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(Stroke. 1996;27:290-295.)
© 1996 American Heart Association, Inc.

Articles

Evaluation of Extracranial Vertebral Artery Dissection With Duplex Color-Flow Imaging

Eva Bartels, MD K.A. Flügel, MD

From the Department of Neurology and Clinical Neurophysiology, Akademisches Lehrkrankenhaus, Städtisches Krankenhaus München-Bogenhausen, Munich, Germany.

Correspondence to Eva Bartels, MD, Department of Neurology and Clinical Neurophysiology, Städtisches Krankenhaus München-Bogenhausen, Englschalkinger Str 77, 81925 Munich, Germany.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Background and Purpose We describe the diagnostic potential of duplex color-flow imaging in the evaluation of extracranial vertebral artery dissection.

Methods Twenty patients with 24 extracranial vertebral artery dissections (four bilateral) were examined with duplex ultrasonography over a period of 6 years. Color-flow imaging was carried out in 16 of these patients. In 15 patients (75%), the dissection was temporally related to trauma. Angiography was available in 18 patients, confirming the diagnosis.

Results In 15 patients, the diagnosis was primarily established with ultrasonography. Five patients with a dissection were referred for follow-up color-flow examinations. Six vertebral arteries were dissected at the origin or in the proximal V1 segment, one in the distal V2 segment, and one at the atlas loop. In contrast to other studies, the most frequent localization of the dissection in our patients was the region between the V1 and V2 segments (n=16), where the most typical dissection site was the entrance of the artery into the transverse foramen of the C6 vertebra (n=11). Typical ultrasonographic findings were irregular stenosis, dissecting membrane with true and false lumen, localized increase in diameter of the artery, pseudoaneurysm, intramural hematoma, and tapering stenosis with distal occlusion. In follow-up examination, a good regression of pathological findings was found in 17 dissections (70.8%). Two occlusions were completely recanalized.

Conclusions Extracranial vertebral artery dissections can be diagnosed noninvasively with duplex color-flow imaging. It is therefore a useful method for early diagnosis and follow-up examination.

Key Words: dissection • duplex scanning • ultrasonics • vertebral artery

	Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Extracranial vertebral artery (ECVA) dissection has been reported with increasing frequency during the last decade.^{1 2 3} The most common clinical findings are brain stem or cerebellar ischemic symptoms preceded by severe neck pain and/or occipital headache. Occasional patients have radicular symptoms.^{4 5}

Angiography is the current method of choice in the diagnosis of cervical artery dissection, whereby irregular stenosis, double lumen, pseudoaneurysm formation, and tapering or occlusion of the vessel can be shown.⁶ Because the investigation of the vertebrobasilar region carries certain risk factors, this procedure is increasingly being replaced by noninvasive techniques.⁷

MRI, MRA, and duplex ultrasonography offer potential advantages in the noninvasive assessment of extracranial vascular disease.^{8 9 10} Duplex color-flow imaging of carotid artery dissection has been described.^{11 12} The hemodynamic findings detected using duplex ultrasonography and transcranial Doppler sonography in vertebral artery (VA) dissection have also been reported.^{13 14}

In a dissection, the findings vary depending on the mechanism of the dissection. Minor trauma usually causes minor alterations of the vessel wall without important lumen narrowing. A major mechanical force can cause a dissection in several segments with a severe stenosis or even an occlusion of the artery.¹

The purpose of this study was to examine the diagnostic potential of duplex color-flow imaging in the evaluation of ECVA dissection and to describe the most pathognomonic, direct ultrasonographic findings after onset of symptoms and during follow-up examinations.

	Subjects and Methods

Top Abstract Introduction Subjects and Methods Results Discussion References

 
In the present study, 20 consecutive patients (10 men and 10 women) aged 18 to 59 years (mean age, 40.3 years) with 24 ECVA dissections were followed up over the last 6 years. Three women and 1 man had bilateral VA dissections.

In 15 patients (75%) the dissection was temporally related to minor or significant trauma, whereas in only 5 patients was the relation of the dissection with potential trauma questionable. In all individuals, the onset of symptoms was very abrupt.

The first 4 patients were examined with the duplex scanner Diasonics DRF 400 with a 7.5-MHz linear-array transducer (Sonotron GmbH). The other 16 patients were monitored with the color Doppler imaging system Acuson 128 XP 10 equipped with a linear-array transducer with 7.0-MHz imaging frequency and 5.0-MHz pulsed-wave Doppler frequency, which we have used since January 1991. As in our standard sonographic examination, the VA and carotid arteries were imaged in both transverse and sagittal planes. We visualized the ECVA at the origin and followed its course longitudinally in a rostral direction up to the transverse process of the C3 vertebra.¹⁵ As is customary, we divided the extracranial portion of the VA into the following segments: V0, origin; V1, between the origin and entry into the transverse foramen of the C6 vertebra; V2, midcervical course between processes C6 to C2 vertebrae; and V3, atlas loop region.¹⁶ Color Doppler evaluation and spectral analysis were used to assess hemodynamic data from the vessels: flow velocity and direction as well as waveform characteristics.¹⁷ The color-flow imaging results were recorded on a color printer (Sony Mavigraph UP-5000 P).

In 15 patients, a dissection was primarily detected with duplex color-flow imaging. In these patients, the interval between the initial clinical symptoms and ultrasound examination was 2.3 days (range, 0.5 to 4 days). Five patients, previously diagnosed with angiography in another hospital, were referred to our ultrasound laboratory for color-flow examination control. Follow-up ultrasonographic data were available for all patients. The mean observation time was 7.9 months (range, 1 to 36 months).

Digital arterial subtraction angiography was available for 14 patients and MRA for 7, confirming the diagnosis. Three patients had both examinations. Control angiography was performed in two cases. In 2 patients with reproducible, clear sonographic findings and with MRI/MRA examination, angiography was not done to avoid risks associated with invasive procedures.

	Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
With the exception of one patient with small, nonstenotic plaques at the origin of the internal carotid arteries, no atherosclerotic lesions were detected in the extracranial segments of the carotid arteries in any of the other patients.

Ultrasonographic abnormalities of VAs were, on the other hand, observed in all patients (Table 1). In 6 patients, the artery was injured at the origin. Thickening of the vessel wall and heterogeneous echogenic structures with irregular surface in the lumen were seen in all patients. In 3 of these patients, the VA was occluded directly at the ostium. More distally, a vessel lumen without detectable blood flow (a very typical sign for a recent occlusion) was recognized.

View this table: [in this window] [in a new window]   Table 1. Color-Flow Duplex Ultrasonographic Findings of ECVA in 20 Patients With 24 ECVA Dissections

The distal V1 and proximal V2 segments were the most frequent localizations of dissection in our patients (16 dissections). The point of entry of the ECVA into the transverse foramen of the C6 vertebra was especially affected (11 dissections). Here a localized increase in diameter of the artery with thickening of a vessel wall was observed (Fig 1). In some cases, within a thickened irregular vessel wall an echolucent intramural hematoma or different intravascular echoes were present (Fig 2). In 2 patients, an intimal flap or a dissecting membrane with true and false lumen underscored the diagnosis (Fig 2, top right). A tapering stenosis (in 3 subjects with distal occlusion) was a very common finding (n=10). Furthermore, variable Doppler spectral waveforms such as biphasic patterns, resistive patterns, and decreased systolic and diastolic flow velocities were observed (Fig 1, bottom right).

View larger version (96K): [in this window] [in a new window]   Figure 1. Findings in patient 10. Top left, Ultrasonographic image of the distal V1/proximal V2 segment showing a localized increase in diameter of the artery at the entrance of the vertebral artery (VA) into the transverse foramen of the C6 vertebrae (diameter distally, 2.1 mm; proximally, 5.7 mm). Top middle and right, Angiography at admission shows occlusion of the right VA 2 cm distal from the origin (middle). Left vertebral angiography shows the retrograde filling of a short intracranial segment of the occluded right VA at the site of the vertebral junction (right). Bottom left, Admission CT scan shows the right cerebellar infarction of this 25-year-old patient. Bottom right, Follow-up color-flow findings 8 months later (with use of the same transducer position) show a lumen reduction on the site of the prior dilatation in the distal V1 segment. VA diameter is 2.8 mm. Red color coding (flowing blood within the artery) indicates recanalization. The vertebral vein (VV; coded blue) runs parallel to the artery.

View larger version (76K): [in this window] [in a new window]   Figure 2. Top left, Color-flow image of patient 11 with bilateral dissection of the vertebral artery (VA; A.V.) expanding from V0 to the distal V2 segment shows origin of the left VA from the subclavian artery (A, sub) and the proximal V1 segment. Two intramural hematomas (arrowheads) appear as echolucent longitudinal formations. Thickening of the vessel wall by 3.2 mm and reduction of the lumen diameter by 2.1 mm were registered. Top right, more distally, in the V2 segment (between processus transversi of C4 and C5 vertebrae), three lumina can be seen. The false lumen with a blood flow (arrowhead) is delineated by a dissecting membrane from the true lumen (arrow). The third parallel lumen is the vertebral vein. The transverse processes C4 and C5 are causing acoustic shadowing. Bottom left, Admission angiogram of the left VA dissection shows distinct irregularities of the vessel wall expanding from the origin to the distal V2 segment. Bottom middle, MRI demonstrates the bilateral cerebellar infarction in this 32-year-old woman. Bottom right, Follow-up examination 7 months later shows good recanalization in the V0/V1 segment, with a normal spectral analysis. Near the origin, only thickening of the vessel wall can be seen.

In 1 patient, there was a pseudoaneurysm formation in the distal V2 segment at the level of the C3 vertebra. In addition to the normal vertebral signal, a weak flow signal with decreased biphasic flow pattern was registered in the partially thrombosed pseudoaneurysm.

Dissection in the V3 segment (n=1) could not be detected directly on the B-scan. The diagnosis was based on indirect signs such as a high-resistance flow pattern with increased pulsatility index and decreased diastolic flow (or even without a diastolic flow component) within normally configured arteries in the V1 and V2 segments.

In follow-up examinations, the abnormal findings regressed in 17 patients (70.8%). In cases of early major structural lesions, a thickening of the vessel wall could still be observed 6 to 12 months later, whereas the hemodynamic parameter returned to normal (Fig 2, bottom right). Two VA occlusions completely recanalized, and three other occlusions partly recanalized via cervical collaterals (Table 2).

View this table: [in this window] [in a new window]   Table 2. Outcome in 20 Patients With 24 ECVA Dissections

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
The ultrasonographic appearance of ECVA dissections depends on their etiology and localization.¹⁸ Atherosclerosis or other underlying vascular disorders were etiologically unimportant in the majority of our patients.

The ultrasonographic abnormalities varied on the basis of the mechanism of the dissection and pathological anatomy. Usually in a dissection, after the primary tear of the intima, blood flows into the arterial wall between the intima and media, causing an intramural hematoma and thickening of the vessel wall. Subintimal hemorrhage can produce various degrees of stenosis; subadventitial hemorrhage can cause a pseudoaneurysm. Rupture back into the lumen can result in a false lumen.^{1 6} Accordingly, the ultrasonographic findings varied from minor lesions (irregularities and thickening of the vessel wall with intramural hematoma and/or narrowing of the lumen without hemodynamic alteration) to major structural lesions such as severe stenosis or occlusion.^{19 20 21}

Regarding localization, in our patients the most common site of dissection was the distal V1 segment, especially at the point of entry into the transverse foramen of the C6 vertebra. This midcervical region is possibly one of the most vulnerable spots, where the artery is exposed to the greatest mechanical injury.^{22 23} Particularly in this area, we were able to image the major pathological findings in the vessel wall, such as intramural hematoma, intimal flap with a true and false lumen, localized increase in diameter of the artery, or an irregular stenosis.

Compared with the other segments of the VA, the midcervical course is the easiest to examine because of clear anatomic conditions (straight course of the artery, interrupted by transverse processes of the vertebrae). Additionally, before the entry of the VA into the transverse foramen of the C6 vertebra, insonation along an extended vessel segment (without acoustic shadowing of the vertebrae) is possible, so that alteration of the vessel wall and an irregular stenosis can be well recognized. In this region, follow-up examinations are most reliable, since the transducer position for the imaging of the midcervical course is relatively constant.

The distal V2 and V3 segments cannot always be satisfactorily imaged; therefore, diagnosis is based on indirect hemodynamic signs. In patients with a typical history and clinical symptoms related to the vertebrobasilar territory, decreased diastolic flow velocity or a missing diastolic component in the spectral analysis, registered in the midcervical course of the affected artery, is very suspicious for a more distal dissection. However, the presence of these high-resistance flow patterns is not specific, since this may also occur in stenosis or occlusion of any etiology. Diagnostic errors also can be made in the case of a hypoplastic VA, particularly if it ends in the posterior inferior cerebellar artery. In this relatively common anatomic variation, a Doppler spectrum similar to that of an intracranial obstruction of the VA can be found.²⁴ For this reason, a measurement of the VA diameter of both sides is mandatory. Different spectral analysis in arteries of equal width mostly indicates VA pathology.

A recanalized dissected ECVA can mimic a vertebral hypoplasia, as has been demonstrated in Fig 1, bottom right. On the other hand, in the case of vertebral hypoplasia, an irregular lumen narrowing of a possible dissection is very difficult to image. In such conditions, diagnosis of a dissection is based mainly on the alteration of the vessel wall. For this purpose, conventional duplex sonography is adequate. On the other hand, the evidence of blood flow in a narrowed artery, false lumen, or recanalized artery can be demonstrated only by means of color coding of Doppler frequencies. Color-flow imaging also allows a more efficient assessment of pathological findings at the origin and improves the potential for identifying the vessel in more complicated anatomic conditions (eg, in the case of tortuosity).

In carotid artery dissection, a special intraluminal alternating Doppler signal has been described.^{25 26}

In our patients, we did not observe any particular acoustic signal suggestive of occlusion of the VA due to dissection.

A dissection of the VA at origin can sometimes result in a proximal occlusion of the artery. Differentiation between an occlusion due to dissection or atherosclerosis can be problematic, since echodense plaques might be difficult to detect in the ostium region. Nevertheless, the absence of any atherosclerotic signs in the carotid bifurcation rules out an occlusion due to atherosclerosis because, in the case of atherosclerosis, the bifurcation is the most commonly affected region.¹⁶

Although patients with dissections are relatively young and therefore usually easy to examine, duplex color-flow imaging can sometimes be limited. The diagnosis of a dissection at the origin can be problematic, particularly on the left side, because of the proximal location of the ostium.¹⁷ In the V2 segment, acoustic shadowing of the transverse vertebral processes makes the visualization of an intramural hematoma or pseudoaneurysm more difficult. Problems can also arise in restless, agitated patients and individuals with short necks. Furthermore, the VAs are more difficult to examine than the carotid arteries and therefore require an experienced sonographer.

In previous studies, the V3 segment was described as the most frequent site of a dissection.²⁷ This region seems to be involved more often in cases of spontaneous dissections. In our patients, on the other hand, the majority of structural lesions were found directly at the V1 to V2 level, which in view of the high number of traumatic cases is not surprising. All dissections diagnosed primarily with ultrasonography were confirmed by angiography. However, our study cannot provide an accurate statistical analysis concerning the detection of VA dissection with color-flow imaging. Since dissections occur relatively rarely, only a multicenter study can give relevant information about the sensitivity and specificity of color-flow imaging in VA dissection. Whereas angiography only shows an alteration of the vessel lumen, duplex color-flow imaging provides additional information about the hemodynamic parameters and pathology of the vessel wall. Because duplex color-flow imaging can be repeated as often as necessary, it is a proven technique for early diagnosis, follow-up examination, and accordingly, therapeutic decisions (ie, the duration of anticoagulant treatment).

In 6 of our patients, the diagnosis was confirmed using noninvasive techniques (CT, MRI, or MRA) without angiography. Recently published studies underscore the advantages of the MRI fat-suppression technique in the imaging of the thickened vessel wall and intramural hematoma in dissection, particularly in the V3 segment.^{27 28 29 30} MRA is increasingly replacing conventional angiography despite certain limitations, eg, overestimation of the degree of stenosis.^{31 32} By using MRA in combination with both hemodynamic and morphological findings revealed in the duplex color-flow evaluation, a reliable diagnosis can be obtained and appropriate treatment with anticoagulants started.

Although angiography still remains the gold standard for detection of ECVA dissection, in appropriate clinical settings noninvasive techniques such as duplex color-flow imaging combined with MRI and MRA can also allow an accurate diagnosis.

	Acknowledgments

 
We would like to thank Professors Conrad, Klingelhöfer, and von Cramon, as well as Drs Sander and Hufnagl, for referring patients 9, 14, and 16 to us and for allowing us to publish this material. We are also grateful to Dr Rodiek for making the angiographic findings available. Finally, we would like to thank Professor Caplan and Dr Ackerstaff for their valuable comments on this manuscript.

Received July 20, 1995; revision received October 6, 1995; accepted October 9, 1995.

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bartels, E. Articles by Flügel, K.A. Search for Related Content PubMed PubMed Citation Articles by Bartels, E. Articles by Flügel, K.A.