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ORIGINAL ARTICLE
Year : 2019  |  Volume : 67  |  Issue : 5  |  Page : 1257-1263

Microvascular Clipping of A1 Segment Aneurysms


Department of Neurosurgery, Armed Forces Medical College, Pune, Maharashtra, India

Date of Web Publication19-Nov-2019

Correspondence Address:
Maneet Gill
Department of Neurosurgery, Armed Forces Medical College, Pune, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.271266

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 » Abstract 


Background: Aneurysms arising from the proximal segment (A1) of the anterior cerebral artery (ACA) are relatively rare. Because of their small size, abnormal location in relation to the parent artery and the risk of damage to the surrounding perforators, their surgical management is a big challenge. We present our experience with 7 patients of A1 segment aneurysms.
Settings and Design: Tertiary care referral center.
Materials and Methods: Seven patients who were diagnosed with A1 aneurysms between 2009 and 2017 were included. Preoperative evaluation included Non-Contrast Computed Tomography (NCCT) head and angiography (Digital Subtraction Angiography with/without CT-Angiography). The clinicoradiological condition of the patients was graded as per World Federation of Neurological Surgeons (WFNS), Fisher and Hunt and Hess (H and H) Grading systems. A retrospective review of clinical features, radiological descriptions, surgical treatment, and outcomes was done.
Results: All patients underwent microneurosurgical clipping. All aneurysms were saccular, ranging in size from 4 to 14 mm and neck size varied from 2 to10 mm. Most aneurysms 5 (71.4%) had a posterior direction. Anatomical variations were noticed in 3 (42.8%) patients. Posteroinferiorly directed aneurysms were difficult to clip. As per Glasgow Outcome scale (GOS), 6 (85.7%) patients had a good outcome, whereas 1 (14.2%) had poor outcome. As per the modified Rankin Scale (mRS) too, 6 (85.7%) had a favorable outcome. There were no deaths.
Conclusion: A1 aneurysms are frequently associated with vascular anomalies and generally rupture when small. A1 aneurysms with a superior and anterior direction are relatively easy to clip whereas those directed postero-inferiorly are difficult. Close association with critical perforators also compounds the situation. Due to the rarity of A1 aneurysms, large series are few in literature.


Keywords: A1 Aneurysms, anterior cerebral artery, fenestrated A1 aneurysm
Key Messages: A1 aneurysms are rare, anatomically variable and angiographically tricky. They diverse clinical manifestations and pose a multitude of challenges to surgical clipping. Proper pre-operative anatomic delineation and planning is an essential pre-requisite to sucessful surgical treatment of these aneurysms.


How to cite this article:
Gill M, Maheshwari V, Mukherjee A, Gadhavi R. Microvascular Clipping of A1 Segment Aneurysms. Neurol India 2019;67:1257-63

How to cite this URL:
Gill M, Maheshwari V, Mukherjee A, Gadhavi R. Microvascular Clipping of A1 Segment Aneurysms. Neurol India [serial online] 2019 [cited 2019 Dec 10];67:1257-63. Available from: http://www.neurologyindia.com/text.asp?2019/67/5/1257/271266




Aneurysms of the proximal segment of anterior cerebral artery (A1segment aneurysm) are rare and account for less than 1% of all intracranial aneurysms.[1] They usually rupture even when small in size, may produce lobar hemorrhage rather than a subarachnoid hemorrhage (SAH) and are frequently elusive in pre-operative angiograms.[2] They are unique in being frequently associated with vascular anomalies and multiple intracranial aneurysms.[2] All this coupled with the highly variable course of the A1 segment of the anterior cerebral artery (ACA), the atypical location of the aneurysm with respect to the parent artery and its proximity to critical perforators makes aneurysms of this region a challenge to treat.[3],[4] As they are encountered relatively infrequently even in high volume neurovascular centers, only a few series have been reportedin the literature.[5],[6] In this study, we report 7 patients diagnosed with A1 aneurysms whom we treated with surgical clipping.


 » Materials and Methods Top


Seven patients with age range 23–75 years were diagnosed with A1 aneurysms and underwent microneurosurgical clipping between 2009 and 2017. The preoperative condition of the patients with a ruptured aneurysm was assessed with the World Federation of Neurological Surgeons (WFNS) grade, Fisher's grading and Hunt and Hess (H and H) SAH Grading System. SAH was graded as per Non-Contrast Computed Tomography (NCCT) head findings. Digital Subtraction Angiography (DSA) was done in all patients to study the aneurysm morphology. Some patients also had a CT-Angiography (CTA). Radiological description included the aneurysm size including dome/neck ratio, location, fundus direction, any associated vascular anomaly, and presence of multiple aneurysms. Clinical outcome was assessed by Glasgow Outcome Scale (GOS) and modified Rankin Scale (mRS) at discharge. The radiological outcomes of surgically treated patients were assessed by postoperative DSA.


 » Results Top


The clinical and angiographic features of the patients are shown in [Table 1] and [Table 2]. There were 7 patients with A1 aneurysms of which 4 were males (57%) and 3 were females (43%). The mean age of the patients at presentation was 49.3 years (range, 23–75 years). Three patients had associated co-morbidities in the form of hypertension, Coronary Artery Disease (CAD) or diabetes mellitus. All patients had ruptured aneurysms and presented with SAH. On admission. H and H grades were Grade 1 in one, Grade 2 in two, Grade 3 in two and Grade 4 in two [Table 1]. The WFNS grades were Grade I in three, Grade II in one, Grade III in two and Grade IV in one [Table 1]. The mean interval between the ictus and surgery was 3.7 days (Range 2-7 days). SAH was seen in all seven patients, two (28.5%) had associated Intra-cerebral hemorrhage (ICH), two (28.5%) had an associated Intra-ventricular hemorrhage (IVH) and one (14.2%) had acute Rt Middle Cerebral Artery (MCA) infarct at presentation [Table 1]. Headache was the most common presentation seen in 5 patients (71.4%). One patient presented to the Neurology Out-patient Department (OPD) with seizures followed by aphasia, left hemiplegia and left Upper Motor Neuron (UMN) VIIth nerve palsy. On NCCT head there was suspicion of acute infarct of the Rt MCA territory. Magnetic Resonance Imaging (MRI) brain confirmed the presence of an infarct and MR Angio revealed an aneurysm arising from the proximal A1 segment just distal to the Internal Carotid Artery (ICA) bifurcation. DSA of this patient confirmed the aneurysm and showed severe spasm of surrounding vessels [Figure 1].
Table 1: Clinical features and outcome of the patients

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Table 2: Angiographic features of the patients

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Figure 1: (a) T2 MRI showing pre-op infarct of the gangliocapsular region on the right side. (b) MR Angio showing aneurysm arising from the proximal A1 segment just distal to the ICA bifurcation. (c) DSA Rt ICA lateral shoot showing the aneurysm along with severe pre-op spasm of the surrounding vessels

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Aneurysms ranged in size from 4 to 14 mm (mean, 7.2 mm), with neck size ranging from 2 to 10 mm (mean, 4.4 mm), dome/neck ratio ranging from 1.4 to 2.0 (mean 1.7) [Table 2]. All aneurysms were saccular and all but 1 were on the right side.

The combined imaging modalities showed morphological variations in 3 (42.8%) patients in the form of contralateral A1 hypoplasia in two patients and azygos A2 of the “bihemispheric type” along with contralateral A1 hypoplasia in one patient [Table 2]. At surgery one case was found to have fenestrated distal A1 with a multilobulated aneurysm arising from the proximal end of the fenestration (Kwon et al. Type 1) [Figure 2]. The pre-op CT Angiogram and DSA had missed the finding of the fenestrated A1 and the aneurysm was reported as an AComm (Anterior Communicating) artery aneurysm. Most A1 aneurysms 3 (42.8%) had a posterior direction while one each were directed postero-superiorly, postero-inferiorly, superiorly and anterosuperior [Table 2]. All the aneurysms except the one arising from the A1 fenestration were located on the proximal A1 segment. There were no patients with multiple aneurysms.
Figure 2: (a) Pre-op CT angio showing the aneurysm reported as arising from A1-Acomm artery junction with non-visualization of the contralateral A1 and a single azygos A2. (b) Pre-op DSA showing the aneurysm arising from the A1- AComm junction with Azygos A2 of the “bihemispheric type”, DSA was reported as AComm artery aneurysm. (c) Pre-op DSA showing hypoplasia of the contralateral A1. (d) Intra-operative picture showing the fenestrated A1 with aneurysm. (e) showing the aneurysm neck clipped with a fenestrated clip. (f) Post-op DSA: both limbs of fenestrated A1 and distal azygous A2 filling well

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Surgically the aneurysms directed posteriorly and posteroinferior were more difficult to clip as these were found to be obscured by the trunk of the A1. The one arising from the distal A1 fenestration was clipped with a fenestrated clip with an inferior limb of the A1 fenestration taken in the fenestration of the clip [Figure 2]e. One large aneurysm with the appearance of an ICA bifurcation aneurysm on pre-operative DSA was found to be arising from the proximal A1 intra-operatively [Figure 3]. The dome of this one overrode the A1 such that control of the parent vessel was especially difficult. In one of the patients with a postero-inferiorly directed aneurysm, mobilization of the ICA and MCA was necessary for clipping the aneurysm [Figure 4]. The dome of the aneurysm in this patient was obscured by the A1 [Figure 4]d. This patient developed a dip in sensorium on the 7th post op day. NCCT head showed no rebleed/infarct. Transcranial Doppler showed vasospasm. Existence of vasopasm of bilateral ACA and MCA was confirmed on DSA [Figure 4]f. He was treated with triple H therapy and intra-arterial milrinone. He had a stormy post op course further complicated with aspiration pneumonitis.
Figure 3: (a) Pre-op CT Angio with showing Large aneurysm arising from the region of the ICA bifurcation. (b and c) Pre-op DSA Rt ICA Lateral and Towne's view showing the aneurysm, A1 is obscured by the aneurysm, the suspicion was that of an ICA bifurcation aneurysm. (d) Intra-operative image showing the dome of the large aneurysm obscuring the Rt A1. (e) Post clipping image showing the broad neck of the aneurysm arising from the proximal A1 just distal to the ICA bifurcation. (f) Post op DSA showing the clip in situ with complete exclusion of the aneurysm, patent Rt A1 and good distal flow

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Figure 4: (a) Pre-op 3D CT Angio images showing the aneurysm hidden behind the A1. (b) Pre-op DSA Rt ICA AP view showing aneurysm arising from the proximal A1. (c) Pre-op DSA Rt ICA Lateral view showing the multilobulated aneurysm with the fundus directed postero-inferiorly. (d) Intra-operative image showing the aneurysm neck with the dome hidden behind the parent A1. (e) Intra-operative image showing the clipped neck of the aneurysm with patent A1. (f) Post Op DSA Rt ICA AP shoot showing the clip in situ with complete exclusion of the aneurysm, severe vasospasm was noted in the Rt ACA and MCA

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There were no intra-operative ruptures, post op hemorrhage or fresh post-op infarcts. Complete aneurysm exclusion was seen in all patients with patency of parent vessel and good distal flow.

Outcomes were assessed as per GOS and mRS [Table 1]. As per (GOS), 6 (85.7%) patients had good outcomes (i.e., GOS 4 and 5). As per mRS also 6 (85.7%) patients had favorable outcomes (i.e., mRS ≤2). Of these two were mRS 0 (no symptoms at all), one mRS 1 (able to carry out all usual duties despite symptoms) and three were mRS 2 (Slight disability but able to look after own affairs without assistance) including the one patient with pre-op hemiplegia whose weakness improved post-operatively. Overall 1 (14.2%) with GOS 3 and mRS 5 at discharge had poor outcomes due to complications like vasospasm and aspiration pneumonitis [Table 1]. There were no deaths.


 » Discussion Top


A1 segment aneurysms are rare and reported to be <1% (range 083.4%) of all intracranial aneurysms in literature.[1],[6],[7] Unlike some of the previous series, ours has more males than females.[8],[9],[10] These aneurysms are usually small and can rupture at a smaller size when compared to other aneurysms. In several series, the size of most ruptured A1 aneurysms has been less than 7 mm.[1],[2],[11],[12] In our series average size of ruptured A1 aneurysms were 7.2 mm (range, 4–14 mm). These aneurysms have a fragile wall and due to their propensity to rupture, unruptured A1 aneurysms require surgical intervention even when they are small. They often present as one in multiple aneurysms. However, in comparison to the previous series which report multiplicity ranging from 18% to as high as 73%, our series had no multiple aneurysms.[2],[3],[7],[13] One of the unique features of these aneurysms is their frequent association with various vascular anomalies.[1],[2][3],[11],[12] Contralateral A1 hypoplasia was seen in three (42.8%) of our patients and one of these three also had an aneurysm arising from the proximal part of fenestrated distal A1 (Kwon et al. Type 1)[14] with azygos A2 of the “bihemispheric type”. During the 18–43 mm stage of embryo, the distal segment of the ACA forms a plexiform anastomosis with the primitive olfactory artery.[15] The failure of fusion of the same, an avascular remnant intercepting the primitive precursors or partial duplication of the A1 may lead to fenestration of the A1 segment of the ACA.[16],[17],[18] The angulation of the artery at the bifurcating point of the A1 fenestration means a larger surface area of the vessel is impacted by the turbulent blood flow leading to its aneurysmal dialatation as has been proposed by some authors.[19] The location of the aneurysm with respect to the A1 fenestration may vary based on which Kwon et al. classified them into three subtypes.[14] Type I located on the proximal end of the A1 fenestration (as seen in our case), Type II arising from the trunk of the fenestrated A1 and Type III which involves multiple aneurysms in the fenestration.

A1 aneurysms are often missed on pre-operative imaging. A posteriorly directed aneurysm overlapped by the main A1segment or covered by the frontal lobe, vasospasm of the parent vessel, associated vascular anomalies in addition to the fact that these are usually small in size when they rupture are some factors that may lead to their non-visualization on the pre-operative angiogram. They can be located proximally or distally on the A1 segment which can frequently be mistaken for an ICA bifurcation or an AComm Artery aneurysm respectively as seen in two of our cases [Figure 2] and [Figure 3]. Hence in pre-operative DSA of these aneurysms accurate assessment of origin of aneurysm neck is important. Visualization of the A1 segment proximal and the distal to the aneurysm is essential.[3] In an ideal scenario, it is useful to distinguish these aneurysms from Acomm or ICA aneurysms pre-operatively for proper surgical planning. The diagnosis of these aneurysms, therefore, requires high a degree of suspicion with performance of multi-dimensional views for corroboration.

Various authors have tried to classify A1 segment aneurysms into proximal, middle, and distal-based on their location on the parent artery as well as their direction.[7] Surgical approaches to those located proximally or distally are more or less similar to ICA bifurcation and Acomm aneurysms respectively while those of the mid-segment have been reported less frequently. In our series all but one were located proximally with the one located distally arising from a fenestrated A1.

One of the unique characteristics of A1segment aneurysms is the perforators surrounding them, those arising from the proximal A1 and the posteriorly directed ones being more vulnerable. Their number ranges from two to 15, with an average of eight supplying the optic chiasm, anterior third ventricle, hypothalamus, anterior commissure, caudate nucleus, globus pallidus, anterior limb of the internal capsule, and superior thalamus.[1],[3] SAH in close proximity with the perforating vessels may lead to ischemia of the gangliocapsular region. One of our patients, as stated previously, had presented with left hemiplegia and left UMN VIIth nerve palsy. MRI brain confirmed the presence of an infarct and DSA revealed an aneurysm arising from the proximal A1 segment just distal to the ICA bifurcation associated with spasm in the surrounding vessels [Figure 1].

Most studies have reported posteriorly directed A1 segment aneurysms to be more common.[1],[2],[6],[11] In these cases, preservation of intimately associated perforators has been found to be more difficult due to their unusual location and being obscured by the parent artery. These perforators are also seldom appreciated in pre-operative DSA or CT angio due to their small size. In our study five aneurysms (71.4%) were directed posteriorly. Among them in those projecting postero-inferiorly, dissecting away the perforators and clipping has been found to be more difficult when compared with those directed otherwise. One of our patients developed severe post-operative vasospasm with abrupt cut-off of the A1 segment and early thrombus build up for which intra-arterial vasodialators and rTPA thrombolysis were instituted. Wide splitting of the Sylvian fissure to mobilize the MCA and ICA improves the visualization of these aneurysms and was strictly followed in all of our cases. A1 segment aneurysms are relatively difficult to dissect than ICA bifurcation or AComm artery aneurysms because their fundus is often buried in the frontal lobe unlike the other two. In the case of ICA bifurcation aneurysm, splitting of the Sylvian fissure gives adequate proximal control and in case of AComm artery aneurysms, gyrus rectus resection does the same. However A1 aneurysms have a high propensity for intra-operative rupture during retraction of the frontal lobe and hence excessive retraction of the frontal lobe during sylvian fissure dissection should be avoided before proximal control could be obtained. There were no intra-operative ruptures in our series. Optimum timing of surgery is debatable and evidence of early surgery leading to good neurological outcome is lacking especially in patients with poor pre op WFNS grades. Present trends are towards early surgery preferably within the first 3 days of bleeding prior to the onset of vasospasm to reduce the risk of rebleeding and for effective treatment of vasospasm.[20],[21] Four (57.1%) of our patients underwent surgery within 3 days of ictus. All of them had good outcome. Three patients underwent late surgery as they presented relatively late after the ictus. Of them, one had severe fresh disability (GOS 3, mRS 5). In our series the pre-op WFNS and H and H grade of the patients influenced the surgical outcome with complications such as vasospasm and neurodeficits leading to poor outcome being more common in Grade III and IV patients.

Endovascular coiling of A1 aneurysms is considered hazardous due to some of their inherent characteristics like small size, sessile nature, wide neck directed along the long axis of the parent vessel (with no bifurcating points) and location on the proximal A1 with predominant posterior direction. Due to these features, there is a high risk of coil slippage, incomplete embolization or rupture.[13],[22] While recent articles on endovascular coiling of A1 aneurysms are reporting encouraging results, till the recent past surgical clipping has formed the mainstay of treatment for A1 aneurysms.[23],[24]

Our study has its limitations with the number of cases in our series being small and all data were retrospectively analyzed.


 » Conclusion Top


A1 segment aneurysms are rare. They are unique and different from other aneurysms due to their increased propensity to rupture when small, association with multiple aneurysms and abnormal location with respect to the parent vessel. They are difficult to visualize and accurately localize to the A1 segment in pre op angiography. The abnormal anatomy, vascular anomalies, and intimate association with critical perforators make them challenging to deal with surgically. Postoperative parent vessel and perforator vasospasm in spite of the best surgical technique is a significant limiting factor to the successful management of these aneurysms. Adequate preoperative anatomic localization and surgical planning is nevertheless the key to the successful management of these aneurysms.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
 » References Top

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Kwon WK, Park KJ, Park DH, Kang SH. Ruptured saccular aneurysm arising from fenestrated proximal anterior cerebral artery: Case report and literature review. J Korean Neurosurg Soc 2013;53:293-6.  Back to cited text no. 14
    
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Sonda I, Basso LS. Fenestrated A1 segment of right anterior cerebral artery associated to duplicated anterior communicating artery: Anatomy 2015;9:42-4.  Back to cited text no. 15
    
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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. 16
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2]



 

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