Rationale and Objectives
The purpose of this study was to determine the effectiveness of combining basi-parallel anatomic scanning (BPAS)–magnetic resonance (MR) imaging findings with those of time-of-flight (TOF)–MR angiography (MRA) for differentiating vertebral artery dissection (VAD) from other causes of true artery narrowing such as atherosclerosis or an anatomical variation such as vertebral artery hypoplasia.
Materials and Methods
Fifteen cases of VAD, 15 of atherosclerotic narrowing, and 8 of hypoplastic vertebral arteries were retrospectively selected for this study. Conventional MR sequences (T1WI, T2WI, and T2*WI, fluid attenuation inversion recovery, TOF-MRA) and BPAS images were analyzed by two readers blinded to the patients’ clinical data and history. Receiver operating characteristic analyses were performed to compare the diagnostic capability of conventional MR sequences with and without BPAS imaging in suspected VAD cases.
Results
The area under the curve increased significantly by combining BPAS imaging findings with those of conventional MRI (0.72 vs. 0.96 and 0.81 vs. 0.99; P = .0022 and P = .0068, respectively, for readers 1 and 2). In addition, the sensitivity was 100% (15/15) for both readers and significantly greater than that of conventional MRI (53.3% [8/15] for both readers, P = .0156); however, specificities were not significantly different (82.6% [19/23] vs. 82.6% [19/23] and 91.33% [21/23] vs. 95.7% [22/23]). The interobserver agreement also improved by adding BPAS imaging.
Conclusions
Adding BPAS imaging to conventional MRI and MRA sequences can improve diagnostic capability and sensitivity in suspected VAD cases and be helpful in differentiating it from other causes of vertebral artery narrowing such as atherosclerosis or hypoplasia.
Vertebral artery dissection (VAD) is a frequent cause of stroke, representing approximately 20% cases in the young population . It presents with a variety of symptoms including headache, neck pain, and evidence of posterior circulation ischemia . It is usually diagnosed using multiple modalities such as digital subtraction angiography, time-of-flight (TOF)–magnetic resonance angiography (MRA), contrast-enhanced three-dimensional MRA, and CT angiography in the presence of a relevant clinical picture by excluding atherosclerosis . These imaging techniques reveal the flow pattern and provide information on the status of the vascular lumen. However, cases of VAD without any obvious stenosis of the arterial lumen at the site of dissection have also been described, which are liable to be overlooked if investigated using only the previously mentioned imaging methods . Similarly, anatomical variations of the vertebrobasilar arterial system, such as hypoplasia, are also sometimes important to differentiate from true arterial narrowing . In cases of complete occlusion of the lumen, these imaging techniques do not provide any useful information regarding the arterial status and morphology .
An imaging method that allows reliable visualization of the outer walls of the artery can help assist the evaluation process and thus the management planning. Basi-parallel anatomic scanning (BPAS)–MR imaging allows visualization of the external contour and surface appearance of the vertebrobasilar artery within the prepontine and medullary cisterns, which is not dependent on the flow characteristics within its lumen . This is a heavily T2-weighted sequence, based on surface anatomic scanning–MR imaging technique and contains a single 2-cm thick, coronal image parallel to the clivus . The combination of findings of BPAS–MR imaging and MRA is reported to increase the accuracy of detecting vertebrobasilar arterial abnormalities and allows differentiation between unilateral aplasia/hypoplasia and occlusive or stenotic conditions .
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Material and methods
Subjects
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Table 1
Patient Demographics and Clinical Data
VAD Atherosclerosis Hypoplasia No. of patients (no. of arteries) 15 (17) 15 (18) 8 (9) Mean age (range), y 49 (15–64) 68.3 (54–84) 52.8 (25–82) Gender (male:female) 14:1 7:8 5:3 Hypertension 3 (20%) 9 (60%) 3 (37.5%) Hypertriglyceridemia 2 (13.3%) 5 (33.3%) 2 (25%) Hypercholesterolemia None 3 (20%) 2 (25%) Diabetes 1 (6.6%) 5 (33.3%) 1 (12.5%) Headache 7 (46.6%) 2 (13.3%) 3 (37.5%) Neck pain 1 (6.6%) 0 0 Dizziness 5 (33.3%) 2 (13.3%) 2 (25%) Sensory or motor impairments 7 (46.6%) 11 (73.3%) 0 Cerebellar signs 4 (26.6%) 0 0 Other causes for imaging including screening 3 (20%) ∗ 1 (6.6%) 4 (50%)
VAD, vertebral artery dissection.
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Imaging Protocol
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Evaluation of MR Images
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Statistical Analyses
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Results
Comparison of Image Sets with and without BPAS
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Table 2
Statistical Results
Without BPAS With BPAS_P_ Value AUC (95% CI) Reader 1 0.72 (0.55–0.86) 0.96 (0.84–1.00) .0022 Reader 2 0.81 (0.65–0.92) 0.99 (0.90–1.00) .0068 Sensitivity (%; 95% CI) Reader 1 8/15 (53.3; 26.6–78.7) 15/15 (100; 78.2–100) .0156 Reader 2 8/15 (53.3; 26.6–78.7) 15/15 (100; 78.2–100) .0156 Specificity (%; 95% CI) Reader 1 19/23 (82.6; 61.2–95) 19/23 (82.6; 61.2–95) 1.0000 Reader 2 21/23 (91.3; 72–99) 22/23 (95.7; 78–100) 1.0000 PPV (%; 95% CI) Reader 1 8/12 (66.7; 35–90) 15/19 (79; 54.4–94) .7340 Reader 2 8/10 (80; 44.4–97.5) 15/16 (93.7; 69.7–99.8) .6623 NPV (%; 95% CI) Reader 1 19/26 (73.1; 52.2–88.4) 19/19 (100; 82.3–100) .0408 Reader 2 21/28 (75.0; 55.1–89.3) 22/22 (100; 84.5–100) .0341
AUC, area under the receiver operating characteristic curve; BPAS, basi-parallel anatomic scanning; CI, confidence interval; NPV, negative predictive value; PPV, positive predictive value.
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Imaging Features
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Table 3
Patient Imaging Findings from Conventional MRI, MRA, and BPAS Sequences
Imaging Features VAD Atherosclerosis Hypoplasia Conventional MRI Evidence of old or new infarction in vertebrobasilar territory 9/15 (60%) 12/15 (80%) None T1-weighted hyperintensity 13/17 (76.5%) None None MRA Septum 7/17 (41.1%) None None Luminal irregularity 11/17 (64.7%) 16/18 (88.9%) None Accompanied vertebral artery aneurysm 4/17 (23.5%) 1/18 (5.6%) None BPAS Dilatation 16/17 (94.1%) 8/18 (44.4%) None Vertebral artery aneurysm 4/17 (23.5%) 1/18 (5.6%) None
BPAS, basi-parallel anatomic scanning; MRA, magnetic resonance angiography; MRI, magnetic resonance imaging.
For evidence of infarction, the values represent the number of patients, but elsewhere the values represent the number of arteries involved.
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Discussion
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Conclusion
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