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|LETTER TO EDITOR
|Year : 2013 | Volume
| Issue : 3 | Page : 315-317
Trilobulated fusiform aneurysm from proximal fenestrated segment of dominant A1 causing subarachnoid hemorrhage
Rajan Kumar, Sanjay Behari, Kamlesh Singh, Rabi N Sahu, Awadhesh K Jaiswal
Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India
|Date of Submission||26-Apr-2013|
|Date of Decision||28-Apr-2013|
|Date of Acceptance||30-May-2013|
|Date of Web Publication||16-Jul-2013|
Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kumar R, Behari S, Singh K, Sahu RN, Jaiswal AK. Trilobulated fusiform aneurysm from proximal fenestrated segment of dominant A1 causing subarachnoid hemorrhage. Neurol India 2013;61:315-7
|How to cite this URL:|
Kumar R, Behari S, Singh K, Sahu RN, Jaiswal AK. Trilobulated fusiform aneurysm from proximal fenestrated segment of dominant A1 causing subarachnoid hemorrhage. Neurol India [serial online] 2013 [cited 2021 Mar 1];61:315-7. Available from: https://www.neurologyindia.com/text.asp?2013/61/3/315/115082
Fenestrations of proximal anterior cerebral artery (ACA) are rare. ,,, This report presents a patient with trilobed, fusiform A1 segment aneurysm associated with proximal A1 fenestration in a dominant ACA and discusses the management options of this rare pathology.
A 47-year-old lady presented with sudden, severe headache with multiple bouts of vomiting and altered sensorium of 10 days duration. Neurologic examination revealed spontaneous eye opening, response to simple commands, no focal deficits and meningeal signs. Computed tomographic scan done on the next day following the ictus revealed basifrontal, suprasellar, prepontine and interpeduncular subarachnoid hemorrhage (SAH) with intraventricular hemorrhage and mild ventriculomegaly [Figure 1]. Computed tomography-angiogram revealed a dominant right A1 segment filling both A2 arteries with a proximal fenestrated segment. There was a trilobed, fusiform aneurysm arising from the inferior surface of the superior fenestration of right A1. Two (anterolateral and anteromedial) lobes of the aneurysm were emerging from either side of the fenestration. The third (anterior) partially thrombosed lobe surrounded by a blood clot extended to the subfrontal area superior to the tuberculum sellae anterior to the anterior communicating artery. The left A1 segment was hypoplastic [Figure 2]. Utilizing a frontotemporal trans-sylvian approach, proximal control of the right A1 segment; and following right gyrus rectus removal, distal control of both A2 segments was undertaken. The inferior fenestrated segment was dissected away from the fundus of the aneurysm that was insinuating in the space between the fenestrated A1 segments. A right-angled fenestrated clip was applied along the neck of the fusiform aneurysm. The patency of superior A1 fenestrated segment was maintained in the loop of the right-angled clip. An additional curved clip bolstered the clipping by obliterating the anterior lateral lobe of the aneurysm resting on the optic nerve and its extension into the third partially thrombosed anterior lobe (that had actually bled) [Figure 3]a, b and c. The lamina terminalis was opened. The post-operative course was uneventful and the patient was discharged on the 7 th post-operative day. She was following commands briskly but remained disoriented. There was no motor deficit.
|Figure 1: Computed tomography showing basifrontal, suprasellar, prepontine, interpeduncular and intraventricular hemorrhage|
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|Figure 2: CT‑angiogram showing (a) right A1 trilobed, fusiform aneurysm (arrow) with absent left A1; (b) The trilobed aneurysm (An 1, 2 and 3) arising from superior A1 fenestration (*) with bilateral A2 (curved arrow), (c‑d) posteromedial (An2) lobe of aneurysm visualized between A1 fenestration (*)|
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ACA fenestrations are seen in 0.1-7.2% patients,  more often in the distal A1 segment. They are often unilateral but bilateral fenestrations have also been encountered. An embryological remnant of the plexiform anastomosis between the primitive olfactory artery and the ACA; partial A1 duplication; its anomalous fusion; or an avascular remnant bifurcating the precursor vasculature are the proposed etiopathological mechanisms. ,,, Saccular aneurysms are frequently encountered on the proximal end of the A1 fenestration usually at the point of bifurcation.  They are due to defects in the tunica media at the bifurcating proximal and distal points of the fenestration. Direct hemodynamic stress on the vessel wall in the dominant A1 segment is also a major causative factor. Only a solitary report exists of a fusiform aneurysm associated with a fenestrated A1. 
The uniqueness of our patient was the existence of the proximal A1 fenestration in the dominant A1 artery. In addition, a fusiform aneurysm arose from the inferior surface of the superior A1 fenestration. Its fundus was insinuated in the space between the fenestrations with trilobulated (anteromedial, anterolateral and anterior) extensions on the sides. SAH due to rupture of a fusiform aneurysm is extremely rare. In our patient, the anterior lobule showed definite evidence of hemorrhage leading to its partial thrombosis with a surrounding extraluminal clot. The wide neck of the fusiform aneurysm may have been due to extension of the defects in the tunica media all along the length of the fenestrated segment. The lateral A1 segment supplies perforators to optic chiasma, anterior third ventricle, hypothalamus, anterior commissure, caudate nucleus, globus pallidus, anterior limb of the internal capsule and superior thalamus.  The points of origin of these perforators may have also been the regions of weakness with vulnerability for aneurysm formation. A wide angulation of the bifurcating point of the A1 fenestration may have led to a direct impact of the turbulent blood flow over a larger area of the wall of the superior fenestration leading to its fusiform dilatation. The rare reports of aneurysms occurring at the distal end of the fenestrated A1 segment may also be due to these proposed etiopathological factors.  The lobulated extension of the aneurysm and its subsequent rupture was probably due to inadequate space between the taut fenestrated A1 segments that forced the thin aneurysmal walls to expand on either side of the fenestration resulting in differential intraluminal pressure gradients.
During surgery, maintenance of luminal patency of both A1 fenestrations is of paramount importance. This is due to the fact that it was impossible to predict if blood flow through each individual fenestration would be adequate to support bilateral distal ACA circulation. A close examination prior to application of fenestrated clip to the neck of the fusiform aneurysm did not reveal any major perforators arising in close proximity.  Perhaps a major share of these perforators was arising from the inferior fenestrated segment of A1 that was dissected clear of the aneurysmal fundus during surgery. The complex anatomy and angulation of the fenestrated segments, the inability to unequivocally establish the ability of individual fenestrated A1 segments to adequately support blood flow to both distal ACAs, the fear of compromising perforating vessels and the risk of dislodging a thrombus (that has a propensity to occur at the site of turbulent blood flow due to the fenestrated vessels), increased the degree of difficulty both for surgery as well as for endovascular stenting or proximal fenestration occlusion.
In conclusion, the presence of A1 fenestration had a significant role in hemodynamic alterations that led to aneurysm formation. A fusiform aneurysm has lesser propensity to bleed. Yet, the anomalous vascular anatomy caused disproportionate pressure differentials in focal intraluminal areas within the fusiform aneurysmal sac leading to SAH.
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[Figure 1], [Figure 2], [Figure 3]