In patients with atheromas, stenosis measurements were made by applying North American Symptomatic Carotid Endarterectomy Trial–style ratio calculations to the vertebral and basilar arteries.
On a curved multiplanar reconstructed image the smallest diameter of the atheromatous vessel was compared to the normal vessel diameter at the distal part of this segment; thus, the percentage of stenosis and the open segment was calculated.
2.4 Magnetic resonance imaging
The study was performed with 1.5-T MRI (Optima 450W, General Electric Medical Systems, Milwaukee, WI). Head coil and immobilization devices were used. The b value was 1000 s/mm2 on diffusion-weighted imaging. Image analysis was performed on a workstation (GE Advantage Workstation AW4.2_08) using functool 2 image analysis software (GE Medical Systems).
2.5 Statistical analysis
The coherence between normal distribution with the data of the patient and the control groups was analyzed. Independent-samples t test was used in variables with normal distribution, and Mann–Whitney U test in non-normal distribution.
The difference of categorical variable distribution according to groups was analyzed with χ2 and/or Fisher exact test.
Descriptive statistics were average ± standard deviation, median, minimum–maximum, and percentage.
Analysis was evaluated with SPSS 11.5 package program (SPSS Inc, Chicago, IL). Margin of error was considered to be 0.05.
A total of 249 patients, of whom 129 (51.8%) had central vertigo and 120 (48.2%) were controls, were included in the study. The control group's ages were between 36 and 85 years with an average of 59.8; the vertigo group's ages were between 31 and 81 years with an average of 62.2.
Of the cases in the vertigo group, 57 (44.2%) were female and 72 (55.8%) were male. In the control group, 54 (45%) were female and 66 (55%) were male. There was no statistically significant difference in terms of age and gender between the vertigo group and the control group (P > 0.05).
The mean diameters of right vertebral arteries in vertigo and control groups were found to be 3.72 ± 1.15 and 3.94 ± 0.9 mm, respectively; the mean diameters of left vertebral arteries were found to be 3.97 ± 1.1 and 4.18 ± 0.8 mm, respectively; and the mean diameters of basilar arteries were found to be 3.33 ± 0.6 and 3.44 ± 0.7 mm, respectively. Although mean diameters of the right and left vertebral arteries and basilar arteries were less in vertigo patients, they were not statistically significant (P > 0.05) (Table 1).
As seen in Table 2, vertebral artery hypoplasia and ≥50% stenosis was more common in vertigo cases (P = 0.000, <0.001). Of the total 78 vertigo cases with ≥50% stenosis, the stenotic segment in 54 (69.2%) patients was in V1 segment, in 9 (11.5%) patients in V2 segment, in 2 (2.5%) patients in V3 segment, and in 13 (16.6%) patients in V4 segment.
Dissecting aneurysm and fibromuscular hyperplasia were not detected in vertigo and control groups. In the vertigo group, 8 (6.2%) patients had vertebral artery hypoplasia associated with ≥50% stenosis of contralateral vertebral artery (Fig. 6A–C). Five of 8 patients were treated with percutaneous transluminal angioplasty and stenting. Three patients did not accept endovascular treatment. In the control group hypoplastic vertebral artery with contralateral vertebral artery stenosis and bilateral vertebral artery stenosis was not detected.
One patient with vertigo had bilateral vertebral artery hypoplasia (Fig. 7A and B); 2 patients had basilar artery hypoplasia accompanied with right vertebral artery hypoplasia.
Five of 78 (6.4%) patients with vertigo had bilateral vertebral artery stenosis and 2 of them were treated with stenting. Surgical treatment was not performed in both groups. Antiplatelet and anticoagulant therapies were given to the 61 (78.2%) vertigo cases with ≥50% stenosis.
Left vertebral artery originated from the aortic arch between the main carotid artery and the left subclavian artery orifice in 12 (9.3%) of the vertigo patients and in 9 (7.5%) of the controls. There was no significant difference between the groups (P > 0.05).
Of the vertigo cases, 9 (6.9%) had vertebral artery V1 segment tortuosity, and 17 (13.1%) had basilar artery tortuosity. Of the control group, 8 (6.6%) had vertebral artery V1 segment tortuosity, and 13 (10.8%) had basilar artery tortuosity. There was no significant difference between the 2 groups (P > 0.05).
Both vertigo and control groups had similar basilar artery hypoplasia and ≥50% stenosis rates (P = 0.800, >0.05) (Table 3).
Atherosclerosis is the most common cause of vertebrobasilar disorders. Stenosis of vertebral and basilar arteries secondary to atherosclerosis leads to vertebrobasilar insufficiency and poor posterior circulation. Vertigo, ataxia, dysarthria, diplopia, visual disturbances, and weakness may be seen in vertebrobasilar insufficiency and ischemia.[4,5] In the presented study, vertebral artery hypoplasia and ≥50% stenosis were more common in central vertigo cases without stroke compared to in the control group. In patients without stroke signs on DWI, the cause of central vertigo was believed to be TIA or vertebrobasilar insufficiency. A single vertebral artery with normal calibration may sufficiently supply the basilar artery. However, if severe bilateral vertebral artery stenosis or occlusion is present, treatment is indicated.[12,13] Treatment options may be medical, endovascular, or surgical. Medical treatment includes antiplatelet and anticoagulant therapy.
Surgery is not considered in most centers because of the technical difficulties. It can be performed when medical treatment fails or the anatomy is unfavorable for endovascular treatment.[12–15] Medical and endovascular treatments were implemented in the patients in our study. In central vertigo cases, CTA may help reveal vertebrobasilar stenosis, anatomic variations, and tortuosity. Being aware of anatomic variations and tortuosity is important before endovascular treatment and surgery because severe tortuosity can preclude safe stent placement.[12–15]
Atherosclerotic stenosis of the posterior circulation is most often seen at vertebral artery origin. At the intracranial segment of the vertebral artery, stenosis is most commonly seen at vertebrobasilar junction level. Another common location is right before branching to posterior inferior cerebellar artery, distal from the dural penetration.[16,17] In the presented study, the most common place of stenosis was at the origin of the vertebral artery. Patients with stenosis of vertebral artery origin were found to have a high risk for vertebrobasilar circulation ischemia.
TIA and stroke can be seen and the risk of recurrent stroke after TIA and minor stroke was found to be as high as that of carotid stroke in vertebrobasilar stenotic disease. A prospective study revealed that the patients who have vertebral stenosis with vertebrobasilar TIA and minor stroke have a 30% risk of recurrent stroke in the first month. These patients may benefit from medical or endovascular treatment. Therefore, it is important to show stenosis of vertebral artery for starting the therapy.[17,18]
In this study, vertebral artery hypoplasia was more commonly seen in vertigo cases than in the control group. However, in the literature, a relationship between vertebrobasilar artery hypoplasia and posterior circulatory strokes has been reported.[19,20] It is important that in the presented study vertebral artery hypoplasia was seen more frequently in vertigo cases without stroke compared to in the control group. Hypoplasia of the vertebral arteries may cause vertigo by decrease of blood supply to the cerebellum and cerebral peduncle. It has been reported that vertebral artery hypoplasia may be commonly accompanied by basilar artery hypoplasia, thus causing posterior circulatory ischemia. Bilateral vertebral artery hypoplasia may present with episodic vertigo attacks. A single vertebral artery with normal calibration may sufficiently supply the basilar artery. However, bilateral vertebral artery hypoplasia or unilateral vertebral artery hypoplasia associated with contralateral vertebral artery stenosis may impair the sufficient blood flow through the posterior circulation.
There are studies reporting that vertigo may also be seen in basilar artery stenosis and the vertigo attacks may improve after stenting of the stenotic arteries. However, no relationship was detected between basilar artery hypoplasia or stenosis and vertigo in our study. The small number of participants with basilar artery hypoplasia and stenosis in both vertigo and control group may have led to this result in the presented study.
In recent years, studies of vertigo related to vertebral and basilar artery tortuosity have been presented. Vertebral artery tortuosity is thought to be caused by mechanical pressure on the artery due to head position resulting in ischemia. It has been reported that basilar artery tortuosity may lead to occlusion and atherosclerosis, thus decreasing the distal blood flow in tortuous vessels.[24,25] In the presented study there was no significant difference between vertebral and basilar artery tortuosity in the vertigo group compared to in the control group.
Vertigo patients and control participants were in the elderly group, and the presence of similar risk factors may have created this consequence.
Diagnostic approach for vertigo patients is complex. Detailed patient history, physical examination, neuro-otological tests, and imaging finding are used.[3–26] It has been shown that MRI is useful in the detection of serious acute vertigo cases related to small posterior fossa infarctions and in the differentiation from vestibular neuritis. Contrast-enhanced MRA has frequently shown pseudostenosis of vertebral artery origin because of weak spatial resolution, intravoxel dephasing, and motion artifact caused by cardiac pulsation and respiration. Khan et al performed a systematic literature review to evaluate the accuracy of duplex ultrasound, contrast-enhanced MRA, and CTA in detecting severe vertebral artery stenosis. The sensitivity and specificity of CTA (100% and 93.9%, respectively) were higher versus those of contrast-enhanced MRA (95.2% and 94.8%, respectively) in detecting severe vertebral artery stenosis. In a recent study comparing contrast-enhanced MRA, CTA, and duplex sonography in detecting ≥50% stenosis of vertebral artery, contrast-enhanced MRA had the highest sensitivity and specificity (83% and 91%, respectively). CTA had good sensitivity (68%) and excellent specificity (92%). On the other hand, CTA had better accessibility, high spatial resolution, and short scanning time than MRA. CTA has better temporal resolution and therefore is less affected by the motion of cardiac pulsation and respiration. It is cheaper and suitable for patients with contraindications to MRI. However, CTA has problems involving radiation, and a potentially nephrotoxic contrast agent as well as inaccuracy for heavily calcified stenosis. Because CTA has higher temporal and spatial resolution than MRA and is less affected by motion artifact and pseudostenosis, we recommend evaluating patients with central vertigo with CTA after brain MRI.
Some limitations exist in the presented study. Vascular risk factors such as ischemic heart diseases and smoking were not included. The patients included in the study were elderly and with higher ischemic heart disease risks. Further limitations were small number of patients with >50% basilar artery stenosis and basilar artery hypoplasia of the controls and vertigo patients.
This study showed that CTA may be helpful to clarify the association between abnormal CTA findings of vertebral arteries and central vertigo. It is believed that CTA may be useful in the arrangement of clinical management.
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Keywords:Copyright © 2017 The Authors. Published by Wolters Kluwer Health, Inc. All rights reserved.
basilar artery; CTA; vertebral artery; vertigo