Diagnostic ultrasound ( PDFDrive )

CHAPTER 26 The Extracranial Cerebral Vessels 929
A
B
C D E
FIG. 26.20 Internal Carotid Artery (ICA) Stenosis. (A) ICA stenosis of 50% to 69% diameter shows a peak systolic velocity (PSV) of 187 cm/
sec. (B) Left ICA demonstrates a visible high-grade stenosis on color Doppler with end diastolic velocities (EDVs) of greater than 180 cm/sec and
PSVs that alias at greater than 350 cm/sec. This is consistent with a very high-grade stenosis. (C) Right carotid bulb seen in longitudinal projection
with color Doppler demonstrates a high-grade narrowing and spectral broadening with an approximately 500 cm/sec velocity in peak systole and
250 cm/sec in end diastole, consistent with an 80% to 95% stenosis. (D) and (E) Power transverse and long images demonstrate high-grade
stenosis of the ICA.
In these cases, correlation with color or power Doppler imaging
is essential to diagnose correctly the severity of the stenoses.
Velocity increases are focal and most pronounced in and immediately
distal to a stenosis, emphasizing the importance of
sampling directly in these regions. Moving further distal from
a stenosis, low begins to reconstitute and assume a more normal
pattern, provided a tandem lesion does not exist distal to the
initial site of stenosis. Spectral broadening results in the jets of
high-velocity low associated with carotid stenosis; however,
correlation with gray-scale and color Doppler images can deine
other causes of spectral broadening. An awareness of normal
low spectra combined with appropriate Doppler techniques can
obviate many potential diagnostic pitfalls.
he degree of carotid stenosis that is considered clinically
signiicant in the symptomatic or asymptomatic patient is in
evolution. Initially, it was thought that lesions causing 50%
diameter stenosis were signiicant; this perception changed as
more information was gathered from two large clinical trials.
As noted earlier, NASCET demonstrated that CEA was more
beneicial than medical therapy in symptomatic patients with
70% to 99% ICA stenosis. 7 ECST demonstrated a CEA beneit
when the degree of stenosis was greater than 60%. 8 Interestingly,
the method used to grade stenoses in the ECST study was
substantially diferent than that used in the NASCET trials. he
NASCET trials compared the severity of the ICA stenosis on
arteriogram with the residual lumen of a presumably more normal
distal ICA. he ECST methodology entailed assessment of the
severity of stenosis with a “guesstimation” of the lumen of the
carotid artery at the level of the stenosis. he ECST assessment
is more comparable to ultrasound’s visible assessment of the
degree of narrowing, whereas velocity tables currently in use
have been derived to correspond to the NASCET angiographic
determinations for stenosis. he ECST method for grading carotid
artery stenosis tends to give a more severe assessment of narrowing
than the NASCET technique (Fig. 26.21).
he initial NASCET trials retrospectively compared velocity
data obtained on the Doppler examination with angiographic
measurements of stenosis. No standardized ultrasound protocol
was employed by the numerous centers involved in the trials.
Despite the lack of uniformity, moderate sensitivity and speciicity
ranging from 65% to 77% were obtained for grading ICA stenoses
using Doppler velocities. If ultrasound technique is standardized
and criteria are validated in a given laboratory, peak systolic
velocity (PSV) and peak systolic ratios have proved to be an
accurate method for determining carotid stenosis. 109 he ECST
group compared three diferent angiographic measurement