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Surg Neurol Int 2012,  3:43

Bilateral A1 fenestrations: Report of two cases and literature review

1 Department of Neurological Surgery, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA,
2 Department of Radiology, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA; Department of Radiology, Ankara University Hospitals, Sihhiye, Ankara, Turkey,
3 Department of Neurological Surgery; Department of Radiology, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA,
4 Department of Pathology and Laboratory Medicine, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA,

Date of Submission06-Feb-2012
Date of Acceptance26-Mar-2012
Date of Web Publication16-Apr-2012

Correspondence Address:
Mustafa K Baskaya
Department of Neurological Surgery, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA

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DOI: 10.4103/2152-7806.94928

PMID: 22574252

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Background: Bilateral fenestration of the A1 segment of anterior cerebral artery (ACA) is an uncommon anomaly. Our objective is to describe two cases with this anomaly and to review the literature.
Case Description: A 50-year-old woman presented with subarachnoid hemorrhage from a ruptured A1 aneurysm. Angiography revealed bilateral A1 segment fenestration as well as an aneurysm on the proximal end of fenestration on the right side. The second case is that of an 86-year-old woman who was found to have bilateral fenestration of A1 segment at autopsy.
Conclusion: Bilateral A1 fenestration is an uncommon anomaly that may be associated with an aneurysm. In surgical clipping of such cases, extreme caution should be exercised to inspect both arms of the fenestration since both may have multiple perforators as demonstrated in our autopsy specimen. This will be the first published pictorial demonstration of these perforators arising from the arms of fenestration.

Keywords: A1 segment, aneurysm, anterior cerebral artery, bilateral fenestration, central nervous system

How to cite this article:
Aktüre E, Arat A, Niemann DB, Salamat M S, Baskaya MK. Bilateral A1 fenestrations: Report of two cases and literature review. Surg Neurol Int 2012;3:43

How to cite this URL:
Aktüre E, Arat A, Niemann DB, Salamat M S, Baskaya MK. Bilateral A1 fenestrations: Report of two cases and literature review. Surg Neurol Int [serial online] 2012 [cited 2015 May 3];3:43. Available from:

   Introduction Top

Fenestrations of the cerebral arteries most commonly occur in the anterior communicating artery, the vertebral artery, the basilar artery, and the middle cerebral artery. [11],[14],[15] Fenestrations of the A1 segment of the anterior cerebral artery (ACA) are uncommon and are found only in 0.14% of the specimens. [4] Furthermore, bilateral A1 fenestrations have only been reported by three authors previously and there is only one case report of bilateral A1 fenestrations associated with an aneurysm involving the fenestrated segment. [1],[5],[18] We report two cases of bilateral A1 fenestrations, one of which is associated with a saccular aneurysm involving the proximal end of a fenestration.

   Case Reports Top

Case 1

A 50-year-old woman with family history of ruptured aneurysms presented with subarachnoid hemorrhage. Computed tomography (CT) angiography performed at our institution revealed a small aneurysm at the proximal end of fenestrated right A1 segment and bilateral fenestrations of the A1 segments [Figure 1]a and b. The left fenestrated A1 was found to be smaller in size than the right one. In addition to these findings, the origins of the posterior inferior cerebellar arteries were found to be extradural bilaterally. The patient underwent surgical clipping of the aneurysm via pterional craniotomy. Surgical exploration revealed the aneurysm just proximal to the right fenestrated A1 segment. The aneurysm was clipped successfully using a bayonet clip across the aneurysmal neck. Post-clipping angiography demonstrated complete obliteration of the aneurysm [Figure 1]c and d. Postoperative course was uneventful and the patient was discharged home neurologically intact. She was doing well for a 50-month follow-up period.
Figure 1: Volume rendered 3-dimensional computerized tomographic angiography (3D CTA) images show bilateral A1 fenestrations (a) (arrows) and saccular aneurysm involving proximal end of the right A1 fenestration (b) (arrowhead). Postoperative digital subtraction angiography shows complete obliteration of the aneurysm involving proximal end of the right A1 fenestration (c) (arrowhead). 3D views of the left carotid circulation obtained from rotational angiogram show the left-sided fenestration (d) (arrow)

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Case 2

An 86-year-old woman with a history of Alzheimer's disease, depression, and hypertension passed away at a nursing home due to complications related to dementia. She did not have any known history of neurovascular diseases or complaints. Her autopsy revealed incidental bilateral fenestrations of A1 segments. The anomalous cerebral vessels (A1 segments, anterior communicating artery, and A2 segments) were isolated for further microscopic examination by cutting A1s proximally and A2s distally [Figure 2]. These vessels were then inspected, photographed, and the perforators were counted under the operating microscope (Leica, Wild M 695 surgical microscope, 3× to 40×). On each side, the fenestrated A1 segments consisted of a larger, lateral segment and a narrower medial segment. Overall, the medial segment on the right side was larger than the medial segment on the left. There were two major and four minor perforators arising from the right lateral segment, while there were two major and five minor perforators associated with the left lateral segments. For the medial segments, there were only five minor perforators on the left and four on the right.
Figure 2: Postmortem specimen showing bilateral A1 fenestrations. Note that one large perforator originates from the large arm of the left fenestration on the left side and two from the large arm of the fenestration on the right side. Also, note very prominent right recurrent artery of Heubner on the right and again very prominent anterior communicating artery perforator. Inlet picture on left bottom corner shows magnified view of two of the perforating branches (arrowheads) originating from the small arm of the left A1 fenestration after the specimen is stained with luxol fast blue to overcome the transparency

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   Discussion Top

Fenestration is the separation of the arterial lumen into two distinct channels, each having its own endothelial, muscular, and adventitial layers. Distally, these two channels merge into a single arterial lumen again. The fenestration of the A1 segment of the ACA is an uncommon entity which was first described by Fawcett and Blachford in 1905. They found its incidence to be 0.14% in 700 brains. [4] Bilateral A1 fenestrations were first described by Adachi et al. in three cases in 1928. [1] Friedlander and Ogilvy reported a case of bilateral A1 fenestration associated with an A1 aneurysm, along with 58 cases of unilateral A1 fenestrations in their literature review. In addition to the data presented in the previous literature review by Friedlander and Ogilvy, [5] we also found that Yaşargil described various fenestrations of the A1 segment including a case with bilateral fenestration. [18] In 1976, Perlmutter and Rhoton reported two cases of unilateral A1 fenestrations in 50 cadaver brains, and no bilateral fenestrations were found in their study. [13] In our review so far, there are 76 reported cases of A1 fenestrations in the literature, 5 of which are bilateral including the cases presented in this study [Table 1]. [1],[3],[5],[6],[7],[8],[9],[10],[11],[17],[18],[19]
Table 1: Seven cases of bilateral A1 fenestrations reported in the literature between 1928 and 2011

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Fenestrations of the cerebral vessels are associated with other vascular anomalies and saccular aneurysms. [5] Of the 76 reported cases, 25 were associated with an aneurysm at the fenestrated segment itself, with one interpreted as fusiform and the remaining being saccular. [3],[5],[6],[7],[8],[9],[10],[11],[12],[16],[17],[18],[19] Saccular aneurysms involved the proximal segment of the fenestration except for one case. [8] In our first case, the saccular aneurysm arose from the proximal part of the fenestration of right A1, and the left A1 was smaller than the right one.

The origin of the A1 perforators in a fenestrated A1 segment is important in both endovascular and open surgical approaches for the treatment of associated aneurysms. The A1 segment generally supplies the optic chiasm, anterior third ventricle and hypothalamus, medial third of the anterior commisure, caudate head, globus pallidus, anterior limb of internal capsule, and rostral thalamus. [2],[13] Perlmutter and Rhoton found that the majority of the A1 perforators originate from the lateral half of the A1 (68%). [13] Thus, the origins of the major perforators should be identified if occlusion of the fenestrated arm is being considered. In the postmortem specimen, we identified the major perforator branches were originating from the larger arm of the fenestrated vessel, which is also situated laterally [Figure 2]. However, small perforating vessels originating from the small medial arm were also identified [Figure 2]. The distribution of perforators amongst the two limbs of the fenestration in the proximal ACA has not been previously demonstrated. The presence of perforators arising from both limbs suggests that perforator distribution infarction may occur if sacrifice of either limb is contemplated during treatment of fenestration-associated aneurysms.

   Conclusion Top

We demonstrated two cases of bilateral fenestrations of the A1 segment of the ACA which is an uncommon variant. The fenestration of the A1 segment is known to be associated with aneurysms, and the fact that the perforators can arise from either limb is important in the planning of the management of such aneurysms.

   References Top

1.Adachi B, Hasebe K. Kyôto Daigaku. Igakubu. In: Das Arteriensystem der Japaner, Anatomie der Japaner. Kaiserlich-japanische Universität zu Kyoto, In kommission bei "Maruzen Co.", Kyoto and Tokyo; 1928. p. 111-34.  Back to cited text no. 1
2.Dunker RO, Harris AB. Surgical anatomy of the proximal anterior cerebral artery. J Neurosurg 1976;44:359-67.  Back to cited text no. 2
3.Evans AL, Corkill RA, Wenderoth JD. Ruptured fusiform aneurysm of fenestrated A1 segment of the anterior cerebral artery. Case report and review of the literature. Neuroradiology 2006;48:196-9.  Back to cited text no. 3
4.Fawcett E, Blachford JV. The Circle of Willis: An Examination of 700 Specimens. J Anat Physiol 1905;40:63.2-70.  Back to cited text no. 4
5.Friedlander RM, Oglivy CS. Aneurysmal subarachnoid hemorrhage in a patient with bilateral A1 fenestrations associated with an azygos anterior cerebral artery. Case report and literature review. J Neurosurg 1996;84:681-4.  Back to cited text no. 5
6.Fujimoto Y, Yamanaka K, Nakajima Y, Yoshimura K, Yoshimine T. Ruptured aneurysm arising from the proximal end of an azygos anterior cerebral artery-Case report. Neurol Med Chir (Tokyo) 2004;44:242-4.  Back to cited text no. 6
7.Kachhara R, Nair S, Gupta AK. Fenestration of the proximal anterior cerebral artery (A1) with aneurysm manifesting as subarachnoid hemorrhage-Case report. Neurol Med Chir (Tokyo) 1998;38:409-12.  Back to cited text no. 7
8.Koh JS, Kim EJ, Lee SH, Bang JS. Ruptured aneurysm arising from the distal end of a proximal a(1) fenestration: Case report and review of the literature. J Korean Neurosurg Soc 2009;45:43-5.  Back to cited text no. 8
9.Koh JS, Lee SH, Bang JS, Kim GK. Three-dimensional angiographic demonstration of plexiform fenestrations of the proximal anterior cerebral artery associated with a ruptured aneurysm. J Korean Neurosurg Soc 2008;44:338-40.  Back to cited text no. 9
10.Leyon JJ, Kaliaperumal C, Choudhari KA. Aneurysm at the fenestrated anterior cerebral artery: Surgical anatomy and management. Clin Neurol Neurosurg 2008;110:511-3.  Back to cited text no. 10
11.Mantatzis M, Kizilkilic O, Albayram S, Kocer N, Islak C. Endovascular treatment of aneurysms associated with fenestrated A1 segment of anterior cerebral artery: Report of two cases. J Neuroimaging 2011;21:165-9.  Back to cited text no. 11
12.Mitsuhara T, Sakamoto S, Kiura Y, Kurisu K. Endovascular coil embolization for ruptured kissing aneurysms associated with A1 fenestration. Surg Neurol Int 2011;2:85.  Back to cited text no. 12
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13.Perlmutter D, Rhoton AL. Microsurgical anatomy of the anterior cerebral-anterior communicating-recurrent artery complex. J Neurosurg 1976;45:259-72.  Back to cited text no. 13
14.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. 14
15.Terui K, Obayashi S, Shimizu M, Ozaki F, Moriwaki H, Ryujin Y, et al. [Unruptured aneurysm arising from fenestration of the horizontal (A1) segment in the anterior cerebral artery: A case report and review of the literature]. No Shinkei Geka 2010;38:545-50.  Back to cited text no. 15
16.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. 16
17.Wanibuchi M, Kurokawa Y, Ishiguro M, Fujishige M, Inaba K. Characteristics of aneurysms arising from the horizontal portion of the anterior cerebral artery. Surg Neurol 2001;55:148-54; discussion 154-5.  Back to cited text no. 17
18.Yasargil M. Operative Anatomy, in Microneurosurgery. Vol. 1. New York: Georg Thieme Verlag; 1984. p. 99-116.  Back to cited text no. 18
19.Zhao H, Fu J, Lu Z, Lü H. Fenestration of the anterior cerebral artery detected by magnetic resonance angiography. Chin Med J 2009;122:1139-42.  Back to cited text no. 19


  [Figure 1], [Figure 2]

  [Table 1]

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