Diagnostic ultrasound ( PDFDrive )

918 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
of the plaque is measured. Several anatomic features diferentiate
the ICA from the ECA. In about 95% of patients, the ICA is
posterior and lateral to the ECA. his may vary considerably,
and the ICA may be medial to the ECA in 3% to 9% of people. 15
he ICA frequently has an ampullary region of dilation just
beyond its origin and is usually larger than the ECA.
One reliable distinguishing feature of the ECA is that it has
branching vessels (Fig. 26.4A). A useful method to identify the
ECA is the tapping of the ipsilateral supericial temporal artery
in the preauricular area, the temporal tap. he pulsations are
transmitted back to the ECA where they cause a sawtooth
appearance on the spectral waveform (Fig. 26.4B). Although the
tap helps identify the ECA, this tap delection may be transmitted
into the CCA and even the ICA in certain rare situations.
he superior thyroid artery is oten seen as the irst branch
of the ECA ater the bifurcation of the CCA. Occasionally, an
aberrant superior thyroid artery branch will arise from the distal
CCA. he ICA usually has no branches in the neck, although
in rare cases the ICA gives rise to the ascending pharyngeal,
occipital, facial, laryngeal, or meningeal arteries. In some patients,
a considerable amount of the ICA will be visible, but in others,
only the immediate origin of the vessel will be accessible. Very
rarely, the bifurcation may not be visible at all. 28 Rarely, the ICA
may be hypoplastic or congenitally absent. 30,31
CAROTID ULTRASOUND
INTERPRETATION
Each facet of the carotid sonographic examination is valuable
in the inal determination of the presence and extent of disease.
In most cases, the gray-scale, color Doppler, and power Doppler
sonographic images and assessments will agree. However, when
there are discrepancies between Doppler ultrasound imaging
indings and measured velocities, every attempt should be made
to discover the source of the disagreement. he more closely the
image and spectral Doppler indings correlate, the higher the
degree of conidence in the diagnosis. Generally, gray-scale and
color or power Doppler images better demonstrate and quantify
low-grade stenoses, whereas high-grade occlusive disease is more
accurately deined by Doppler spectral analysis. For plaque
characterization, assessment must be made in gray-scale only,
without color or power Doppler ultrasound.
FIG. 26.3 Carotid Bifurcation. Longitudinal image demonstrates
common carotid artery (C); external carotid artery (E); and large, posterior
internal carotid artery (I).
Visual Inspection of Gray-Scale Images
Vessel Wall Thickness and Intima-Media
Thickening
Longitudinal views of the layers of the normal carotid wall
demonstrate two nearly parallel echogenic lines, separated by
a hypoechoic to anechoic region (Fig. 26.5). he irst echo,
bordering the vessel lumen, represents the lumen-intima interface;
the second echo is caused by the media-adventitia interface. he
media is the anechoic/hypoechoic zone between the echogenic
lines. he distance between these lines represents the combined
thickness of the intima and media (I-M complex). he far wall
of the CCA is measured. Many consider measurement of
A
B
FIG. 26.4 Normal External Carotid Artery (ECA). (A) Color Doppler ultrasound of bifurcation demonstrates two small arteries originating from
the ECA. (B) ECA spectral Doppler shows the relected temporal tap (TT) as a serrated (sawtooth) low disturbance.