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 »  Abstract
 » Introduction
 »  Materials and Me...
 » Results
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ORIGINAL ARTICLE
Year : 2012  |  Volume : 60  |  Issue : 1  |  Page : 45-49

Fenestrations accompanied by intracranial aneurysms assessed with magnetic resonance angiography


Institute of Diagnostic and Interventional Radiology, The Sixth Affiliated People's Hospital, Shanghai Jiao Tong University, No. 600, Yi Shan Road, Shanghai, China

Date of Submission30-May-2011
Date of Decision20-Jun-2011
Date of Acceptance26-Oct-2011
Date of Web Publication7-Mar-2012

Correspondence Address:
Ming-Hua Li
No. 600, Yi Shan Road, Shanghai - 200 233
China
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Source of Support: National Natural Scientific Fund of China (contract no. 30970793), the Shanghai Important Subject Fund of Medicine (contract no. 05 III 023) and the Program for Shanghai Outstanding Medical Academic Leader (contract no. LJ 06016), Conflict of Interest: None


DOI: 10.4103/0028-3886.93588

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 » Abstract 

Background and Purpose: The aim of this study was to evaluate the anatomical changes and investigate the prevalence in intracranial aneurysm with fenestrations using magnetic resonance angiography (MRA). Materials and Methods: Between June 2008 and October 2010, 4652 patients (aged 23-73 years) with suspected intracranial aneurysm or other cerebrovascular diseases underwent MRA examination. MRA was performed using a three-dimensional time-of-flight technique (3D-TOF) with volume rendering (VR) and maximum intensity projection reconstruction methods. The presence and location of fenestrations and aneurysms was reviewed. When fenestrations were present in combination with aneurysms, we noted the relationship of the locations. The classification of fenestration accompanied by intracranial aneurysm was divided into three types according to the anatomical relationship as follows: Type I, aneurysm adjacent to but not on a fenestration; Type II, aneurysm located on the fenestration; type III, aneurysm located at a position remote from a fenestration. Results: Among the 4652 patients examined, 409 patients were defined with 412 intracranial aneurysms, and the prevalence of aneurysms was 8.8%. One hundred and forty-one patients were identified with fenestrations; 24 of these patients were confirmed with intracranial aneurysms. Seven cases were classified as type I, three as type II and 14 as type III. The prevalence of intracranial aneurysm with fenestrations was 17.0%, with significant statistical difference compared with aneurysms unaccompanied with fenestrations (P=0.0064). Conclusion: The anatomical relationship between fenestrations and intracranial aneurysms was visualized by MRA with VR, which displayed pathologies with sufficient clarity to enable diagnosis. Furthermore, the results of this study suggest that physicians should be alerted to the occurrence of intracranial aneurysm following the detection of fenestrations by MRA.


Keywords: Fenestrations, intracranial aneurysm, magnetic resonance angiography


How to cite this article:
Sun ZK, Li M, Li MH, Li YD, Sun WP, Zhu YQ. Fenestrations accompanied by intracranial aneurysms assessed with magnetic resonance angiography. Neurol India 2012;60:45-9

How to cite this URL:
Sun ZK, Li M, Li MH, Li YD, Sun WP, Zhu YQ. Fenestrations accompanied by intracranial aneurysms assessed with magnetic resonance angiography. Neurol India [serial online] 2012 [cited 2019 Oct 16];60:45-9. Available from: http://www.neurologyindia.com/text.asp?2012/60/1/45/93588



 » Introduction Top


Fenestrations of intracranial arteries are rare variants resulting from the incomplete fusion of primitive vessels. An association has been observed between fenestration and the occurrence of intracranial aneurysm formation. [1] Such findings suggest a causal relationship between fenestrations and the formation of intracranial aneurysms.

Digital subtraction angiography (DSA) is currently considered the modality of choice for the imaging of intracranial aneurysms. However, DSA is a relative invasive test accompanied by potential complications, and it is impossible to investigate a large cohort of fenestrations with intracranial aneurysms using this method.

Magnetic resonance angiography (MRA) is considered a safe investigative technique because it is non-invasive, non-radioactive, technically simple and does not require the administration of a contrast agent. Furthermore, this technique allows three-dimensional imaging of intracranial structural details.

The purpose of this study was to evaluate the anatomical change and investigate the prevalence in intracranial aneurysm with fenestrations with the use of three-dimensional time-of-flight (3D-TOF) MRA at 3.0 T.


 » Materials and Methods Top


Patients

Between June 2008 and October 2010, MRA was performed in a total of 4652 patients aged between 23 and 73 years (average age, 48.82 years) with suspected intracranial aneurysm or other cerebrovascular diseases (1960 males and 2692 females). All patients were Chinese. Outpatients and inpatients were included.

MRA

In all cases, (MRA) was performed on a 3.0 T system (Achieva X-Series; Intera-achieva SMI-2. 1, Philips Medical System, Best, Netherlands) with a Sense-Head-8 receiver head coil. TOF-MRA was obtained using 3D T1-weighted fast field echo (3D-T1-FFE) sequences with TR/TE, 35/7; flip angle, 20°; field-of-view (FOV), 250 × 190 × 108; four slabs (180 slices) with slice thickness 0.8 mm; matrix, 732 × 1024; and acquisition time, 8 min 56 s. Parallel imaging was performed using a generalized autocalibrating partially parallel acquisition algorithm based on autocalibration of simultaneous acquisition of spatial harmonics and parallel acquisition. The acquired image data sets were then transferred to a workstation (EWS 2.5.3.0; Philips Medical Systems) where the 3D images were reconstructed with a 1024 × 1024 matrix by maximum intensity projection (MIP) and volume rendering (VR) using a 3D software package (Volume Inspection; Philips Medical Systems).

Image analysis

The principle diagnostic criteria were as follows: Fenestrations of intracranial arteries are segmental duplications of the lumen into two distinct endothelium-lined channels, which may or may not share their adventitial layer. [1],[2],[3],[4],[5] The classification of fenestration was divided into three main types according to the anatomical relationship between fenestration and aneurysm as follows: [6] type I - the intracranial aneurysm is located at the proximal end of the fenestration; type II - the intracranial aneurysm is located on the fenestrations; type III - the intracranial aneurysm and fenestration are located at the posterior or anterior cerebral arterial circulation, respectively, or aneurysms and fenestrations are both located at the same cerebral arterial circulation although the aneurysm is located in a position remote from the fenestrations.

Blinded analysis of the MRA images was carried out by three neuroradiologists who diagnosed and classified the intracranial aneurysms and fenestrations according to the VR and MIP images and the source data. There was no interobserver difference in the detection and classification of fenestrations accompanied by intracranial aneurysm. Multi-directional images (2D and 3D) were reconstructed by the VR and MIP techniques and the course of fenestration accompanied by intracranial aneurysm in the source data was incorporated. Thus, the three neuroradiologists were able to achieve similar results.

Data analysis

The prevalence of between intracranial aneurysm with fenestrations and aneurysms without fenestrations was compared. For comparison of proportions, the χ2 test was used. A P-value less than 0.05 was considered significant.


 » Results Top


In this study, 409 patients were defined with 412 intracranial aneurysms, and the prevalence of aneurysms was 8.8%. One hundred and forty-one cases having fenestrations were detected in the 4652 patients studied. Twenty-four of these were accompanied by at least one intracranial aneurysm. Seven (29.2%) cases were classified as type I, three (12.5%) as type II and 14 (58.3%) as type III [Figure 1],[Figure 2] and [Figure 3]. Fenestrations in these 24 cases were located as follows: Four (16.7%) in AComA, four (16.7%) in A1 and A2, three (12.5%) in middle cerebral artery, six (25.0%) in basilar artery, six (25.0%) in vertebral artery and one (4.1%) in the P1 segment of the posterior cerebral artery [Table 1]. A total of 27 intracranial aneurysms were confirmed in the 24 affected patients and were distributed as follows: A single aneurysm (n=22), two aneurysms (n =1) and three aneurysms (n=1). These were located as follows: Seven (25.9%) in AComA, three (11.1%) in A1 of the anterior cerebral artery, two (7.4%) in the middle cerebral artery, five (18.5%) in the posterior communicating artery, one (3.7%) in the C4 of Internal carotid artery', two (7.4%) in the clinoid artery, four (14.8%) in the ophthalmic artery, one (3.7%) in the cervical segment of ICA and two (7.4%) in the vertebral artery [Table 1].
Figure 1: A three-dimensional time-of-flight magnetic resonance angiography shows an anterior communicating artery fenestration (wide arrow) associated with aneurysm (thin arrow).The anatomical relationship between fenestration and aneurysm was classified type I

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Figure 2: (a) Computed tomography image shows a 48-year-old woman with subarachnoid hemorrhage (b) Three-dimensional time-of-flight magnetic resonance angiography, (c) computed tomographic angiography and (d) digital subtraction angiography image show a proximal basilar artery fenestration (wide arrow) associated with an aneurysm (thin arrow). The anatomical relationship between fenestration and aneurysm was classified as type II

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Figure 3: A three-dimensional time-of-flight magnetic resonance angiography shows a proximal basilar artery fenestration (wide arrow) associated with two aneurysms (thin arrow) in the left C7 segment. The anatomical relationship between the fenestration and the aneurysm was classified as type III

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Table 1: Classification of fenestrations accompanied by intracranial aneurysms

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 » Discussion Top


Fenestration is a rare cerebrovascular variation, the prevalence of which is estimated by angiography to be between 0.3 and 0.9%. [2],[7] Even the anterior communicating arteries can only be demonstrated to be fenestrated in approximately 5% of the cases by angiography. [8] However, the true frequency of fenestration of intracranial arteries is difficult to ascertain. Cerebral angiography is a relative invasive diagnostic method. Generally, studies on the diagnosis of fenestration using this technique have been conducted with a small sample size, and the subjects included in these studies have obvious proneness. Consequently, results obtained using this technique cannot be considered to be objective and, therefore, may be responsible for the large variation in the reported prevalence of fenestration. In 59 of 208 patients, 61 fenestrations were detected (28%) for 3D rotational angiography (3DRA), [6] the frequency of fenestrations was obviously higher than that in old-fashioned angiography and in our institute by MRA. One reason is that in the former 208 patients with suspected intracranial aneurysms, fenestrations should occur more often than in others. Another possible reason may be that much duplication (a duplication is defined as two distinct arteries with separate origins and no distal arterial convergence [6] ) in the ACom artery was not included in the fenestration groups.

MRA is considered as a safe and comparatively inexpensive examination technique. Little data is available on the detection of fenestrations with MRA, although the frequency is lower than that reported with both 3D DSA and computed tomographic angiography. [4],[9],[10] The frequency of fenestrations identified in this study was higher than in previous reports. [2],[7] However, the advanced post-processing techniques of 3D-TOF-MRA provide the potential to evaluate cerebral vessels from any angle, allowing investigation of the complex vascular anatomy and, therefore, effective detection of vessel fenestrations. The patient group studied was based on a retrospective review of 4652 subjects who had undergone MRA and were selected on suspicion or identification of intracranial aneurysms related to fenestrations. Therefore, a definite relationship between fenestrations and aneurysms can be concluded from this study, and the higher frequency of intracranial aneurysm with fenestrations may result in no bias.

Most fenestrations do not cause any clinical symptoms, although an association has been observed between fenestrations and aneurysm formation. It has been postulated that turbulent flow created by defects in the tunica media at the proximal and distal ends of a fenestrated segment leads to aneurysm formation. [1] These gaps in the media, combined with increased hemodynamic stress, are believed to contribute to the increased prevalence of aneurysms among patients with fenestration. [11],[12] In two studies of 5190 and 4500 cerebral angiograms, fenestrations were reported in 0.7 and 0.07%, respectively. The incidence of an aneurysm being present when a fenestration is observed is reported to be 7%. [1],[2] However, the incidence of a fenestration being present when a vertebrobasiliar junction aneurysm is observed is reported to be 35.5%. [13] Therefore, in the presence of a vetebrobasilar junction fenestration, an associated aneurysm should be suspected. [14],[15]

The observations of this study demonstrated that the three types of fenestrations accompanied by intracranial aneurysm were distributed among the three classification groups as follows: Type I (29.2%), type II (12.5%) and type III (58.3%). Types I and II are associated with turbulent flow alterations due to the significant thinning of the subendothelium therefore increasing the risk of aneurysm development. [16] However, in our study, the incidence of type III was greater than that of the other types of fenestration accompanied by intracranial aneurysm. The reasons for this are unknown - a coincidence or an underlying reason? A further study based on a larger sample volunteer was carried out at the same time at our institute. We wish a causal relationship between fenestrations and the formation of intracranial aneurysms could be explained.

In conclusion, the outstanding spatial visualization afforded by 3D-TOF MRA with VR makes this a valuable technique for evaluating the anatomical relationship between fenestration and aneurysms. Although fenestrations are not generally related to aneurysms [Figure 3], a relationship between fenestrations in combination with aneurysms was suggested in this study by their identification in rare locations [Figure 1] and [Figure 2]. Furthermore, the currently available data indicate that fenestrations in specific locations (bifurcation such as vertebrobasilar artery) could be easily associated with aneurysms.


 » Acknowledgments Top


This study was supported by the National Natural Scientific Fund of China (contract no. 30970793), the Shanghai Important Subject Fund of Medicine (contract no. 05 III 023) and the Program for Shanghai Outstanding Medical Academic Leader (contract no. LJ 06016).

 
 » References Top

1.Sanders WP, Sorek PA, Mehta BA. Fenestration of intracranial arteries with special attention to associated aneurysms and other anomalies. AJNR Am J Neuroradiol 1993;14:675-80.  Back to cited text no. 1
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3.San-Galli F, Leman C, Kien P, Khazaal J, Phillips SD, Guerin J. Cerebral arterial fenestrations associated with intracranial saccular aneurysms. Neurosurgery 1992;30:279-83.  Back to cited text no. 3
    
4.Uchino A, Nomiyama K, Takase Y, Kudo S. Anterior cerebral artery variations detected by MR angiography. Neuroradiology 2006;48:647-52.  Back to cited text no. 4
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6.Van Rooij SB, van Rooij WJ, Sluzewski M, Sprengers ME. Fenestrations of intracranial arteries detected with 3D rotational angiography. AJNR Am J Neuroradiol 2009;30:1347-50.  Back to cited text no. 6
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7.Osborn RE, Kirk G. Cerebral arterial fenestration. Comput Radiol 1987;11:141-5.  Back to cited text no. 7
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11.Black SP, Ansbacher LE. Saccular aneurysm associated with segmental duplication of the basilar artery. J Neurosurg 1984;61:1005-8.  Back to cited text no. 11
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12.De Caro R, Serafini MT, Galli S, Parenti A, Guidolin D, Munari PF. Anatomy of segmental duplication in the human basilar artery: Possible site of aneurysm formation. Clin Neuropathol 1995;14:303-9.  Back to cited text no. 12
    
13.Campos J, Fox AJ, Vinuela F, Lylyk P, Ferguson GG, Drake CG, et al. Saccular aneurysms in basilar artery fenestration. AJNR Am J Neuroradiol 1987;8:233-6.  Back to cited text no. 13
    
14.Peluso JP, van Rooij WJ, Sluzewski M, Beute GN. Aneurysms of the vertebrobasilar junction: Incidence, clinical presentation, and outcome of endovascular treatment. AJNR Am J Neuroradiol 2007;28:1747-51.  Back to cited text no. 14
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1]

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