Diagnostic ultrasound ( PDFDrive )

CHAPTER 26 The Extracranial Cerebral Vessels 951
B
C
S
FIG. 26.48 Normal Vertebral Artery and Vein. Longitudinal color
Doppler image shows a normal vertebral artery (A) and vein (V) running
between the transverse processes of the second to sixth cervical
vertebrae (C2-C6), which are identiied by their periodic acoustic shadowing
(S).
FIG. 26.47 Vertebral Artery Course. Lateral diagram of vertebral
artery (arrows) shows its course through the cervical spine transverse
foramina en route to joining the contralateral vertebral artery to form
the basilar artery (B). C, Carotid artery; S, subclavian artery.
in patients with carotid occlusive disease. Evaluation of the
extracranial vertebral artery seems a natural extension of carotid
duplex and color Doppler imaging. 232,233 Historically, however,
these arteries have not been studied as intensively as the carotids.
Symptoms of vertebrobasilar insuiciency also tend to be rather
vague and poorly deined compared with symptoms referable
to the carotid circulation. It is oten diicult to make an association
conidently between a lesion and symptoms. Furthermore, interest
in surgical correction of vertebral lesions has been limited. he
anatomic variability, small size, deep course, and limited visualization
resulting from overlying transverse processes make the
vertebral artery more diicult to examine accurately with
ultrasound. 232,234-236 he clinical utility of vertebral artery duplex
scanning in diagnosing subclavian steal and presteal phenomena
is well established. 237-239 Less clear-cut is the use of vertebral
duplex scanning in evaluating vertebral artery stenosis, dissection,
or aneurysm. 240
Anatomy
he vertebral artery is usually the irst branch of the subclavian
artery (Fig. 26.47). However, variation in the origin of the vertebral
arteries is common. In 6% to 8% of people, the let vertebral
artery arises directly from the aortic arch proximal to the let
subclavian artery. 234,241 In 90%, the proximal vertebral artery
ascends superomedially, passing anterior to the transverse process
of the seventh cervical vertebra (C7), and enters the transverse
foramen at the C6 level. he rest of the vertebral arteries enter
into the transverse foramen at the C5 or C7 level and, rarely, at
the C4 level. he size of vertebral arteries is variable, with the
let larger than the right in 42%, the two vertebral arteries equal
in size in 26%, and the right larger than the let in 32% of cases. 242
One vertebral artery may even be congenitally absent. Usually,
the vertebral arteries join at their conluence to form the basilar
artery. Rarely, the vertebral artery may terminate in a posterior
inferior cerebellar artery.
Sonographic Technique and
Normal Examination
Vertebral artery visualization with Doppler low analysis can be
obtained in 92% to 98% of vessels 232,243 (Fig. 26.48). Vertebral
artery duplex examinations are performed by irst locating the
CCA in the longitudinal plane. he direction of low in the CCA
and jugular vein is determined. A gradual sweep of the transducer
laterally demonstrates the vertebral artery and vein running
between the transverse processes of C2 to C6, which are identiied
by their periodic acoustic shadowing. Angling the transducer
caudad allows visualization of the vertebral artery origin in 60%
to 70% of the arteries, in 80% on the right side, and in 50% on
the let. his discrepancy may relate to the let vertebral artery
origin being deeper and arising directly from the aortic arch in
6% to 8% of cases. 234,241
he presence and direction of low should be established.
Visible plaque should be assessed. he vertebral artery usually
has a low-resistance low pattern similar to that of the CCA,
with continuous low in systole and diastole; however, wide
variability in waveform shape has been noted in angiographically