-SPACE images and 3D TOF MRA images were registered and reconstructed in short and long axis views for assessing BA plaque’s morphological features.
BA stenosis was estimated on 3D T1WI-SPACE images. The stenosis degree was calculated as percent stenosis = [1 − (
Intraplaque hemorrhage (IPH) was defined as plaque with hyperintensity signal (solid arrow) which was >150% of the extraocular muscle (dotted arrow) on precontrast 3D T1WI-SPACE images.
The plaque of BA was evaluated by dividing into four equal arcs (dorsal, ventral, right, and left) on the short axial.
SPSS 19.0 package for Windows (SPSS Inc., Chicago, IL, USA) was used for statistical analysis. We divided the patients into asymptomatic and symptomatic groups. Chi-square tests were used to assess plaque morphological features in both groups. The following variables were analyzed: age, gender, hypertension, hyperlipidemia, diabetes, smoking, severe stenosis, eccentric plaque, focal thickening, enhancement, and IPH. Multivariate logistic analysis with a forward stepwise method was performed including all variables with a probability value < 0.05 in the univariate analysis.
Fifty-seven consecutive patients (mean age:
Demographic data and vascular risk factors of patients.
Asymptomatic ( |
Symptomatic ( |
| |
---|---|---|---|
Age (mean ± SD) | 59.3 ± 9.3 | 62.0 ± 8.5 | 0.434 |
Male gender | 70.8 (17) | 81.8 (27) | 0.329 |
Hypertension | 66.7 (16) | 60.6 (20) | 0.640 |
Diabetes | 50.0 (12) | 54.5 (18) | 0.734 |
Hyperlipidemia | 12.5 (3) | 27.3 (9) | 0.177 |
Smoking | 33.3 (8) | 60.6 (20) | 0.042 |
Analyses of plaque’s morphological features were illustrated in Table
Morphology analysis of basilar artery stenosis.
Asymptomatic |
Symptomatic |
| |
---|---|---|---|
Eccentric plaque | 91.7 (22) | 78.8 (26) | 0.277 |
Focal thickening | 95.8 (23) | 84.8 (28) | 0.384 |
IPH | 33.3 (8) | 42.4 (14) | 0.486 |
Enhancement |
45.8 (11) | 81.8 (27) | 0.004 |
Severe stenosis | 37.5 (9) | 33.3 (11) | 0.745 |
IPH: intraplaque hemorrhage.
Images from a 65-year-old man with subacute bilateral brachium pontis infarction. (a) MRA shows stenosis of BA (solid arrow) and right anterior inferior cerebellar artery (dashed arrow). (b) T1WI-SPACE images (coronal) show plaque on BA (solid arrow), right anterior inferior cerebellar artery (dashed arrow), and anatomical relationship between orifices of right anterior inferior cerebellar artery and plaque.
Plaque enhancement was graded by grade 0, grade 1, and grade 2. Grade 0 indicates no enhancement of plaque; grade 1 indicates that enhancement of plaque was less than the pituitary; grade 2 indicates that enhancement of plaque was similar to or greater than the pituitary.
In univariate analysis, posterior ischemic events in patients with BA stenosis > 50% were more frequently observed in smokers (
Univariate analysis of posterior ischemic stroke event with BA stenosis > 50%.
Variable | OR | 95% CI |
|
---|---|---|---|
Age | 0.930 | (0.862, 1.003) | 0.060 |
Male gender | 1.853 | (0.532, 6.454) | 0.333 |
Hypertension | 0.769 | (0.256, 2.309) | 0.640 |
Hyperlipidemia | 2.625 | (0.627, 10.990) | 0.187 |
Diabetes | 1.200 | (0.418, 3.441) | 0.734 |
Smoking | 3.077 | (1.025, 9.235) | 0.045 |
Severe stenosis | 0.833 | (0.278, 2.500) | 0.745 |
Eccentric plaque | 0.338 | (0.064, 1.795) | 0.203 |
Focal thickening | 2.434 | (0.027, 2.235) | 0.212 |
Enhancement | 5.318 | (1.610, 17.563) | 0.006 |
IPH | 1.474 | (0.493, 4.401) | 0.487 |
OR: odds ratio; CI: confidence interval; IPH: intraplaque hemorrhage.
Multivariate analysis of posterior ischemic stroke event with BA stenosis > 50%.
Variable | OR | 95% CI |
|
---|---|---|---|
Enhancement | 7.193 | (1.880, 27.517) | 0.004 |
Smoking | 4.402 | (1.218, 15.909) | 0.024 |
OR: odds ratio; CI: confidence interval.
The enhancement grade of plaque was different in symptomatic group and asymptomatic group (Figure
Degree of enhancement in asymptomatic and symptomatic patients.
The distribution of BA plaques was shown in Table
Distribution of basilar artery atherosclerotic plaque.
Asymptomatic ( |
Symptomatic ( |
|
---|---|---|
Ventral | 20.8 (5) | 39.3 (13) |
Dorsal | 8.3 (2) | 12.1 (4) |
Left | 33.3 (8) | 15.1 (5) |
Right | 25.0 (6) | 12.1 (4) |
≥2 arcs | 12.5 (3) | 21.2 (7) |
In this study, we evaluated plaque’s morphology and compared morphological features of symptomatic and asymptomatic patients with BA stenosis > 50%. We demonstrate that (1) contrast enhancement of plaque was significantly high in symptomatic group and that (2) enhancement of plaque was found to be an independent risk factor for posterior ischemic events.
In our current analysis, contrast enhancement of plaque in the symptomatic group was more frequent than that in the asymptomatic group (
In multivariate analysis, smoking and plaque enhancement act as independent risk factors for posterior ischemic events when patient’s BA stenosis is >50%. Smoking has been proven to be an important risk factor for stroke in many studies over the past decade [
The main sites of plaque distribution were different in the two groups. In symptomatic group, plaques were commonly found at ventral site and tend to involve more than one arc. This finding is consistent with a previous study, which included 38 posterior circulation symptomatic patients; the BA plaque more likely involved the ventral wall [
In the present study, T1WI-SPACE sequence was used for evaluating the morphological features of the atherosclerotic plaque on BA. Compared with conventional MRA, T1WI-SPACE sequence provided more detailed information about atherosclerotic stenosis, such as plaque’s spatial distribution and plaque’s components. The T1WI-SPACE sequence has been widely applied for contrast-enhancement examination to observe the carotid and intracranial arterial plaque [
This study has several limitations. First, pathological validation was not performed; thus, no pathological evidence was found to explain the mechanism of intracranial plaque enhancement on HRMRI. Second, due to scan time limitations, precontrast and postcontrast 3D T1WI-SPACE images were acquired, but 3D T2WI-SPACE sequence was not included in the imaging protocol. T2WI-SPACE sequence had better contrast-to-noise ratio for lipid core than 3DT1WI-SPACE sequence. IPH has various intensity signals on T2W-SPACE sequence in different periods. Finally, the sample size of our study is relatively small, and larger patient cohorts are needed to validate our findings.
HRMRI is a promising vessel wall imaging technique for the delineation of BA plaque’s morphology and components beyond luminal imaging. Enhancement of plaque may identify plaque’s vulnerability and act as a novel imaging marker to predict posterior ischemic events.
The authors declare that they have no conflicts of interest.
This study was supported by the National Institutes of Health (Grant no. 2R01HL096119), the National Natural Science Foundation of China (81471649), National Key R&D Program (2016YFC1301701), Beijing Municipal Science and Technology Project (D171100003017003), and Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support (ZYLX 201609).