Diagnostic ultrasound ( PDFDrive )

CHAPTER 26 The Extracranial Cerebral Vessels 923
Plaque Ulceration
Sonography has a low sensitivity (38%) and high speciicity (92%)
for plaque ulceration. 86 However, when identiied, all ulcerated
plaques it into the heterogeneous plaque pattern. 46,81,87,88 Sonographic
indings that suggest plaque ulceration include a focal
depression or break in the plaque surface, causing an irregular
surface or an anechoic area within the plaque that extends to
the plaque surface without an intervening echo between the
vessel lumen and the anechoic plaque region. Color and power
Doppler ultrasound may improve sonographic identiication
of plaque ulceration. 88 Color or power Doppler ultrasound or
B-low imaging (a proprietary non-Doppler imaging technique)
may demonstrate slow-moving eddies of color within an
anechoic region in plaque, which would suggest ulceration 78,88
(Fig. 26.10). he demonstration of these low vortices was
94% accurate in predicting ulcerative plaque at surgery in one
study. 89 Contrast-enhanced ultrasound represents a promising
tool in the characterization of vulnerable carotid plaque
with improved detection of intraplaque vascularization and
ulceration. 90-92
Ultrasound Features Suggestive of Plaque
Ulceration
Focal depression or break in plaque surface
Anechoic region within plaque extending to vessel lumen
Eddies of color within plaque
A potential pitfall in the diagnosis of plaque ulceration results
from a mirror-image artifact producing pseudoulceration of
the carotid artery. Highly relective plaque can produce a color
Doppler ghost artifact simulating ulceration. However, the region
of color within the plaque can be recognized as artifactual because
the spectral waveform and color shading within the pseudoulceration
are of lower amplitude, but otherwise identical to those
within the true carotid lumen. 93 Conversely, pulsed Doppler
traces from within ulcer craters show low-velocity dampened
waveforms (Fig. 26.11).
Although the diagnosis of ulceration varies, the ability to
predict intraplaque hemorrhage reliably, with its associated clinical
implications, underscores the importance of ultrasound plaque
characterization. he presence of heterogeneous, irregular plaque
should be noted because of the association of heterogeneous
plaque, and intraplaque hemorrhage even in a stenosis of less
than 50% may warrant medical therapy. Many now consider
heterogeneous plaque to be the “vulnerable,” unstable form of
plaque that should be treated diferently than the more stable
homogeneous form of plaque. 94 Plaque characterization should
be considered when determining the type of therapy to use in
carotid intervention. Angioplasty and subsequent stenting of
carotid vessels might be safer if performed in patients with
homogeneous plaque than those with heterogeneous plaque. 94
Gray-Scale Evaluation of Stenosis
Measurements of carotid diameter and area stenosis should be
made in the transverse plane, perpendicular to the long axis of
the vessel, using gray-scale, B-low, or power Doppler sonographic
imaging 45 (Fig. 26.12, Videos 26.12 and 26.13). Measurements
made on longitudinal scans may overestimate or underestimate
the severity of stenosis by partial “voluming” through an eccentric
plaque. he percentage of diameter stenosis and the percentage
of area stenosis are not always linearly related. Clinical records
should state the type of stenosis measured. Asymmetrical stenoses
are most appropriately assessed with “percentage of area stenosis”
measurements, 45 although these are oten time consuming and
technically diicult. he cephalocaudal extent and length of
plaques should be noted, along with the presence of tandem
plaques. Recently, three-dimensional ultrasound has been used
A
B
FIG. 26.10 Plaque Ulceration. (A) Color Doppler and (B) power Doppler longitudinal images show blood low (arrow) into hypoechoic ulcerated
plaque.