The management of complex basilar artery aneurysms (BAA) is among the most difficult challenges in neurointerventions, as both microsurgical and endovascular approaches are associated with substantial risks. These aneurysms are challenging to manage because of their deep anatomical location and proximity to critical perforating arteries, compounded by factors such as fusiform morphology and proximal stenosis, which increase the risk of thromboembolic events and limit device options (1). Historically, surgical clipping and deconstructive techniques often required parent vessel sacrifice with uncertain collateral support and high morbidity. The introduction of flow diverters (FD) has transformed aneurysm management by enabling parent artery preservation and promoting intra-aneurysmal thrombosis (2, 3). While FDs are highly effective in the anterior circulation, their use in the posterior circulation, particularly for fusiform and large BAAs, remains technically demanding (4). In such cases, a single FD may not achieve sufficient effect, potentially leading to persistent filling, delayed thrombosis, or even rupture. Long-segment reconstructions are also technically complex and may increase the risk of malapposition, incomplete expansion, or migration (5). To address these challenges, telescopic placement of multiple FDs has been developed to enhance flow modification and improve construct stability (6).

In this report, we describe a case of a complex BAA with pre-aneurysmal stenosis managed in a single session using balloon angioplasty followed by telescopic FD reconstruction. The procedure was complicated by instability at the junction of two telescopically deployed stents, resulting in a potential risk of migration into the aneurysm. This case underscores the evolving role of adjunctive stenting in posterior circulation aneurysm management and highlights the importance of adaptive endovascular strategies for high-risk vascular reconstructions.

Endovascular techniques for complex BAAs have advanced significantly, with flow diversion becoming a key strategy for managing large and fusiform aneurysms in anatomically challenging locations (5, 7–9). In this context, the potential link between proximal stenosis and aneurysm formation remains an important consideration, as stenotic segments can induce hemodynamic alterations that contribute to vascular remodeling. These changes may increase wall stress, predisposing the vessel to progressive dilation and, over time, aneurysm development (1).

Unlike conventional stent-assisted coiling, which relies on mechanical occlusion often fails to reduce the mass effect in large aneurysms (10), FD promotes intra-aneurysmal thrombosis while reconstructing the parent artery. Additionally, stent-assisted coiling may not effectively reduce the mass effect in large aneurysms, as the aneurysm sac remains packed with coils, potentially exerting continued pressure on adjacent brainstem structures (7, 11–14). In contrast, FD treatment has been shown to achieve favorable volumetric reduction and aneurysm sac shrinkage, often resulting in radiologically confirmed reversal of mass effect and clinical improvement in most cases (15).

However, in large and fusiform BAAs, a single FD may not provide adequate coverage. In this case, the landing zones were limited by the long-segment aneurysm and proximal stenosis, leaving insufficient healthy vessel for stable anchoring and thereby increasing the risk of malapposition, incomplete coverage, and device instability (5, 16, 17).

Given these challenges, telescopic flow diversion, or double-stent embolization, involves deploying multiple overlapping FDs in a staged or sequential manner to achieve durable vessel reconstruction. In our case, the stents were deployed in a distal-to-proximal sequence. This approach facilitated easier navigation and ensured stable anchoring in the distal healthy segment before extending coverage proximally across the aneurysm. Conversely, a proximal-to-distal deployment strategy may in some cases provide stronger anchorage at the vertebral side and reduce the risk of foreshortening, though it is technically more demanding and increases the risk of distal device migration (16, 18, 19).

In wide-neck complex aneurysms, telescopic stenting offers several advantages over single FD deployment (2, 16, 20). First, it increases metal coverage, enhancing flow diversion and accelerating aneurysm occlusion. Second, it improves construct stability in long-segment or fusiform aneurysms by reducing the risk of device migration or shortening. Third, when the initial FD fails to fully expand due to vascular tortuosity or poor wall apposition, an additional FD can optimize device conformation and adherence, minimizing the risk of residual aneurysm filling.

A key factor in our treatment strategy was the presence of proximal preaneurysmal stenosis, which significantly altered basilar artery hemodynamics and influenced our approach to endovascular reconstruction. This stenosis introduced several challenges, including an elevated risk of postprocedural thromboembolic complications and potential inadequate device expansion (21). To address this, we performed balloon angioplasty before FD deployment to optimize vessel diameter, ensuring proper FD expansion and reducing the risk of malapposition (16). The angioplasty was carefully executed to minimize the risk of endothelial injury or dissection.

Initially, we chose a telescopic FD approach over a single-device strategy. However, despite its theoretical advantages, we encountered FD instability, necessitating additional intervention to secure the construct and prevent stent malapposition (16). Instability was likely related to a combination of FD shortening after expansion, a known issue in long-segment reconstructions, and the presence of proximal stenosis, which further compromised device anchoring and contributed to the risk of migration.

To stabilize the construct, we employed a stent-within-a-stent technique, deploying an additional FD to enhance metal coverage, improve FD wall apposition, and provide mechanical support (18, 19). This approach is supported by previous studies showing that additional stenting provides several important benefits. First, it enhances metal coverage, increasing construct density and further reducing inflow into the aneurysm, thereby accelerating thrombosis. Second, it improves device wall apposition, which is particularly crucial in large-caliber vessels where incomplete FD expansion may lead to endoleaks and persistent aneurysm perfusion. Third, it stabilizes the flow diverters, reducing the risk of migration or displacement—a well-documented concern in basilar artery reconstructions due to high-flow dynamics and the frequent need for long-segment coverage.

Despite its advantages, this approach carries certain risks, including an increased metal burden that can elevate thrombogenicity and necessitate prolonged dual antiplatelet therapy, thereby increasing the risk of hemorrhagic complications. Moreover, overlapping stents may lead to flow stagnation in critical perforators, potentially heightening the risk of ischemic events. Stent rigidity and vessel wall irritation could also contribute to delayed in-stent stenosis or endothelial dysfunction. Another limitation of telescopic deployment is the substantially increased procedural cost, primarily due to the use of multiple devices.

Oversized stenting has been considered as an alternative to telescopic flow diversion in cases of large and fusiform aneurysms. By deploying a larger-diameter FD, operators aim to achieve sufficient metal coverage while minimizing the need for multiple overlapping devices. However, this approach presents several challenges. Studies have shown that excessive oversizing can reduce the diversion effect by altering the porosity of the device, leading to suboptimal aneurysm occlusion (22). Additionally, oversizing has been associated with an increased risk of in-stent stenosis, which may compromise long-term vessel patency and necessitate further intervention (23). Another concern is the difficulty in achieving adequate wall apposition in cases of significant size mismatch, increasing the risk of device migration and malapposition, particularly in tortuous vascular anatomy (24).

Previous studies have shown that triple stent therapy can be more effective than single or double stenting while achieving a metal coverage rate comparable to that of flow diverters (6). As a result, it remains a viable treatment option for complex posterior circulation aneurysms. The development of long-length flow diverters may offer a promising alternative to multiple stenting, improving construct stability while reducing procedural complexity and metal burden in complex aneurysm treatment.

The management of complex BAAs requires carefully tailored endovascular strategies to achieve durable reconstruction and effective flow diversion. This case illustrates the value of telescopic stenting and adjunctive techniques in stabilizing the construct and overcoming device-related challenges. However, safety considerations must also be emphasized: implanting multiple FDs in perforator-rich territories such as the BA carries inherent risks, including ischemic complications, increased thrombogenicity, and the need for prolonged dual antiplatelet therapy. Individualized patient selection and meticulous procedural planning are therefore essential to balance efficacy with safety in high-risk aneurysm reconstructions.