Treatment of posterior inferior cerebellar artery aneurysms using flow-diverter stents: A single-center experience

Abstract

Introduction

The effectiveness and reliability of flow-diverter stents, which are commonly used in aneurysms of the anterior circulation, have been demonstrated previously. However, the use of these devices is associated with higher rates of perforator and branch ischemia following the treatment of aneurysms of the posterior circulation.

Methods

This work involved a single-center; retrospective study reviewing eight patients who had aneurysms related to the posterior inferior cerebellar artery (PICA) and who were treated with flow-diverter stents from September 2013 to May 2017.

Results

The mean aneurysm diameter was 7.6 mm (range, 5 to 11 mm). The types of aneurysm included five aneurysms that were saccular, two that were fusiform, and one that was dissecting. All saccular aneurysms in the neck involved the PICA origin, and one dissecting aneurysm was localized in the proximal part of the PICA. Procedural success was 100% (8/8), and there were no ischemic complications. One patient with subarachnoid hemorrhage died because of rebleeding (modified Rankin Scale (mRS), 6). Other than this patient all of the patients’ mRS scores were zero at discharge and at the clinical follow-up period (mean, 2.5 years). All of the aneurysms were completely occluded according to the latest angiographic controls (mean follow-up period of 19.5 months).

Conclusions

Treatment of PICA aneurysms with flow-diverter stents showed positive results with a high rate of technical success and low complication and mortality rates. The use of flow-diverter stents in the treatment of PICA aneurysms should be considered a safe and effective endovascular treatment option.

Introduction

Flow-diverter stents have opened a new era in the treatment of intracranial aneurysms, and their use has become increasingly widespread worldwide. The effectiveness and reliability of these devices, which are commonly used in anterior circulation aneurysms, have been proven, and the area of use is continually expanding (e.g. distal anterior circulation aneurysms, ruptured aneurysms).^1–4 The risk of rupture of posterior circulation aneurysms is higher than that for anterior circulation aneurysms, and they have a worse clinical course with regards to rupturing.⁵ Because posterior circulation aneurysms are a heterogeneous group (e.g. saccular, fusiform, dissecting/pseudo and partial thrombosis aneurysms), their treatments can also be challenging. The use of flow-diverter stents is still controversial because of the working principle of flow diverters and perforators and arterial branches in close proximity to aneurysms in this location. Flow-diverter stents are endovascular devices based on the concept of diverting flow into an aneurysm. This has been achieved by providing high surface coverage (35% to 55%) and low porosity. The use of these devices is associated with higher rates of perforator and arterial branch ischemia in the treatment of posterior circulation aneurysms that are richer in perforator and end arterial branches compared with anterior circulation. This results in high mortality rates that make the use of flow-diverter stents controversial for the treatment of posterior circulation aneurysms.^6–9

Fusiform aneurysms of the vertebral artery V4 segment including the posterior inferior cerebellar artery (PICA) origin, PICA origin aneurysms, and PICA trunk aneurysms defined as PICA aneurysms are challenging treatment cases. Covering the origin of PICA with a flow-diverter stent is still controversial in terms of ischemic complications. Here, we present the treatment and follow-up of eight patients with aneurysm-related PICA in the posterior circulation using flow-diverter stents via our single-center experience.

Material and methods

This retrospective study was conducted by utilizing a prospectively collected database of patients treated using a flow-diverter stent in our center. Between September 2013 and May 2017, eight patients with aneurysms related to the PICA and who were treated with flow-diverter stents were identified. Demographic characteristics, procedural details of the treatment, and clinical and angiographic follow-up results of these patients were obtained from the hospital database. Written informed consent was obtained from each patient or the patient’s relatives before the procedure. All patients were administered a dual-antiplatelet regimen (75 mg clopidogrel/10 mg prasugrel and 300 mg aspirin daily) and were confirmed to have sufficient platelet inhibition. Following administration of general anesthesia, all stent placement procedures were performed through microcatheters (Marksman; Stryker, Neurovascular, Fremont, CA, USA, or Rebar 27; ev3/Covidien, Mansfield, MA, USA) using a triaxial guiding system. In these eight patients treated with flow-diverter stents, two kinds of stents were used: the Pipeline Embolization Device (PED; Medtronic Neurovascular, Irvine, CA, USA) and the Flow Re-Direction Endoluminal Device (FRED; MicroVention, Tustin, CA, USA).

Patient demographics and aneurysm characteristics were recorded. The primary end points were aneurysm occlusion rate and clinical outcomes, and the secondary end points were periprocedural adverse events (especially ischemia-related PICA) and PICA patency at follow-up. Imaging findings were obtained from the digital subtraction angiography (DSA) images. Aneurysm occlusion was assessed according to the O’Kelly-Marotta grading scale: complete filling, A; subtotal filling, B; entry remnant, C; and no filling, D.¹⁰

Results

Eight patients with eight aneurysms related to the PICA were treated with a flow-diverter stent between September 2013 and May 2017. Half of the patients were female, and the mean age was 55 years (range, 34 to 71). The presentations of the patients were as follows: Three patients had a headache, four patients had a subarachnoid hemorrhage (SAH), and one patient was asymptomatic. The mean aneurysm diameter was 7.6 mm (range, 5 to 11 mm). The types of aneurysm were as follows: Five aneurysms were saccular, two aneurysms were fusiform and one aneurysm was dissecting. All saccular aneurysms in the neck involved the PICA origin, and one dissecting aneurysm was localized in the proximal part of the PICA. The PICA originated from a fusiform vertebral artery V4 segment aneurysm in two patients (Table 1).

Table 1.

Patient characteristics and angiographic findings and follow-up.

Case no.	Sex	Age	Presentation	Aneurysm location	Type	Size (mm)	Device	Follow-up (months)	Aneurysm filling grade per O’Kelly-Marotta grading scale	PICA patency	mRSa
1	F	67	Headache	PICA origin	Saccular	7 × 6	1 (PED, 3.00 mm × 18 mm)	12	D	P	0
2	M	57	SAH	PICA origin	Saccular	6 × 4	1 (PED, 3.00 mm × 18 mm)	7	D	P	0
3	F	71	SAH	PICA origin	Saccular	8 × 6	2 (PED, 3.25 mm × 18 mm, PED, 3.00 mm × 20 mm)	NA	NA	NA	6
4	M	70	Incidental	VA, involving PICA origin	Fusiform	9 × 5	2 (PED, 3.75 mm × 18 mm, PED, 4.00 mm × 16 mm)	6	D	P	0
5	M	38	SAH	PICA origin	Saccular	5 × 4	1 (FRED, 4.00 mm × 18 mm)	46	D	P	0
6	F	58	Headache	PICA origin	Saccular	9 × 8	1 (FRED, 4.00 mm × 23 mm)	6	D	P	0
7	F	34	Headache	VA, involving PICA origin	Fusiform	11 × 6	1 (FRED, 4.00 mm × 44 mm)	36	D	T	0
8	M	45	SAH	Proximal PICA	Dissecting	6 × 5	1 (FRED, 4.00 mm × 18 mm)	24	D	P	0
Mean		55				7.6	1.25	19.5b

F: female; FRED: Flow Re-Direction Endoluminal Device; M: male; mRS: modified Rankin Scale; P: patent; PED: Pipeline Embolization Device; PICA: posterior inferior cerebellar artery; SAH: subarachnoid hemorrhage; T: tiny; VA: vertebral artery.

^aMean clinical follow-up period was 2.5 years.

^bCase 3 was not included in the mean follow-up period.

Procedural success was 100% (8/8), and there were no ischemic complications. All stents were deployed along the vertebral artery V4 segment, and a coil was not used for any of the patients. The PICA origin had to be covered with flow-diverter stents in all patients (Case No. 1, Figure 1). The proportion of patients using PED and FRED was half and half. We observed that the proximal part of the stent shortened and migrated in two patients. In one patient (Case No. 3), we deployed a second stent telescopically. In another patient (Case No. 4), who had a right fusiform vertebral artery V4 segment aneurysm involving the right PICA origin, the proximal part of the stent shortened and the stent completely dropped into the aneurysm. We deployed a second stent, and the first one was jailed in the aneurysm. At the six-month follow-up DSA, the aneurysm was totally occluded, and the PICA was patent (Figure 2).

Figure 1.

A 67-year-old female patient with a headache (Case No. 1). (a, b) Digital subtraction angiography (DSA) and three-dimensional DSA images revealed a saccular aneurysm originating in the posterior inferior cerebellar artery (PICA) origin. (c, d) After placement of a 3 × 18 mm Pipeline Embolization Device Flex, balloon angioplasty was performed with a 4 × 7 mm HyperForm (Medtronic Neurovascular, Irvine, CA, USA) balloon because of apposition defects ((c) white arrow) in the proximal part of the stent. (e) After balloon angioplasty, the control Dyna computed tomography image showed complete apposition of the stent. (f) In the first-year DSA control, while the stent and PICA were patent, the aneurysm was totally occluded.

Figure 2.

A 70-year-old male patient who had a right vertebral artery V4 segment incidental fusiform aneurysm (Case No. 4). (a) Digital subtraction angiography (DSA) image demonstrating a right vertebral artery V4 segment fusiform aneurysm involving the right posterior inferior cerebellar artery (PICA) origin. (b) The road-map image shows that the stent was dropped into the aneurysm sac, which passed near the stent. (c-e) Fluoroscopic, DSA and Dyna computed tomography images showing the final state; the second stent and the first stent were jailed in the aneurysm. (f) At the six-month follow-up DSA, the aneurysm was totally occluded, and the PICA was patent.

In one patient (Case No. 8), who had a dissecting aneurysm in the proximal segment of the PICA, a stent was deployed in the vertebral artery to cover the PICA origin. In the 2-year follow-up angiography, it was observed that the aneurysm was totally occluded by remodeling of the PICA vessel wall, and the PICA was also patent (Figure 3).

Figure 3.

A 45-year-old male patient who had a posterior inferior cerebellar artery (PICA) proximal segment-dissecting aneurysm presenting with a subarachnoid hemorrhage (Case No. 8). (a) Computed tomography (CT) image revealing that the subarachnoid hemorrhage was predominantly in the left pre-pontine cistern. (b) Digital subtraction angiography (DSA) image demonstrating a left PICA proximal segment-dissecting aneurysm. (c) After the 4.00 mm × 18 mm Flow Re-Direction Endoluminal Device stent was deployed into the vertebral artery V4 segment, an immediate DSA image showed the filling of the aneurysm and the PICA. (d) At the second-year DSA control, full patency of the PICA and total occlusion of the aneurysm were seen.

Four patients presented with SAH, and three of them (Case Nos. 2, 3 and 8) developed impairment of consciousness secondary to acute hydrocephalus. Lumbar drainage was performed at regular intervals considering the changes in the patient’s state of consciousness. Hydrocephalus did not persist in the chronic period in any patient, and external ventricular drainage was not necessary.

No intracranial hemorrhage or delayed rupture was observed, except in one patient with acute SAH. This patient (Case No. 3) presented with SAH and was treated in the acute period but died because of rebleeding two weeks after the procedure (mRS, 6). Other than this patient, all the patient mRS scores were zero at discharge and at the clinical follow-up period (mean 2.5 years). However, our mortality rate was 12.5%.

There was at least one DSA at follow-up for seven patients, and the mean follow-up period was 19.5 months (range, 6 to 46 months). All aneurysms were totally occluded (100%) according to the last angiographic controls. In-stent stenosis was not observed in any patient. PICA diameter loss and thinning were observed in only one patient (Case No. 7, Figure 4), while PICA diameter in the other patients remained unchanged.

Figure 4.

A 34-year-old female patient with a headache (Case No. 7). (a) Digital subtraction angiography (DSA) image demonstrated a left vertebral artery V4 segment fusiform aneurysm involving the left posterior inferior cerebellar artery (PICA) origin. (b) Fluoroscopic image showing the stagnation of the contrast medium in the aneurysm sac. (c) In the third-year DSA control, diameter loss of the PICA (arrow) and total occlusion of the aneurysm were seen.

Discussion

To the best of our knowledge of the literature, this study is the largest single-center case series of PICA-related aneurysms treated with flow-diverter stents. In our series, we deployed the device into the vertebral artery to cover the neck of the aneurysm, and we simultaneously covered the PICA origin with the device because of its proximity to the aneurysm. Because the PICA is an end branch, its total occlusion may result in severe cerebellum infarction and clinical worsening. We did not encounter ischemic events related to the PICA at the periprocedural or follow-up periods. In only one patient did we observe that the PICA was thinner at follow-up, but the patient was asymptomatic.

Although endovascular aneurysm treatment approaches are focused on filling the aneurysm sac with coils, the flow-diverter approach has gained popularity. Reconstruction of the parent artery harboring the aneurysm with flow-diverter stents is the basis for the treatment. Flow-diverter stents hemodynamically promote flow stasis and thrombosis within the aneurysmal sac with flow redirection and provide a scaffold in the vessel wall to develop endothelial and neointimal tissue overgrowth, consequently closing the aneurysm neck. This is possible with higher metal coverage including 70% ideal porosity and a braided metallic design.¹¹ However, problems may arise with the covered side branch. The blood flow through the flow diverter for the covered side branch depends on the flow demand and the presence of an alternative collateral pathway.¹²

The treatment of posterior circulation aneurysms with flow-diverter stents has been a problematic approach because of the rich perforator and end branches. The International Retrospective Study of Pipeline Embolization Device (IntrePED) retrospectively assessed neurological complication rates with PED, and the overall rate of neurological morbidity and mortality was 8.4% for all intracranial aneurysms; the rate was highest in posterior circulation aneurysms (16.4%).² The use of flow-diverter stents in this region has resulted in high mortality and ischemic complication rates reported in the literature.^6–9,13,14 A recent meta-analysis⁹ reported that the stroke rate was 23% and the mortality rate was 21%. Another noted that the mortality rate was 15% and ischemic and perforator infarcts were 11% and 7% in patients, respectively.⁸

Posterior circulation aneurysms are quite complicated because of the localization and type of this aneurysm. Although PICA aneurysms vary in aneurysm type, they are localized in the vertebral artery V4 segment and characterized by relatively fewer perforator branches. Srinivasan et al. reported a multicenter study involving 10 cases of PICA aneurysms treated with flow diverters. They successfully treated all patients; no patients suffered from a medullary or cerebellar stroke.¹⁵ They deployed the stent entirely in the PICA in three patients. Bhogal and colleagues reported 100% technical success with the flow-diverter stent deployed entirely in the PICA in three patients with aneurysms located in the PICA.¹⁶ In one of our patients, for treatment of a dissecting aneurysm localized proximal to the body of the PICA, we deployed the flow-diverter stent in the vertebral artery to cover the PICA origin. Our objective here was to reduce the severity of flow into the PICA and secondary to the aneurysm and to assist with remodeling of the vessel wall. Additionally, we opted for this to avoid vascular injury, acute stent thrombosis and ischemic events that can occur when deploying a flow-diverter stent into a thin vascular such as the PICA.

One of the most effective factors associated with ischemic complications is the use of effective antiplatelet drugs in flow-diverter stent use. In our case series, half the patients had a ruptured aneurysm. Our antiplatelet regimen involved a dual-drug treatment (clopidogrel/prasugrel and aspirin), one week in the unruptured aneurysms and a loading dose (300 mg clopidogrel at night and 300 mg aspirin) the night before the procedure in the ruptured aneurysms. On the morning of the procedure, all patients were confirmed to have sufficient platelet inhibition. Maus et al.¹⁴ applied antiplatelet therapy in 15 patients with a ruptured aneurysm of the posterior circulation as follows: Administration of tirofiban (Aggrastat, Merck, West Point, PA, USA) was started intraoperatively before flow-diverter placement for 16–24 hours, followed by oral dual-antiplatelet therapy. Only one patient had asymptomatic cerebellar infarction in their case series. However, they reported a mortality rate of 47% (7/15) due to poor-grade SAH. They did not have events of rebleeding after endovascular treatment. In our series, we had rebleeding in one patient resulting in death. Otherwise, no other adverse events (e.g. ischemia) were observed during the periprocedural or follow-up period.

In the postprocedural period and the long-term follow-up, one patient died because of rebleeding. As a result, our mortality rate was 12.5%. Srinivasan et al.¹⁵ reported 0% mortality rate and no ischemic events in their study involving the treatment of PICA aneurysms using a flow-diverter stent. Considering that their study and our study focused on PICA aneurysms, despite the low number of patients, the mortality and morbidity rates, mostly attributed to ischemic complications, were lower than in a recent meta-analysis associated with the total posterior circulation aneurysms treated flow diverters.^8,9 We believe the vertebral artery V4 segment is the safest location for the placement of flow-diverter stents for posterior circulation system aneurysms.

The end branch covered with flow-diverter stents always brings the risk of infarction of its territory and acute branch occlusion. In a study evaluating the side branch covered with PED in the anterior circulation, acute branch occlusion did not occur in the periprocedural period, while 15.8% of the branches were occluded at the long-term (mean follow-up period of 10 months) angiographic follow-up, but all patients remained asymptomatic. End branch occlusions such as those involving the anterior choroidal artery were not observed.¹⁷ In our case series, PICA diameter loss and thinning were observed in only one patient, while PICA diameter in the other patients remained unchanged. All aneurysms were totally occluded according to the latest angiographic controls (mean follow-up period of 19.5 months, ranging from 6 to 46 months). In-stent stenosis was not observed in any patient.

The major limitations of this study were its retrospective design and small sample size. Another limitation of this small case series is that half of the patients presented with SAH.

In conclusion, the treatment of PICA aneurysms with flow-diverter stents in the management of posterior circulation aneurysms shows favorable results with high technical success, few complications and low mortality rates. The use of flow-diverter stents in the treatment of PICA aneurysms should be considered a safe and effective endovascular treatment option. However, prospective studies with a large sample size are needed to evaluate the use of flow-diverter stents in the treatment of PICA aneurysms.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.