Ruptured Basilar Artery Perforator Aneurysm: Nightmare of a Treating Neurosurgeon

Abstract

Objectives Subarachnoid hemorrhage (SAH) resulting from rupture of basilar artery perforator aneurysm (BAPA) is a neurological rarity. With increased awareness and advancements in imaging modalities, they are now more frequently detected. However, concerns regarding their suboptimal treatment and lack of proper analysis still exist. We are hereby reporting our experience of treating this entity in a small cohort.

Materials and Methods It is a retrospective study of all the cases of SAH resulting from rupture of BAPA, which were treated by the same surgical team. Demographic data, treatment characteristics, and follow-up data of our cases along with published literature were studied.

Results Our cohort comprised of five patients (mean age 55 years). Three cases were treated with flow diverter alone and the rest underwent flow diverter and overlapping stent placement. Initial diagnostic cerebral angiography (digital subtraction angiography) was negative in three of them. There was one mortality and favorable outcome was encountered in the remaining cases. All of them demonstrated complete occlusion of the aneurysm in follow-up.

Conclusion Following treatment, all the cases demonstrated complete angiographic occlusion of the aneurysm. In available literature, studies have small sample sizes. Future randomized studies in a larger cohort and proper reporting and analysis of outcomes will help us formulating a treatment protocol for BAPA.

 

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Keywords

BAPA - DSA - FD - SAH - DAPT

Introduction

In clinical practice, incidence of basilar artery perforator aneurysm (BAPA) is very low and it continues to remain an enigma to the treating interventionist in the absence of an established management protocol. Ghogawala et al way back in 1996 reported the first case of BAPA.[1] Since then less than 100 cases of BAPA have been reported in the literature.[2] They often mimic basilar blister aneurysms and incidence is further affected because of the challenges associated with their detection in digital subtraction angiography (DSA). Aboukais et al defined these aneurysms based on the location of the aneurysm neck in a basilar perforator away from the parent trunk.[3] Most recently, Satti et al proposed a more detailed classification system based on angiographic images incorporating the tiny blister-like aneurysms in type 1 of the classification system.[4] BAPA can often escape detection in view of their tiny morphology, spontaneous thrombosis, and vasospasm of the very small feeding artery.[5] In view of their infrequent diagnosis and complicated natural history, there is no consensus regarding their ideal management protocol. Gardijan et al in their systemic review concluded that stenting can be considered as an effective occlusion method with an acceptable complication rate.[6] In this article, we are sharing our experience of treating ruptured BAPA in five cases by endovascular methods.

 

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Materials and Methods

It is a retrospective study of all the cases of BAPA treated by us via endovascular methods within a span of 5 years from May 2018 to May 2023. All of them initially presented with clinical symptoms and computed tomography (CT) findings suggestive of subarachnoid hemorrhage (SAH) involving the basal cisterns and posterior fossa. They were initially posted for urgent CT angiography (CTA) but irrespective of CTA findings, all of them underwent DSA within 24 hours of admission as per the standard imaging protocol. Both the vertebral arteries were injected with strong pump injections instead of hand injections. High-quality biplanar three-dimensional (3D) reconstructed spin and 3D rotational angiography images were routinely processed. Images were analyzed and reported at two separate levels to increase the diagnostic yield. BAPA was diagnosed based upon the DSA findings as per the classification system proposed by Satti et al.[4] Cases excluded in this study comprised of blister aneurysms except those which can be classified as type 1 according to the Satti classification, BAPA associated with another primary pathology like high-flow arteriovenous malformations/traumatic aneurysms, location of the SAH not correlating with the ruptured BAPA, and aneurysm arising from the main branches of the basilar artery. As per the institution protocol, patients with ruptured BAPA at our hospital were initially offered endovascular treatment. Neurosurgical backup was always available if required for procedural complications. Flow diverting stent was the initial device of choice. If the postdeployment vaso-CT showed incomplete apposition of the device to the vessel wall, angioplasty and/or an overlapping stent was deployed. For this, we routinely used the laser cut, nitinol, self-expanding Neuroform Atlas stent due to its unique hybrid design with proximal closed cells to facilitate microcatheter recrossing. They also have open cells distally to allow for better anchoring and wall apposition. If the initial DSA showed BAPA, patient was immediately placed on double antiplatelet regimen comprising of aspirin 75 mg daily and ticagrelor 90 mg twice daily for 5 days before the procedure. If the first DSA was negative, another DSA was repeated after 1 week. If the second DSA was positive for BAPA, therapeutic intervention was planned in the same setting under the cover of bolus Integrilin infusion instead of the standard regimen of double antiplatelet therapy (DAPT). The main idea behind it was to avoid any further delay in treatment due to concerns with rebleeding. The infusion was carried on till 6 hours postprocedure with overlapping DAPT. Immediate postprocedure contrast-enhanced magnetic resonance imaging (MRI) with magnetic resonance angiography was done within 24 hours of the procedure to rule out any ischemic complications and to look out for residual filling of aneurysm. Postprocedure, they were kept on regular follow-up. DSA was repeated after 3 months from the date of the procedure to check the degree of occlusion of the aneurysm. For angio-negative cases even after the second procedure, another DSA was proposed after a period of 3 months. At the time of discharge, patients were prescribed DAPT for a duration of 6 months followed by another MRI and were switched to aspirin monotherapy depending upon imaging findings.

 

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Illustrative Cases

Case Number 1

A 52-year-old male patient presented with World Federation of Neurosurgical Societies grade I and Fisher grade III SAH suggestive of bleeding from the rupture of a posterior circulation aneurysm. CTA failed to detect any aneurysm. DSA demonstrated a 6 × 7 mm distal BAPA. Patient was put on DAPT and flow diversion was planned after 5 days. However, angiography during the proposed therapeutic intervention showed no evidence of the aneurysm. Third angiography was performed after a week, and it demonstrated reappearance of a larger and irregularly shaped BAPA. Given the highly unstable nature of the pathology, a decision was taken to proceed with flow diverter (FD) placement under general anesthesia and bolus intravenous Integrilin infusion. A 4.5 × 10 mm Pipeline Flex (Medtronics) flow diversion device was deployed carefully covering the origin of the aneurysm. Vaso-CT confirmed good expansion but suboptimal stent apposition to the basilar artery. Therefore, a Scepter XC balloon catheter was prepped and advanced over the FD followed by angioplasty. Subsequently, an overlapping Neuroform Atlas 4.5 × 21 mm stent was deployed through the balloon catheter, which extended into the proximal left P1 to cover adequate length of the vessel. Control runs and final vaso-CT findings were satisfactory. Postprocedure MRI on day 1 did not reveal any adverse findings and he was discharged after 2 weeks on standard DAPT. After 1 week of discharge, the patient developed headache, vomiting, photophobia, and neck pain. On eliciting history, he informed about forgetting to take the prescribed antiplatelet medications. DAPT were restarted. Although initial clinical examination and CT brain did not reveal any alarming findings, subsequent MRI demonstrated evidence of evolving posterior circulation infarcts. Over the next few days, he had a steady neurological decline. Urgent DSA was performed to rule out any stent complications. It showed no evidence of stent occlusion or residual aneurysm but demonstrated partial nonopacification of the origin of the bilateral superior cerebellar artery. Subsequently, he developed bilateral cerebellar and brainstem infarcts. Urgent decompressive craniectomy was performed, but despite our best efforts he could not be saved ([Fig. 1]).

Fig. 1 Detailed figures of case 1. (A) Initial computed tomography (CT) scan demonstrating the subarachnoid hemorrhage (SAH). (B and C) Initial digital subtraction angiography (DSA) showing the basilar artery perforator aneurysm (BAPA) as indicated by the arrow. (D) Second DSA on the DSA showing resolution of the aneurysm. (E) Magnetic resonance imaging (MRI) with vessel wall imaging showing enhancement of the top of the basilar artery. (F) Follow-up DSA redemonstrating the aneurysm. (G and H) Post-flow diverter (FD and overlapping stent deployment still showing the filling of the aneurysm. (I and J) Follow-up DSA showing complete occlusion of the aneurysm. (K and L) Extensive infarcts visualized in MRI.

 

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Case Number 3

A 57-year-old patient with previous history of hypertension, presented with clinical and imaging findings suggestive of SAH resulting from rupture of BAPA. As per the standard protocol already described, a Pipeline Flex flow diversion (3.75 × 10 mm) device was deployed. Vaso-CT confirmed optimal placement of the device. Immediate postprocedure recovery and remaining hospital stay were uneventful. Following discharge, repeat DSA was performed after 3 months, which demonstrated complete occlusion of the aneurysm ([Fig. 2]).

Fig. 2 Details of case 3. (A) Computed tomography (CT) scan showing subarachnoid hemorrhage (SAH). (B and C) Digital subtraction angiography (DSA) images showing basilar artery perforator aneurysm (BAPA) as indicated by the arrow. (D) Follow-up DSA showing complete occlusion of the treated BAPA with patent appearance of the flow diverter stent.

 

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Case Number 5

A 71-year-old male with no significant past medical history presented with features suggestive SAH. Immediate CTA was nonconclusive, and DSA performed on the same day also failed to detect the culprit lesion. Repeat DSA performed a week later detected a BAPA measuring 3 × 2.5 mm. A Silk Vista flow diverting device (Balt) was deployed in the proximal basilar artery under the cover of bolus Integrilin infusion followed by angioplasty. Postdeployment runs were satisfactory. Postprocedure imaging showed a hematoma in the left cerebellopontine angle along with edema involving the brainstem up to the cervicomedullary junction. No restricted diffusion was seen in the medulla or pons. This could be explained by venous infarction or vasogenic edema rather than arterial ischemia. Patient finally recovered well and was discharged in stable condition with no new deficits. Follow-up DSA performed after 3 months showed complete occlusion of the BAPA ([Fig. 3]).

Fig. 3 Treatment details of case 5. (A) Computed tomography (CT) scan showing the subarachnoid hemorrhage (SAH). (B) Initial digital subtraction angiography (DSA) where no aneurysm is seen. (C) Delayed DSA demonstrating the aneurysm. (D) Flow diverter (FD) placement. (E) Post-FD DSA showing complete occlusion of the aneurysm. (F) Postprocedure magnetic resonance imaging (MRI) findings as described.

 

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Results

Five patients with BAPA were treated by us with endovascular approach. Three of them underwent only FD placement and in the rest FD with an overlapping stent were used. Demographic data and clinical findings of all the cases are included in [Table 1]. All of them presented to the emergency ward with symptoms suggestive of aneurysmal rupture. Aneurysmal risk factors were present in three cases. All of them had thick SAH suggestive of Fisher's grade 2 and above, but none of them had any neurological deficits at presentation. Initial DSA was able to detect BAPA in only two cases. Negative DSAs were again studied retrospectively to ensure that the reporting was correct. None of the patients in our cohort had rebleed. One of them experienced delayed ischemic complications. The single mortality in our series was due to brainstem and cerebellar infarcts secondary to stent thrombosis resulting from noncompliance of antiplatelet medications. Mean size of the BAPA was 3 × 3.7 mm. Majority of the patients belonged to Satti type IIA.

Table 1 Demographic and clinical data of the treated patients

No.	Age (y), Sex	Risk factors for SAH	Site of SAH in CT	CTA	WFNS grade	Fisher's grade	Any other procedure pre- or post-flow diversion
1	52, Male	Smoking	Basal cisterns	Negative	1	3	Decompressive craniectomy for posterior fossa infarcts
2	39, Female	None	Posterior fossa, basal cisterns	Negative	1	2	None
3	57, Male	Hypertension	Primarily basal cistern, B/L Sylvian fissure, and anterior interhemispheric fissure	Negative	1	3	None
4	55, Female	Hypertension	Posterior fossa, basal cisterns	Negative	1	2	None
5	71, Male	None	Basal cisterns, posterior fossa, B/L cerebellopontine angle (L > R)	Negative	1	3	None

Abbreviations: B/L, bilateral; CT, computed tomography; CTA, computed tomography angiography; L, left; R, right; SAH, subarachnoid hemorrhage; WFNS, World Federation of Neurosurgical Societies.

The regimen of antiplatelet drugs was decided as per our standard protocol. The angiographic data and outcome of treatment are detailed in [Tables 2] and [3]. Only one patient in our series had demonstrated complete occlusion of the aneurysm immediately following FD placement. All the surviving four cases did not have any long-term morbidities.

Table 2 Angiographic data of patients

No.	Size of the aneurysm (mm)	Satti type	Initial DSA	Number of diagnostic DSA performed prior to intervention	Regimen of antiplatelet drugs for treatment	Re bleeding	Radial/Femoral
1	6 × 7	IIA	Positive	3	DAPT with bridging Integrilin	No	Femoral
2	2 × 3	IIb	Positive	1	DAPT	No	Femoral
3	1 × 2	I	Negative	4	DAPT	No	Radial
4	3 × 4	IIA	Negative	1	DAPT	No	Radial
5	3 × 2.5	IIA	Negative	2	DAPT with bridging Integrilin	No	Femoral

Abbreviations: DAPT, double antiplatelet therapy; DSA, digital subtraction angiography.

Table 3 Outcome of treatment following endovascular Intervention

No.	Immediate satisfactory occlusion (according to OKM scale)	Occlusion observed in follow-up DSA (according to OKM scale)	Rescue treatment	Ischemic complications	Follow-up duration (mo)	Good outcome (mRS < 2)	Mortality
1	B	D	Overlapping stent	Yes	N/A	N/A	Yes
2	B	D	Overlapping stent	No	12	0	−
3	B	D	None	No	6	1	−
4	A	D	None	No	10	0	−
5	B	D	None	No	24	0	−

Abbreviations: DSA, digital subtraction angiography; mRS, modified Rankin Scale; N/A, not available; OKM, O'Kelly–Marotta.

 

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Discussion

In published literature, contribution of BAPA to aneurysmal SAH is minimal.[7] We came across 28 published articles of BAPA-related SAH and all of them were either observational case series or individual case reports ([Table 4]) suggesting rarity of the studied entity. Their actual incidence is underestimated by their low detection rate due to vasospasm of the tiny perforators in acute setting. They are also prone to spontaneous thrombosis resulting in negative DSA findings. Even in our small cohort, we had to perform more than one DSA prior to intervention in 60% of our cases (n = 3). Chavent et al in their article have reported around 50% overall diagnostic difficulties, which are encountered with an initial negative angiogram in ruptured BAPA.[8] We feel that to increase the detection rates, it is very important to have a proper dedicated imaging protocol with strong pump injections in a relaxed patient with optimum sedation. We also recommend injecting both the vertebral arteries to overcome flow artifacts in the main basilar trunk. Timing of repeat DSA following the initial negative DSA is still controversial and our literature search failed to find any conclusive opinion regarding it.[8] [9] [10] We also did not find any separate etiological factors for BAPA other than the already established factors for aneurysms in general. Interestingly, Sanchez et al in their article highlighted the DSA findings that can be suggestive of vessel dissection as the etiological factor.[11]

Table 4 List of different treatment modalities reported for the treatment of BAPA in 80 patients

Primary method of treatment	No. of patients	Complete occlusion of aneurysm	Sub optimal occlusion (A)	No long-term DSA follow- up	Long-term morbidity (mRS > 2)	Re bleeding (B)	Mortality	Rescue treatment (C)	Treatment failure (A + B + C)
Conservative	16	12	4	4	3	2	2	0	6
Surgery	6	6	−	0	2	0	0	0	0
Flow diversion	31	29	2	2	5	0	2	0	2
Overlapping stents	11	8	2	1	1	1	1	1	4
Coiling	10	7	0	0	2	0	0	3	3
Electrolysis	3	2	0	0	0	0	1	1	1
Others	3	2	1	0	1	0	0	0	1

Abbreviations: BAPA, basilar artery perforator aneurysm; DSA, digital subtraction angiography; mRS, modified Rankin Scale.

Regarding the management, several authors in the past have emphasized the satisfactory outcome of these aneurysms with conservative treatment alone, thereby mitigating the associated treatment risks and complications.[10] [12] It is also to be remembered that while planning for endovascular treatment in ruptured BAPA, it is often very difficult to have proper working projections due to difficulty in visualizing the orientation of the neck of the aneurysm with the perforator. Granja et al in their very recently published systematic review, found that both active treatment and conservative approaches are used to treat nontrunk BAPAs with positive outcomes and the rate of successful functional outcome were similar between the two groups.[2] They reported satisfactory aneurysm resolution on conservative management and mean duration of time taken for it to happen was 3.6 months. Most recently, Gardijan et al has also compared the results between stenting and conservative management of posterior circulation perforator aneurysms and their analysis showed no statistically significant difference between the groups, except for the occlusion rate, which was higher in the treatment group.[6]

When contemplated, treatment of BAPA is very challenging. Marinković and Gibo in their article described three groups of basilar perforators: caudal, middle, and rostral, and discussed the possible clinical significance of the anatomical data.[13] In the past, there have been many publications outlining results of surgical management of BAPA.[1] [11] [13] [14] [15] [16] However, there are inherent difficulties associated with clipping for BAPA as depicted by Sanchez et al in view of lack of a proper neck. Mathieson et al also mentioned about technical challenges in securing proximal control, dissecting the subpial plane around the aneurysmal sac and preserving the adjacent critical neurovascular structures in surgery.[15] Different methods of endovascular treatment have also been successfully employed in the past to treat BAPA, although it is not without significant challenges.[2] [3] [5] [6] [7] [9] From the work of Marinković and Gibo, the caliber of middle perforators of basilar artery is relatively larger and cannulation of them with a micro-guidewire may be feasible for coiling without causing occlusion of the vessel. However, micromanipulation within BAPA is associated with hazards as reported by Darsaut et al.[17] Ma et al in 2021 have published their initial work of treating three cases of BAPA with endovascular electrothrombosis, which has the potential to be a promising alternative by eliminating the need of coils and stents, but it requires further research to confirm the safety and efficacy.[18]

In our small cohort, we have treated all the cases exclusively with endovascular methods. The logic to opt for therapeutic intervention and not for conservative management in part has been influenced by the fact that all our cases presented with good neurological status and any episode of rebleeding during conservative management would have had an adverse outcome. In acute setting, there is increased propensity of vasospasm of the already tiny perforators and hence we did not try to cannulate these vessels to occlude the aneurysm. We preferred the use of FDs to overlapping stents mainly because they have lower porosity, thereby having the potential to cause occlusion of the aneurysm within a shorter span of time. This also translates to lower risk of rebleeding. However, lower porosity can act like a double-edged sword too as they are more prone to cause ischemic complications than stents as is evident in [Table 4]. In our series, there was one mortality that translates to overall rate of 20%. However, the main cause of mortality was ischemic complications resulting from the noncompliance of DAPT and was not related to procedural complications. Diligent antiplatelet management must be emphasized to all the patients after any therapeutic intervention to prevent ischemic complication resulting from noncompliance of the same. Our literature search yielded wide variations in antiplatelet regimens in different cohorts, although it did not affect the long-term outcome of FD.[19]

Another challenging aspect of FD is that they have a very narrow landing zone proximal to basilar bifurcation. It is further complicated by the fact that these devices also shorten in length after deployment. Therefore, to achieve the desired level of accuracy in deployment, it requires a lot of technical competence. We did not encounter any treatment failure suggested by combination of unsatisfactory occlusion of the aneurysm, conversion to a second rescue procedure, and a rebleeding episode. The encouraging results of FD in our cohort may also be related to the fact that all the cases were related to the middle group of basilar perforators, which are bigger vessels compared with rostral and caudal perforators.[13] In larger cohorts the incidence of ischemic complications post-FD are very high and are reportedly seen in more than a quarter of the cases.[5] [19] Despite this associated risk, the functional significance of these vessels based on site is unclear given the extensive anastomosis within themselves.[13] Gardijan et al in their recent meta-analysis of smaller cohorts of BAPA managed by stenting (single stents [10%], telescoping stents [stent-in-stent, n= 45%], or FD stents [45%]) reported overall favorable outcome of 90% in their review. Various flow studies done in the past have also demonstrated the beneficial effects of stents in perforator aneurysms.[20] [21] The porosity of the stent is inversely proportional to the hemodynamic effects on the aneurysm and risk of perforator occlusion.[21] The studies that were reviewed by us were limited to those in humans and there were no restrictions in terms of language and study design. We also went through the references of individual articles and studied the relevant articles. We could not find any randomized controlled study for BAPA and hence based our opinion upon case series and individual case reports.

 

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Conclusion

Considering the paucity of available literature, natural history and progression of BAPA still remain an unsolved mystery to the treating interventionist as also the overall long-term efficacy and incidence of ischemic complications of FD. It is further compounded by the fact that in around 15% cases presenting with spontaneous SAH, initial imaging fails to demonstrate the etiology[22]; yet, the share of BAPA's contribution to it remain relatively uninvestigated. Based on our literature search, initial conservative trial in a very tiny BAPA associated with a small perforator may be a viable option, although the risk of rebleeding persists. We also do not think that coiling should be attempted in BAPA more so in acute setting. However, by now there is plenty of evidence to suggest the efficacy of FD in their treatment even in giant BAPA[23] with good long-term outcome. While planning for FD, benefits of the procedure with potential risks too should be taken into consideration. Future randomized multicenter prospective trials in this direction are the need of the hour to investigate this rare entity and shed light in areas that are still obscure to us.

 

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Conflict of Interest

None declared.

Authors' Contributions

P.S. contributed to the concept, design, data collection and analysis, review of literature, and manuscript writing. A.A. was involved in manuscript writing and data collection, while A.K.S. also contributed to manuscript writing and data collection.

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Publication History

Article published online:
06 March 2025