Diagnostic ultrasound ( PDFDrive )

952 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
W
R
L
FIG. 26.49 Normal Vertebral Artery Waveform. Normal lowresistance
waveform of the vertebral artery with illing of the spectral
window.
S
normal vessels. 244 Because the vessel is small, low tends to
demonstrate a broader spectrum. he clear spectral window seen
in the normal carotid system is oten illed in the vertebral artery 102
(Fig. 26.49).
he vertebral vein (oten a plexus of veins) runs parallel and
adjacent to the vertebral artery. Care must be taken not to mistake
its low for that of the adjacent artery, particularly if the venous
low is pulsatile. Comparison with jugular venous low during
respiration should readily distinguish between vertebral artery
and vein. At times, the ascending cervical branch of the thyrocervical
trunk can be mistaken for the vertebral artery. his can be
avoided by looking for landmark transverse processes that
accompany the vertebral artery and by paying careful attention
to the waveform of the visualized vessel. he ascending cervical
branch has a high-impedance waveform pattern similar to that
of the ECA. 237
TCD sonographic examination of the vertebrobasilar artery
system can be performed as an adjunct to the extracranial evaluation.
he examination is conducted with a 2-MHz transducer
with the patient sitting, using a suboccipital midline nuchal
approach, or with the patient supine, using a retromastoidal
approach. Color or power Doppler facilitates TCD imaging of
the vertebrobasilar system. 245
Subclavian Steal
he subclavian steal phenomenon occurs when there is highgrade
stenosis or occlusion of the proximal subclavian or
innominate arteries with patent vertebral arteries bilaterally. he
artery of the ischemic limb “steals” blood from the vertebrobasilar
circulation through retrograde vertebral artery low, which may
result in symptoms of vertebrobasilar insuiciency (Fig. 26.50).
Symptoms are usually most pronounced during exercise of the
FIG. 26.50 Hemodynamic Pattern in Subclavian Steal Syndrome.
Proximal left subclavian artery occlusive lesion (arrowhead)
decreases low to the distal subclavian artery (S). This produces retrograde
low (large arrows) down the left vertebral artery (L) and stealing from
the right vertebral artery (R) and other intracranial vessels through the
circle of Willis (W).
upper extremity but can be produced by changes in head position.
However, there is oten poor correlation between vertebrobasilar
symptoms and the subclavian steal phenomenon. In most cases,
low within the basilar artery is unafected unless severe stenosis
of the vertebral artery supplying the steal exists. 245 Also, surgical
or angioplastic restoration of blood low may not result in relief
of symptoms. 246 he subclavian steal phenomenon is most oten
caused by atherosclerotic disease, although traumatic, embolic,
surgical, congenital, and neoplastic factors have also been
implicated. Although the proximal subclavian stenosis or occlusion
may be diicult to image, particularly on the let, the vertebral
artery waveform abnormalities correlate with the severity of the
subclavian disease.
Doppler evaluation of the vertebral artery reveals four distinct
abnormal waveforms that correlate with subclavian or vertebral