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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5760_Библиотеки_им_академика_М_И_Перельмана.pdf
294
Ophthalmic artery
Circle of Willis
Right common carotid ar
ab
EF
Chapter 5 · Extracranial Cerebral Arteries
Supraorbital artery
Supratrochlear artery
Superficial
temporal artery
5
Facial artery
Right vertebral artery
Right subclavian artery
tery
Aorta
Internal carotid artery
External carotid artery
Left common carotid
artery
Left vertebral artery
Left subclavian artery
AB CD
c
. Fig. 5.1 a Diagram of the arteries supplying the brain (marked are the sites for taking representative measurements and documenting
results). b Variants resulting from elongation of the internal carotid artery (ICA) (shown for the left artery): A C-shaped course, B S-shaped course,
C coiling, D double coiling, E kinking, F double kinking. c Color ow image showing severe kinking of the ICA (corresponding to E in b), indicated
by a change in blood ow direction relative to the transducer (change from blue to red color coding). d Color ow image showing coiling of the
ICA (corresponding to C in b), indicated by a change in color coding due to a change in ow direction relative to the transducer (blue– away from
transducer/toward the heart; red– toward transducer)
e normal brachiocephalic trunk on the right has a length
of 4–5 cm. It crosses under the brachiocephalic vein and,
behind the right sternoclavicular joint, divides into the right
subclavian artery and the right CCA.
e two CCAs course cranially accompanied by the vagus
nerve and the internal jugular vein, which runs anterolateral
to the carotids. e carotid bifurcation is usually located at the
C4–C5 level, which roughly corresponds to the level of the
thyroid cartilage, but there is wide interindividual variation
(. Fig.5.2). Typically, the larger ICA arises from the posterolateral aspect. It has a widened portion at its origin, called the
carotid bulb. Unlike the external carotid artery (ECA), the
ICA does not give o branches along its extracranial course.
d
Elongation of the ICA is associated with kinking (90°
angle between adjacent segments) or coiling (360° loop)
(. Fig.5.1b–d). Carotid elongation develops with age. Arterial hypertension is considered a predisposing factor. Kinking or coiling results from the limited space available between
the two points of xation, the bifurcation and the base of
skull, but even severe kinking rarely causes hemodynamically signicant stenosis (see . Fig.5.51 (Atlas)).
e ECA arises from the anteromedial aspect of the ICA;
in approx. 10% of individuals its point of origin is lateral or
posterolateral. On its course, it rst gives o the superior thyroid artery (STA) and then branches to supply the skin and
extracranial organs (facial and temporal arteries).
trunk
5.1 · Normal Vascular Anatomy andImportant Variants
a
Carotid
ICA
295
5
V3
V2
b
c
. Fig. 5.2 Transducer positions for examination of the extracranial
carotid artery and vertebral artery (courses indicted by thick black
lines). a Anterolateral transducer position (in front of sternocleidomastoid muscle) for scanning the carotid artery. b Posterolateral position
(behind sternocleidomastoid muscle) for scanning the carotid artery.
c Transducer position for scanning the origin of the vertebral artery
5.1.2 Vertebral Arteries
e two vertebral arteries originate from the ipsilateral subclavian arteries at the C6 level and then pass through the
transverse foramina of the corresponding vertebrae, thus
Superior
thyroid artery
CCA
Vertebral artery
Subclavian artery
. Fig. 5.3 Vascular anatomy of the extracranial cerebral arteries.
Transducer positions for imaging the carotid bifurcation and the extracranial vertebral artery segments (V0/1, V2, and V3)
V0/1
Thyrocervical
taking a partially intraosseous course on their way to the
skull base. ey oen dier in caliber and may exhibit unilateral hypoplasia or aplasia, which is compensated for by contralateral hypertrophy. e le vertebral artery typically has a
larger caliber and, in up to 4% of the population, arises
directly from the aortic arch.
Somewhat distal to the vertebral artery, the thyrocervical
trunk arises from the subclavian artery. e dierentiation is
signicant in the duplex ultrasound examination. For a precise description of the site of lesions, the vertebral artery is
divided into ve segments (
. Fig.5.3):
5 e V0 segment, which is the origin of the vertebral
artery from the subclavian artery
5 e V1 segment, which extends from the origin to the
C6 transverse process
5 e V2 segment, which is the part coursing through the
cervical vertebral foramina
5 e V3 segment, which takes an arched course around
the atlas and is therefore also referred to as the atlas loop
5 e V4 segment, which is the intracranial part of the
vertebral artery.
e V2 segment of the vertebral artery communicates with
branches of the thyrocervical trunk and the V3 segment with
the occipital artery (ECA branch).
Anatomic variants of the vertebral artery render the diagnosis more dicult. ese include unilateral hypoplasia, an
origin directly from the aortic arch (5% for the le vertebral
artery, no risk of subclavian steal syndrome), and an abnormal course (entry into the cervical spine below or sometimes
above the C6 level in 10% of individuals).
296
Chapter 5 · Extracranial Cerebral Arteries
5.2 Examination Technique andProtocol
Sonomorphologically, the normal arterial wall is com-
posed of three layers: an inner layer depicted as a hyperechoic
Given their supercial location, the cerebral arteries can be
examined with a high-frequency transducer (5–7.5MHz or
even 10MHz), yielding B-mode images with high spatial
resolution. e ultrasound examination is performed with
the patient in the supine position and the head slightly
hyperextended. While some examiners prefer to sit to the
right of the patient, it is recommended that the examiner sit
at the patient’s head, from were all transducer positions
5
(anterolateral, posterolateral) can be reached with little
movement and without exerting undue pressure because
his or her elbow can rest on the edge of the couch (. Fig.5.2).
is is important for continuously evaluating the course of
the carotid artery and for performing the temporal artery
tap maneuver to identify the ECA and dierentiate it from
the ICA (. Fig. 5.6). e course of the arteries and the
carotid bifurcation are identied in the transverse plane,
while the Doppler waveform is sampled longitudinally. As
in the ultrasound examination of other body regions, the
le of the screen is superior and the right is inferior.
line next to the lumen; a middle zone seen as a somewhat
broader, hypoechoic layer; and an outer layer of slightly
higher echogenicity, which is poorly demarcated from the
perivascular fatty tissue. Since ultrasound does not visualize
tissues or tissue layers directly but rather the echoes reected
by interfaces between zones of dierent acoustic impedance,
the three layers seen do not exactly match the three anatomic
wall layers– the intima, media, and adventitia. e intima
and media are sonographically indistinguishable, which is
why it is not possible to evaluate the intima alone. It is therefore common practice to measure the thickness of the
intima–media complex instead.
e sonographic
thickness of the intima–media complex
is used as an early indicator of subclinical atherosclerosis and
a measure of therapeutic outcome in interventional studies
(e.g., to monitor statin therapy). It is therefore desirable that a
standardized method for measuring carotid intima–media
thickness (IMT) be used to minimize interobserver variability.
A perpendicular angle of incidence ensures optimal evaluation of the vessel wall, which is the case if the target vessel
courses parallel to the skin surface. If the angle is smaller, the
examiner should move the transducer back and forth or rotate
5.2.1 Carotid Arteries
it slightly to ensure that the wall is evaluated in a plane show-
ing the maximum vessel diameter. IMT is measured in the far
e examination begins by obtaining a survey of the carotid
bifurcation in transverse orientation to determine the location and course of the internal carotid artery (ICA) and
external carotid artery (ECA) in relation to each other. e
following variants may be encountered:
5 In approx. 90% of the population, the ICA courses
posterolateral to the ECA.
5 In approx. 10% of individuals, the ICA is seen at the
same level and medial to the ECA.
5 In rare cases, the ICA is located anterior to the ECA.
wall of the CCA to exploit the blood-lled lumen as an acous-
tic window for optimal visualization of the two echogenic lines
demarcating the intimal and medial layers. e leading-edge
method (see
7 Sect. 1.1.2.4 and . Fig.5.5) is recommended to
minimize blooming artifacts (which appear at boundaries
with a large mismatch in acoustic impedance). Serial IMT
measurements should always be performed at the same site;
most investigators prefer the far wall 2–3cm proximal to the
carotid bifurcation. Use of a high-frequency transducer (>
10MHz) is recommended for evaluation of the wall as axial
resolution and measurement accuracy increase with transFor Doppler angle correction and precise identication of
stenosis or plaque, the examiner must move the transducer
around to obtain a view depicting the carotid bifurcation as a
tuning fork. ere are three standardized approaches for longitudinal imaging:
5 Positioning of the transducer between the larynx and
sternocleidomastoid muscle for sagittal anteroposterior
sections (. Fig.5.2a)
5 Lateral approach through the sternocleidomastoid
muscle
5 Posterolateral approach with the transducer posterior to
the sternocleidomastoid muscle (. Fig.5.2b)
ducer frequency (see . Table 1.2). Note, however, that
although it is technically feasible, dierentiation of structures
smaller than 0.01mm is beyond the resolution capacity of the
human eye (and may introduce measurement errors, bloom-
ing, etc.). Finally, it is recommended that the measurement of
IMT be performed at end diastole to minimize variations
through the cardiac cycle (Meyer and Strobel 2008).
No agreement exists regarding the need for detailed
sonomorphologic characterization of plaque in routine clinical examination. While most patients with over 70% stenosis
(according to ECST criteria, which corresponds to 50% stenosis according to NASCET criteria) are candidates for surgery based on this degree of stenosis alone, plaque
e posterolateral transducer position will enable good visualization of the bifurcation in most patients whose ICA follows a normal course. In this position the ICA is depicted
near the transducer.
B-mode ultrasound is used for preliminary exploration of
carotid artery anatomy and for obtaining initial information
on the vessel wall in transverse orientation and in the longitudinal views presented above (. Fig.5.4).
morphology becomes relevant for therapeutic decisions in
patients with 60–70% stenosis and in patients with asymptomatic high-grade stenosis.
e morphologic evaluation of the vessel wall and plaque
is followed by spectral Doppler measurement in the longitudinal plane. Color duplex imaging can provide clues regarding steno-occlusive lesions: stenosis is suggested by aliasing
and an occlusion by the absence of color lling in the lumen.
ICA
a
5.2 · Examination Technique andProtocol
297
5
ICA
ECA
CCA
ECA
ICA
ECA
ICA
STA
STA
CCA
ICA
ICA
CCA
AS
AS
1
b
2
c
. Fig. 5.4 a Diagrams illustrating the ultrasound examination of the carotid bifurcation. The leftmost drawing illustrates the sites of transverse
examination for an overview and identication of the carotid arteries. The second drawing illustrates the posterolateral transducer position,
which usually depicts the carotid bifurcation as a tuning fork with the internal carotid artery (ICA), which runs posteriorly, appearing closer to
the transducer and the external carotid artery (ECA) appearing farther away from it. Often, this transducer position allows sonoanatomic identication of the ICA by demonstrating its wider bulb and also of the ECA by visualizing the superior thyroid artery (STA) arising from it; this position
also enables evaluation of plaque morphology. The third drawing illustrates the anterior transducer position, which is used for plaque evaluation
or spectral Doppler interrogation in cases where acoustic shadowing due to calcied plaque impairs imaging in the posterolateral position.
b Diagram illustrating how posterior acoustic shadowing (AS) obscuring the lumen can be circumvented by rotating the transducer from position 1 (e.g., posterolateral position) to position 2 (e.g., anterior position) to enable evaluation of plaque morphology/surface and assessment of
stenosis in the presence of calcied plaque. Position 2, unlike position 1, will also allow spectral Doppler imaging. The drawings illustrate how
even a small, calcied plaque can impair evaluation of the vascular lumen if the vessel is examined in only one plane. c The left image (obtained
with the transducer in a posterolateral position) illustrates how acoustic shadowing from calcied plaque in the carotid bulb completely
eliminates ow signals from the ICA and ECA and obscures vascular structures in the B-mode. The second image, obtained after changing the
transducer position to circumvent the sickle-shaped calcied plaque, allows evaluation of both the bulb and the ICA.There are no signs of
hemodynamically relevant luminal narrowing. No ow acceleration is demonstrated by color duplex or spectral Doppler, ruling out relevant
stenosis caused by the plaque
Moreover, the color duplex mode can facilitate identication
of the course of a kinked or coiled ICA.
While color duplex imaging is optional for initial orientation, angle-corrected Doppler waveforms in the longitudinal
plane must be obtained for quantication of blood ow velocity in the CCA, ICA, and ECA (. Table5.2). Spectral Doppler
sampling should be performed in the ICA at short intervals.
Use of a larger sample volume will oen enable continuous
examination of the CCA and ICA in the duplex mode, especially from the posterolateral approach. In this way, a continuous spectrum can be obtained and analyzed throughout the
CCA and ICA, similar as with CW Doppler ultrasound. e
ECA is scanned only at its origin for dierentiation from the
ICA and for the identication of possible stenosis.
e posterolateral transducer position is usually superior
to the anterior position for spectral Doppler interrogation.
From this transducer position, the bifurcation appears as a
tuning fork with the ICA close to the transducer, and the
CCA, the bulb, and long segments of the ICA and ECA can
be evaluated in a single view. is facilitates angle correction,
and the intervening so tissue improves visualization. However, when the ICA is kinked or coiled, dierent scanning
planes are necessary to identify a long enough straight segment of the artery for angle correction.
298
ternal bright line
method
Chapter 5 · Extracranial Cerebral Arteries
To minimize errors in flow velocity measurement in
the ICA
angle of < 60°
, the examiner should try to achieve a Doppler
(see . Fig. 1.23 and 7 Sect. 1.1.4.6). is
requires selection of an adequate transducer. When a linear
transducer with beam steering is used, even maximum cranial deection (technically limited to 20°) gives an angle of
insonation no smaller than 70° for an artery coursing parallel to the skin surface (90°−20°=70°). While a linear transducer provides the best resolution for morphologic
assessment of the vessel wall in the B-mode, a curved-array
5
transducer with a small footprint aords greater exibility
in achieving an adequate angle for spectral Doppler interrogation along the tortuous course of the ICA. Curved-
array transducers are also superior to linear transducers in
patients with short necks and in interrogating vessel segments near the base of the skull. e view is optimal when
the artery is depicted with parallel walls along the entire
width of the monitor. In the 10% of individuals with a
medial origin of the ICA, the tuning fork view of the bifurcation is occasionally obtained when an anterior approach
is used. If this is not possible, the transducer is rst tilted for
selective visualization of the origin of the ECA and then
tilted laterally for visualization of the origin of the ICA.
Longitudinally, the ICA is continuously followed to the
base of the skull, for which the posterolateral transducer
position
works best in most patients. Dierent approaches
may be required to follow a coiled or kinked ICA and to identify concomitant stenosis. Whenever the duplex ndings are
inconclusive, a Doppler waveform should be obtained.
A lower-frequency (5 MHz) curved-array transducer
Ex
Internal bright line
(with a small footprint) should be used in patients with poor
insonation conditions or for evaluation of the deeper portions of the extracranial ICA near the base of the skull.
When
IMT
using
leading-edge
and pulse repetition frequency (PRF) must be chosen so as to
ensure good color lling of the vessel lumen without aliasing
(color reversal from red to blue or vice versa). Transverse
color-coded duplex ultrasound is used, the gain
views are obtained with the transducer slightly tilted to achieve
. Fig. 5.5 Measurement of intima–media thickness (IMT). The intima
and media cannot be distinguished sonographically. The rst bright
echo is the interface between the blood and the intima (interface
between tissues of dierent acoustic impedance) with the second
bright echo representing the border between the adventitia and the
perivascular connective tissue. The wall layer between these two reections is the intima–media complex. Its thickness is measured using the
leading-edge method (see . Figs. 1.28 and 5.52 (Atlas))
an adequate Doppler angle. With adequate instrument settings, changes in the color ow pattern suggest pathology,
which must then be conrmed by spectral Doppler analysis.
Calcied plaques completely reect the ultrasound
pulse and thus cast acoustic shadows, impairing both color
duplex and conventional duplex as well as B-mode imaging.
Color coding is most severely aected by acoustic shadow-
. Table 5.2 Ultrasound examination of the carotid arteries (sequence of steps)
Ultrasound method Purpose
B-mode: transverse plane Course, possibly dierentiation of ICA/ECA (STA origin,
vessel diameter)
B-mode: longitudinal plane (anterior and posterolateral transducer
positions)
Color duplex (optional): posterolateral transducer position, anterior
approach as needed
Spectral Doppler (PW Doppler): in longitudinal orientation (never
transverse plane); posterolateral or anterior transducer position (angle
<60°). Adequate Doppler angle may be easier to achieve using a curved
array transducer with a small radius (can be tilted)
Additional B-mode examination with high-resolution transducer (linear
array) for evaluation of plaque morphology: patients with 60–70% ICA
stenosis by ECST criteria/local degree (equivalent to 40–50% NASCET
stenosis)/stage II or 60–80% stenosis/stage I
Power mode, B-ow mode, or CEUS in selected patients Plaque ulcer, detailed evaluation of plaque surface
CEA carotid endarterectomy, CEUS contrast-enhanced ultrasound, ECA external carotid artery, ECST European Carotid Surgery Trial, GSM
gray-scale median, ICA internal carotid artery, NASCET North American Symptomatic Carotid Endarterectomy Trial, STA superior thyroid
artery, PW pulsed wave
Search for plaque, plaque characterization, dierentiation of
nonatherosclerotic vascular disease
Course (kinking, coiling), initial clues regarding the presence
of stenosis (aliasing). Supplementary information when ICA/
ECA dierentiation is dicult (STA origin)
Conrmation of stenosis, stenosis grading
Dierentiation of ICA and ECA (temporal artery tap)
Indication for surgery (CEA)
Plaque morphology: echolucent/echogenic, homogeneous/
inhomogeneous, smooth/irregular surface; standardized
analysis of echogenicity, e.g., GSM, may be used (indication
for repair and type of repair)
5.2 · Examination Technique andProtocol
. Table 5.3 Criteria for dierentiating the ICA and ECA
Criterion Reliability
ICA posterolateral to ECA This is the case in only 90% of individuals, while 10% have a medial
ICA origin
Less pulsatile ow (large diastolic ow component) in ICA
compared to ECA
Larger lumen of ICA, especially of bulb Fairly reliable under normal conditions but not valid in the presence
Doppler waveform from ECA shows pulsation transmitted upon
intermittent tapping of temporal artery
ECA gives o arterial branches (1st branch: STA) and ICA does not Reliable if origins can be identied but often impaired by multiple
ECA external carotid artery, ICA internal carotid artery, STA superior thyroid artery
Reliable under normal conditions; patients with ECA stenosis will
also have a large diastolic ow component in the ECA waveform
of multiple (calcied) plaques
Reliable
plaques with acoustic scattering and shadowing
299
5
ing. In such situations, the pulsed Doppler, enabling focused
application of a higher beam intensity with a high gain, will
usually provide a Doppler waveform with a weak amplitude
that still allows assessment of blood ow. If the calcication
does not involve the entire inner circumference, the examiner can try and improve ow evaluation in the residual
lumen by insonating the vessel from a dierent direction to
obtain a view that depicts the calcied plaque on the wall
away from the transducer (. Fig.5.4).
Under normal conditions, the ICA and ECA are easily dif-
ferentiated
on the basis of their sonoanatomic relationship,
the demonstration of branches arising from the external but
not from the internal carotid artery, and the widened bulb at
the origin of the ICA.Compared with the ICA, the ECA has
more pulsatile ow with a smaller diastolic component in the
Doppler waveform. However, in patients with high-grade stenosis of the carotid bifurcation, acoustic scattering and shadowing may impair B-mode evaluation, and the stenosis-related
hemodynamic changes also aect the ow prole in the ECA
in that diastolic ow increases and the waveform becomes less
distinct from the ICA waveform. Internalization is also
observed when the ECA is recruited as a collateral for an
occluded ICA.In such cases, the examiner can use the temporal tap sign to identify the ECA.e temporal tap maneuver
involves rhythmical tapping of the temporal artery (anterior
to the ear). e oscillations will be transmitted to the ECA
and appear in the Doppler waveform from the ECA origin,
especially in diastole (. Table5.3), regardless of whether the
artery is normal or whether stenosis is present (. Fig.5.6).
Weaker transmission will still be noted in the CCA, while the
tap maneuver has no eect on the ICA waveform.
5.2.2 Vertebral Arteries
e vertebral artery can be examined by ultrasound from its
origin to just before the atlas loop in the longitudinal plane
from a lateral approach in the supine patient. It is not possible
to scan the entire length of the vertebral artery because seg-
ments of it are obscured by the transverse processes of the
cervical vertebrae. e origin from the subclavian artery is
best appreciated using a curved-array transducer with a small
radius, while the remainder can also be scanned with a linear
probe, ideally with a frequency of 5–7.5MHz. e
ment
with its accompanying vein is easiest to identify
V2 seg-
between the acoustic shadows from the transverse processes.
Because the paired vertebral arteries are linked via several
pathways, steno-occlusive disease in one branch has dierent
hemodynamic eects than an obstruction in an unpaired,
organ-supplying artery. In terms of ow physiology, the vertebral circulation constitutes a parallel circuit of vascular
resistances. Kirchho’s second law states that, in a parallel
circuit, current is inversely proportional to resistance.
According to the Hagen-Poiseuille law, a small change in vascular diameter (hyperplastic vertebral artery, atherosclerotic
stenosis, or luminal narrowing caused by dissection) will
markedly reduce ow in the artery because the eect that
vascular diameter has on ow in the equation is raised to the
fourth power. Because the vertebral arteries are paired,
60–70% stenosis will reduce blood ow by 90–95%, and the
contralateral artery largely maintains blood supply to the
posterior circulation, spontaneous thrombosis of the vertebral artery is quite common when higher-grade stenosis is
present.
Stenosis at the origin of the vertebral artery may be dicult to identify and evaluate, especially in obese patients with
a short neck. In addition, marked tortuosity of the vertebral
artery at its origin from the subclavian artery can impair
Doppler angle correction. Tortuosity may further contribute
to poor ow, but this is not uncommon at the origin of the
vertebral artery and does not necessarily mean that stenosis
is present. Identication of vertebral stenosis by color duplex
imaging is easier and more reliable in the V2 segment, but
higher-grade stenosis of the V2 segment is rare, and luminal
narrowing of this segment is more commonly caused by dissection. e technically less challenging examination of the
V2 segment is sucient in patients with suspected subclavian
steal syndrome. In general, however, the V0/V1 segment
300
bc
de
Chapter 5 · Extracranial Cerebral Arteries
. Fig. 5.6 Duplex ultrasound
examination of the carotid
bifurcation and dierentiation of
the internal carotid artery (ICA)
and external carotid artery (ECA).
Flow in the ECA is more pulsatile
and is modulated by the signal
transmitted upon rhythmical tapping of the temporal artery (a I
and b), especially during diastole
(X). The oscillations resulting from
the temporal tap do not aect
5
the waveform from the ICA (a I
and c). When stenosis is present,
dierentiation between the ICA
and ECA on the basis of pulsatility
is dicult, and plaque may impair
identication of the superior
thyroid artery (A.T.S) arising from
the ECA or of the wider bulb of
the ICA.The temporal artery tap,
however, still provides a clearcut
dierentiation, as the oscillation
is not transmitted into a stenotic
ICA (a II and d). The Doppler
waveform from a stenotic ECA
(a III and e) shows similar pulsatility of ow as the waveform from
a stenotic ICA, and transmission
of the oscillations produced by
temporal tapping (X) into the ECA
allows dierentiation of the two
arteries in this situation
a
III III
should be examined because it is the preferred site of vertebral artery pathology (curved-array transducers are more
suitable than linear transducers).
To evaluate the vertebral arteries, the examiner can pro-
ceed in one of two ways: in slender patients with good
insonation conditions, the vertebral artery is
its origin from the subclavian artery
(. Figs.5.2c and 5.3),
identied at
where stenosis can be ruled out by obtaining a Doppler waveform in longitudinal orientation. In patients with a poor
acoustic window or complex sonoanatomy, the examiner
rst locates the CCA longitudinally to then identify the vertebral artery between the transverse processes of the cervical
vertebrae; this is accomplished by slight posterolateral movement and medial angulation of the transducer (see . Fig.5.87
(Atlas)). Acoustic shadowing from the transverse processes
at regular intervals precludes complete evaluation of the V2
segment (. Fig.5.7). From the V2 segment, the examiner can
then follow the artery downward to identify its origin. e
atlas loop will come into view when the transducer is moved
cranially and angled (. Fig.5.87 (Atlas)).
In the color duplex mode, the examiner follows the
length of the vertebral artery to its origin, looking for luminal
narrowing or aliasing. Any luminal narrowing should be
quantied by obtaining a Doppler waveform.
A full evaluation includes measurement of the vertebral
artery diameter and comparison with its counterpart in order
to dierentiate a
pathology. Arterial diameters are determined in the V2 segment (B-mode).
When a patient with trauma and suspected vertebral
artery dissection
examination should be on the segment running through the
cervical vertebral foramina (V2 segment). When looking for
atherosclerotic vertebral artery stenosis, on the other hand, it
is the origin from the subclavian artery which requires close
attention. To locate the origin, it may be necessary to rst identify the subclavian artery in the cervical triangle and then use the
color mode to identify the vertebral origin (V0/V1) at the cranial edge of the subclavian artery. Because of its tortuous course
at the origin, the vertebral artery may easily move out of the scan
plane. e vertebral artery origin must not be confused with the
thyrocervical trunk, which arises more distally and is easier to
visualize. e two can be distinguished from one another by
rhythmically tapping the vertebral artery below the mastoid
(atlas loop); this signal is transmitted to the vertebral artery and
modulates the Doppler waveform from the vertebral artery origin (see procedure described for identication of the ECA using
the temporal tap at the end of 7 Sect. 5.2.1 and . Fig.5.7b).
hypoplastic artery from other vascular
is examined, the focus of the ultrasound
5.4 · Normal Findings
a
301
5.3 Documentation
Normal ndings should be documented in longitudinal
views (B-mode) of both CCAs, ICAs, and ECAs, vertebral
arteries (V1 or V2 segment), and subclavian arteries with the
corresponding Doppler waveforms (including anglecorrected ow velocity measurements) (see sites for taking
representative measurements in . Fig.5.1a). Abnormal ndings are documented in additional B-mode images and the
corresponding Doppler waveforms obtained from the sites of
pathology in longitudinal orientation. Systolic and enddiastolic ow velocities obtained with angle correction must
reect the degree of stenosis. Finally, the report should contain information on the localization of stenotic and nonstenotic plaques (B-mode images for documentation) and a
description of plaque morphology.
5.4 Normal Findings
5.4.1 Carotid Arteries
5
b
. Fig. 5.7 a Image showing the V2 segment of the vertebral artery
(A) between the vertebral processes (WK, acoustic shadowing). A
segment of the vertebral vein (blue) is also seen (SA=mirror artifact). b Vertebral artery (A.VERT) at its origin (V0/V1 segment) from
the subclavian artery (A.S.) with a monophasic waveform typical of
low-resistance flow. The peak systolic velocity (PSV) is 72cm/s, and
the end-diastolic velocity (EDV) is 18cm/s. Oscillations generated by
tapping the vertebral artery below the mastoid are transmitted to
the vertebral artery and appear in the waveform (left portion)
In the vertebral artery, spectral Doppler evaluation is also
important to determine the direction of blood ow. In
patients with normal vertebral artery ow at rest and suspected exercise-induced subclavian steal syndrome due to
subclavian artery stenosis or occlusion, the increased demand
during muscle activity can be reproduced during the examination. With continuous spectral Doppler recording in the
vertebral artery, a blood pressure cu around the upper arm
is inated to over 250mmHg and then released aer 3–5min
to induce reactive hyperemia in the arm. If high-grade stenosis or occlusion of the proximal subclavian artery with subclavian steal and vertebrovertebral crossover is present, this
maneuver will induce ow reversal in the ipsilateral vertebral
artery and an increase in ow velocity in the contralateral
vertebral artery.
e common carotid artery (CCA) has a constant luminal
diameter of approx. 7mm. Flow is pulsatile with a large diastolic component. e internal carotid artery (ICA) has a
peak systolic velocity (PSV) ranging from 60 to 100cm/s
(. Table5.4). At its origin, the wider lumen (bulb) and vessel
branching lead to eddy currents even under normal conditions. PSV is lower in the bulb, and ow separation may lead
to retrograde ow on the side opposite the external carotid
artery (ECA), seen as color reversal in color duplex images
(see . Figs.5.49 (Atlas) and . 1.45b).
e normal thickness of the intima–media complex
measured in the B-mode (from the lumen–intima interface,
the rst bright line, to the media-adventitia interface, the second bright line) is 0.5–0.6mm and increases somewhat with
age.
Supplying the brain, the ICA has low-resistance ow with a
Doppler waveform that is characterized by a steep systolic
upslope followed by monophasic ow with a fairly large dia-
. Table 5.4 Average blood ow velocities and diameters of
the extracranial cerebral arteries (meta-analysis)
Artery PSV (cm/s) EDV (cm/s) D (mm)
CCA 50–80 15–30 6.0–7.5
ICA 60–90 20–40 4–6
ECA 60–100 10–20 3.5–4.5
Vertebral artery 20–70 5–35 3–5
CCA common carotid artery, D diameter, ECA external carotid
artery, EDV end-diastolic velocity, ICA internal carotid artery, PSV
peak systolic velocity
302
Chapter 5 · Extracranial Cerebral Arteries
. Table 5.5 Causes of abnormal pulsatility (Doppler
waveform) in the extracranial cerebral arteries
Change Cause
Reduced pulsatility High-grade proximal ow obstruction
AV stula or angioma in distal segment
Hyperperfusion (e.g., in hyperthyroidism)
Aortic stenosis
Increased pulsatility High-grade distal ow obstruction
Increased intracranial pressure
5
AV arteriovenous
Severe cerebral microangiopathy
Aortic insuciency
Low heart rate
5.5 Clinical Role ofDuplex Ultrasound
5.5.1 Carotid Arteries
e carotid bifurcation is the preferred site of carotid artery
stenosis. An important underlying mechanism is turbulent
ow with increased wall tension resulting from the abrupt
change in diameter in the bulb and ow division in the bifurcation. is mechanism and shear forces cause higher intimal stress in the carotid bulb. As a result, carotid plaque
tends to develop along the outer wall opposite the ow
divider (. Fig. 5.10). is stressful hemodynamic situation
with ow division is also visible on color duplex ultrasound
(. Figs. 1.44b and 5.49 (Atlas)).
e aim of sonographic assessment of the extracranial
cerebral arteries is to prevent cerebral infarction with its
harmful sequelae and permanent decits (. Fig.5.8).
stolic component. Conversely, ow in the ECA is more pulsatile
with a smaller diastolic component. e common carotid
artery, supplying both territories, has a mixed waveform. As in
all other vascular territories, pulsatility in the carotid system is
determined by peripheral resistance and vessel elasticity and
therefore increases with age (
. Table5.5).
Several duplex ultrasound parameters can contribute to
estimating a patient’s cardiovascular risk. Besides intimamedia thickness (IMT) measured in the common carotid
artery (CCA), the resistive index (Pourcelot index) determined in the internal carotid artery (ICA) is gaining signicance in the assessment of early stages of atherosclerosis and
as a predictor of cardiovascular morbidity and mortality. A
study investigating RI progression from a baseline RI of
5.4.2 Vertebral Arteries
0.66 ±0.08 found a continuous increase in cardiovascular
events as the RI increased (Utho etal. 2008).
Published data on blood ow velocities in the vertebral arteries vary widely from 19 to 98cm/s for peak systolic velocity
(PSV) and from 6 to 30 cm/s for end-diastolic velocity
(EDV). e resistance index (RI) ranges from 0.62 to 0.75
(Tratting et al. 1992). Assessment of the vertebral artery,
especially at its origin, is impaired by caliber variation and
the occurrence of congenital hypoplasia. At the same time,
evaluation of the origin is important because it is the most
common site of stenosis.
e normal diameter of the vertebral artery is 3–5mm
but it is common for one vertebral artery to be larger than the
other, resulting in right–le diameter dierences of over
2mm.
In case of lateral dierences in ow velocity and poor
visualization of the origin, the examiner must dierentiate a
proximal stenosis from hypoplasia.
e following criteria suggest hypoplasia:
5 Unilateral caliber reduction (luminal diameter typically
<2cm)
5 Contralateral hyperplasia (luminal diameter typically
>3.5) and side dierence typically >2mm
5 Flow velocity (PSV) lower than on the contralateral side
5 Unchanged waveform; however, ow is oen more
pulsatile with a reduced diastolic ow component (see
. Figs.5.87 (Atlas), 5.39, and 5.40).
While diagnostic ultrasound and treatment of peripheral
vessels are symptom-oriented, the purpose of carotid artery
evaluation is prognosis-oriented in that it aims at identifying
patients at risk for stroke and initiating adequate preventive
measures in these high-risk patients (. Tables 5.6 and 5.7).
Duplex ultrasound examinations of the extracranial cerebral
arteries are performed for the following reasons:
5 Identication of the underlying cause in patients with a
transient ischemic attack (TIA), prolonged reversible
ischemic neurologic decit (PRIND), or stroke (addi-
tional CT and echocardiography)
5 Workup of asymptomatic carotid artery stenosis
suspected on clinical grounds (auscultation, risk factors,
atherosclerosis with coronary heart disease or pelvic
artery stenosis)
5 Indication for operative treatment of carotid stenosis:
plaque morphology, hemodynamic stenosis grading
5 Workup of a pulsatile neck mass (aneurysm, transmis-
sion of pulsation through extravascular tumor)
5 Workup of traumatic intimal dissection
5 Diagnostic evaluation for inammatory disease (Takaya-
su’s arteritis, temporal arteritis)
5 Workup of disturbed perfusion in the posterior circula-
tion (vertebral artery stenosis, subclavian steal syndrome
due to subclavian artery occlusion)
5 Diagnosis of brain death
In contrast, stenosis is indicated by less pulsatile ow, a
smaller systolic component, and more pronounced diastolic
ow in the waveform obtained downstream of the lesion.
5 Follow-up aer surgical repair (carotid endarterectomy)
or PTA with stenting (immediately aer intervention,
then at 6-month intervals).
5.5 · Clinical Role ofDuplex Ultrasound
StageClinical presentation/symptoms
303
5
Stage I
Asymptomatic carotid artery stenosis
IA Asymptomatic stenosis without high-grade contralateral carotid
stenosis or contralateral occlusion
IB Asymptomatic stenosis with high-grade contralateral carotid
stenosis or contralateral occlusion
Stage II
Symptomatic carotid stenosis: ipsilateral transient deficit within the
preceding 6 months
IIA Amaurosis fugax
IIB
Hemispheric symptoms reversible within 24 h (TIA)
Stage III Indications for emergency carotid TEA
IIIA Crescendo TIA
IIIB Acute/Progressive stroke
Stage IV
Symptomatic carotid stenosis: ipsilateral stroke within the
preceding 6 months
Rankin 0Stroke with fully reversible neurologic deficits (duration > 24h,
PRIND)
Rankin 1Stroke without significant disability
Rankin 2Mild stroke with slight disability and/or slight aphasia
Rankin 3Moderate stroke with moderate disability with preserved ability to
walk and/or moderately severe aphasia
Rankin 4Severe stroke, unable to walk without assistance, and/or complete
aphasia
Rankin 5Stroke with severe disability: patient bedridden or requiring
wheelchair (exceptional indication)
Severity
III A
Duration
III B
. Fig. 5.8 Classication of extracranial carotid artery stenosis. Higher-grade carotid stenosis ≥50% (by NASCET criteria) or ≥70% (by ECST criteria)
based on angiography or ultrasound. Graphic representation of the duration (horizontal axis) and severity (vertical axis) of the respective neurologic decits. PRIND prolonged reversible ischemic neurologic decit, TEA thromboendarterectomy, TIA transient ischemic attack
. Table 5.6 Risk of stroke in surgically versus medically managed patients with carotid artery stenosis. Perioperative risk (stroke/death)
and absolute risk reduction (ARR) of ipsilateral stroke over a 5-year period in patients with symptomatic carotid artery stenosis
Degree of carotid
stenosis (%)
< 30 6.7 12 10.0 2.2 0.05
30–49 8.4 15 18.2 3.2 0.6 31
50–69 8.4 14 18.6 4.6 0.04 22
70–99 6.2 10 26.0 15.9 < 0.001 6
ECST European Carotid Surgery Trial, NASCET North American Symptomatic Carotid Endarterectomy Trial, NNT number needed to treat
a
Summary of results obtained in 6029 randomized patients from the ECST (n=3018), the VA (Veterans Aairs) trial 309 (n=189), and the
NASCET (n=2885)
b
All strokes/deaths occurring within 30days; a total of 3248 patients were operated on
c
Including perioperative stroke/death
Operative riskb (%) Risk of stroke ARRc (%) P NNT
Surgical (%) Medical (%)
a
–