Diagnostic ultrasound ( PDFDrive )

916 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
stroke, hospital readmission, and severe disability than other
types of stroke. 6
Carotid atherosclerotic plaque with resultant stenosis usually
involves the internal carotid artery (ICA) within 2 cm of the
carotid bifurcation. his location is readily amenable to examination
by sonography as well as surgical intervention. Carotid
endarterectomy (CEA) initially proved to be more beneicial
than medical therapy in symptomatic patients with carotid
stenoses of more than 70%, as reported in the North American
Symptomatic Carotid Endarterectomy Trial (NASCET) and
the European Carotid Surgery Trial (ECST). 7,8
Subsequent NASCET results for moderate stenoses have shown
a net beneit for surgical intervention with carotid narrowing
between 50% and 69% of vessel diameter. A 15.7% reduction in
the 5-year ipsilateral stroke rate was seen in patients treated
surgically versus 22.2% stroke reduction in those treated medically.
hese results are not as compelling as those for the higher degree
of stenosis seen in the earlier NASCET trial. he beneit from
surgery was greatest in men, patients with recent stroke, and
those with hemispheric symptoms. In addition, the NASCET
trials dealing with moderate carotid stenoses required rigorous
surgical expertise, such that the risks for disabling stroke or
death should not exceed 2% to achieve the statistical surgical
beneit. 9 he Asymptomatic Carotid Atherosclerosis Study
(ACAS) trials published in 1995 reported a reduction in ipsilateral
stroke in asymptomatic patients with greater than 60% ICA
stenoses who undergo CEA. 3 However, these results were less
clear-cut than the NASCET trials. According to the Carotid
Revascularization Endarterectomy Versus Stenting Trial (CREST),
carotid artery stenting has been shown to be comparable to CEA
with respect to rates of ipsilateral stroke and death. However,
there are increased adverse efects in women and elevated stroke
rates and deaths in older patients. 10 With implementation of new
medical management regimens—including aspirin, clopidogrel,
statins, antihypertensive medications, diabetic management,
smoking cessation, and lifestyle changes—future trials may change
how carotid disease is treated. 10
Accurate diagnosis of carotid stenosis clearly is critical to
identify patients who would beneit from surgical treatment. In
addition, ultrasound can assess plaque morphology, such as
determining heterogeneous or homogeneous plaque, known to
be an independent risk factor for stroke and transient ischemic
attack (TIA).
Carotid sonography is the principal screening method
for suspected extracranial carotid atherosclerotic disease.
Gray-scale examination, color Doppler, power Doppler, and
pulsed Doppler imaging techniques are routinely employed
in the evaluation of patients with neurologic symptoms and
suspected extracranial cerebral disease. 11,12 Ultrasound is an
inexpensive, noninvasive, and highly accurate method of
diagnosing carotid stenosis. Magnetic resonance angiography
(MRA) and computed tomography angiography (CTA) are
additional noninvasive screening tools for the identiication of
carotid bifurcation disease as well as for clariication of ultrasound
indings. Angiography is oten now reserved for those
patients for whom the ultrasound or MRA was equivocal or
inadequate.
Other carotid ultrasound applications include the evaluation
of carotid bruits, monitoring the progression of known atherosclerotic
disease, 11,13,14 assessment during or ater CEA or stent
placement, 15 screening before major vascular surgery, and evaluation
ater the detection of retinal cholesterol emboli. 11 Also,
nonatherosclerotic carotid diseases can be evaluated, including
follow-up of carotid dissection, 16-21 examination of ibromuscular
dysplasia or Takayasu arteritis, 22-24 assessment of malignant carotid
artery invasion, 25,26 and workup of pulsatile neck masses and
carotid body tumors. 27-29
Indications for Carotid Ultrasound
Evaluation of patients with hemispheric neurologic
symptoms, including stroke, transient ischemic attack,
and amaurosis fugax
Evaluation of patients with a carotid bruit
Evaluation of pulsatile neck masses
Evaluation of patients scheduled for major cardiovascular
surgical procedures
Evaluation of nonhemispheric or unexplained neurologic
symptoms
Follow-up of patients with proven carotid disease
Evaluation of patients after carotid revascularization,
including stenting
Intraoperative monitoring of vascular surgery
Evaluation of suspected subclavian steal syndrome
Evaluation of a potential source of retinal emboli
Follow-up of carotid dissection
Follow-up of radiation therapy to the neck in select
patients
CAROTID ARTERY ANATOMY
he irst major branch of the aortic arch is the innominate
or brachiocephalic artery, which divides into the right subclavian
artery and right common carotid artery (CCA).
he second major branch is the let CCA, which is generally
separate from the third major branch, the let subclavian artery
(Fig. 26.1).
he right and let CCAs ascend into the neck posterolateral
to the thyroid gland and lie deep to the jugular vein and sternocleidomastoid
muscle. he CCAs have diferent proximal conigurations,
with the right originating at the bifurcation of the
innominate (brachiocephalic) artery into the common carotid
and subclavian arteries. he let CCA usually originates directly
from the aortic arch but oten arises with the brachiocephalic
trunk. his is known as a “bovine arch” coniguration. he CCA
usually has no branches in its cervical region. Occasionally,
however, it may give of the superior thyroid artery, vertebral
artery, ascending pharyngeal artery, and occipital or inferior
thyroid artery. At the carotid bifurcation, the CCA divides into
the external carotid artery (ECA) and the internal carotid artery
(ICA). he ICA usually has no branching vessels in the neck.
he ECA, which supplies the facial musculature, has multiple
branches in the neck. he ICA may demonstrate an ampullary
region of mild dilation just beyond its origin.