Introduction
Intracranial blister aneurysms are uncommon vascular pathology with difficulties encountered
in diagnosis as well as management compared with the classical berry aneurysms. Ohara
et al reported the first case series of supraclinoid internal carotid artery (ICA)
aneurysm involving its dorsal wall and nonbranching site with extremely fragile nature.
They described these aneurysms as wide neck, half dome-shaped and nonbranching site
aneurysm with adjacent parent artery involvement. Furthermore, an emphasis was given
on their management, as these aneurysms require different surgical techniques to exclude
them completely from the cerebral circulation compared with traditional one for classical
berry aneurysm.[1] Takahashi used the word “blister” for the first time for these types of aneurysms
in 1988 in Japanese literature.[2]
The overall incidence of blister aneurysm is approxi- mately 0.5 to 2% among all ruptured
cerebral aneurysms.[1] Few case series have kept the term blister aneurysm restricted to only the supraclinoid
ICA segment. However, other locations described in English literature are anterior
communicating artery (ACOM), basilar artery (BA), and middle cerebral artery (MCA).[3]
[4]
Pathology
Histopathological analysis of these aneurysms has been studied extensively and described
for the ICA blister location. Ishikawa et al reported blisters as focal arterial wall
defect covered with thin fibrous tissue. It is basically platelet plug overlying thin
adventitia, which covers defect in intima and media lacking the collagen layer. These
features resemble pseudoaneurysms more in comparison to classical berry aneurysms,
which show thickened media and adventitia.[5] This unique morphology of blister aneurysm is responsible for the change in size
as well as shape of blister aneurysm in a short period of time. Two basic pathologies
have considered to be responsible for blister aneurysm formation, dissection, and
atherosclerosis. Focal dissections have been reported, based on angiography and intraoperative
findings, but never proved on histopathological analysis. Association of blister aneurysms
and atherosclerosis has been proved, based on histopathological analysis. Based on
these findings, atherosclerosis and subsequent ulceration can be a factor in the formation
of blister aneurysm.[6] Ogawa et al have suggested association between location of blister aneurysm and
systemic hypertension with subsequent increased hemodynamic stress.[7] Exact pathogenesis is still unclear, but all these associations lead to extremely
fragile aneurysms with adjacent parent artery involvement and high tendency to rupture.
Diagnosis
Considering aggressive natural history of blister aneurysms, diagnosis becomes the
key for the early and better management. Computed tomography (CT) and magnetic resonance
angiography (MRA) may miss these lesions, owing to their small size, adjacent bony
structures, and atypical location. Diagnostic cerebral angiography is gold standard
for the diagnosis of blister aneurysm. Typical angiographic features are wide neck,
different shapes (fusiform, sessile and saccular) at nonbranching location, adjacent
parent artery involvement near the neck of aneurysm, stasis of contrast, and change
in morphology over short duration. Changes in aneurysm morphology is considered secondary
to organization of blood clot covering the focal arterial wall defect.[8] These morphological features separate them from the classical berry aneurysm of
cerebral circulation.[9] Digital subtraction angiography (DSA) with three dimensional (3D) rotational angiography
helps in correct diagnosis as well as proper treatment planning of blister aneurysm.
In the authors’ experience, performing DSA in the angles determined using 3D images
reveals the true morphology of these aneurysms. In case of initial negative angiogram,
early repeat cerebral angiogram is recommended in suspicious cases.
Management
Considering their extremely fragile wall, lack of definitive neck, small size, and
tendency to rerupture as well as regrowth, management of these aneurysms also differs
considerably in terms of surgical as well as endovascular approaches. Surgical clipping
as a standalone technique has high rates of intraoperative rupture, ischemic complications,
and significant recurrence. Gonzalez et al have reported overall intraoperative rupture
risk of 28% for blister aneurysms.[10] Modifications in surgical approach such as clipping plus wrapping, parallel clipping
with involvement of adjacent parent artery, clipping with vascular encircling graft,
and trapping with or without bypass have been applied in clinical practice.[8]
[11]Peschillo et al in their meta-analysis of 334 patients of ruptured blister aneurysms
reported better clinical outcome in endovascular arm (78.9%) in comparison to surgical
arm (67.4%). Combined perioperative morbidity-mortality was more in surgical arm (20
vs. 9%).[9] Meta-analysis of surgical management of blister aneurysms has reported surgical
morbidity and mortality of approximately 21% and 17%, respectively.[10] In a systematic review, clipping alone had highest risk of postoperative aneurysm
regrowth (30%).[12] In comparison to surgical arm, endovascular approach has significant less morbidity
as well as mortality. Ren et al published their retrospective single center data of
ruptured blister aneurysm (n = 83) managed with microsurgery (n = 33) and endovascular (n = 50) approaches. Clipping alone (27/33) and stent-assisted coiling (49/50) were most
commonly used techniques in microsurgical and endovascular treatment, respectively.
They reported more intraoperative aneurysm rupture in the surgical group (14 vs. 4).
Favorable clinical outcome was seen in endovascular group in comparison to microsurgery
(76 vs. 54%). Rebleed rates and retreatment rates were not statistically significant
among two groups.[12] Overall, endovascular group had favorable clinical outcome, less morbidity-mortality,
and less incidence of vasospasm-related complications in comparison to the microsurgery
group. In meta-analysis of large studies of blister aneurysm treated with endovascular
techniques, overall reported morbidity-mortality was 13.4 and 7.3%, respectively.[13] Recently, endovascular approach has gained popularity in treatment of blister aneurysms,
especially after the introduction of flow diverters (FD), which has become the standard
method of treatment over the last few years. Overall, endovascular techniques are
divided into the deconstructive and reconstructive approach. Deconstructive approach
involves parent artery occlusion with or without bypass. Reconstructive approach involves
balloon/stent-assisted coiling, single/overlapping stents, covered stent placement,
balloon/stent-assisted onyx embolization of the aneurysm sac, and FD stents.[13]
Reconstructive Technique
Reconstructive technique mainly aims to exclude the aneurysm from cerebral circulation
by maintaining parent artery blood flow.
Aneurysm Coiling
Small size of the aneurysm sac and extremely fragile dome makes the aneurysm sac catheterization
extremely difficult with high risk of intraoperative rupture. Wide neck of the aneurysm
poses significant doubts about coil mass stability inside the aneurysm sac. Coil prolapse
and thromboembolic complications are very high in these cases. Dynamic nature of the
underlying disease can result in high chance of aneurysm regrowth and rerupture in
future. Park et al have reported regrowth of the aneurysm in all four cases of endovascular
primary coil embolization of blister aneurysm with two of them rebleed.[15] Overall, simple/balloon-assisted coiling has high risk of intraoperative rupture,
thromboembolic complications secondary to coil prolapse, recurrence, and rerupture.
In fact, balloon inflation can be potentially hazardous in blister aneurysm, as underlying
parent vessel near the neck is mostly involved in blister aneurysms.
Stent (Monotherapy or Overlapping)/Stent-Assisted Coiling
Stent-assisted coiling can provide potential advantages of coiling (leading to immediate
aneurysm occlusion) and stenting (parent artery reconstruction to avoid recurrence).
However, it is technically challenging and increases complexity of the procedure.
Multiple case series have reported the use of stent-assisted coiling, overlapping
stents, and stent monotherapy for the treatment of blister aneurysm.[11]
[16]
[17]
Stent monotherapy or telescoping stent treatment options in blister aneurysm was reported
in a few case series. The rationale for using stent without additional coils was to
decrease the intra-aneurysmal blood flow and wall shear stress with progressive endothelization,
leading to complete exclusion of aneurysm (
[Fig. 1]
). This avoids catheterization of aneurysm sac for coiling and hence probably avoiding
fatal intraoperative rupture. Walsh et al in their case series (n = 8) of stenting without additional coiling showed 75% complete or stable aneurysm
occlusion with two patients (25%) requiring retreatment in the form of parent vessel
occlusion. They used overlapping stent in seven patients and one patient was treated
with stent monotherapy. Good clinical outcome was noted in all patients without any
rerupture. They suggested that stent monotherapy or telescoping stent technique (preferably)
is safe and feasible technique in the management of blister aneurysms.[11]
Fig. 1 A 58-year-old male patient presented with acute subarachnoid hemorrhage (SAH). 3D
rotational angiographic solid-state drive (SSD) image and corresponding 2D digital
subtraction angiography (DSA) image showed classical blister aneurysm of supraclinoid
internal carotid artery (ICA) (arrows in A and B). This patient was treated with two overlapping stents (Enterprise-Codman Neuro)
across the blister aneurysm (arrow. in C). Six-month follow-up DSA images showed complete aneurysm occlusion (D).
Stent-assisted coiling has theoretical advantage of immediate aneurysm sac protection
in comparison to only stent approach. Meckel et al in their case of 11 patients of
ruptured blister aneurysm treated with stent-assisted coiling using Neuroform stent
(Stryker Neurovascular, California) showed complete/stable angiographic occlusion
of the aneurysm during follow-up in 10 cases. One patient had asymptomatic rebleed
and was treated with parent vessel occlusion. Two patients had recurrent aneurysm
growth at 1-month follow-up angiogram which was treated with parent artery occlusion
in one and coiling in another patient. Good clinical outcome was seen in 10/11 patients.
They concluded that stent-assisted coiling is a viable option but may need early follow-up
angiogram and retreatment if necessary.[17]
Closed cell design stents may provide potential advantage of resheath and reposition
of the device in comparison to the open cell design stent in addition to coil mass
support. Xu et al in their study (n = 44) of ruptured blister aneurysms, 9 were treated with single stent-assisted coiling
and 35 with telescoping stents using closed cell design Enterprise (Cordis Neurovascular).
Two patients in the single-stent group had recurrence, which was addressed by using
second stent. The patient treated with telescoping stents had better immediate complete
aneurysm occlusion as compared with single stent.[18] These case series have highlighted the importance of the multiple overlapping stents
with the intention of additional FD effect. Another study has reported good clinical
outcome in 14/17 patients in their single center experience of 17 ruptured blister
aneurysms. A total of six patients were treated with single stent (Enterprise), five
with overlapping stents, and six with single stent assisted coiling. Among single
stent patient subgroup, two patients (2/6) had aneurysm regrowth, which were treated
with additional stent placement at the time of early angiogram (10–14 days). One interesting
finding in their study was high probability of arterial dissection in the patients
of blister aneurysm during diagnostic angiogram and therapeutic procedure (3/17),
raising the possibility of underlying connective tissue disorder. Complete aneurysm
occlusion was noted in 11/14, incomplete stable occlusion in 1/14, and retreatment
in 2/14.[19] Their result showed that overlapping stent group had better aneurysm occlusion with
less rates of retreatment.
Gonzalez et al in their systematic review have reported combined morbidity-mortality
of 10% and 8% for stent-assisted coiling and overlapping stent, respectively. The
rate of regrowth (38%) and rebleed (12.5%) was higher in the stenting alone subgroup.
They further suggested that only stenting may not always provide immediate aneurysm
protection, considering the aggressive natural history of blister aneurysms.[10] One of the authors’ experience also showed incomplete aneurysm occlusion (30%) in
only stent/overlapping stents without coiling, exposing to the risk of repeat hemorrhage.[19]
Flow Diverter (FD)
FD stents are basically braided stents with high-pore density and low porosity. Deployed
FD modifies intra-aneurysmal blood flow to decrease wall shear stress along with maintaining
laminar blood flow in the parent artery. Computation flow dynamics study in the aneurysm
treated with FD placement has showed significantly decreased intra-aneurysm flow velocity,
flow volume, and wall shear stress (WSS).[20] Progressive thrombosis of the aneurysm and endothelization of the stent result in
healing of the aneurysm neck with complete exclusion from the circulation.
FD use in blister aneurysms was considered in clinical practice, as it leads to decreased
flow into the aneurysm sac with subsequent endothelization, preserved flow in covered
side branches, and no need for the aneurysm catheterization for adjuvant coiling.
However, issues like lack of immediate aneurysm sac exclusion from circulation and
probable long waiting time for complete occlusion do pose challenges for their practical
consideration in blister aneurysms. Another important aspect of FD treatment in ruptured
cerebral aneurysms is proper antiplatelet regimen, its timing, as well as dose modification
in relation to other surgical interventions like external ventricular drain (EVD)/ventriculoperitoneal
(VP) shunt/tracheostomy/decompressive craniectomy.
Recently, a few case series have reported safety and efficacy of the FD in treatment
of blister aneurysm using pipeline embolization device (PED, Medtronic). Ryan et al
in their series of 13 ruptured blister aneurysms patients showed good clinical outcome
in 77% (10/13) and combined morbidity-mortality in three patients. There was one intraprocedural
complication of wire-related perforation during the delivery of second overlapping
FD, leading to significant morbidity and requiring decompressive craniectomy. In their
case series, only two patients were treated using telescoping FD stents. As much as
50% patients (5/10) had complete aneurysm occlusion on 3 months follow-up angiogram
and remaining at 12 months. Two patients, who had residual filling or increased remnant
of the aneurysm during follow-up, were treated with another FD. No patient had procedural
or delayed aneurysmal rebleeding. They concluded that FD is safe and effective in
the treatment of blister aneurysms, especially in good clinical grade patients (Hunt
and Hess Grade of I-III).[21]
Yoon et al in their multicenter case series of 11 patients showed 83% good clinical
outcome with no procedural or post-FD aneurysm rerupture. Significant morbidity-mortality
was reported in three patients secondary to vasospasm, thromboembolic complications,
and monocular blindness secondary to covered ophthalmic artery decreased flow after
telescoping FD placement. One patient had asymptomatic complete stent thrombosis with
ICA occlusion during follow-up. In this series, most patients were treated with single
FD (7/11) with complete aneurysm occlusion during follow-up.[22]
Mokin et al in their multicenter retrospective study of 43 patients with ICA blister
aneurysm treated with PED reported complete aneurysm occlusion in 88% of patients
on 4 months follow-up angiogram and rest with either reduced filling or residual filling.
One patient has aneurysm rerupture on day 4 of the treatment, which might suggest
toward difference of blood pressure targets in blister aneurysm compared with another
aneurysm treated with FD. Thromboembolic complications were noted in 5/43 patients
with intraprocedural rupture in one patient. The use of adjuvant coiling did not affect
the aneurysm occlusion during follow-up angiogram. Another important observation was
lack of contrast stasis in blister aneurysm post deployment of FD, which is not predictor
of complete aneurysm occlusion during follow-up angiogram. Overall, FD treatment is
safe and effective in ruptured blister aneurysms.[23]
Meta-analysis of all 62 ruptured blister aneurysms treated with FD showed complete
occlusion in 91% mid to long-term follow-up. Compared with other reconstructive techniques,
FD group showed more complete occlusion (91 vs. 68%) and lower rates of retreatment
(6.6 vs. 30.7%). No significant difference was noted in early rebleeding; however,
procedural complications and perioperative stroke were noted in FD group compared
with other reconstructive techniques.[13] We further discuss the technical issues and antiplatelet dosage dilemma during FD
treatment of blister aneurysm ([Table 1]).
Table 1
Different studies of FD experience in blister aneurysm
|
Study
|
No. of patients
|
Angiographic outcome
|
Clinical outcome
(mRS < 2)
|
Procedure-related complications
|
Remarks
|
|
Abbreviations: FD, flow diverter; ICA, internal carotid artery; ICH, intracerebral
hemorrhage; IVH, intraventricular hemorrhage; mRS, modified Rankin score.
|
|
Chalouhi et al[27]
|
8
|
Complete occlusion (⅚), partial filling in one
|
All
|
None
|
Seven aneurysms were located at ICA and one at basilar artery
|
|
Hu et al[41]
|
3
|
Complete occlusion (3/3)
|
All
|
None
|
All the aneurysms were located at ICA
|
|
Lin et al[42]
|
7
|
Complete occlusion (7/7)
|
All
|
None
|
|
|
Linfante et al[43]
|
10
|
Complete occlusion (9/10)
|
9/10
One mortality secondary to severe vasospasm
|
None
|
8/10 aneurysms were located at ICA, 2/10 were located at MCA.
All were treated with single device.
|
|
Ryan et al[21]
|
13
|
Complete occlusion in 5/11, reduced filling in two and retreatment in two patients.
|
10/11
mRS 4 in one patient
|
1.Wire perforation leading to ICH.
2.Worsening IVH leading to death
3. Rupture of another aneurysm leading to death
|
11 patients received one device and two patients were treated with telescoping device
(ICA)
|
|
Yoon et al[22]
|
11
|
Complete occlusion (7/11)
Partial filling in one.
|
9/11
|
1. Thromboembolic
2. Vision loss
3. ICH resulting in death
|
During follow up one patient had asymptomatic in-stent stenosis (ICA)
|
|
Mokin et al[23]
|
43
|
Complete occlusion in 87% (28/32), three with reduced filling and one with persistent
filling of the aneurysm
|
26/38 (68%)
|
1. Thromboembolic in five patients.
2. Intraprocedural rupture in one patient.
3. Worsening of IVH in one patient.
4. Rerupture of aneurysm in one patient on day 4 of treatment.
|
All the aneurysms were located at ICA
|
Single versus Overlapping FD
Although overlapping FD might appear to be beneficial approach in achieving high degree
of flow diversion, it has its own limitation in terms of more thromboembolic complications
and technical complexity.[24] Xiang et al in their in vitro study showed that single device strategy of the FD
might work for the treatment of the blister aneurysm. Single FD with compaction of
device near the aneurysm neck or inflow will significantly reduce the intra-aneurysm
blood flow velocity as well as wall WSS.[20]
Overlapping FD placement increases the risk of thromboembolic complications, technical
complexity, and more risk of side branch occlusion and in-stent stenosis.[25] One of the authors has reported good clinical outcome with a single FD device in
blister aneurysms, with compaction near the neck of the aneurysm and good wall apposition
(
[Fig. 2]
).[26]
Fig. 2 A 34-year-old male patient presented with acute subarachnoid hemorrhage (SAH) (Grade
III) on CT brain (A). 3D rotational solid-state drive (SSD) image showed broad neck small aneurysm along
dorsomedial wall of supraclinoid internal carotid artery (ICA), the typical site of
blister aneurysm (arrow in B and C). Since patient was drowsy (Glasgow coma scale [GCS]-E3V4M5), external ventricular
drain (EVD) placement was done prior to procedure. Repeat CT showed EVD in place (arrow
in D) with no fresh bleed, following which antiplatelet loading dose was done. After pipeline
embolization device (PED) placement, digital subtraction angiography (DSA) image showed
aneurysmal filling with stasis of contrast in the aneurysm in delayed phase (arrow
in F only). Vaso-CT image showed stent compaction near the neck of the aneurysm with good
wall opposition of the device (arrow in G). 6-month follow-up DSA showed complete aneurysm occlusion with preserved flow in
covered side branches (H).
Antiplatelets
One of the most important issues for FD use in ruptured blister aneurysms is antiplatelet
regimen selection and their proper timing in relation to the procedure. The best protocol
is to have antiplatelet drugs which have maximum activity in circulatory system close
to time of FD deployment in order to avoid thromboembolic complications as well as
potentially avoiding rebleed before the treatment. Although few case series have highlighted
the use of FD after the acute phase of SAH to avoid antiplatelet related issues, deferring
the treatment especially in case of blister aneurysm is debatable, considering their
aggressive natural history.[27] Most reported case series of FD in blister aneurysm have reported antiplatelet protocol
of aspirin (650 mg) and clopidogrel (600 mg) at least 6 to 8 hours prior to treatment,
considering the maximal platelet inhibition of these two drugs.[21]
[27]
[28] Another case series used intravenous aspirin (500 mg) just prior to FD deployment
and oral clopidogrel (600 mg) after the procedure.[25] Intravenous aspirin is not available in India and resistance to clopidogrel is well-known
from the cardiac literature ranging from 5 to 44%.[29] Platelet function assays have shown significant variation in terms of results and
predictability. All these issues have led to consideration of newer antiplatelet agents
in the endovascular procedures. Prasugrel is thienopyridine prodrug, which is less
likely to get affected by genetic polymorphism of cytochrome enzymes in comparison
to clopidogrel. In addition to this, it achieves faster and higher platelet aggregation
inhibition in comparison to clopidogrel.[30] Another new antiplatelet agent, ticagrelor, is a reversible direct inhibitor of
the P2Y12 ADP receptors. Ticagrelor does not need metabolic conversion and has faster
onset of action than clopidogrel.[31]
The author has reported use of loading dose of prasugrel (50 mg loading dose followed
by 10 mg maintenance) and aspirin (300 mg loading followed by 150 mg maintenance)
in nine patients with no rebleed, ischemic complications, or in-stent thrombus formation.[26] The protocol was to time the drug administration 2 hours prior to FD deployment.
The other option is to use ticagrelor (180 mg loading dose followed by 90 mg maintenance),
particularly in patients with recent transient ischemic attacks/stroke (clinical and
or imaging) and old age (age more than 75 years).[31] Recent meta-analysis has reported reduced thromboembolic complications with newer
antiplatelets (ticagrelor and prasugrel) in comparison to clopidogrel without higher
risk of hemorrhagic complications. They concluded that both ticagrelor and prasugrel
are safe and effective alternative to clopidogrel for patients treated with FD, especially
in hyporesponders/nonresponders.[32] Most of the case series had reported protocol of dual antiplatelets for 3 to 6 months
followed by aspirin monotherapy till 1 year.[27]
[28] In the author’s institution, dual antiplatelets are given for a 1-year period and
aspirin monotherapy continues lifelong.
Another option for antiplatelet regimen is to use intravenous GPIIb/IIIa inhibitors
in the setting of FD placement for ruptured blister aneurysms. Limaye et al have used
IV tirofiban infusion just before deployment of FD/stent followed by oral antiplatelets
loading for the patients requiring EVD. They used 0.10 ug/kg/min IV tirofiban infusion
as monotherapy without any loading dose followed by dual antiplatelet loading postprocedure
in 19 patients. In their series, two patients had asymptomatic EVD tract-related hemorrhages.
One patient had transient weakness after stopping the tirofiban infusion after antiplatelet
loading. One patient had significant thrombocytopenia which was reversible within
24 hours after discontinuation of tirofiban infusion. They concluded that IV tirofiban
infusion as monotherapy is safe and effective whenever stent or FD use is anticipated
in aneurysm treatment.[33]
One of the challenges in using dual antiplatelets in acutely ruptured aneurysms is
surgical interventions in the form of EVD change/removal, VP shunt placement, decompressive
craniectomy (DC), and tracheostomy, which may be needed in these patients (
[Fig. 2]
). Systemic meta-analysis has reported 3 to 10% EVD-related radiographic hemorrhagic
complications in the patients on dual antiplatelets in comparison to 0.9% in convention
coiling group.[34] Recent retrospective single center analysis has showed no clinically significant
hemorrhagic complications after EVD placement/EVD change/VP shunt placement even through
radiological hemorrhages were more in patients receiving dual antiplatelets (9 vs.
1 patient).[35]
[36] At the author’s institution, the following approach is followed in these circumstances
for any SAH patient on dual antiplatelets requiring additional surgical interventions:
-
In acute SAH with hydrocephalus, EVD is placed prior to procedure with controlled
drainage. We repeat CT brain 2 hours after EVD placement to confirm tube position
and assess for tract hemorrhage prior to antiplatelet loading dose administration.
-
In case of a patient requiring EVD change, one may have to time if possible such that
4 to 5 half-lives (at least 2 half-lives) have elapsed from the last dose of ticagrelor
or prasugrel. This is to ensure the transfused platelets are functionally active in
vivo to prevent hemorrhage during this process.
FD and Cerebral Vasospasm
Cerebral vasospasm following acute SAH poses unique challenge for FD placement in
terms of proper sizing of device and wall apposition for adequate flow diversion.
The author performs gradual intra-arterial nimodipine infusion prior to sizing of
the device as well as deployment. Another issue is the risk of FD retraction during
vasospasm period, leading to loss of aneurysm neck coverage and rerupture. One case
report has mentioned this phenomenon probably secondary to ICA vasospasm at the time
of FD placement with subsequent dilatation of vessel and rerupture on day five, leading
to retreatment in form of parent vessel occlusion with external carotid artery (ECA)-MCA
bypass.[37] In the author’s experience, selection of proper distal landing zone and adequate
distal anchoring of flow diverter is recommended to avoid foreshortening of the device.
This also enables dynamic push-pull maneuver to achieve the device compaction near
the neck of the aneurysm. Since there is risk of reduced flow in covered side branches,
sometimes this can be detrimental in patients of cerebral vasospasm following acute
SAH (
[Fig. 3]
). Medical management of cerebral vasospasm in the form of aggressive hypertension
is still unclear, especially in cases of persistent aneurysm filling after FD.
Fig. 3 A 50-year-old female patient presented with acute subarachnoid hemorrhage (SAH).
Cerebral angiogram showed the aneurysm in dorsal supraclinoid internal carotid artery
(ICA)-typical location for blister aneurysms (arrow in A). Distal intracranial arteries showed diffuse vasospasm. Magnified image of blister
aneurysm with adjacent parent artery involvement (white line indication neck of the
aneurysm in B). Flow diverter (FD) (Pipeline. Medtronic) placement for the treatment of blister
aneurysm with stent compaction near the aneurysmal segment of ICA (arrow in C). The FD expansion has remodeled the artery in the areas of spasm. This has ensured
proper apposition to the arterial wall. Six months follow-up angiogram showed complete
aneurysm occlusion with parent artery reconstruction (D). (Reprinted with permission from Indian journal of neurosurgery from the review
article. “Endovascular Management of Cerebral Aneurysm: The Recent Trends” by Gupta
et al. August 2018).
Recent Advances in FD Technology
Pipeline shield technology–Surface coated PED shield technology is basically phosphorylcholine
coating of 3 nm along the braids of FD. This coating reduces platelet adhesion and
subsequent aggregation to the FD surface, reducing thromboembolic complications. In
vitro studies using this shield technology have shown early stent endothelialization
compared to PED. Recently, one single center case series of 14 patients of ruptured
aneurysm treated with this technology has shown good clinical outcome using single
antiplatelet aspirin. Two aneurysms in their series were blister aneurysm with complete
occlusion in follow-up.[38] They used aspirin loading dose with intra-operative bridging of abciximab in a few
patients. Five patients were started on postoperative heparin infusion in addition
to aspirin, two of whom had rebleeding from aneurysm. They concluded that in addition
to aspirin, no other antiplatelets/anticoagulation therapy is necessary for pipeline
shield for prevention of ischemic complications. Trivelato et al also reported safe
use of pipeline shield in blister aneurysm with complete aneurysm occlusion.[39]
Other Approaches
Covered Stents
Even though covered stents are used routinely for cervical ICA aneurysms/pseudoaneurysms,
intracranial application of these devices is limited. The most common reasons are
their flexibility and navigation issues in tortuous anatomy of intracranial ICA. Recent
development in guide catheters can solve these issues by their optimal support for
stent navigation as well as stent delivery. Willis covered stent is a balloon expandable
device, specifically designed for the intracranial vasculature. Fang et al have reported
use of the Willis covered stent in 11 patients of ruptured ICA blister aneurysm with
good clinical outcome in all patients. Complete aneurysm occlusion was noted in all
the patients in follow-up angiograms. Ophthalmic artery in one and anterior choroidal
artery in another patient was covered during stent placement, but none developed clinical
symptoms. Two patient had in-stent stenosis secondary to neointimal hyperplasia for
which dual antiplatelet were continued.[40] Even though initial results are promising, device availability, longer follow-up,
and fate of covered side branches, especially anterior choroidal artery, are issues
that remain and make the practical consideration of this treatment selection debatable,
especially in the current FD era.
Balloon/Stent Assisted Onyx Embolization
Ashour et al have reported intrasaccular blister aneurysm embolization using Onyx
HD 500 with balloon and/or stent assistance. In this technique, slow injection of
the onyx was done in view to secure the aneurysm sac with inflated balloon. If needed,
this was followed by the stent placement through another microcatheter to avoid onyx
cast migration.[8] Operator’s comfort and experience is of utmost important to prevent thromboembolic
complications. Onyx has the advantage of forming immediate solid cast confirming the
aneurysm morphology and least possibility of aneurysm sac rupture during the procedure
in comparison to coils. However, there are very few reports and in view of weakened
vessel wall, the aneurysm may keep growing with this approach. In the era of FD, this
approach may not be practical in the management of blister aneurysm.
