Diagnostic ultrasound ( PDFDrive )

948 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
A
B
C
D
E
FIG. 26.41 Carotid Artery Dissection. (A) Abnormal high-resistance waveforms (arrow) at the origin of the right ICA with no evidence of low
distal to this point (curved arrow). (B) Gray-scale evaluation of the vessel in the area of the occlusion demonstrates only a small, linear echogenic
structure (arrow) without evidence of signiicant atherosclerotic narrowing. (C) Subsequent angiogram demonstrates the characteristic tapering to
the point of occlusion (arrow) associated with carotid artery dissection and thrombotic occlusion. (D) Transverse and (E) longitudinal images of
another patient show an intimal lap (arrow) in an ECA. I, Internal carotid artery.
well-encapsulated masses located at the carotid bifurcation. 29
hese tumors may be bilateral, particularly in the familial variant,
and are very vascular, oten producing an audible bruit. 29 Some
of these tumors produce catecholamines, leading to sudden
changes in blood pressure during or ater surgery. Color Doppler
ultrasound demonstrates an extremely vascular sot tissue mass
at the carotid bifurcation 29 (Fig. 26.42). Color Doppler ultrasound
can also be used to monitor embolization or surgical resection
of carotid body tumors. A classic nonmass is the ectatic
innominate/proximal CCA, frequently occurring as a pulsatile
supraclavicular mass in older women. he request to rule out a
carotid aneurysm almost invariably shows the classic normal
features of these tortuous vessels (Fig. 26.43).
Extravascular masses (e.g., lymph node masses [Fig.
26.44], hematomas, abscesses) that compress or displace the
carotid arteries can be readily distinguished from primary
vascular masses, such as aneurysms or pseudoaneurysms.
Posttraumatic pseudoaneurysms can usually be distinguished
from true carotid aneurysms by the characteristic to-and-fro
waveforms in the neck of the pseudoaneurysm, as well as the
internal variability (yin-yang) characteristic of a pseudoaneurysm
(Fig. 26.45).
TRANSCRANIAL DOPPLER
SONOGRAPHY
In transcranial Doppler (TCD) ultrasound, a low-frequency
2-MHz transducer is used to evaluate blood low within the
intracranial carotid and vertebrobasilar system and the circle of
Willis. Access is achieved through the orbits, foramen magnum,
or, most oten, the region of temporal calvarial thinning (transtemporal
window). 222,223 However, many patients (up to 55% in
one series 224 ) may not have access to an interpretable TCD
examination. Women, particularly African American women,
have a thick temporal bone through which it is diicult to insonate
the basal cerebral arteries. 224,225 his diiculty limits the feasibility
of TCD imaging as a routine part of the noninvasive cerebrovascular
workup. 223,224