Viewing vertebral arteries by duplex scan: what to expect

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Comparing the most likely sites of stenotic lesions in the carotid and the vertebral arte ries, there is one important difference: in the carotid arteries most stenoses occur at the level of the bifurcations, whereas in the vertebral arteries stenoses must be expected mainly at their origins [3, 4].

The carotid bifurcations are easily accessible by ultrasound: they are close to the surface, their diameter is large, and there is no bony structure in the way of the ultrasonic beam. On the other hand, the origins of the vertebral arteries and their prevertebral parts lie deeper below the surface and, at times, they are already behind the clavicular bones. Therefore the examination of these parts of the arteries can be difficult, especially when using a relatively large transducer.

For our investigations Diasonic RA-1 and DRF-300 sector-scanners with 7,5 MHz duplex probes were used. Distances were calculated by readings between cursor positions; because of an axial resolution of the probes of only 0,3—0,4 mm, these measurments could only be approximations.

NORMAL FINDINGS

Examining 122 successive patients (61 male, 61 female), the origins of the vertebral arteries were visualized in about 50% of the men and 65% of the women — the sex difference probably being the result of the smaller necks most women had. The rest of the prevertebral parts and the further course of the vertebral arteries in the intertransversal spaces C_5/6 and C_4/5 was visible in more than 90% of the cases; C_3/4 could be inspected in about 70 to 80% and C_2/3 in about 10 to 30% (fig. 1,2). In only 1,4% of 1131 patients no part of a vertebral artery could be visualized, either on one or on both sides. Si milar findings were reported by Touboul et al. and Visona et al. [7, 8].

Fig. 1. Vertebral arteries. Visibility by duplex-scan. Male

Fig. 2. Vertebral arteries. Visibility by duplex scan. Female

The lumina of the vertebral arteries differ more between right and left than in the carotid arteries. In about one half of 1131 patients the lumina of both vertebral arteries were identical within 0,5 mm. The left artery was dominant in 33%, the right artery in 17% of the cases. A left/right-difference of more than 1 mm in lumen was found in 33% (24% l.r., 9% r. 1.). Hypoplasias (lumen equal or less than 1,5 mm) were seen in 3,1% of the right, 1,9% of the left vertebral arteries: 3 of 1131 patients (0,3%) had hypoplasias of both vertebral arteries. The mean cumulative lumen of both vertebral arteries increased by age from 6,0 mm in patients younger than 30 years to 7,9 mm in patients older than 80 years without a significant sex difference ( + /-1,1 mm for each agegroup) (fig. 3).

Fig. 3. Cumulative mean lumen of both vertebral arteries

PATHOLOGICAL FINDINGS

Hemodynamically important stenoses of the vertebral arteries were found only at their origins. Some plaques were also visualized in the prevertebral, few in the intertransversal parts. In most cases the degree of stenosis could not be determined, as sufficient В-mode cross-sections were not possible; estimations had to rely on the doppler-signal. For this reason all clearly visible plaques are included under the term "stenosis" in the following data.

Occlusions of vertebral arteries can be difficult to demonstrate, since the diagnosis must rely on a missing doppler signal in several parts of the artery, and reopenings by collateral pathways cannot always be visualized. Angiography was performed in 4 of our 7 cases, confirming the duplex findings.

Vertebral steal-phenomena can easily be detected by ultrasound-duplex-scan (table 1).

Table 1. 127 cases of stenoses, occlusions and vertebral steal in 1131 patients

The percentage of pathological findings in the vertebral arteries increased by age from 3% in patients in their 4th decade to 16% in those over 80 years of age. In the same group of patients, carotid stenoses of more than 50% occured somewhat more frequently in most age groups (fig. 4).

Fig. 4. Vertebral a: steal phenomena, all stenoses. Carotid a: stenoses >50%

Of all 1131 patients, 16% had at least one carotid-stenosis of more than 50%, versus 11% of pathological vertebral findings. Among specific diseases intracranial infarctions in the vertebro-basilar territory and peripheral vascular disease (without neurological signs or symptoms) were particularly associated with pathological vertebral findings. It is doubtful whether vertebral hypoplasias are of any diagnostic importance; yet they seem to coincide more frequently with cases of infarctions or transitory disturbances in the vertebro-basilar supplied areas of the brain (table 2).

Table 2. Pathological duplex-scans of carotids (stenoses >50%), vertebral arteries (all stenoses, steal-effect), and vertebral hypoplasias in several identical diagnostic groups (% of each diagnostic group)

DISCUSSION

Arteriosclerotic changes in the vertebral arte ries will rarely lead to surgical intervention; however their presence can influence the decision whether to treat carotid stenoses conservatively or surgically. Although conventional doppler sonography can already reveal many hemody namically significant stenoses at the origins of the vessels [5], duplex-scanning will help to identify the vessels more clearly and to place the sample volume of the pulsed-doppler system right at the area of interest. The usefulness of this approach has already been described by others [1, 2]. Our investigation of more than 1000 patients confirmed their findings, adding interesting diagnostic details.

Our previous studies by ultrasound duplex scan revealed that in 88% of the cases with a carotid-stenosis of more than half the lumen on one side, atheromatosis was also present in the contralateral carotid artery. We expected a somewhat lower coincidence in the vertebral arteries [6]. This assumption was confirmed by the present ultrasound study. We decided to compare the percentage of carotid stenoses of more than 50% with all pathological findings in the vertebral arteries including non-stenotic plaques. This seems to be justified, because plaques in the vertebral arteries are not as easy to detect by ultrasound as in the carotid arteries: В mode and Doppler signals are more difficult to interpret, because the arteries lie deeper and are surrounded by bony structures; hence small plaques will not be recognized as easily in the vertebral as in the carotid arteries. Cross sections of the vertebral arteries will seldom reveal the exact degree of stenosis. Plaques of low echo density, even difficult to distinguish in the vessels close to the surface, are rare in the duplex scans of the vertebral arteries.

In spite of these restrictions we demonstrated a tendency of high proportions of pathological vertebral findings in patients having infarctions of the posterior parts of the brain and in cases of TIA, vertigo and peripheral vascular disease without neurological signs or symptoms. Hypo plasia of a vertebral artery (defined by a lumen <1,5 mm) was also more frequent in vertebrobasilar infarctions than in other diagnostic groups.

We therefore propose to include the investigation of the vertebral arteries in duplex examinations of the neck of patients with clear vertebro basilar symptoms, and also in every person in whom surgery of a carotid artery is under consideration.

About the authors

М. Salaschek

Author for correspondence.
Email: info@eco-vector.com
Germany, Ibbenbueren, FRG

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2. Fig. 1. Vertebral arteries. Visibility by duplex-scan. Male

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3. Fig. 2. Vertebral arteries. Visibility by duplex scan. Female

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4. Fig. 3. Cumulative mean lumen of both vertebral arteries

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5. Fig. 4. Vertebral a: steal phenomena, all stenoses. Carotid a: stenoses >50%

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