DOI:10.2214/AJR.05.0762
AJR 2007; 188:W367-W369
© American Roentgen Ray Society
MDCT Detection of Fibromuscular Dysplasia of the Internal Carotid Artery
Cécile de Monyé1,
Diederik W. J. Dippel2,
Marcel L. Dijkshoorn1,
Hervé L. J. Tanghe1 and
Aad van der Lugt1
1 Department of Radiology, Erasmus University Medical Center, Dr. Molewaterplein
40, Rotterdam 3015 GD, The Netherlands.
2 Department of Neurology, Erasmus University Medical Center, Rotterdam 3015 GD,
The Netherlands.
Received May 4, 2005;
accepted after revision December 27, 2005.
WEB This is a Web exclusive article.
Address correspondence to A. van der Lugt
(a.vanderlugt{at}erasmusmc.nl).
Abstract
OBJECTIVE. The purpose of this article is to describe two cases in
which fibromuscular dysplasia of the internal carotid artery was diagnosed
with CT angiography.
CONCLUSIONS. CT angiography can depict the characteristic findings
of fibromuscular dysplasia. If patients with cerebrovascular symptoms undergo
screening with CT angiography of the supraaortic vessels, more cases of
fibromuscular dysplasia will be recognized as a cause of neurologic
symptoms.
Keywords: cardiovascular imaging • CT • CT angiography • neuroimaging
Introduction
Fibromuscular dysplasia (FMD) of the cervical arteries is a possible
cause of stroke. It can be detected with conventional angiography and less
sensitively with duplex sonography and MR angiography. In 2002, we started a
study in which we used CT angiography (CTA) to screen patients with symptoms
of transient ischemic attack or minor stroke for atherosclerosis and stenosis
of the carotid artery. Since then, two cases of FMD of the internal carotid
artery (ICA) have been encountered in a group of 400 consecutively screened
patients. To our knowledge, except for a report by Castillo and Wilson
[1], descriptions of CTA of FMD
of the carotid artery have not been published. Castillo and Wilson in 1994
reported the cases of two patients with carotid FMD diagnosed with digital
subtraction angiography although CTA findings suggested carotid occlusion. We
present two cases in which FMD of the ICA was diagnosed with CTA.
Observed Cases
Patient 1
A 39-year-old woman presented with acute hemiparesis of the left side of
the body and mild dysarthria. The patient was a heavy smoker and used oral
contraceptives. Findings on CT of the brain were normal. Duplex sonography of
the carotid arteries showed no signs of atherosclerosis. CTA of the carotid
arteries, from the ascending aorta to the intracranial circulation, was
performed with a 16-MDCT scanner (Sensation 16, Siemens Medical Solutions).
Scanning parameters were as follows: individual detector width, 0.75 mm; table
feed per rotation, 12 mm (pitch of 1); gantry rotation time, 0.5 second; 120
kV; effective tube current, 180 mAs; scanning time, 10-14 seconds. Eighty
milliliters of contrast material (iodixanol 320 mg I/mL, Visipaque, Amersham
Health) and a 40-mL saline bolus chaser were injected through an 18- to
20-gauge IV cannula in an antecubital vein, both at an injection rate of 4
mL/s with a double-head power injector (Stellant, Medrad). Synchronization
between passage of contrast material and data acquisition was achieved with
real-time bolus tracking. Images were reconstructed with the following
parameters: effective slice width, 1 mm; reconstruction interval, 0.6 mm;
field of view, 120 mm; convolution kernel, B30f (medium smooth). CTA showed no
signs of atherosclerosis in any vessel, and the anatomic features of the
circle of Willis were normal. The right ICA had a typical string-of-beads
appearance at the level of the first, second, and third cervical vertebrae
(Fig. 1). The left ICA and
vertebral arteries had no abnormalities. Therapy with alteplase was started
within 3 hours after onset of symptoms and resulted in partial resolution of
symptoms. The patient was treated with antiplatelet drugs and did not
experience new symptoms during follow-up.
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Fig. 1 —39-year-old woman with acute hemiparesis of left side of body and
mild dysarthria. Coronally reformatted CT angiogram of right and left internal
carotid arteries shows string-of-beads appearance of right internal carotid
artery (arrowheads). Left internal carotid artery (curved
arrow) is normal. Signs of atherosclerosis, especially at level of
carotid bifurcation (straight arrow), are absent.
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Patient 2
A 78-year-old woman presented with left amaurosis fugax and mild
hypertension. CT of the brain showed no abnormalities. Duplex sonography of
the carotid arteries showed no signs of atherosclerosis. CTA performed with
the protocol used for patient 1 showed only small calcifications in the
brachiocephalic trunk and the left subclavian artery. There were no signs of
atherosclerosis in other vessels. The distal cervical portion of both ICAs had
a typical string-of-beads appearance (Fig.
2A,
2B). The vertebral arteries had
no abnormalities. The patient was treated with antihypertensive and
antiplatelet drugs and had no symptoms during follow-up.
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Fig. 2A —78-year-old woman with left amaurosis fugax. Volume-rendered CT
angiograms of left (A) and right (B) carotid arteries.
String-of-beads appearance of internal carotid artery is visible at distal
extracranial internal carotid artery on both sides.
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Fig. 2B —78-year-old woman with left amaurosis fugax. Volume-rendered CT
angiograms of left (A) and right (B) carotid arteries.
String-of-beads appearance of internal carotid artery is visible at distal
extracranial internal carotid artery on both sides.
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Discussion
FMD is an uncommon segmental, nonatheromatous, noninflammatory arterial
disease of unknown causation that affects small to medium-sized vessels in
many areas of the body. The renal arteries are the most commonly affected,
followed by the cervicocephalic vessels
[2]. Cervicocephalic FMD
involves the extracranial part of the ICA in nearly 75% of patients
[3]. The vertebral artery is
involved in 15-25% of patients, and multiple vessels are involved in 60-75% of
patients [3]. FMD of the
cervicocephalic vessels is most often encountered in the fifth decade of life
and occurs predominantly in women.
Cervicocephalic FMD is often asymptomatic and an incidental finding on
imaging or at autopsy. It also, however, can manifest itself with a variety of
specific neurologic symptoms, including transient ischemic attack, amaurosis
fugax, and stroke or nonspecific symptoms such as headache and tinnitus
[2]. On arteriograms, the most
common appearance of FMD is multifocal concentric luminal narrowing
alternating with areas of mural dilatation that are wider than the original
lumen [4]. This finding is also
described as the string-of-beads appearance and is present in 80-90% of
patients with FMD [5]. Less
common imaging findings include focal or tubular stenosis, a septum, and a
diverticulum [5]. The condition
is also associated with arterial dissection, intracranial aneurysms, and
arteriovenous fistulas. Duplex sonography and color Doppler imaging can depict
FMD of the ICA only when the lesion is located proximally
[6]. Color Doppler imaging
reveals the segmental string-of-beads pattern with alternating regions of
luminal narrowing and vascular dilatation distal to a completely normal
segment of vessel. High-grade distal FMD stenosis also can be detected on the
basis of indirect hemodynamic criteria. On time-of-flight MR angiography,
artifacts caused by patient motion and swallowing or related to in-plane flow
and susceptibility gradients may mimic the appearance of FMD and tend to
decrease both sensitivity and specificity for detection of cervicocephalic
FMD. The increased resolution and decreased scanning time of contrast-enhanced
MR angiography may solve this problem.
Cervicocephalic FMD is an uncommon cause of cerebral ischemia. The
diagnostic evaluation of patients with cerebrovascular symptoms commonly
includes CT of the brain and duplex sonography of the cervical arteries to
detect significant atherosclerotic disease in the carotid artery. Until
recently, duplex sonography was used as a screening instrument to select
patients for digital subtraction angiography. The implication is that with
this policy, assessment of FMD relies on the sensitivity of duplex sonography
in detection of this disease. FMD is most commonly localized in the middle and
distal portions of the ICA at the level of the first and second cervical
vertebrae. This unfavorable localization results in much lower sensitivity of
duplex sonography than of angiography in the detection of FMD of the ICA
[6]. Therefore, many cases of
cervical FMD as a cause of cerebral ischemia can be missed.
With the introduction of helical CT scanners, especially MDCT scanners, CTA
of the carotid artery has entered clinical practice. The technique has high
sensitivity and specificity in the detection of carotid artery stenosis and
may replace digital subtraction angiography and MR angiography. Because it is
noninvasive, faster, and more accurate than duplex sonography, CTA may replace
sonography in screening for vascular abnormalities in patients with
cerebrovascular symptoms. Since 2002, all patients in our department with
ischemic neurologic symptoms have been screened with CTA. Among the 400
patients screened as of this writing, we encountered two (0.5%) cases of FMD,
a higher frequency than reported in a review of autopsies (0.02%)
[7] and equal to the
frequencies in reviews of cerebral angiography (0.25-0.68%)
[7]. The higher incidence of
FMD in our series compared with that in the autopsy series can be explained by
the higher frequency of FMD in a population with ischemic neurologic symptoms.
Both patients had the characteristic string-of-beads appearance of the ICA,
one unilateral and one bilateral. Neither of the patients had atherosclerotic
lesions at the carotid bifurcation, although coexistent atherosclerotic
involvement of the carotid bifurcation is found in approximately 25% of cases
[8].
In conclusion, CTA can depict the characteristic findings of FMD. It is
expected that if patients with cerebrovascular symptoms are screened with CTA
of the supraaortic vessels, more cases of FMD will be recognized as a possible
cause of the neurologic symptoms.
References
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- Furie DM, Tien RD. Fibromuscular dysplasia of arteries of the head
and neck: imaging findings. AJR 1994;162
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- Osborn AG, Anderson RE. Angiographic spectrum of cervical and
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Abstract
Introduction
