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Neuroradiology |
1 From the Department of Diagnostic and Therapeutic Neuroradiology, Foch Hospital, 40 rue Worth, BP 36, 92151 Suresnes, France. Received March 17, 2000; revision requested April 26; revision received June 29; accepted August 29. Address correspondence to L.P. (e-mail: l.pierot@hopital-foch.org).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Sixty-eight consecutive patients with intracranial aneurysms were included in the prospective study. The goal was to evaluate 3D time-of-flight MR angiography versus DSA for the detection of a residual aneurysm neck or residual flow inside the coil mesh.
RESULTS: Eighty-one MR angiographic and 83 DSA examinations were performed; 15 patients were examined with both modalities twice. MR angiography was not possible in two patients. In another patient, the quality of MR angiography was not sufficient to assess the treated aneurysm. In 72 of the remaining 80 MR angiographic and DSA examinations, there was good correlation between the two modalities. In 54 cases, neither image type showed remnants or recurrence, but in 18, both showed residual aneurysm. In eight cases, the MR angiographic and DSA results differed. In one of these cases, MR angiography depicted residual aneurysm but DSA depicted an arterial loop. In seven cases, a small (<3-mm) remnant was not detected at MR angiography.
CONCLUSION: Because very small aneurysm remnants or recurrences probably are not clinically important, MR angiography is an option for following up intracranial aneurysms treated with detachable coils and may partly replace DSA.
Index terms: Aneurysm, intracranial, 17.73 • Aneurysm, rupture, 17.73 • Aneurysm, therapy, 17.1264, 17.1267, 17.1269 • Angiography, comparative studies, 17.12142, 17.124 • Interventional procedures, 17.1264, 17.1267, 17.1269
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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In two patients, who were claustrophobic, MR examination was not possible. Therefore, 66 patients (36 women, 30 men; mean age, 45 years) harboring 70 aneurysms treated with GDCs were examined by using DSA and three-dimensional, gadolinium-enhanced (gadopentetate dimeglumine [Magnevist]; Schering, Lys-Lez-Lannois, France), time-of-flight MR angiography.
Fifty-two patients had subarachnoid hemorrhage. Endovascular treatment was performed in the acute phase (<14 days) in 51 cases. Fourteen patients had nonruptured aneurysms. The locations of the aneurysms were as follows: anterior communicating artery in 25 cases (36%), internal carotid artery in 24 cases (34%), middle cerebral artery in 18 cases (26%), and other vessel in three cases (4%). The size of the aneurysm was 3 mm or smaller in nine cases (13%), 4–7 mm in 31 cases (44%), 7–15 mm in 27 cases (39%), and larger than 15 mm in three cases (4%).
At the end of the procedure, the occlusions were classified, according to the method of Cognard et al (7), as follows: total (100%) occlusion—that is, the aneurysm sac and neck are densely packed—which occurred in 48 (69%) cases; subtotal (95%–99%) occlusion—that is, the sac is occluded but there is a tiny neck remnant—which occurred in 20 cases (29%); or incomplete (<95%) occlusion—that is, the aneurysm sac and neck are loosely packed or there is either persistent opacification of the sac or a neck remnant—which occurred in two cases (3%).
Patients were examined by using MR angiography and DSA either once (51 patients) or twice (15 patients) during the follow-up period. During that period, 81 comparisons of MR angiography and DSA were theoretically possible. However, in one case, the MR angiogram was not interpretable, so a total of 80 comparisons were performed. Thirty-nine of these studies were performed 3 months after EVT; 30, 12–18 months after EVT; and 11, more than 24 months after EVT.
MR Imaging Techniques
MR examinations were performed with a 1.5-T unit (Signa; GE Medical Systems, Milwaukee, Wis). The standard MR examinations included the acquisition of sagittal T1-weighted spin-echo images (340/14 [repetition time msec/echo time msec], 256 x 256 matrix, 25-cm field of view, 5-mm-thick sections with a 1.5-mm intersection gap), transverse T2-weighted fast spin-echo images (3,000/22 and 100, 256 x 256 matrix, 24-cm field of view, 5-mm-thick sections with a 1.5-mm intersection gap), and coronal T2-weighted fast spin-echo images (4,000/96, 512 x 256 matrix, 24-cm field of view, 4-mm-thick sections with a 0.5-mm intersection gap).
Three-dimensional time-of-flight MR angiography was performed after injection of 0.2 mL of gadopentetate dimeglumine per kilogram of body weight to shorten the sequence. Imaging parameters were as follows: spoiled gradient-echo sequence, 26.0/2.4, 30° flip angle, 256 x 512 matrix, 24 x 18 field of view, 60 partitions, 1-mm section thickness, posterior saturation, one acquisition, and acquisition time of 5 minutes 23 seconds. Magnetization transfer was not used because it was not available at the beginning of the study.
DSA Technique
DSA was performed by using a biplanar angiographic system (BV 3000; Philips Integris, Best, the Netherlands). Selective catheterization of the vessel harboring the aneurysm was performed by using a 5-F catheter with the femoral approach. Eight to ten milliliters of nonionic contrast material (iobitridol [Xenetix 300]; Guerbet, Roissy, France) was injected into the internal carotid or vertebral artery with a power injector at 4–5 mL/sec. Multiple views were obtained.
Image Interpretation
The MR angiograms—individual transverse sections and maximum intensity projection reconstructions—were evaluated by one of the authors (A.B.) without knowledge of the DSA findings, because DSA was always performed the day after MR angiography. The DSA examinations were performed by the other author (L.P.), and the resultant images were assessed in all cases by both authors by means of consensus. At each examination, the following features were evaluated: (a) presence or absence of a neck remnant; (b) size of the neck remnant, if present, by means of direct measurement on the MR angiograms and by means of comparison with the diameter of the internal carotid artery at DSA; (c) presence or absence of flow in the coil mesh; and (d) size of the remnant when residual flow was seen in the coil mesh.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MR Angiography Feasibility and Quality
In three (4%) of the 68 patients for whom MR angiography was recommended, MR angiography was either not possible (two patients) or not informative (one patient). The latter patient harbored multiple aneurysms, one of which was pericallosal and treated surgically by using a clip. Artifacts were responsible for the poor quality of the MR angiogram, which did not enable evaluation of the middle cerebral aneurysm treated with GDC placement.
MR Angiography versus DSA
As stated previously, 80 correlations between MR angiography and DSA were evaluated. In 72 cases (90%), the MR angiography results regarding the presence or absence of a residual aneurysm correlated well with those of DSA. In 54 of the 72 correlations, neither MR angiography nor DSA depicted any remnant or recurrence. These 54 correlations were observed in 48 aneurysms, six of which were examined twice (mean size, 6.3 mm).
In 18 of the 72 good correlations, a remnant was identified at both DSA and MR angiography in 16 aneurysms (mean size, 8 mm). The evaluations of remnant size did not differ between the two techniques: smaller than 3 mm in eight cases (50%), 3–5 mm in five cases (31%), and greater than 5 mm in three cases (19%).
In eight (10%) of the 80 comparisons, the results of MR angiography and DSA were different. In one anterior communicating artery aneurysm, the feature identified at MR angiography as a remnant was visualized at DSA as a loop of the anterior circulation complex. In the other seven cases, the remnants identified at DSA were not detected at MR angiography. In six cases (four aneurysms, two evaluated twice), the remnant measured less than 2 mm (Figs 1–3). In one case, the remnant was 2.5 mm and the patient underwent a second treatment; there was a persistent flow in the coil mesh close to the aneurysmal neck, which was not visible at MR angiography (Fig 4). The sensitivity and specificity of MR angiography were, therefore, 72% (18 of 25 correlations) and 98% (54 of 55 correlations), respectively, for depicting an aneurysm remnant.
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Additional Treatment
In nine of the 21 patients who harbored an aneurysm remnant, additional treatment was attempted and resulted in total occlusion in four cases and subtotal occlusion in one case.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Stability of Occlusion after EVT of Intracranial Aneurysms
As the results of two recent studies (6,7) made clear, the stability of aneurysm occlusion after EVT with GDCs must be regularly evaluated: This procedure has sometimes been followed by immediate incomplete occlusion or a recurrence. In a cooperative study performed in the United States (2), a small neck remnant was observed in 21% of small aneurysms with a small neck, 57% of large aneurysms, and 50% of giant aneurysms. As observed by Hope et al (6), such small remnants may enlarge by means of coil compaction or the aneurysm may grow. In other cases, the residual aneurysm may shrink or disappear.
In a series of 169 aneurysms reported by Cognard et al (7), subtotal or incomplete occlusion was initially observed in 20 cases (12%). The evolution of the aneurysm remnants varied. In a large proportion of cases (62%), no modification of these remnants was observed during follow-up. Regrowth of the aneurysm pouch occurred in some cases (33%), and repeat treatment was sometimes performed. Initial total occlusion was achieved in a very large number of cases, but 3–40 months after the initial treatment, recurrence occurred in 24 (14%) of the 169 cases, and six (25%) of these recurrences were re-treated.
Clinical Importance of Aneurysm Remnants or Recurrences
Because EVT of intracranial aneurysms by using GDCs is a relatively new technique, it is difficult to determine the clinical importance of an aneurysm remnant or recurrence. In the series of Cognard et al (7), no rebleeding occurred during the follow-up period, even in the patients with residual aneurysms or recurrence. In the series of Viñuela et al (2), rebleeding was observed in 2.2% of cases during the 6 months after treatment. In all of the cases, the aneurysms were incompletely treated. In a large surgical series, Feuerberg et al (13) reported a risk of rebleeding caused by an aneurysm remnant in 0.38%–0.79% of cases.
Follow-up of Patients Selectively Treated with GDCs
We determined from our review that a residual pouch may occur after selective EVT of intracranial aneurysms by means of GDCs. The clinical importance of these residual pouches is not clear, but we know from the surgery literature that the risk of such pouch formation cannot be neglected. It is, therefore, necessary to plan a follow-up of such patients. Usually, this follow-up is conducted by performing DSA 3 months, 1 year, and 3 years after treatment (7). However, DSA has a risk of neurologic complications, which are estimated to occur in 0.5%–4.0% of cases (14). Consequently, repeated DSA examinations may increase the morbidity and/or mortality rate of EVT for intracranial aneurysms, and, therefore, the efficacy of nontraumatic follow-up methods should be evaluated.
MR angiography is a potentially good candidate for use in this follow-up, because it is generally well tolerated, except by patients who are claustrophobic. Even when gadolinium-based contrast material is injected, the risk remains low. The three-dimensional time-of-flight technique, with and without gadolinium-based contrast material injection and with and without magnetization transfer, has been evaluated for the detection of intracranial aneurysms with good results (15–17). Moreover, Hartman et al (18) and Shellock et al (19) found GDCs to be compatible for MR imaging and to produce few or no artifacts.
To our knowledge, few reports have addressed the value and place of MR angiography in the follow-up of intracranial aneurysms treated with GDCs, and the number of patients examined in these reports, 14–49, has been too small to yield valid conclusions. In the largest study (12), there was a high percentage of cases (11%) with artifacts due to the presence of GDCs. The sensitivity of MR angiography, as compared with DSA, for the detection of residual aneurysms was 97%, and the specificity was 100%.
In our study, gadolinium-enhanced three-dimensional time-of-flight MR angiography was used because some authors (20,21) have observed the accuracy of this technique for the brain vasculature, especially intracranial aneurysms. Moreover, our goal was to increase signal intensity in the residual pouches, where flow can be slow. Finally, this technique shortened the sequence and thus allowed the maximum number of patients to undergo MR imaging.
We focused on the evaluation of residual aneurysms or recurrences because in the long term, these constitute the real problem. Although patency of the parent vessel is one of the problems in the treatment phase, it is usually evaluated correctly by performing angiography postoperatively or, in cases of neurologic symptoms, during the days following treatment.
The aim of EVT is to obtain dense packing of the coils in the aneurysmal sac to occlude the neck and suppress blood flow in the sac. In a few cases, this aim is not fulfilled because of anatomic or technical reasons, and residual flow is sometimes observed in the coils near the neck. In such cases, the evolution usually ends in the compaction of the coils in the fundus of the aneurysmal sac, which leads to remnant formation in the neck (6). In this case, residual aneurysms or recurrences can have two different forms: (a) a residual pouch between the coil mesh and the aneurysmal neck or (b) residual flow in the coil mesh. In our series, the first form was the most frequent: It occurred in 20 of 21 cases of remnant or recurrence.
Discrepancies between DSA and MR angiography were observed in 10% of cases, reducing sensitivity to 72%; specificity was assessed to be 98%. As in the detection of untreated aneurysms (22), the critical size is less than 3 mm. In our series, only small aneurysm neck remnants (<3 mm) were visualized at DSA but not at MR angiography (Figs 1–4). In all but one case, no additional treatment was proposed and follow-up was continued. In one case, residual flow in the coils close to the neck was visualized at DSA but not at MR angiography, and additional treatment was performed (Fig 4).
Most of the discrepancies between MR angiography and DSA were encountered at the beginning of our study. Just as there is a learning curve for EVT of aneurysms, there probably is such a curve for the interpretation of MR angiograms of treated intracranial aneurysms. Retrospective evaluation performed at the time this article was written showed that in some cases, the interpretations of MR angiograms during our prospective study differed from later evaluations.
The value of contrast material administration in the examination of patients was not demonstrated in our study, because none of the MR angiograms were obtained without contrast material. Anzalone et al (12) compared nonenhanced and contrast material–enhanced MR angiography in 25 GDC-treated aneurysms and found that contrast-enhanced MR angiography was useful for evaluating the residual patency in large and giant aneurysms and for depicting distal branch arteries.
Follow-up of GDC-treated Intracranial Aneurysms
Our study results indicate that MR angiography is probably able to depict clinically important aneurysm neck remnants larger than 3 mm, but a larger series of patients is probably necessary to confirm this.
The follow-up described by Cognard et al (7) consisted of DSA performed 3 months, 1 year, and 3 years after treatment. If our results are confirmed in a larger series, then the DSA examination performed at 3 months can probably be replaced by MR angiography. At 1 year, both DSA and MR angiography should be performed and their results compared, and if these results are not discrepant, follow-up can then be based on MR angiography findings.
The most useful duration of follow-up is unknown, but the use of MR angiography allows very long-term examination of the treated patients without increasing the overall morbidity and/or mortality of the technique.
In summary, MR angiography can depict residual aneurysms larger than 3 mm, which are probably the clinically important aneurysms. Therefore, MR angiography is probably a good noninvasive tool for the follow-up of intracranial aneurysms treated by using GDCs, and it may partly replace DSA.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, L.P.; study concepts, L.P.; study design, L.P., A.B.; literature research, L.P., A.B.; clinical studies, A.B.; data acquisition, A.B.; data analysis/interpretation, L.P., A.B.; manuscript preparation, L.P.; manuscript definition of intellectual content, L.P., A.B.; manuscript editing, L.P.; manuscript revision/review, L.P.; manuscript final version approval, L.P.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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