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Vertebral Artery Dissection: Spectrum of Imaging Findings with Emphasis on Angiography and Correlation with Clinical Presentation¹

¹ From the Department of Diagnostic Radiology, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Poongnap-Dong, Songpa-Ku, Seoul 138-736, South Korea. Presented as a scientific exhibit at the 1999 RSNA scientific assembly. Received March 2, 2000; revision requested April 5 and received May 15; accepted May 16. Address correspondence to D.C.S. (e-mail: dcsuh@www.amc.seoul.kr).

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion Summary References

 
A study was performed to evaluate the relationship between the imaging features and clinical presentation of vertebral artery (VA) dissection. Twenty-two patients with 24 VA dissections at angiography and clinical evaluation also underwent computed tomography and magnetic resonance imaging. The angiographic patterns of VA dissection were categorized as aneurysmal (n = 10) or steno-occlusive (n = 14). All 10 patients (10 lesions) with the aneurysmal pattern had dissection in the V4 (intradural) segment and presented with headache (n = 5), neurologic deficit (n = 2), dizziness (n = 2), or altered mentality (n = 1). However, the 12 patients (14 lesions) with the steno-occlusive pattern had dissection from the V1 segment to the V4 segment and presented with neurologic deficits caused by infarction of an embolic nature. Overall, the most frequent VA dissection site was the V4 segment. The distribution of the dissection sites and the clinical presentation tended to differ according to the angiographic patterns of aneurysm or stenosis-occlusion.

Index Terms: Angiography, comparative studies, 1751.1243 • Computed tomography (CT), comparative studies, 1751.12116 • Magnetic resonance (MR), comparative studies, 1751.12142 • Magnetic resonance (MR), vascular studies, 1751.12142 • Vertebral arteries, dissection, 1751.74 Vertebral arteries, stenosis or obstruction, 1751.74

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion Summary References

 
Dissection of the internal carotid artery or the vertebral artery (VA) causes only 0.4%–2.5% of all strokes in the general population but 5%–20% of strokes in young patients (1). Recently, VA dissection has become increasingly recognized as a source of stroke and subarachnoid hemorrhage (SAH). VA dissection can be classified into aneurysmal and steno-occlusive types according to the morphology at angiography. A treatment plan, such as anticoagulation or surgery including interventional therapy, depends entirely on the location and radiologic type of the VA dissection, such as aneurysmal or steno-occlusive, and the clinical presentation and imaging features at computed tomography (CT) or magnetic resonance (MR), including SAH or infarction. Therefore, familiarity with these angiographic findings and correlation with the clinical presentation and imaging features at CT or MR are very important.

In this article, we present the imaging features of VA dissection (with emphasis on angiography) and correlate them with its clinical features.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion Summary References

 
Between November 1994 and December 1998, 24 VA dissections, including two cases of bilateral lesions, were diagnosed in 22 patients. The diagnoses were made on the basis of (a) the characteristic radiologic findings, (b) the appropriate clinical presentation, and (c) absence of atherosclerotic disease elsewhere in the cerebrovascular circulation (2,3).

Cerebral angiography was performed with a cut-film or digital subtraction technique (Integris BN 3000; Philips Medical Systems, Best, the Netherlands) in all 22 patients. Brain CT (Somatom Plus S; Siemens, Erlangen, Germany) was performed in 13 patients. MR imaging was performed in 17 patients, and MR angiography was performed in four. MR imaging was performed with a 1.0-T system (SMT-100X; Shimadzu, Kyoto, Japan) or a 1.5-T system (Signa ADV [GE Medical Systems, Milwaukee, Wis] or Magnetom Vision [Siemens]). MR angiography consisted of intracranial three-dimensional time-of-flight studies and studies of major neck vessels with two-dimensional time-of-flight and contrast material–enhanced three-dimensional MR angiography. Analysis of the conventional angiograms focused on the possible presence of an aneurysm or stenosis-occlusion in addition to the dissection site. Each lesion was correlated with the clinical presentation, the presence of hemorrhage, and infarcted areas at CT or MR imaging. Abnormal signal intensity or abnormal configuration of the dissected artery was analyzed at MR imaging or MR angiography. All images were reviewed by two neuroradiologists (J.H.S., D.C.S.). Agreement was reached by means of consensus.

The locations of the dissections were classified as V1, V2, V3, or V4 (Fig 1). V1 is the segment of the VA that passes into the neck and enters the transverse foramen of C6 (3–5). V2 is the segment that ascends through the transverse foramen from C6 to C2. V3 exits the transverse foramen of C2, winds around C1 posteriorly in a tortuous manner, and enters the dura at the foramen magnum. V4 begins at the foramen magnum and unites with the contralateral VA to form the basilar artery.

View larger version (32K): [in this window] [in a new window] [Download PPT slide]   Figure 1.   Classification of segments of the VA. V1 is proximal to entry into the transverse foramen of C6. V2 is within the transverse foramen from C6 to C2. V3 is from the transverse foramen of C2 but before entry into the dura. V4 is after entry into the dura.

	Results

Top Abstract Introduction Materials and Methods Results Discussion Summary References

The most common site of dissection was V4 (n = 14 [58%]) followed by V2 (n = 4), V3 (n = 3), V1 (n = 2), and V2–V4 (n = 1). An aneurysm was the dominant finding in 10 lesions (42%); a stenosis-occlusion was the dominant finding in 14 (58%).

Aneurysmal Pattern
Ten patients (patients 1–10) were found to have an aneurysm. The six men and four women were aged 30–59 years (average, 48.2 years). All 10 patients with an aneurysmal pattern had dissection in V4. The clinical presentations were headache (n = 5), neurologic deficit (n = 2), dizziness (n = 2), and altered mentality (n = 1). Hypertension was found in three patients (30%). Cerebral infarction was found in one patient, and SAH was found in four patients. One patient (patient 3) had undergone a massage several hours before the clinical attack.

The four patients with SAH at CT were treated with balloon or coil embolization (n = 3) or conservative management (n = 1), which resulted in clinical improvement in two patients and death in two. Anticoagulation therapy was not used in the patients with SAH. The six patients without SAH at CT were treated with anticoagulation or antiplatelet therapy (n = 3), balloon or coil embolization (n = 2), or surgical VA clipping (n = 1), which resulted in clinical improvement in four patients, no significant interval change in one patient, and progression to quadriparesis in one. Anticoagulation or antiplatelet therapy was used in three patients with neurologic deficits (n = 2) or dizziness (n = 1) but without SAH at CT because we thought these symptoms were caused by cerebral ischemia or infarction due to emboli or flow disturbance related to a dissecting aneurysm.

Conventional Angiographic Findings.—The most common conventional angiographic finding was focal dilatation (Figs 2, 3), which was found in six patients. This was the only conventional angiographic finding in three patients. In two patients, there was also proximal or distal stenosis (Fig 2); in one patient, there was also a string of pearls appearance (alternating regions of narrowing and dilatation), which suggests fibromuscular dysplasia. Four patients had fusiform aneurysmal dilatation (Fig 4), which extended approximately 1–3 cm.

View larger version (168K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.   Aneurysmal pattern of VA dissection in a 43-year-old man with right lateral medullary syndrome (patient 3). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show focal aneurysmal dilatation (arrow) with distal stenosis (arrowhead) involving V4. (c) Axial T2-weighted MR image shows focal high signal intensity in the right lateral medulla (arrow), a finding that represents infarction. The crescent of high signal intensity in the right distal VA (arrowhead) suggests an intramural hematoma.

View larger version (164K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.   Aneurysmal pattern of VA dissection in a 43-year-old man with right lateral medullary syndrome (patient 3). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show focal aneurysmal dilatation (arrow) with distal stenosis (arrowhead) involving V4. (c) Axial T2-weighted MR image shows focal high signal intensity in the right lateral medulla (arrow), a finding that represents infarction. The crescent of high signal intensity in the right distal VA (arrowhead) suggests an intramural hematoma.

View larger version (163K): [in this window] [in a new window] [Download PPT slide]   Figure 2c.   Aneurysmal pattern of VA dissection in a 43-year-old man with right lateral medullary syndrome (patient 3). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show focal aneurysmal dilatation (arrow) with distal stenosis (arrowhead) involving V4. (c) Axial T2-weighted MR image shows focal high signal intensity in the right lateral medulla (arrow), a finding that represents infarction. The crescent of high signal intensity in the right distal VA (arrowhead) suggests an intramural hematoma.

View larger version (177K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.   Focal dissecting aneurysm involving the left VA in a 51-year-old man with left-sided paresthesia (patient 2). (a-c) Anteroposterior (a) and lateral (b) left vertebral angiograms and coronal contrast-enhanced three-dimensional MR angiogram (c) show focal aneurysmal dilatation involving left V4 (arrow) just proximal to the posterior inferior cerebellar artery. (d, e) Axial T1-weighted (d) and T2-weighted (e) MR images show a high-signal-intensity crescent (arrow), which represents an intramural thrombus. (f) Axial source image for contrast-enhanced three-dimensional MR angiography clearly shows the intimal flap (arrow) between the true and false lumina.

View larger version (183K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.   Focal dissecting aneurysm involving the left VA in a 51-year-old man with left-sided paresthesia (patient 2). (a-c) Anteroposterior (a) and lateral (b) left vertebral angiograms and coronal contrast-enhanced three-dimensional MR angiogram (c) show focal aneurysmal dilatation involving left V4 (arrow) just proximal to the posterior inferior cerebellar artery. (d, e) Axial T1-weighted (d) and T2-weighted (e) MR images show a high-signal-intensity crescent (arrow), which represents an intramural thrombus. (f) Axial source image for contrast-enhanced three-dimensional MR angiography clearly shows the intimal flap (arrow) between the true and false lumina.

View larger version (114K): [in this window] [in a new window] [Download PPT slide]   Figure 3c.   Focal dissecting aneurysm involving the left VA in a 51-year-old man with left-sided paresthesia (patient 2). (a-c) Anteroposterior (a) and lateral (b) left vertebral angiograms and coronal contrast-enhanced three-dimensional MR angiogram (c) show focal aneurysmal dilatation involving left V4 (arrow) just proximal to the posterior inferior cerebellar artery. (d, e) Axial T1-weighted (d) and T2-weighted (e) MR images show a high-signal-intensity crescent (arrow), which represents an intramural thrombus. (f) Axial source image for contrast-enhanced three-dimensional MR angiography clearly shows the intimal flap (arrow) between the true and false lumina.

View larger version (180K): [in this window] [in a new window] [Download PPT slide]   Figure 3d.   Focal dissecting aneurysm involving the left VA in a 51-year-old man with left-sided paresthesia (patient 2). (a-c) Anteroposterior (a) and lateral (b) left vertebral angiograms and coronal contrast-enhanced three-dimensional MR angiogram (c) show focal aneurysmal dilatation involving left V4 (arrow) just proximal to the posterior inferior cerebellar artery. (d, e) Axial T1-weighted (d) and T2-weighted (e) MR images show a high-signal-intensity crescent (arrow), which represents an intramural thrombus. (f) Axial source image for contrast-enhanced three-dimensional MR angiography clearly shows the intimal flap (arrow) between the true and false lumina.

View larger version (169K): [in this window] [in a new window] [Download PPT slide]   Figure 3e.   Focal dissecting aneurysm involving the left VA in a 51-year-old man with left-sided paresthesia (patient 2). (a-c) Anteroposterior (a) and lateral (b) left vertebral angiograms and coronal contrast-enhanced three-dimensional MR angiogram (c) show focal aneurysmal dilatation involving left V4 (arrow) just proximal to the posterior inferior cerebellar artery. (d, e) Axial T1-weighted (d) and T2-weighted (e) MR images show a high-signal-intensity crescent (arrow), which represents an intramural thrombus. (f) Axial source image for contrast-enhanced three-dimensional MR angiography clearly shows the intimal flap (arrow) between the true and false lumina.

View larger version (177K): [in this window] [in a new window] [Download PPT slide]   Figure 3f.   Focal dissecting aneurysm involving the left VA in a 51-year-old man with left-sided paresthesia (patient 2). (a-c) Anteroposterior (a) and lateral (b) left vertebral angiograms and coronal contrast-enhanced three-dimensional MR angiogram (c) show focal aneurysmal dilatation involving left V4 (arrow) just proximal to the posterior inferior cerebellar artery. (d, e) Axial T1-weighted (d) and T2-weighted (e) MR images show a high-signal-intensity crescent (arrow), which represents an intramural thrombus. (f) Axial source image for contrast-enhanced three-dimensional MR angiography clearly shows the intimal flap (arrow) between the true and false lumina.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.   Aneurysmal pattern of VA dissection in an unconscious 43-year-old man (patient 6). (a) Nonenhanced axial CT scan shows diffuse SAH in the basal cistern, ambient cistern, and both Sylvian cisterns. (b, c) Anteroposterior (b) and lateral (c) right vertebral angiograms show sausagelike fusiform enlargement (arrows) due to a dissecting aneurysm involving V4 at the level of the posterior inferior cerebellar artery.

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.   Aneurysmal pattern of VA dissection in an unconscious 43-year-old man (patient 6). (a) Nonenhanced axial CT scan shows diffuse SAH in the basal cistern, ambient cistern, and both Sylvian cisterns. (b, c) Anteroposterior (b) and lateral (c) right vertebral angiograms show sausagelike fusiform enlargement (arrows) due to a dissecting aneurysm involving V4 at the level of the posterior inferior cerebellar artery.

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 4c.   Aneurysmal pattern of VA dissection in an unconscious 43-year-old man (patient 6). (a) Nonenhanced axial CT scan shows diffuse SAH in the basal cistern, ambient cistern, and both Sylvian cisterns. (b, c) Anteroposterior (b) and lateral (c) right vertebral angiograms show sausagelike fusiform enlargement (arrows) due to a dissecting aneurysm involving V4 at the level of the posterior inferior cerebellar artery.

Steno-occlusive Pattern
Twelve patients (patients 11–22) had a stenosis-occlusion. Two of them had a steno-occlusive pattern in bilateral VA dissections. The nine men and three women were aged 27–56 years (average, 45.3 years). There was a relatively even distribution of involvement from V1 to V4. All patients with the steno-occlusive pattern presented with a neurologic deficit, such as dizziness, vertigo, ataxia, or dysarthria, caused by disturbance of the posterior circulation. Hypertension was found in four patients (33%). Four patients had a history of trivial trauma or physical activity: massage (n = 2) or golf (n = 2). Systemic lupus erythematosus was confirmed in one patient. All 12 patients were treated with anticoagulation or antiplatelet therapy, which resulted in clinical recovery in 11 and death in one.

Conventional Angiographic Findings.—The most common conventional angiographic finding was a tapered or abrupt occlusion (Figs 5 –7), which was found in eight cases. There was distal reconstitution of the occluded artery by collateral vessels in three cases (Fig 8). Five cases demonstrated an irregular segmental or long stenosis (Figs 9, 10). Intimal flaps were found in two cases (Fig 10), and filling defects within the lumen were also found in two cases (Fig 9). Conventional angiograms were highly suspicious for fibromuscular dysplasia in one patient (Fig 10).

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.   Tapered occlusion of the right VA in a 42-year-old man with right medial medullary syndrome (patient 20). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show a tapered complete occlusion of right V4 (arrow). The ipsilateral posterior inferior cerebellar artery is faintly opacified, an appearance that suggests involvement of posterior inferior cerebellar artery origin. (c) Axial T1-weighted MR image shows intermediate signal intensity in the right distal VA (arrow), a finding suggestive of an intraluminal thrombus. The normal left distal VA demonstrates a signal void (arrowhead). (d) Axial T2-weighted MR image shows high signal intensity in the right medial medulla (arrow), a finding that represents infarction.

View larger version (130K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.   Tapered occlusion of the right VA in a 42-year-old man with right medial medullary syndrome (patient 20). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show a tapered complete occlusion of right V4 (arrow). The ipsilateral posterior inferior cerebellar artery is faintly opacified, an appearance that suggests involvement of posterior inferior cerebellar artery origin. (c) Axial T1-weighted MR image shows intermediate signal intensity in the right distal VA (arrow), a finding suggestive of an intraluminal thrombus. The normal left distal VA demonstrates a signal void (arrowhead). (d) Axial T2-weighted MR image shows high signal intensity in the right medial medulla (arrow), a finding that represents infarction.

View larger version (152K): [in this window] [in a new window] [Download PPT slide]   Figure 5c.   Tapered occlusion of the right VA in a 42-year-old man with right medial medullary syndrome (patient 20). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show a tapered complete occlusion of right V4 (arrow). The ipsilateral posterior inferior cerebellar artery is faintly opacified, an appearance that suggests involvement of posterior inferior cerebellar artery origin. (c) Axial T1-weighted MR image shows intermediate signal intensity in the right distal VA (arrow), a finding suggestive of an intraluminal thrombus. The normal left distal VA demonstrates a signal void (arrowhead). (d) Axial T2-weighted MR image shows high signal intensity in the right medial medulla (arrow), a finding that represents infarction.

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 5d.   Tapered occlusion of the right VA in a 42-year-old man with right medial medullary syndrome (patient 20). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show a tapered complete occlusion of right V4 (arrow). The ipsilateral posterior inferior cerebellar artery is faintly opacified, an appearance that suggests involvement of posterior inferior cerebellar artery origin. (c) Axial T1-weighted MR image shows intermediate signal intensity in the right distal VA (arrow), a finding suggestive of an intraluminal thrombus. The normal left distal VA demonstrates a signal void (arrowhead). (d) Axial T2-weighted MR image shows high signal intensity in the right medial medulla (arrow), a finding that represents infarction.

View larger version (154K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.   Abrupt occlusion of the right VA in a 41-year-old man with right lateral medullary syndrome (patient 16). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show abrupt complete occlusion of right V3 (arrow). (c) Axial T2-weighted MR image shows focal high signal intensity in the right lateral medulla (arrow), a finding that represents infarction. Focal high signal intensity is seen in the right VA (arrowhead) and represents an intraluminal thrombus.

View larger version (148K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.   Abrupt occlusion of the right VA in a 41-year-old man with right lateral medullary syndrome (patient 16). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show abrupt complete occlusion of right V3 (arrow). (c) Axial T2-weighted MR image shows focal high signal intensity in the right lateral medulla (arrow), a finding that represents infarction. Focal high signal intensity is seen in the right VA (arrowhead) and represents an intraluminal thrombus.

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 6c.   Abrupt occlusion of the right VA in a 41-year-old man with right lateral medullary syndrome (patient 16). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show abrupt complete occlusion of right V3 (arrow). (c) Axial T2-weighted MR image shows focal high signal intensity in the right lateral medulla (arrow), a finding that represents infarction. Focal high signal intensity is seen in the right VA (arrowhead) and represents an intraluminal thrombus.

View larger version (175K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.   Abrupt occlusion of both VAs in a 27-year-old woman with systemic lupus erythematosus and ataxia (patient 22). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show abrupt complete occlusion of right V3 (arrow). (c) Lateral left vertebral angiogram shows abrupt complete occlusion of left V3 (arrow). (d) Axial T2-weighted MR image shows multiple infarcts (arrowheads) involving both cerebellar hemispheres and the left medulla.

View larger version (159K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.   Abrupt occlusion of both VAs in a 27-year-old woman with systemic lupus erythematosus and ataxia (patient 22). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show abrupt complete occlusion of right V3 (arrow). (c) Lateral left vertebral angiogram shows abrupt complete occlusion of left V3 (arrow). (d) Axial T2-weighted MR image shows multiple infarcts (arrowheads) involving both cerebellar hemispheres and the left medulla.

View larger version (137K): [in this window] [in a new window] [Download PPT slide]   Figure 7c.   Abrupt occlusion of both VAs in a 27-year-old woman with systemic lupus erythematosus and ataxia (patient 22). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show abrupt complete occlusion of right V3 (arrow). (c) Lateral left vertebral angiogram shows abrupt complete occlusion of left V3 (arrow). (d) Axial T2-weighted MR image shows multiple infarcts (arrowheads) involving both cerebellar hemispheres and the left medulla.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 7d.   Abrupt occlusion of both VAs in a 27-year-old woman with systemic lupus erythematosus and ataxia (patient 22). (a, b) Anteroposterior (a) and lateral (b) right vertebral angiograms show abrupt complete occlusion of right V3 (arrow). (c) Lateral left vertebral angiogram shows abrupt complete occlusion of left V3 (arrow). (d) Axial T2-weighted MR image shows multiple infarcts (arrowheads) involving both cerebellar hemispheres and the left medulla.

View larger version (162K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.   Complete occlusion of the left VA in a 51-year-old man with visual blurring and vertigo (patient 12). (a, b) Midphase (a) and later phase (b) anteroposterior left subclavian angiograms show complete occlusion of the left VA, which is reconstituted by adjacent collateral vessels in the later phase (arrows). (c) Axial T2-weighted MR image shows high signal intensity in the right medial occipitotemporal gyrus (arrows), a finding that represents infarction. The infarcted side is opposite to the affected VA, suggesting the embolic nature of the infarction. (d) Coronal contrast-enhanced three-dimensional MR angiogram shows occlusion of left V1 and V2 (arrowheads), an appearance consistent with the angiographic findings.

View larger version (167K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.   Complete occlusion of the left VA in a 51-year-old man with visual blurring and vertigo (patient 12). (a, b) Midphase (a) and later phase (b) anteroposterior left subclavian angiograms show complete occlusion of the left VA, which is reconstituted by adjacent collateral vessels in the later phase (arrows). (c) Axial T2-weighted MR image shows high signal intensity in the right medial occipitotemporal gyrus (arrows), a finding that represents infarction. The infarcted side is opposite to the affected VA, suggesting the embolic nature of the infarction. (d) Coronal contrast-enhanced three-dimensional MR angiogram shows occlusion of left V1 and V2 (arrowheads), an appearance consistent with the angiographic findings.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 8c.   Complete occlusion of the left VA in a 51-year-old man with visual blurring and vertigo (patient 12). (a, b) Midphase (a) and later phase (b) anteroposterior left subclavian angiograms show complete occlusion of the left VA, which is reconstituted by adjacent collateral vessels in the later phase (arrows). (c) Axial T2-weighted MR image shows high signal intensity in the right medial occipitotemporal gyrus (arrows), a finding that represents infarction. The infarcted side is opposite to the affected VA, suggesting the embolic nature of the infarction. (d) Coronal contrast-enhanced three-dimensional MR angiogram shows occlusion of left V1 and V2 (arrowheads), an appearance consistent with the angiographic findings.

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 8d.   Complete occlusion of the left VA in a 51-year-old man with visual blurring and vertigo (patient 12). (a, b) Midphase (a) and later phase (b) anteroposterior left subclavian angiograms show complete occlusion of the left VA, which is reconstituted by adjacent collateral vessels in the later phase (arrows). (c) Axial T2-weighted MR image shows high signal intensity in the right medial occipitotemporal gyrus (arrows), a finding that represents infarction. The infarcted side is opposite to the affected VA, suggesting the embolic nature of the infarction. (d) Coronal contrast-enhanced three-dimensional MR angiogram shows occlusion of left V1 and V2 (arrowheads), an appearance consistent with the angiographic findings.

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.   Irregular stenosis with multiple filling defects involving the left VA in a 37-year-old man with dizziness and ataxia (patient 17). (a) Anteroposterior left vertebral angiogram shows an irregular long segmental stenosis (arrows) and multiple filling defects (arrowheads) in left V2, which represent intramural or intraluminal thrombi. The left posterior inferior cerebellar artery was occluded on later angiograms. (b, c) Axial T2-weighted MR images (c obtained at a higher level than b) show regions of high signal intensity, which represent multiple infarcts. The infarcts involve the territory of the left posterior inferior cerebellar artery and middle cerebellar peduncle, an appearance that suggests the embolic nature of the infarction.

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.   Irregular stenosis with multiple filling defects involving the left VA in a 37-year-old man with dizziness and ataxia (patient 17). (a) Anteroposterior left vertebral angiogram shows an irregular long segmental stenosis (arrows) and multiple filling defects (arrowheads) in left V2, which represent intramural or intraluminal thrombi. The left posterior inferior cerebellar artery was occluded on later angiograms. (b, c) Axial T2-weighted MR images (c obtained at a higher level than b) show regions of high signal intensity, which represent multiple infarcts. The infarcts involve the territory of the left posterior inferior cerebellar artery and middle cerebellar peduncle, an appearance that suggests the embolic nature of the infarction.

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 9c.   Irregular stenosis with multiple filling defects involving the left VA in a 37-year-old man with dizziness and ataxia (patient 17). (a) Anteroposterior left vertebral angiogram shows an irregular long segmental stenosis (arrows) and multiple filling defects (arrowheads) in left V2, which represent intramural or intraluminal thrombi. The left posterior inferior cerebellar artery was occluded on later angiograms. (b, c) Axial T2-weighted MR images (c obtained at a higher level than b) show regions of high signal intensity, which represent multiple infarcts. The infarcts involve the territory of the left posterior inferior cerebellar artery and middle cerebellar peduncle, an appearance that suggests the embolic nature of the infarction.

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.   Irregular stenoses and intimal flaps of both VAs in a 56-year-old woman with vertigo and diplopia (patient 11). (a-d) Anteroposterior (a) and lateral (b) right vertebral angiograms and anteroposterior (c) and lateral (d) left vertebral angiograms show multiple irregular stenoses (short arrows) and linear filling defects (arrowheads), which represent multiple intimal flaps. Note the small pseudoaneurysm in right V2 at the C2 level (long arrow). Fibromuscular dysplasia was highly suspected on the basis of these findings. (e) Coronal two-dimensional time-of-flight MR angiogram shows the intimal flaps as linear areas of low signal intensity (arrows). At follow-up angiography of both VAs 3 years later, these findings had nearly disappeared.

View larger version (107K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.   Irregular stenoses and intimal flaps of both VAs in a 56-year-old woman with vertigo and diplopia (patient 11). (a-d) Anteroposterior (a) and lateral (b) right vertebral angiograms and anteroposterior (c) and lateral (d) left vertebral angiograms show multiple irregular stenoses (short arrows) and linear filling defects (arrowheads), which represent multiple intimal flaps. Note the small pseudoaneurysm in right V2 at the C2 level (long arrow). Fibromuscular dysplasia was highly suspected on the basis of these findings. (e) Coronal two-dimensional time-of-flight MR angiogram shows the intimal flaps as linear areas of low signal intensity (arrows). At follow-up angiography of both VAs 3 years later, these findings had nearly disappeared.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 10c.   Irregular stenoses and intimal flaps of both VAs in a 56-year-old woman with vertigo and diplopia (patient 11). (a-d) Anteroposterior (a) and lateral (b) right vertebral angiograms and anteroposterior (c) and lateral (d) left vertebral angiograms show multiple irregular stenoses (short arrows) and linear filling defects (arrowheads), which represent multiple intimal flaps. Note the small pseudoaneurysm in right V2 at the C2 level (long arrow). Fibromuscular dysplasia was highly suspected on the basis of these findings. (e) Coronal two-dimensional time-of-flight MR angiogram shows the intimal flaps as linear areas of low signal intensity (arrows). At follow-up angiography of both VAs 3 years later, these findings had nearly disappeared.

View larger version (140K): [in this window] [in a new window] [Download PPT slide]   Figure 10d.   Irregular stenoses and intimal flaps of both VAs in a 56-year-old woman with vertigo and diplopia (patient 11). (a-d) Anteroposterior (a) and lateral (b) right vertebral angiograms and anteroposterior (c) and lateral (d) left vertebral angiograms show multiple irregular stenoses (short arrows) and linear filling defects (arrowheads), which represent multiple intimal flaps. Note the small pseudoaneurysm in right V2 at the C2 level (long arrow). Fibromuscular dysplasia was highly suspected on the basis of these findings. (e) Coronal two-dimensional time-of-flight MR angiogram shows the intimal flaps as linear areas of low signal intensity (arrows). At follow-up angiography of both VAs 3 years later, these findings had nearly disappeared.

View larger version (108K): [in this window] [in a new window] [Download PPT slide]   Figure 10e.   Irregular stenoses and intimal flaps of both VAs in a 56-year-old woman with vertigo and diplopia (patient 11). (a-d) Anteroposterior (a) and lateral (b) right vertebral angiograms and anteroposterior (c) and lateral (d) left vertebral angiograms show multiple irregular stenoses (short arrows) and linear filling defects (arrowheads), which represent multiple intimal flaps. Note the small pseudoaneurysm in right V2 at the C2 level (long arrow). Fibromuscular dysplasia was highly suspected on the basis of these findings. (e) Coronal two-dimensional time-of-flight MR angiogram shows the intimal flaps as linear areas of low signal intensity (arrows). At follow-up angiography of both VAs 3 years later, these findings had nearly disappeared.

	Discussion

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In medium-sized arteries, such as the vertebral artery, the three layers—intima, media, and adventitia—are well-defined. The outer limits of the intima and media are the internal and external elastic laminae, respectively (6). Intracranial dissections usually involve both the intima and the media, and the most common location of an intramural hematoma is between the internal elastic lamina and the media. The primary event causing medial hemorrhage in VA dissection is unclear, but it may involve an intimal tear that allows blood from the lumen to extravasate into the media or a hemorrhage from the vasa vasorum within the media (7,8). Several predisposing factors, such as hypertension, oral contraceptive use, migraine, or underlying vascular disease including fibromuscular dysplasia, cystic medial necrosis, and Marfan syndrome, might predispose to arterial dissection (9).

Spontaneous VA dissection most commonly occurs in the extradural VA, although intradural and combined intradural-extradural dissections are also seen (3,4,10). The location of the dissection may determine the clinical presentation and suggest subsequent management. Severe stenosis or occlusion of the extradural VA may result in brainstem or cerebellar ischemia if there is concomitant dissection of the contralateral VA, which limits collateral flow. An intraluminal clot thus formed can then break off, embolize, and occlude branches anywhere in the posterior circulation distal to the source. Patients with intradural dissection usually present with severe headache and SAH, as well as symptoms of possible brainstem or cerebellar ischemia (11). The intradural VA is more susceptible to rupture than the extradural VA because the intradural VA has a thicker internal elastic lamina but no external elastic lamina, a thinner adventitia, and fewer elastic fibers in the media (10,12).

Conventional angiography has been used for many years to establish the diagnosis of cervical artery dissection and is still considered the standard method of establishing this diagnosis. In the aneurysmal pattern, the conventional angiographic findings consist of focal or fusiform aneurysmal dilatation with or without proximal or distal stenosis. In our series, the involved VA segment in cases of the aneurysmal pattern was V4. Pseudoaneurysm develops when the dissection proceeds through the media to the subadventitial layer and causes dilatation of the outer wall of the vessel. However, dissection more commonly extends inward, thereby narrowing or occluding the vessel. In this steno-occlusive pattern, there is no predominantly affected segment and conventional angiographic findings consist of tapered or abrupt occlusion with or without distal reconstitution by collateral vessels. Narrowing of a long segment of the artery, which is thought to be characteristic of dissection, is referred to as the "string sign" (13) or, when there is focal narrowing with a distal site of dilatation, as the string of pearls sign (14). These two characteristic signs demonstrate dynamic changes at follow-up angiography, that is, resolution of the stenosis or progression to complete occlusion (15).

Recently, MR imaging and MR angiography have been widely used for investigation of arterial dissection. The value of MR imaging is due to its particularly high resolution in the posterior fossa and the capability for direct visualization of intramural hematomas, although the smaller size of the VA may make visualization of an intramural hematoma more difficult than visualization of carotid artery dissection (16). The typical MR imaging appearance of an intramural hematoma consists of an increased external diameter of the artery, an eccentric region of high signal intensity, and narrowing of the arterial lumen. The region of high signal intensity is due to the methemoglobin blood products within the hematoma. The signal intensity of an intramural hematoma varies on T1-weighted images according to its age (17,18). It appears isointense or slightly hyperintense for the first few days after onset and then becomes hyperintense in the subacute stage. The abnormal signal intensity resolves after several months (19). Therefore, the chronologic changes of signal intensity in a hematoma should be considered when MR imaging is used for screening or follow-up (15). In contrast, T2-weighted images seem to have less diagnostic value in cases of intramural hematoma because the hematoma merges with hyperintense cerebrospinal fluid (17). However, disappearance of the flow void on T2-weighted images suggests total occlusion of the affected vessel, as was seen in our series (Fig 6). The shape of an intramural hematoma varies according to the relationship between the axis of the dissected vessel and the imaging plane (20). Previous reports have described crescentic, oval, and circumferential intramural hematomas (20–22). In elderly patients, atheromatous plaques associated with severe intimal disease could mimic the MR imaging findings in VA dissection.

MR angiography has been used to demonstrate luminal abnormalities related to dissection, such as aneurysmal dilatation, an intimal flap, or occlusion, and shows promise as a noninvasive modality for diagnosis and follow-up (16). Most of the MR angiographic findings in our study corresponded well to the conventional angiographic findings, although it was difficult to accurately evaluate luminal stenosis. Therefore, it may be difficult to differentiate luminal stenosis from hypoplasia, vasospasm, or dysplasia without dissection (20). Sometimes, the intimal flap between the true and false lumina can be seen on axial source images (for maximum-intensity projection images) from MR angiography (Fig 3).

The typical clinical course of extradural VA dissection is reported to be a single neurologic event followed by recovery over a few weeks or months (23). Progression is thought to result from propagation of a thrombus or distal embolization. This fact is the rationale for use of anticoagulation in treatment of extradural VA dissection. The treatment of intradural VA dissection remains controversial. Anticoagulation is contraindicated in patients with hemorrhagic infarction or SAH from intradural VA dissection because the clinical course in these cases may worsen following anticoagulation (11). Balloon or coil embolization or surgical aneurysm clipping is necessary in cases of a dissecting aneurysm.

	Summary

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Patients with the aneurysmal pattern had dissection in V4 and commonly presented with SAH; in patients with the steno-occlusive pattern, there was a relatively even distribution of involvement from V1 to V4. All patients with the steno-occlusive pattern presented with a neurologic deficit. An embolic pattern of infarcts in the posterior circulation was detected at CT or MR imaging in most of these patients. In conclusion, the distribution of the dissection sites and the clinical presentation tended to differ according to the dissimilar conventional angiographic patterns of aneurysm or stenosis-occlusion. Therefore, familiarity with the imaging features of VA dissection, particularly the conventional angiographic findings, helps determine subsequent patient care.

	Footnotes

 
Abbreviations: SAH = subarachnoid hemorrhage, VA = vertebral artery

	References

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