# Imaging follow-up of unruptured intracranial aneurysms treated with flow diverter: Insights from a French collaborative survey

Thomas Marque, Victor Dumas, Thibault Agripnidis, François Zhu, Guillaume Charbonnier, Baptiste Donnard, Quentin Holay, Jean Darcourt, Luca Scarcia, Alexis Guédon, et al.

► To cite this version:

Thomas Marque, Victor Dumas, Thibault Agripnidis, François Zhu, Guillaume Charbonnier, et al. "Imaging follow-up of unruptured intracranial aneurysms treated with flow diverter: Insights from a French collaborative survey." Journal de Neuroradiologie / Journal of Neuroradiology, 2025, 52 (3), pp.101338. 10.1016/j.neurad.2025.101338. hal-05043915

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Original Article

# Imaging follow-up of unruptured intracranial aneurysms treated with flow diverter: Insights from a French collaborative survey

<figure><img src="image_2.png" /></figure>

Thomas Marque<sup>a</sup>, Victor Dumas<sup>b</sup>, Thibault Agripnidis<sup>c</sup>, François Zhu<sup>d</sup>, Guillaume Charbonnier<sup>e</sup>, Baptiste Donnard<sup>f</sup>, Quentin Holay<sup>g</sup>, Jean Darcourt<sup>h</sup>, Luca Scarcia<sup>i</sup>, Alexis Guédon<sup>j</sup>, Vincent L'Allinec<sup>k</sup>, Jean-Baptiste Girot<sup>k</sup>, Gaultier Marnat<sup>l</sup>, Géraud Forestier<sup>m</sup>, Guillaume Bellanger<sup>n</sup>, Quentin Alias<sup>o</sup>, Louis Bonnard<sup>p</sup>, Romain Bourcier<sup>q</sup>, Julien Allard<sup>r</sup>, Martin Bretzner<sup>s</sup>, Romain Coudert<sup>t</sup>, Aymeric Rouchaud<sup>t</sup>, Jean-François Hak<sup>c</sup>, Margaux Lefebvre<sup>a</sup>, Emmanuel Gerardin<sup>a</sup>, Chrysanthi Papagiannaki<sup>a</sup>, Julien Burel<sup>a,*,</sup> JENI-Research Collaborative

ARTICLE INFO

Article History:

Available online 31 March 2025

Keywords:

Intracranial aneurysm

Flow diverters

Digital subtraction angiography

Magnetic resonance imaging

Interventional neuroradiology

A B S T R A C T

**Purpose:** The absence of standardized guidelines for imaging follow-up of unruptured intracranial aneurysms treated with flow diverters (FD) results in significant variability across centers. This survey aims to provide a comprehensive overview of current imaging follow-up practices in French academic centers.

**Methods:** In April 2024, a 49-question survey was distributed to interventional neuroradiology centers in France through the trainee-led research collaborative network, Jeunes En Neuroradiologie Interventionnelle-Research Collaborative (JENI-RC). The survey covered follow-up protocols for digital subtraction angiography (DSA), magnetic resonance imaging (MRI), and computed tomography (CT), as well as potential modifications for specific cases.

**Results:** Twenty interventional neuroradiology centers responded to the survey. Most centers (n = 14, 70 %), conducted a single systematic DSA either at 6 or 12 months post-procedure. In most centers (n = 13, 65 %), a second DSA was scheduled only based on the results of the first, specifically in cases of non-occluded aneurysm, intimal hyperplasia, or in-stent stenosis. MRI follow-up varied, with most centers (n = 12, 60 %) performing three MRIs over five years. Only two centers included CT scans in their protocols.

**Conclusion:** This survey highlights the substantial heterogeneity in imaging follow-up protocols for FD-treated unruptured intracranial aneurysms among French academic centers. The findings underscore the urgent need for standardized guidelines to harmonize practices, optimize patient outcomes, and improve

Abbreviations: FD, flow diverter; DSA, digital subtraction angiography; MRI, magnetic resonance imaging; MRA, magnetic resonance angiography; JENI-RC, jeunes en neuroradiologie interventionnelle-research collaborative; CT, computed tomography; CE, contrast-enhanced; TOF, time of flight

* Corresponding author.

E-mail address: bureljulien@live.fr (J. Burel).

A B S T R A C T

<footnote><sup>a</sup> Department of Radiology, Rouen University Hospital, Rouen, Normandy, France</footnote>

<footnote><sup>b</sup> Radiology Department, Poitiers University Medical Center, Poitiers, Vienne, France</footnote>

<footnote><sup>c</sup> Department of Neuroradiology, APHM La Timone, Marseille, France</footnote>

<footnote><sup>d</sup> Department of Diagnostic and Therapeutic Neuroradiology, University Hospital of Nancy, Nancy, France</footnote>

<footnote><sup>e</sup> Interventional Neuroradiology Department, Besançon University Hospital, Besançon, France</footnote>

<footnote><sup>f</sup> Diagnostic and Interventional Neuroradiology Department, University Hospital of Tours, Tours, France</footnote>

<footnote><sup>g</sup> Radiology Department, Hôpital d'Instruction des Armées Sainte-Anne, Toulon, France</footnote>

<footnote><sup>h</sup> Radiology Department, Clinique des Cèdres, Toulouse, France</footnote>

<footnote><sup>i</sup> Neuroradiology Unit, Henri Mondor Hospital, Creteil, France</footnote>

<footnote><sup>j</sup> Department of Neuroradiology, Lariboisière Hospital, AP-HP, Paris, France</footnote>

<footnote><sup>k</sup> Radiology Department, Angers University Hospital, Angers, France</footnote>

<footnote><sup>l</sup> Interventional and Diagnostic Neuroradiology, University Hospital Centre Bordeaux, Bordeaux, Aquitaine, France</footnote>

<footnote><sup>m</sup> Department of Neuroradiology, Clermont-Ferrand University Hospital, Clermont-Ferrand, France</footnote>

<footnote><sup>n</sup> Department of Neuroradiology, Purpan University Hospital, Toulouse, France</footnote>

<footnote><sup>o</sup> Department of Diagnostic and Therapeutic Neuroradiology, University Hospital of Rennes, Rennes, France</footnote>

<footnote><sup>p</sup> Interventional Neuroradiology Department, Strasbourg University Hospitals, Strasbourg, France</footnote>

<footnote><sup>q</sup> Department of Diagnostic and Therapeutic Neuroradiology, University Hospital of Nantes, Thorax Institute, Nantes, France</footnote>

<footnote><sup>r</sup> Department of Interventional Neuroradiology, Hopitaux Universitaires Pitie Salpetriere-Charles Foix, Paris, France</footnote>

<footnote><sup>s</sup> Department of Interventional Neuroradiology, CHU Lille, University of Lille, Lille, France</footnote>

<footnote><sup>t</sup> Department of Radiology, Limoges University Hospital, CHU Dupuytren, Limoges, France</footnote>
resource utilization. Additionally, innovations in FD technology, advancements in MRI sequences, and the advent of photon-counting CT will likely influence follow-up practices in the near future.

© 2025 The Authors. Published by Elsevier Masson SAS. This is an open access article under the CC BY license

(http://creativecommons.org/licenses/by/4.0/)

## Introduction

Flow diversion is an effective and now widely used technique worldwide in the treatment of unruptured intracranial aneurysms.¹ Although the rate of complete occlusion after flow diverter (FD) treatment varies across studies, it gradually increases due to the remodeling of the parent vessel over time. Reported complete occlusion rates in the literature range from 55 % to 75 % at 6 months, 80 % to 90 % at 12 months, and reach about 95 % at 3–5 years post-treatment.²⁻⁵ Several factors have been associated with incomplete aneurysm occlusion after flow diversion, including large aneurysm size, branch arising from the dome or neck, older age, and absence of smoking.⁶,⁷ Such incomplete occlusions may, in some cases, lead to retreatment.⁸ The overall retreatment rate is low, at around 3 %.⁵ These occasionally necessary retreatments almost exclusively concern persistent aneurysms despite the placement of the FD, as aneurysmal recanalizations after FD treatment are exceptional.⁹,¹⁰ Thus, an aneurysm treated with an FD, which has been proven completely occluded by angiography, is generally considered definitively occluded.⁵,¹¹⁻¹⁴

Currently, there are no specific recommendations regarding imaging follow-up after the treatment of intracranial aneurysms with FDs. Most centers use a combination of digital subtraction angiography (DSA) and magnetic resonance imaging (MRI) at varying intervals.¹⁵,¹⁶ The objectives of follow-up imaging are multiple. First, it is essential to assess aneurysm occlusion, which is best evaluated with digital subtraction

angiography (DSA), although MRI has shown good diagnostic performance for this purpose. Second, follow-up aims to detect potential parenchymal complications, both ischemic and hemorrhagic, which are primarily assessed using MRI. Third – and this is specific to aneurysms treated with stents, whether flow diverters or not – it is important to monitor the parent artery, particularly the stented segment, for which DSA remains the reference technique, as MRI is still insufficient in this regard.⁴,⁵,¹² This segment requires surveillance due to the possible development of intimal hyperplasia, which, although most often asymptomatic, may occasionally result in significant in-stent stenosis – reported in approximately 3–5 % of cases – and delayed ischemic complications. Therefore, monitoring is essential to allow timely adjustment of antithrombotic therapy, the addition of statins, or even interventional treatment, in order to prevent such ischemic events.¹²,¹⁷

Therefore, the aim of this study was to evaluate the imaging follow-up strategies used in the monitoring of patients treated for unruptured aneurysms with FD.

## Materials and methods

### *Study design and data sources*

Through the French trainee-led research collaborative "Jeunes En Neuroradiologie Interventionnelle-Research Collaborative (JENI-RC),¹⁸,¹⁹ under the aegis of the French network of Neuroradiologists "Société française de

<table><caption>**Table 1**
5-Year systematic DSA follow-up after successful flow diversion for unruptured intracranial aneurysms.</caption><thead><tr><th>Center</th><th>6-week DSA</th><th>3-month DSA</th><th>6-month DSA</th><th>9-month DSA</th><th>1-year DSA</th><th>18-month DSA</th><th>2-year DSA</th><th>3-year DSA</th><th>4-year DSA</th><th>5-year DSA</th><th>Number of DSA performed</th></tr></thead><tbody><tr><td>Center 1</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 2</td><td></td><td>1</td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td>2</td></tr><tr><td>Center 3</td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 4</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td></td><td></td><td>2</td></tr><tr><td>Center 5</td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td>2</td></tr><tr><td>Center 6</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 7</td><td>No systematic DSA</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 8</td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 9</td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 10</td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 11</td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 12</td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 13</td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 14</td><td></td><td>1</td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td>2</td></tr><tr><td>Center 15</td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 16</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 17</td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 18</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 19</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td>1</td></tr><tr><td>Center 20</td><td></td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td>2</td></tr><tr><td>Total</td><td>1</td><td>3</td><td>8</td><td>1</td><td>7</td><td>3</td><td>0</td><td>1</td><td>0</td><td>0</td><td></td></tr></tbody></table>

DSA: Digital Subtraction Angiography
Neuroradiologie", a survey written in French was distributed electronically to a delegate physician (a member of the network) at each of the 31 interventional neuroradiology center in metropolitan France in April 2024. For internal validity, the survey was initially sent randomly to three interventional neuroradiologists (INR) and modified to consider the comments received during this first step. The new version was then approved by a scientific committee (T.M., an INR fellow, J.B., a senior INR with three years of experience; C.P. an INR with over 20 years of experience). We excluded partial or duplicate responses and contacted the delegate physician in cases of any difficulties concerning the answers.

A total of 49 questions were included in the questionnaire. The questions were divided into two parts: the first part addressed classical cases, asking physicians to respond as follows: "This is an incidentally discovered intracranial aneurysm of the non-giant saccular type. The procedure and immediate aftermath were straightforward. There are no complications during follow-up (aside from intimal hyperplasia, in-stent stenosis, or lack of aneurysmal occlusion)." This first part was itself divided into three sub-sections, concerning follow-ups using DSA, MRI, and possibly computed tomography (CT) scans. The second part focused on specific cases and potential modifications of follow-up protocols. The full version of the survey is available in English in the **Online Supplemental Data**.

## Statistical analysis

Given the study's non-random sample selection, the statistical approach was primarily descriptive. Quantitative variables were presented as medians and ranges, while categorical variables were shown as counts and percentages.

## Results

Thirty-one French interventional neuroradiology centers were invited to participate in the survey, and twenty responded (64.5 %). All respondents completed the entire questionnaire.

### DSA follow-up

The 5-year systematic DSA follow-up protocol for patients who underwent successful flow diversion for unruptured intracranial aneurysms included multiple regimens, as detailed in Table 1. Most centers (n = 14, 70 %) performed only one systematic DSA, primarily at 6 months or 12 months post-procedure.

Most of the centers (n = 13, 65 %) indicated that they scheduled a second DSA only based on the results of the first DSA. Specifically: 2 centers scheduled a second DSA if the aneurysm was not occluded on the first DSA; 5 centers scheduled a second DSA if there was intimal hyperplasia or in-stent stenosis; and 6 centers scheduled a second DSA if either one of the two conditions (non-occluded aneurysm or intimal hyperplasia or in-stent stenosis) was present. Most of these centers (n = 8, 62 %) opted for a delay of 6 months for the second DSA in these conditional scenarios, while some (n = 5, 38 %) opted for a delay of 1 year.

### MRI follow-up

The 5-year systematic MRI follow-up protocol for patients who underwent successful flow diversion for unruptured intracranial aneurysms included multiple regimens, as detailed in Table 2. Most centers (n = 12, 60 %) performed 3 MRIs within this initial period of

<table><caption>**Table 2**
5-Year systematic MRI Follow-Up after successful flow diversion for unruptured intracranial aneurysms.</caption><thead><tr><th>Center</th><th>3-month MRI</th><th>6-month MRI</th><th>9-month MRI</th><th>1-year MRI</th><th>18-month MRI</th><th>2-year MRI</th><th>3-year MRI</th><th>4-year MRI</th><th>5-year MRI</th><th>Number of MRI performed</th></tr></thead><tbody><tr><td>Center 1</td><td>1</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td>3</td></tr><tr><td>Center 2</td><td></td><td></td><td></td><td></td><td></td><td>1</td><td>1</td><td></td><td></td><td>2</td></tr><tr><td>Center 3</td><td>1</td><td></td><td></td><td></td><td>1</td><td></td><td>1</td><td></td><td></td><td>3</td></tr><tr><td>Center 4</td><td></td><td>1</td><td></td><td></td><td>1</td><td></td><td>1</td><td></td><td></td><td>3</td></tr><tr><td>Center 5</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td>1</td><td></td><td>1</td><td>3</td></tr><tr><td>Center 6</td><td></td><td>1</td><td></td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td>3</td></tr><tr><td>Center 7</td><td>1</td><td></td><td></td><td>1</td><td></td><td>1</td><td>1</td><td></td><td>1</td><td>5</td></tr><tr><td>Center 8</td><td></td><td></td><td></td><td>1</td><td></td><td>1</td><td>1</td><td></td><td></td><td>3</td></tr><tr><td>Center 9</td><td>No systematic MRI</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 10</td><td></td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td></td><td>1</td><td>3</td></tr><tr><td>Center 11</td><td>1</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td>2</td></tr><tr><td>Center 12</td><td></td><td>1</td><td></td><td></td><td></td><td>1</td><td></td><td>1</td><td></td><td>3</td></tr><tr><td>Center 13</td><td>1</td><td></td><td></td><td></td><td>1</td><td></td><td>1</td><td></td><td></td><td>3</td></tr><tr><td>Center 14</td><td>No systematic MRI</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 15</td><td>1</td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td></td><td>1</td><td>4</td></tr><tr><td>Center 16</td><td></td><td>1</td><td></td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td>3</td></tr><tr><td>Center 17</td><td></td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td></td><td>1</td><td>3</td></tr><tr><td>Center 18</td><td></td><td>1</td><td></td><td>1</td><td></td><td></td><td></td><td></td><td></td><td>2</td></tr><tr><td>Center 19</td><td>1</td><td></td><td></td><td></td><td></td><td>1</td><td></td><td></td><td>1</td><td>3</td></tr><tr><td>Center 20</td><td>1</td><td></td><td></td><td></td><td>1</td><td></td><td></td><td></td><td></td><td>2</td></tr><tr><td>Total</td><td>8</td><td>5</td><td>0</td><td>6</td><td>5</td><td>9</td><td>10</td><td>1</td><td>9</td><td></td></tr></tbody></table>

MRI: Magnetic Resonance Imaging
<table><caption>**Table 3**
MRI sequences included in the standardized imaging protocol for unruptured intracranial aneurysms treated with FD.</caption><thead><tr><th>Center</th><th>FLAIR sequence</th><th>3D-TOF-MRA</th><th>CE-MRA</th><th>T2* or other magnetic susceptibility sequence</th><th>Non-contrast T1-weighted sequence</th><th>CE-T1-weighted sequence</th><th>Time resolved MRA</th></tr></thead><tbody><tr><td>Center 1</td><td>X</td><td>X</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 2</td><td>X</td><td>X</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 3</td><td>X</td><td>X</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 4</td><td>X</td><td>X</td><td></td><td>X</td><td>X</td><td>X</td><td></td></tr><tr><td>Center 5</td><td>X</td><td></td><td>X</td><td></td><td></td><td></td><td></td></tr><tr><td>Center 6</td><td>X</td><td>X</td><td></td><td>X</td><td></td><td></td><td></td></tr><tr><td>Center 7</td><td>X</td><td>X</td><td></td><td>X</td><td>X</td><td>X</td><td></td></tr><tr><td>Center 8</td><td>X</td><td>X</td><td></td><td></td><td></td><td>X</td><td>X</td></tr><tr><td>Center 9</td><td>X</td><td>X</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 10</td><td>X</td><td>X</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 11</td><td>X</td><td></td><td>X</td><td>X</td><td></td><td></td><td></td></tr><tr><td>Center 12</td><td>X</td><td></td><td>X</td><td></td><td></td><td>X</td><td></td></tr><tr><td>Center 13</td><td>X</td><td></td><td></td><td></td><td></td><td></td><td>X</td></tr><tr><td>Center 14</td><td>X</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Center 15</td><td>X</td><td></td><td>X</td><td></td><td></td><td></td><td></td></tr><tr><td>Center 16</td><td>X</td><td></td><td>X</td><td></td><td></td><td></td><td></td></tr><tr><td>Center 17</td><td>X</td><td></td><td>X</td><td></td><td></td><td></td><td></td></tr><tr><td>Center 18</td><td>X</td><td></td><td>X</td><td></td><td></td><td></td><td>X</td></tr><tr><td>Center 19</td><td>X</td><td></td><td>X</td><td></td><td>X</td><td></td><td></td></tr><tr><td>Center 20</td><td>X</td><td></td><td>X</td><td></td><td></td><td></td><td></td></tr><tr><td>Total</td><td>20</td><td>17</td><td>3</td><td>8</td><td>3</td><td>4</td><td>3</td></tr></tbody></table>

MRA: Magnetic Resonance Angiography; CE: contrast-enhanced; TOF: time of flight

5 years, with an early MRI (at 3 or 6 months post-procedure), then an MRI at 2 or 3 years, and finally an MRI at 5 years.

### MRI protocol

The standardized MRI protocols included a variety of sequences, as shown in Table 3. Seven centers (35 %) used only a combination of a FLAIR sequence and a 3D-TOF-MR Angiography (MRA) sequence. Eight centers (40 %) used a magnetic susceptibility sequence.

Additional information regarding the injection of gadolinium, the type of MRI machine used (3.0T versus 1.5T), the use of a 2D or 3D FLAIR sequence, and the type of magnetic susceptibility sequence, is provided in Fig. 1.

### CT follow-up

Only 2 out of 20 centers (10 %) used CT scans during the systematic follow-up of patients treated with FD for unruptured intracranial aneurysms. Notably, center 16 performed dual-energy CT immediately post-operatively.

### Follow-Up duration

After complete exclusion of the aneurysm, the duration of imaging follow-up varied between centers. Most centers (n = 14, 70 %) followed the patients for their lifetime (see Fig. 2).

### Dual antiplatelet therapy

The protocols for modifying dual antiplatelet therapy after FD treatment of unruptured intracranial aneurysms varied. Some centers waited for the results of the first DSA, the first MRI, or both, while others modified these treatments independently of these examinations. This is shown in Fig. 3.

### Specific cases and potential modifications of follow-up protocols

Almost no center modified its imaging follow-up protocol based on the size of aneurysms treated with FD, the type of FD used, the use of additional devices (such as coils, WEB, or other devices) either simultaneously or in cases of secondary recanalization of a coiled aneurysm, posterior circulation aneurysms, sylvian aneurysms, and distal aneurysms (e.g., M2 bifurcation, P2 bifurcation, pericallosal). Only Center 7, which did not perform systematic follow-up DSA, performed a DSA instead of MRI in cases of micro-aneurysms deemed impossible to follow with MRI, or giant aneurysms with uncertainty about their occlusion.

### Discussion

This study provides comprehensive insights into the imaging follow-up practices for unruptured intracranial aneurysms treated with FD across 20 French interventional neuroradiology centers. The survey reveals significant variability in follow-up protocols, reflecting the absence of standardized guidelines. Most centers utilize a
**Does the protocol always include a Gadolinium injection?**

<figure><img src="image_3.png" /></figure>

**Is the FLAIR sequence a 2D or 3D sequence?**

<figure><img src="image_4.png" /></figure>

**Is the MRI performed on a 1.5T or 3.0T machine?**

<figure><img src="image_5.png" /></figure>

**Which magnetic susceptibility sequence do you use?**

<figure><img src="image_6.png" /><figcaption>**Fig. 1.** Details on gadolinium injection, MRI machine type, FLAIR sequence, and magnetic susceptibility sequence.</figcaption></figure>

combination of DSA and MRI at various intervals, tailored to monitor both aneurysmal occlusion and the condition of the parent artery.

The objectives of follow-up imaging are multiple. First, it is essential to assess aneurysm occlusion, which is best evaluated with digital subtraction angiography (DSA), although MRI has shown good diagnostic performance for this purpose. Second, follow-up aims to detect potential parenchymal complications, both ischemic and hemorrhagic, which are primarily assessed using MRI. Third – and this is specific to aneurysms treated with stents, whether flow diverters or not – it is important to monitor the parent artery, particularly the stented segment, for which DSA remains the reference technique, as MRI is still insufficient in this regard.⁴,⁵,¹²

Our findings indicate that while most centers perform an initial DSA at 6 or 12 months post-procedure, subsequent DSAs are often conditional, dependent on the results of the initial imaging. Notably, one center reported not performing any systematic follow-up DSA, illustrating an even more conservative imaging approach. This approach aligns with the necessity to balance the invasiveness and risks associated with DSA²⁰ against the benefits of detailed vascular imaging. The high reliance on DSA for detecting intimal hyperplasia or in-stent stenosis underscores its critical role in the follow-up of FD-treated aneurysms. Moreover, while MRI has excellent diagnostic performance in evaluating aneurysmal occlusion,²¹⁻²³ it remains less accurate compared to DSA in evaluating parent artery patency.²⁴⁻²⁷

<figure><img src="image_7.png" /><figcaption>**Fig. 2.** Imaging follow-up duration for unruptured aneurysms treated with flow diverters.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 3.** Influence of follow-up imaging on the modification of dual antiplatelet therapy after flow diverter treatment. “Yes” indicates that imaging findings influence the decision to modify DAPT (e.g., prolongation in case of in-stent stenosis, or conversely, withdrawal of one antiplatelet agent). “No” indicates that DAPT duration is predefined and not influenced by imaging.</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>Fig. 4. Proposed follow-up protocol for unruptured intracranial aneurysms treated with FD.</figcaption></figure>

The varying intervals and conditional nature of further DSAs high-
light a need for clearer guidelines to optimize patient outcomes and
resource utilization.

MRI follow-up protocols also exhibit considerable variation, with most centers opting for three MRIs over the first five years. The preference for MRI, particularly for long-term follow-up, is justified by its non-invasive nature, its lower cost compared to DSA and its capability to detect parenchymal complications, which are crucial for comprehensive patient management. Beyond ischemic and hemorrhagic complications, it is also important to look for potential signs suggestive of non-ischemic cerebral enhancing (NICE) lesions, which are increasingly recognized as a rare inflammatory complication and may require contrast-enhanced MRI for proper assessment.²⁸,²⁹ The diversity in MRI sequences, including the frequent use of FLAIR and 3D-TOF-MRA and the occasional use of contrast-enhanced sequences, reflects the ongoing evolution in imaging technology and techniques aimed at improving diagnostic accuracy.²⁴⁻²⁷ While FLAIR appears essential to detect parenchymal complications, SWI seems to be optionally used only in cases where abnormalities are detected on FLAIR, particularly to help differentiate between ischemic and hemorrhagic lesions. Recent innovative MRI sequences, particularly the improvements in high-resolution vessel wall imaging sequences,²⁶ as well as silent MR angiography,²⁴ which combines arterial spin labeling and an ultrashort time echo, are noteworthy. These advancements are particularly interesting for studying both aneurysmal occlusion and intimal hyperplasia or in-stent stenosis without the need for gadolinium injection.

The minimal utilization of CT in follow-up protocols, with only
two centers incorporating it, indicates a limited role for CT in the rou-
tine monitoring of FD-treated aneurysms. However, recent advance-
ments in CT imaging technology have the potential to revolutionize
flow diversion imaging follow-up, particularly with the advent of
photon-counting detector CT imaging. The capability of ultra-high-
resolution photon-counting CT to assess coronary stent patency³⁰,³¹
suggests its potential applicability for evaluating intracranial FDs.³²
Despite the requirement for iodinated contrast media and the expo-
sure to ionizing radiation, its non-invasive nature positions it as an
alternative to consider to DSA. When available in routine clinical
practice, optical coherence tomography could also be incorporated
into the imaging follow-up of FDs.³³⁻³⁵ However, its invasiveness
will limit its use to complex cases.

On the one hand, an aneurysm treated with a FD that has been
proven to be completely occluded is generally considered perma-
nently occluded.⁵ Moreover, long-term adverse events appear to be
exceptional. A recent meta-analysis on the long-term (>1 year)

outcomes of FD for unruptured intracranial aneurysms, including
1186 patients, reported no delayed ruptures and only one case of
delayed ischemic stroke.¹⁷ On the other hand, patients with one
aneurysm are at risk of developing de novo aneurysms,³⁶,³⁷ justifying
the lifetime follow-up adopted by many centers.

Regarding practices in other western countries, Gupta et al.<sup>12,15</sup> recently studied the imaging follow-up practices of 26 U.S. centers for FD. They observed an aneurysmal occlusion rate of 38.2 % at 6 months and 77.8 % at 12 months. Based on these findings, they propose not performing angiography at 6 months, instead conducting the first examination at 12 months. If complete occlusion is not observed at 12 months, they suggest performing an MRI 1 year later, as a small (but significant) proportion of aneurysms that were not occluded in the first year became occluded in the following year. Due to a trend towards a decrease in the cumulative incidence of aneurysmal occlusion in patients aged 70 years or older, an alternative follow-up strategy is proposed.

A few remarks can be made regarding this follow-up strategy: the
authors observed a relatively low occlusion rate at 6 months com-
pared to other studies in the literature.²⁻⁵ Additionally, the benefit of
being able to adjust dual antiplatelet therapy during follow-up, and
thus avoiding its possible complications, is not addressed.

The protocols for modifying dual antiplatelet therapy after FD treatment of unruptured intracranial aneurysms varied between centers. The optimal regimen of antiplatelet therapy for FD remains unknown because current regimens lack high-quality evidence to guide them.³⁸ Additionally, FDs with surface modifications are increasingly being used in the treatment of unruptured intracranial aneurysms, which will alter the antiplatelet protocols used for FD placement.³⁹ Therefore, the optimal duration of antiplatelet therapy for FD, which can prevent both ischemic events associated with inadequate antiplatelet therapy and bleeding events associated with prolonged dual antiplatelet therapy, needs to be assessed by prospective studies. This question is complex, likely device-dependent, and may evolve with the increasing use of surface-modified flow diverters.³⁹

Based on the data collected from these 20 French academic cen-
ters treating unruptured intracranial aneurysms with FDs, Fig. 4
presents a proposed follow-up protocol for these patients.

This study has several limitations. First, the data collected are
based on self-reported practices from survey responses, which may
introduce response bias and variability in the interpretation of survey
questions. Second, the survey was conducted only among French
interventional neuroradiology centers, limiting the generalizability of
the findings to other countries and healthcare systems with different
practices and resources. Third, the survey did not capture detailed
reasons behind each center's choice of follow-up protocol, which
could provide valuable context for the variations observed. Fourth,
the responses were collected at the center level, which may introduce
bias as there can sometimes be intra-center practice variations.
Lastly, the study did not evaluate clinical outcomes associated with
the different follow-up strategies, making it difficult to determine the
effectiveness and safety of the various protocols used.

Conclusion

This survey highlights the substantial heterogeneity in imaging
follow-up protocols for FD-treated unruptured intracranial aneur-
ysms among French centers. The findings underline the urgent need
for standardized guidelines to harmonize practices, optimize patient
outcomes, and improve resource utilization. Additionally, innova-
tions in FD technology, advancements in MRI sequences, and the
advent of photon-counting CT will likely change follow-up practices
in the near future.

Declaration of competing interest

We have no Conflict of Interest.

Supplementary materials

Supplementary material associated with this article can be found,
in the online version, at doi:10.1016/j.neurad.2025.101338.

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