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1
Service de Radiologie, Hôpital Saint-Antoine,
184 rue du Faubourg Saint-Antoine, 75012 Paris, France.
2
Sevice de Neurologie, Hôpital
Lariboisière, 2 rue Ambroise
Paré, 75010 Paris, France.
Received March 19, 1999;
accepted after revision September 3, 1999.
Address correspondence to H. Djouhri.
Abstract
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MATERIALS AND METHODS. We retrospectively reviewed the records of 101 consecutive patients with dissecting aneurysms of the extracranial ICA. Twenty patients with 26 spontaneous dissecting aneurysms were followed up with MR angiography every 1-2 years (men, 16; women, four; age range, 28-67 years; mean age, 51 years).
RESULTS. The mean duration of follow-up was 41 months (range, 10-93 months). At MR angiography follow-up, 20 aneurysms did not change, four decreased from their original size by 33-53% (mean, 43%), and two resolved. One patient had an asymptomatic recurrent dissecting aneurysm of the extracranial ICA. Clinically, no patient had a thromboembolic stroke or transient ischemic attack during the follow-up period.
CONCLUSION. MR angiography revealed that dissecting aneurysms of the extracranial ICA remain stable, decrease in size, or resolve—but they do not increase in size.
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We used MR angiography to examine and follow up the changes of 26 dissecting aneurysms of the extracranial ICA.
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Diagnosis of Aneurysm
The criteria used to diagnose dissecting aneurysms of the extracranial ICA
with MR angiography or with conventional angiography included the presence of
an extraluminal pouch (saccular aneurysm) or a segmental dilatation of the
lumen (fusiform aneurysm). The diagnosis of dissecting aneurysm of the ICA was
made in less than 30 days after the onset of symptoms in 19 patients and in
more than 30 days in five patients (range, 30-160 days). The diagnoses were
made with conventional angiography in 18 patients (24 aneurysms) and with
time-of-flight MR angiography in six patients (six aneurysms). All aneurysms
diagnosed with conventional angiography were analyzed and confirmed with
time-of-flight MR angiography 3 months after the initial diagnosis. Each
patient's MR angiography was considered the standard of reference for the
follow-up study. The size of aneurysms was considered small if they measured
less than 1 cm, medium if they measured between 1 and 2 cm, and large if they
measured more than 2 cm.
MR Angiography Protocol
MR angiography was performed on a 1.0-T system (Magnetom SP; Siemens,
Erlangen, Germany) with an emitting—receiving quadrature head coil.
Images were obtained in the coronal and axial planes. The protocol for the
coronal plane included a three-dimensional time-of-flight technique with
first-order motion compensation in the section-selection direction and in the
readout direction (fast imaging with steady-state precession). The volume
explored was 64-mm thick with an individual slab thickness of 1 mm. The field
of view was 230 mm. Acquisition parameters included a TR/TE of 40/11 and a
flip angle of 15° for an acquisition matrix of 230 x 256. Two
presaturation slabs 30-mm thick were applied in the axial plane to image
transverse sinuses.
The protocol for the axial plane centered on the aneurysm with a three-dimensional time-of-flight technique and fast imaging with steady-state precession. The volume explored was 52-mm thick, with an individual slab thickness of 0.8 mm. The field of view was 230 mm. Acquisition parameters included a TR/TE of 45/10 and a flip angle of 20° for an acquisition matrix of 256 x 512.
We used maximum intensity projection for the postprocessing of images. One angiographic reconstruction was performed for the coronal sequence (head—feet rotation), and two angiographic reconstructions were performed for the axial sequence (right—left and head—feet rotation axes).
MR Angiography Data Analysis
Two neuroradiologists retrospectively performed data analysis. For all
patients, we focused on reference and follow-up MR angiography including
angiographic reconstructions and source images. The length and width of
aneurysms were measured on the source image using digital calipers. Each
radiologist examined the initial and follow-up MR images on different dates
separate from one another. On a third date, each radiologist collated his
results to determine the time course of aneurysms. Finally, on a fourth date,
the two radiologists compared their results. When interpretations did not
correlate, the MR angiograms were reviewed in conference with a third
neuroradiologist to reach consensus.
To correlate changes on MR images and clinical follow-up, baseline characteristics of the aneurysms were examined, including the time period from the first MR angiography examination to the last follow-up MR angiography examination; changes in the size of the aneurysms (resolved, decreased, unchanged, or increased); changes in luminal stenosis (when it appeared on MR angiography); and recurrence of the dissection of the extracranial ICA.
Follow-Up
During follow-up, all patients had clinical and MR angiography follow-up
evaluations every 1-2 years. MR angiography protocol was similar to the
protocol used during the initial evaluation. For all patients, MR angiography
and clinical follow-up were performed during the same week.
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Initial MR Angiography Study
Eleven aneurysms were located on the right ICA and 15 aneurysms were
located on the left ICA. Three patients had bilateral ICA aneurysms: one
patient had two aneurysms located on each ICA, one patient had two aneurysms
on the left ICA and one aneurysm on the right ICA, and one patient had one
aneurysm on each ICA. One patient had carotid and vertebral aneurysms.
Aneurysms were saccular in 19 patients and fusiform in seven patients. The
size of aneurysms was small in 13 patients, medium in nine, and large in four.
Aneurysms were located on the subpetrous segment of the ICA in 19 patients, on
the mid cervical segment in five patients, and on the suprabulbar segment in
two patients. In six patients, a luminal stenosis was associated with the
aneurysm.
Follow-Up MR Angiography Study
Of 26 aneurysms, 20 (77%) remained unchanged, four (15.4%) decreased in
size, and two (7.7%) resolved. Of the 20 that did not change, 14 were located
on the subpetrous segment of the ICA (Fig.
1A,1B,1C,1D),
four were on the mid cervical segment, and two were on the suprabulbar
segment. The size of the aneurysm was small in seven patients, medium in nine,
and large in four. Of the four aneurysms (15.4%) that decreased from their
original size by 33-53% (mean, 43%), all were saccular and small. Three were
located on the subpetrous segment of the ICA, and one was on the mid cervical
segment (Fig.
2A,2B,2C,2D).
Of the two aneurysms that resolved (7.7%), both were small saccular aneurysms
located on the subpetrous segment of the ICA. The luminal stenosis resolved in
four patients and did not change in two.
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The mean follow-up period for patients with aneurysms that decreased in size or resolved was 36 months (range, 10-54 months). Therefore, no significant difference of follow-up duration was found between the decreased or resolved aneurysms and the stable aneurysms.
An asymptomatic recurrent dissecting aneurysm of the extracranial ICA occurred in one patient. This patient initially had bilateral dissecting aneurysms (two aneurysms located on the left ICA and one on the right ICA). The new recurrent aneurysm was located on the subpetrous segment of the left ICA.
Clinically, no patient had thromboembolic stroke or aneurysmal rupture during the follow-up period. At the time of examination, 17 patients were treated with antiplatelet agents (aspirin, 100-300 mg; mean, 250 mg) and three had stopped their treatment (3 months-1 year after the onset of dissection).
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In a retrospective study of 34 aneurysms with a follow-up interval from 2 weeks to 3.5 years, Mokri [10] revealed that dissecting aneurysms of the extracranial ICA did not change in 30% of patients, decreased in size in 40%, and resolved in 20%. Traumatic dissecting aneurysms of the extracranial ICA did not change in 36% of patients, decreased in size in 14%, and resolved in 7%. The remaining patients were treated with surgery. Mokri's results do not agree with our findings because the follow-up period was significantly longer in our series (our range, 10-93 months; Mokri's range, 0.5-42 months). In fact, Mokri's study was partly performed with digital venous angiography, a technique that uses two incidences; therefore, some smaller aneurysms might have been over-looked using this technique.
In our study and others, dissecting aneurysms of the extracranial ICA did not increase in size [11,12,13,14,15,16,17]; moreover, rupture rarely occurs, confirming the results reported in the literature [1, 2, 10, 11]. However, in one patient, an asymptomatic recurrent dissecting aneurysm developed on a previously involved artery. This occurrence is rare and a recurrent dissection at the level of a previously dissected ICA has been documented in only six patients [18]. In fact, the risk of recurrent ICA dissection was determined in a study by Schievink et al. [19] to be 1% per year and usually occurs in a previously uninvolved artery. Other studies have examined the accuracy of time-of-flight MR angiography to diagnose the dissection of the extracranial ICA [6,7,8,9, 20,21,22,23,24,25]. In the acute phase of ICA dissection, sensitivity and specificity of time-of-flight MR angiography is estimated at 95% and 99% [6], respectively.
At our institution, we have had difficulty using time-of-flight MR angiography to diagnose dissecting aneurysms of the extracranial ICA during the acute phase. To avoid this problem, we perform time-of-flight MR angiography 3 months after the onset of ICA dissection. In fact, using the gradient echo sequence, the high signal intensity of turbulent flow in the aneurysmal dilatation may not be distinguished from the high signal intensity of the intramural hematoma. After 1 month, time-of-flight MR angiography becomes a reliable method to diagnose and examine aneurysms because the high signal intensity of the intramural hematoma decreases to an iso or hyposignal, permitting the visualization of aneurysmal dilation.
Different surgical treatments (resection and reconstruction with grafting, carotid ligation, and cervical-to-intracranial bypass) and endovascular treatments (Wallstent, detachable coils, and balloon) have been proposed to treat dissecting aneurysms [26,27,28,29]. Our study showed that these treatments may be unnecessary because none of our patients had thromboembolic stroke or aneurysm rupture, conditions that warrant surgical or endovascular treatment.
In conclusion, we used MR angiography to examine and follow up the changes of dissecting aneurysms of the extracranial ICA. Radiologically, dissecting aneurysms have a good outcome because all the aneurysms we studied remained stable, decreased in size, or resolved—but they did not increase in size. However, our study had several limitations. Our results do not exactly reflect the spontaneous changes of dissecting aneurysms of the extracranial ICA because 17 of 20 patients were treated with antiplatelet agents. Also, recruitment bias may have affected our results because our study population was recruited from a medical neurologic center, and patients with initial serious complications might have been referred elsewhere. Additional studies are needed to determine the long-term changes of dissecting aneurysms of the extracranial ICA.
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