Abstract
Introduction
Posterior inferior cerebellar artery (PICA) aneurysms are rare but associated with high rupture rates and significant morbidity and mortality. Both surgical and endovascular treatments can be technically challenging. This study evaluates the efficacy and safety of indirect flow diversion using flow-diverting stents (FDS) deployed in the vertebral artery, covering the PICA origin.
Patients and methods
We retrospectively reviewed all patients treated at our center between March 2013 and March 2024 for proximal saccular PICA aneurysms using FDS deployed in the V4 segment of the vertebral artery. Clinical and aneurysm characteristics, procedural details, imaging follow-up, and clinical outcomes were collected and analyzed.
Results
Fourteen patients were treated, including eight (57%) as first-line procedures. Adequate aneurysm occlusion (O’Kelly–Marotta grade C or D) was achieved in 50% of cases at last follow-up (median: 38.5 months (interquartile range: 29.5–48.0; total: 47.6 person-years)). No hemorrhagic or clinically significant ischemic events occurred. One asymptomatic ischemic lesion (7%) was detected on magnetic resonance imaging. No aneurysm growth or rupture was observed during follow-up. PICA patency was preserved in all cases, with non-significant narrowing in two patients. Neointimal hyperplasia was observed in six patients (43%).
Conclusion
Indirect flow diversion with vertebral artery FDS coverage of the PICA origin appears to be a technically feasible and safe strategy. Although complete occlusion rates may be lower than in other anatomical locations, the long-term stability and low complication rates support its use as a therapeutic option in selected cases.
Keywords: PICA aneurysm, indirect flow diversion, embolization, stent
Introduction
Aneurysms involving the posterior inferior cerebellar artery (PICA) are rare, accounting for only 0.5–3% of all intracranial aneurysms.1,2 However, they have been reported to carry a high risk of rupture, 3 and several studies have described significant morbidity and mortality in patients with ruptured PICA aneurysms. 4
PICA aneurysms differ from vertebrobasilar aneurysms in both location and morphology, with saccular and proximal PICA aneurysms being the most common subtypes. 5
There is currently no consensus on an optimal treatment strategy for these lesions. Although microsurgical management is highly effective, 6 it is often technically demanding and may not be suitable as a first-line option. Endovascular therapy offers a valuable alternative, including stand-alone coiling, balloon- or stent-assisted coiling, and parent vessel sacrifice in distal aneurysms. 1
Flow diversion with stents deployed entirely within the PICA remains technically challenging, primarily due to the tortuosity of the artery and the difficulty in achieving a suitable proximal landing zone. Indirect flow diversion, in which a flow-diverting stent (FDS) is placed in the vertebral artery (VA) across the PICA origin, appears more feasible. This strategy can be considered in highly challenging cases where direct catheterization of the PICA is deemed unsafe due to unfavorable anatomy. However, concerns persist regarding its effectiveness, particularly when treating aneurysms located distally in small-caliber vessels via stents deployed in a larger parent artery.7–9
The objective of our study was to report our 11-year single-center experience with indirect flow diversion for the treatment of saccular PICA aneurysms using FDS deployed in the V4 segment of the vertebral artery.
Methods
Data collection and analysis
This is a retrospective, single-center study. Clinical and radiological data from patients who underwent FDS placement in the V4 segment of the vertebral artery for proximal saccular PICA aneurysms at our institution between March 2013 and March 2024 were retrospectively analyzed. Inclusion criteria comprised of unruptured saccular aneurysms arising at the vertebral artery–PICA junction including cases with prior endovascular treatment and significant recanalization. Cases involving ruptured aneurysms or FDS placement entirely within the PICA were excluded.
Collected data included baseline patient characteristics (sex, age, history of ischemic stroke or aneurysmal subarachnoid hemorrhage, comorbidities, and modified Rankin Scale scores pre-treatment, post-treatment, and at follow-up), aneurysm characteristics (morphology and size), procedural details (type of FDS used and intraoperative heparin dosage), and post-procedural complications (neurological and non-neurological).
Endovascular procedure
All treatment decisions were approved in a multidisciplinary meeting involving vascular neurosurgeons, neurointerventionists, and neurologists. It should be emphasized that these cases were selected in a highly restrictive manner and indirect flow diversion was used only when no safer alternative existed. All procedures were performed by two senior neurointerventionists, each with over 20 years of experience in the endovascular treatment of intracranial aneurysms. The procedures were performed under general anesthesia in a GE Innova biplane angiosuite. After femoral access was obtained, a triaxial technique was consistently employed. The specific embolization technique and choice of FDS were left to the operator's discretion.
Five different types of FDS were used: a pipeline embolization device (PED; Medtronic Neurovascular, Irvine, CA, USA), a Flow Re-Direction Endoluminal Device (FRED; Microvention, Tustin, CA, USA), a surpass streamline (SS; Stryker Neurovascular, Fremont, CA, USA), a Surpass Evolve (SE; Stryker Neurovascular, Fremont, CA, USA), and a SILK Vista (Balt, Montmorency, France). In all cases, a single device was implanted.
Antiplatelet and heparin protocols
All patients received a loading dose of 180 mg ticagrelor the evening before the procedure, followed by a second dose immediately before the endovascular intervention. Postoperative treatment began the same evening, with 90 mg of ticagrelor administered twice daily (morning and evening) for 3 months.
Aspirin therapy was initiated during the procedure with an intravenous dose of 250 mg, followed by a daily oral dose of 160 mg for 12 months. As no biological test is recommended for monitoring ticagrelor efficacy, no antiplatelet response tests were performed.
An intravenous heparin bolus was administered during the procedure at a dose of 70 or 50 IU/kg on the operator's discretion.
Study outcomes
The primary outcome was the aneurysm occlusion rate at 6 months and at the last follow-up.
Safety outcomes included peri-procedural complications, cerebral ischemic events on magnetic resonance imaging (MRI) follow-up, delayed aneurysm rupture, PICA patency, and the presence of neointimal hyperplasia on digital subtraction angiography (DSA) follow-up.
Patient follow-up
The follow-up protocol included brain MRI at 3 months, incorporating T2 fluid-attenuated inversion recovery and time-of-flight sequences, as well as DSA at 6 months to assess aneurysm occlusion status and stent patency. Subsequently, a brain MRI was performed 1 year after the first DSA. Beyond this period, MRI was conducted every 2 years, while DSA was performed at the operator's discretion, typically if changes in the appearance of the treated aneurysm were observed.
Imaging analysis
Follow-up MRI and DSA were independently evaluated by two neuroradiologists: a senior with 30 years of experience and a junior with 4 years of experience in diagnostic neuroradiology. The radiological outcomes were reported using the most recent recommendations. 10 Aneurysm occlusion was assessed using the O’Kelly–Marotta (OKM) grading scale, ranging from A (complete filling) to D (no filling). 11
Statistical analysis
Baseline characteristics were analyzed using descriptive statistics. Categorical variables were reported as counts and percentages, and continuous variables were expressed as mean (standard deviation, SD) or median (interquartile range, IQR), depending on their distribution. A chi-square test was used for comparisons of categorical variables, and the Wilcoxon rank-sum test was applied for continuous variables.
Ethical approval
This study was a non-interventional, retrospective analysis using de-identified data, and therefore, written informed consent was waived. The ethics committee approval was not required, but a commitment to compliance was filed with the French National Information Science and Liberties Commission for National Healthcare Data, in accordance with the General Data Protection Regulation.
Results
Patients, aneurysms, and procedures characteristics
Among 2070 treated aneurysms and 677 FDS treatment, we identified 14 patients with unruptured saccular aneurysms located at the origin of the PICA who were treated using indirect flow diversion with FDS deployed in the V4 segment of the vertebral artery between March 2013 and March 2024 (Table 1, Supplemental table and Figure 1).
Table 1.
Cohort baseline characteristics.
| Patients characteristics | All patients (n = 14) |
|---|---|
| Age (mean) (SD) (years) | 54.5 (8.4) |
| Sex, female | 13 (93%) |
| History of other aneurysmal subarachnoid hemorrhage | 4 (28%) |
| Family history of first-degree relative aneurysm rupture | 3 (21%) |
| Comorbidities | |
| Smoker | 8 (57%) |
| Hypertension | 3 (21%) |
| Aneurysm discovery mode | |
| Sub-arachnoid hemorrhage | 6 (43%) |
| Incidentally found | 6 (43%) |
| Other ruptured aneurysm | 2 (14%) |
| Aneurysm dimension (mm) | |
| Size, median (IQR) (mm) | 4 (3–5) |
| Treatment session | |
| First line | 8 (57%) |
| Previously treated by coils | 5 (36%) |
| Previously treated by WEB | 1 (7%) |
| Number of stents used | |
| 1 | 14 (100%) |
| Complications | |
| Ischemic stroke (asymptomatic) | 1 (7%) |
| Aneurysm occlusion at 6 month follow-up (OKM scale) | |
| Incomplete (grades A and B) | 11 (79%) |
| Adequate (grades C and D) | 3 (21%) |
| Neointimal lining | |
| No | 8 (57%) |
| Non-significant (<50%) | 6 (43%) |
| Aneurysm occlusion at last follow-up (OKM scale) | |
| Incomplete (Grades A and B) | 7 (50%) |
| Adequate (Grades C and D) | 7 (50%) |
| PICA caliber | |
| Unchanged | 12 (86%) |
| Thinner (<50%) | 2 (14%) |
SD: standard deviation; IQR: interquartile range; WEB: Woven EndoBridge (Microvention); OKM: O’Kelly–Marotta scale (grade A: total filing >95%, grade D: no filing = total occlusion); PICA: posterior inferior cerebellar artery.
Figure 1.
Patient in their 40s with a history of a ruptured sylvian aneurysm presented with acute subarachnoid hemorrhage in the perimedullary cistern (not shown). Digital subtraction angiography (DSA) revealed a saccular aneurysm at the origin of the posterior inferior cerebellar artery (PICA) (a), which was initially treated with coiling. Follow-up angiography at 6 months (b) and 30 months (c) showed progressive recanalization of the aneurysm, also demonstrated on time-of-flight (TOF) magnetic resonance (MR) sequences (d). A 3.5 × 18 mm pipeline embolization device (PED; Medtronic Neurovascular) was deployed in the vertebral artery, covering the PICA origin (not shown). At the 6 month follow-up DSA (e) and the 18 month follow-up magnetic resonance imaging (MRI) (f), the aneurysm was completely occluded, while the PICA and the stent remained patent, with moderate neointimal hyperplasia and less than 50% narrowing of the PICA.
Mean patient age was 54.5 years (SD, 8.4 years). Thirteen patients were female (93%). Four patients had a previous history of aneurysmal subarachnoid hemorrhage due to the rupture of an aneurysm other than the PICA aneurysm and none had a history of ischemic stroke. The mean and median aneurysm size were 4.6 mm (SD, 2) and 4 (range, 2–9), respectively. Follow-up imaging was available in 14 patients (100%) with a median period of 38.5 months (IQR: 29.5–48.0; total: 47.6 person-years).
Eight interventions were first-line endovascular treatments (57%). For the remaining six patients (43%), the endovascular procedures were retreatments due to recanalization: five aneurysms (36%) were initially ruptured and treated with coils, while one aneurysm was initially ruptured and treated with a Woven EndoBridge (Microvention, Aliso Viejo, CA, USA) device.
An SE (Stryker Neurovascular) was used in six patients, a PED (Medtronic Neurovascular) in three patients, an FRED (Microvention) in two patients, an SS (Stryker Neurovascular) in two patients, and a SILK Vista (Balt) in one patient.
Primary outcomes
Follow-up imaging was available in 14 patients (100%). The 6 month follow-up showed adequate occlusion (OKM grades C and D) in three aneurysms (21%) and in seven aneurysms (50%) at last follow-up according to the OKM grading scale.
The seven remaining aneurysms (50%) were not occluded at follow-up but no aneurysm enlargement or rupture was observed during follow-up.
Safety outcomes
There were no technical and peri-procedural complications during the embolization procedures.
No delayed aneurysm rupture was reported during follow-up (median period of 38.5 months (IQR: 29.5–48.0; total: 47.6 person-years)).
On MRI follow-up, one asymptomatic ischemic lesion was found at 3 months in the PICA territory (1/14; 7%).
On DSA follow-up, the PICA was patent in all cases. In two patients (14%), a narrowing of the PICA was observed without clinical significance. Additionally, neointimal lining was observed in six stents (43%) but was not significant (less than 50% diameter stenosis).
The FDS wall apposition was deemed adequate in all cases (100%) during the per-procedural assessment and there was no evidence of significant braid changes on DSA follow-up.
Discussion
This study examined the use of indirect flow diversion to treat proximal saccular PICA aneurysms using FDS deployed in the V4 segment of the vertebral artery, covering the PICA origin. Adequate aneurysm occlusion rates were 50% at last follow-up (median: 38.5 months (IQR: 29.5–48.0; total: 47.6 person-years)).
These rates are lower than those typically reported for anterior circulation aneurysms treated with FDS, where occlusion rates approach 80%. 12 A meta-analysis by Alwakeal et al. 13 found a 65.1% complete occlusion rate for posterior circulation aneurysms treated with FDS. The lower occlusion rate in our series may reflect the specific strategy of indirect flow diversion intended to reduce flow into the PICA and aneurysm, thereby minimizing the risk of rupture or rebleeding. This approach—deploying an FDS proximally in the parent artery without fully covering the aneurysm neck—has emerged as a viable treatment for off-centered bifurcation aneurysms involving efferent branch origins (Figure 2).10,14
Figure 2.
Artist's illustration depicting the concept of indirect flow diversion for saccular aneurysms located at the origin of the posterior inferior cerebellar artery (PICA). In this example, a saccular aneurysm arises from the PICA origin at the junction with the vertebral artery (a, b). Device placement within the PICA itself won’t be feasible due to the vascular anatomy (a, b). Treatment is achieved by deploying a flow-diverting stent (FDS) in the V4 segment of the vertebral artery, covering the origin of the PICA (c).
Few comparable case series exist, with reported occlusion rates ranging from 42% to 100%, often involving small and heterogeneous patient cohorts, including fusiform and distal aneurysms treated with FDS deployed entirely within the PICA. 15
All aneurysms in our study were proximal, saccular, and located at the vertebral artery–PICA junction making endovascular access and embolization technically challenging due to their small size and hazardous anatomy. According to the classification by Srinivasan et al., 7 all aneurysms were type 1a (saccular, arising at the VA–PICA junction), and none had a sufficient landing zone to allow for FDS placement entirely within the PICA. This restricted anatomical subtype highlights the rarity and technical difficulty of such cases.
Despite a seemingly modest 50% complete occlusion rate, no aneurysm ruptures or growth were observed during a median follow-up of 38.5 months (IQR: 29.5–48.0; total: 47.6 person-years). In the literature, Oğuz et al. 16 reported one fatal rebleed 2 weeks after treatment of a ruptured aneurysm, and Chow et al. 17 described a delayed fatal rupture 10 days after FDS deployment in a patient with a giant aneurysm.
Regarding safety, we observed only one asymptomatic ischemic lesion (7%) on MRI at 3 months. PICA patency was maintained in all patients, with two cases (14%) showing asymptomatic PICA narrowing on DSA—findings consistent with previous reports.7,16 The main safety concern with FDS in the posterior circulation is ischemic stroke due to thromboembolic events, necessitating dual antiplatelet therapy. 18 In our literature review, Wallace et al. 19 reported one PICA territory infarct post-FDS, and Sathya et al. 8 reported one cerebellar stroke 22 months post-procedure. Other series reported no ischemic complications.7,16 These low rates of ischemia may relate to the end-arterial nature of the PICA, similar to the ophthalmic artery in anterior circulation. Our use of dual antiplatelet therapy with ticagrelor and aspirin—ticagrelor being a more potent P2Y12 inhibitor with fewer resistance issues than clopidogrel—may have contributed to favorable outcomes. 20
Neointimal lining was observed in six cases (43%), without resulting in clinically significant stenosis (less than 50% diameter stenosis) or necessitating any therapeutic adjustment during follow-up. Despite the absence of clinical consequences in our study, long-term imaging follow-up should be maintained due to the risk of delayed progression.
Flow diversion is now standard for anterior circulation aneurysms, 21 allowing for vessel reconstruction and high occlusion rates, despite procedural risks. However, its application to the posterior circulation remains controversial, with increased ischemic stroke risk likely due to perforator coverage.21,22 The vertebrobasilar system contains a higher density of perforators and end arteries, 23 and while emerging evidence suggests side branches may remain patent in the absence of competing flow, 24 risks remain, especially in relation to the anterior spinal artery and perforators of the upper medulla. 25
FDS deployment in the PICA remains off-label, and feasibility is limited by the vessel's small caliber and tortuosity. Additionally, ticagrelor may pose a higher bleeding risk compared to traditional aspirin–clopidogrel regimens. 26 Nevertheless, no hemorrhagic complications or intraoperative adverse events were reported in our study.
Posterior circulation aneurysms are less common (≤15% of intracranial aneurysms) but are associated with higher rupture risk, higher rebleeding rates, and worse clinical outcomes.27,28 PICA aneurysms, typically located at the VA–PICA junction, are especially fragile and prone to rupture even when small, necessitating early and aggressive management.5,29 While surgery is an effective first-line treatment, it is technically demanding due to the proximity of the brainstem and cranial nerves. 30 Endovascular treatment is also challenging due to the tortuosity and size of the PICA, making FDS deployment in the relatively straight vertebral artery an appealing alternative.
In a recent meta-analysis, Petr et al. 1 reported high technical success and long-term occlusion rates for both surgical and endovascular treatment of PICA aneurysms. However, neurological morbidity and mortality remained high: 14.4% and 9.8% for surgery, versus 15.1% and 17.1% for endovascular treatment. In contrast, our study reported only one asymptomatic ischemic lesion (7%) and no hemorrhagic complications.
Limitations of this study include its retrospective design, single-center nature, small sample size, absence of a control group, and the use of various FDS types. This technique should be reserved for highly selected cases.
Conclusion
The treatment of saccular PICA aneurysms using indirect flow diversion with FDS deployment in the vertebral artery appears to be a safe strategy. Although this method seems to be associated with a lower complete aneurysm occlusion rate compared to other aneurysm locations, no aneurysm rupture or enlargement was reported during our long-term follow-up.
Supplemental Material
Supplemental material, sj-docx-1-ine-10.1177_15910199251368702 for Indirect flow diversion for the treatment of saccular posterior inferior cerebellar artery aneurysms: An 11-year single-center retrospective study by Baptiste Donnard, Gregoire Boulouis, Cyrille Kuntz, Fouzi Bala, Richard Bibi, Heloise Ifergan, Valere Barrot, Clemence Hoche, Thibault Agripnidis, Johannes Kaesmacher, Denis Herbreteau and Kevin Janot in Interventional Neuroradiology
Footnotes
ORCID iDs: Baptiste Donnard https://orcid.org/0009-0003-2427-2625
Kevin Janot https://orcid.org/0000-0002-7305-3125
Ethical approval: This study was a non-interventional, retrospective analysis using de-identified data, and therefore, written informed consent was waived. The ethics committee approval was not required, but a commitment to compliance was filed with the French National Information Science and Liberties Commission for National Healthcare Data, in accordance with the General Data Protection Regulation.
Authors’ contributions: B. Donnard: conceptualization, acquisition of data, and writing—original draft preparation.
G. Boulouis: conceptualization, reviewing, and editing.
C. Kuntz: conceptualization, reviewing, and editing.
F. Bala: conceptualization, acquisition of data, and writing—original draft preparation.
R. Bibi: reviewing and editing.
H. Ifergan: reviewing and editing.
V. Barrot: reviewing and editing.
C. Hoche: reviewing and editing.
T. Agripnidis: reviewing and editing.
J. Kaesmacher: reviewing and editing.
D. Herbreteau: reviewing and editing.
K. Janot: conceptualization, acquisition of data, and writing—original draft preparation.
Funding: The authors received no financial support for the research, authorship, and/or publication of this article.
The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: GB reports consulting for Siemens. DH reports consulting for Terumo Neuro and Phenox. KJ reports consulting for Balt. The other authors reported no competing interests.
Data availability statement: Data are available upon reasonable request.
Supplemental material: Supplemental material for this article is available online.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Supplemental material, sj-docx-1-ine-10.1177_15910199251368702 for Indirect flow diversion for the treatment of saccular posterior inferior cerebellar artery aneurysms: An 11-year single-center retrospective study by Baptiste Donnard, Gregoire Boulouis, Cyrille Kuntz, Fouzi Bala, Richard Bibi, Heloise Ifergan, Valere Barrot, Clemence Hoche, Thibault Agripnidis, Johannes Kaesmacher, Denis Herbreteau and Kevin Janot in Interventional Neuroradiology