Delayed posterior tilting of a giant basilar tip aneurysm following stent-assisted coiling with therapeutic P1 occlusion: A case report

Abstract

Background:

Giant basilar tip aneurysms remain difficult to treat due to their location, bifurcation anatomy, adjacent perforators, and potential for mass effect. Endovascular treatment, including stent-assisted coiling, is a valuable option. Despite angiographic occlusion, mass effect may still be clinically significant.

Case Description:

A 67-year-old man presented with headache and was diagnosed with a 27 × 17-mm giant unruptured basilar tip aneurysm. Preoperative angiography demonstrated perforators arising predominantly from the left P1 segment and a well-developed right posterior communicating artery (PComA), while the left PComA was hypoplastic. Stent-assisted coiling was performed with stent placement from the basilar artery to the left posterior cerebral artery and occlusion of the non-stented right P1 segment. The early postoperative course was uneventful. Posterior tilting of the coiled aneurysm was first noted 1 week after treatment and subsequently progressed. Approximately 3 months after treatment, mass effect resulted in midbrain compression and obstructive hydrocephalus. Skull radiographs in different body positions demonstrated posture-dependent displacement of the coil mass, suggesting a role of gravity. Levodopa administration and ventriculoperitoneal shunting resulted in partial symptomatic improvement. Angiographic follow-up through 3 years demonstrated stable occlusion without recurrence, with no substantial progression of posterior tilting after the first postoperative year.

Conclusion:

Stent-assisted coiling with therapeutic P1 occlusion may contribute to durable angiographic occlusion in selected giant basilar tip aneurysms. However, delayed posterior tilting of the coiled aneurysm may occur as a postoperative phenomenon. This potential delayed complication, leading to mass effect, should therefore be considered in treatment strategy and postoperative follow-up.

INTRODUCTION

Basilar tip aneurysms remain among the most challenging intracranial aneurysms due to their deep location, bifurcation anatomy, and close relationship to critical perforators and surrounding neurovascular structures.[6,11] Large or giant lesions are particularly difficult because they are associated with a higher risk of rupture, partial thrombosis, mass effect, and limited durability after treatment.[9,21] Microsurgical treatment, including direct clipping and flow alteration strategies with bypass, may provide more durable aneurysm occlusion but remains technically demanding and carries a risk of treatment-related morbidity.[11,12,15,21] Endovascular treatment offers a less invasive alternative and may be associated with more favorable clinical outcomes, although long-term angiographic durability remains a challenge.[11,21] Conventional coiling and stent-assisted coiling have been widely used for these aneurysms, and Y-stenting may be a useful reconstructive option for complex bifurcation anatomy.[3,23] However, Y-stenting is technically more complex, and thromboembolic complications remain a concern.[17] More recently, intrasaccular devices have expanded the endovascular armamentarium, but their applicability to large or giant basilar tip aneurysms is limited.[2] Even when durable angiographic occlusion is achieved, however, persistent or progressive mass effect may remain clinically important in giant basilar tip aneurysms.[21] Herein, we report a case of a giant unruptured basilar tip aneurysm treated with stent-assisted coiling combined with therapeutic occlusion of the non-stented P1 segment. Despite durable aneurysm occlusion on long-term angiographic follow-up, delayed posterior tilting of the coiled aneurysm caused new brainstem compression and obstructive hydrocephalus. Skull radiographs obtained in different body positions also demonstrated posture-dependent displacement of the coil mass.

CASE DESCRIPTION

A 67-year-old man with a history of hypertension and diabetes mellitus presented with headache. A giant unruptured basilar tip aneurysm was identified, and he was referred to our hospital. Neurological examination was unremarkable. Computed tomography angiography demonstrated a giant basilar tip aneurysm with slight thrombosis along its anterior aspect [Figure 1a and b]. The aneurysm extended into the anterior third ventricle on magnetic resonance imaging (MRI) [Figure 1c]. Digital subtraction angiography (DSA) of the right vertebral artery demonstrated a giant basilar tip aneurysm measuring 27 × 17 × 18 mm with a neck width of 11 mm, incorporating both posterior cerebral arteries (PCAs) symmetrically [Figure 1d-g]. Perforators near the basilar tip arose predominantly from the left P1 segment. Right internal carotid angiography demonstrated a well-developed right posterior communicating artery (PComA), and this collateral pathway was also visualized on the right vertebral angiography with the right carotid compression (Allcock test) [Figure 1h]. The left PComA was hypoplastic.

Figure 1:

Preoperative imaging findings of the giant basilar tip aneurysm. (a) 3D CTA volume rendered image showing a giant basilar tip aneurysm. (b) Axial CTA demonstrating the aneurysmal sac with slight anterior thrombosis. (c) Axial FLAIR MRI showing extension of the aneurysm into the anterior third ventricle near the foramen of Monro. (d) Right vertebral angiography (anteroposterior view) demonstrating a giant basilar tip aneurysm. (e-g) 3D rotational angiography of the right vertebral artery in the anterior (e), left lateral (f), and posterior (g) views, showing relatively symmetric branching of the PCAs, perforators arising predominantly from the left P1 segment (yellow arrows), and a well-developed right PComA (yellow arrowhead). (h) Right vertebral angiography (anteroposterior view) with right carotid compression (Allcock test) confirming collateral flow through the right PComA. 3D: Three-dimensional, CTA: Computed tomography angiography, FLAIR: Fluid-attenuated inversion recovery, MRI: Magnetic resonance imaging, PCA: Posterior cerebral artery, PComA: Posterior communicating artery.

Because the aneurysm was considered to carry a high risk of rupture, endovascular treatment was planned. To improve treatment durability, we elected to combine stent-assisted coiling with therapeutic occlusion of the right P1 segment, with a stent extending from the left PCA to the basilar artery to convert the aneurysm into a sidewall-type configuration. Dual antiplatelet therapy with aspirin (100 mg) and clopidogrel (75 mg) was initiated preoperatively. Under general anesthesia and systemic heparinization, the procedure was performed through bilateral femoral arterial access [Figure 2a-f]. Through a 6-Fr guiding catheter positioned in the right vertebral artery, a Headway 21 microcatheter (MicroVention, Aliso Viejo, CA, USA) was navigated into the left PCA, and an Excelsior 1018 microcatheter (Stryker, Fremont, CA, USA) was advanced into the aneurysmal sac. Through a second guiding system positioned in the left vertebral artery, a Phenom 17 microcatheter (Medtronic, Irvine, CA, USA) was navigated into the right PCA. A low-profile visualized intraluminal support (LVIS) stent (4.0 × 28 mm; MicroVention, Aliso Viejo, CA, USA) was deployed from the left PCA to the mid basilar artery through the Headway 21 microcatheter [Figure 2b]. Coil embolization of the aneurysmal sac was then performed through the Excelsior 1018 microcatheter [Figure 2c]. In the final stage, the right P1 segment was embolized through the Phenom 17 microcatheter [Figure 2d]. A total of 19 coils, with a cumulative length of 673 cm, were deployed, resulting in a volume embolization ratio of 20.1%. The estimated total coil weight was 6.5 g, based on the weights of reference coil samples of the corresponding product types. Final angiography demonstrated occlusion of the right P1 segment with a small neck remnant of the aneurysm (Raymond– Roy class II) [Figure 2e and f]. The treatment strategy is schematically illustrated in Figure 2g.

Figure 2:

Stent-assisted coiling combined with therapeutic right P1 occlusion. (a) Right vertebral angiography obtained in the working projection demonstrating the giant basilar tip aneurysm and its relationship to the basilar artery and PCAs. (b) Low contrast cone-beam CT obtained immediately after stent deployment, demonstrating an LVIS stent (4.0 × 28 mm) deployed from the left PCA to the basilar artery, with an Excelsior 1018 microcatheter positioned within the aneurysmal sac and a Phenom 17 microcatheter positioned in the right PCA. (c) Fluoroscopic image demonstrating coiling of the aneurysmal sac before right P1 occlusion. (d) Fluoroscopic image demonstrating therapeutic occlusion of the right P1 segment (yellow arrowhead), completing the intended treatment configuration. (e) Final angiography demonstrating right P1 occlusion and a small neck remnant. (f) Final 3D rotational angiography confirming occlusion of the right P1 segment and satisfactory aneurysm embolization. (g) Schematic illustration of the treatment strategy showing stent deployment from the left PCA to the basilar artery and therapeutic occlusion of the non-stented right P1 segment, aiming to convert a bifurcation aneurysm into a sidewall-type configuration. The red component represents the parent arteries and aneurysm, the green component represents the LVIS stent, the gray component represents the deployed coils, and the yellow arrow indicates blood flow. (h) Diffusion-weighted MRI obtained on postoperative day 3 demonstrating no ischemic lesions. PCA: Posterior cerebral artery, CT: Computed tomography, LVIS: Low-profile visualized intraluminal support, 3D: Three-dimensional, MRI: Magnetic resonance imaging.

The patient experienced mild headache postoperatively, but no neurological deficits were observed. Diffusion-weighted MRI obtained on postoperative day 3 revealed no ischemic lesions [Figure 2h], and the early postoperative course was uneventful. Although preoperative MRI showed extension of the aneurysm into the anterior third ventricle, MRI obtained 1 week after treatment demonstrated posterior displacement of the coiled aneurysm toward the posterior third ventricle, with subtle narrowing around the cerebral aqueduct [Figure 3a and b]. These findings gradually progressed on imaging at 1 and 2 months postoperatively, suggesting posterior tilting of the coil mass, although he remained asymptomatic. By 3 months, however, the patient developed gait disturbance, cognitive decline, urinary dysfunction, and intermittent hand tremor, requiring hospital admission. MRI demonstrated increased midbrain compression with near obstruction of the cerebral aqueduct [Figure 3c]. By 4 months postoperatively, obstructive hydrocephalus became clinically evident due to progressive posterior tilting [Figure 3d-h]. Repeat DSA demonstrated no aneurysm recurrence, but the coil mass appeared to be tilted posteriorly relative to its immediate postoperative position [Figure 3i-k]. Levodopa was initiated for suspected parkinsonian syndrome, and a right ventriculoperitoneal shunt was placed [Figure 3l]. Following these interventions, his symptoms partially improved. To further evaluate the positional behavior of the coil mass, skull radiographs were obtained 3 months after treatment in the upright, supine, and prone positions. These images demonstrated posture-dependent displacement of the coil mass, with posterior displacement in the supine position and mild anterior displacement in the prone position relative to the upright position, suggestive of gravity-related movement [Figure 4]. Within the 1^st postoperative year, the patient had a modified Rankin scale score of 3 and remained at approximately this level through 3 years of follow-up. Angiographic follow-up at 3 months, 1 year, and 3 years demonstrated a stable neck remnant without recurrence [Figure 5a-c]. Posterior tilting progressed between 3 months and 1 year but showed no substantial change from 1 to 3 years on serial lateral non-subtracted angiographic images [Figure 5d-f].

Figure 3:

Serial imaging demonstrating progressive posterior tilting of the coiled aneurysm. (a–c) Heavily T2-weighted axial MRI before treatment (a), 1 week after treatment (b), and 3 months after treatment (c), showing progressive posterior displacement of the coiled aneurysm and increasing mass effect on the midbrain. (d) Axial FLAIR MRI obtained 4 months after treatment, showing midbrain compression and aqueductal narrowing. (e–g) Heavily T2-weighted sagittal MRI before treatment (e), 1 week after treatment (f), and 3 months after treatment (g), also demonstrating progressive posterior displacement of the coiled aneurysm. (h) Axial FLAIR MRI obtained 4 months after treatment at another slice level, demonstrating ventricular enlargement suggestive of obstructive hydrocephalus. (i–k) Lateral-view non-subtracted angiographic images obtained before treatment (i), immediately after treatment (j), and 3 months after treatment (k), demonstrating progressive posterior tilting of the coil mass. (l) Axial CT obtained after ventriculoperitoneal shunting, showing reduction in ventricular size. MRI: magnetic resonance imaging, FLAIR: fluid-attenuated inversion recovery, CT: computed tomography

Figure 4:

Posture-dependent displacement of the coil mass on skull radiographs. (a-c) Skull radiographs obtained 3 months after treatment in the prone (a), upright (b), and supine (c) positions, showing mild anterior displacement of the coil mass in the prone position and posterior displacement in the supine position relative to the upright position. (d) Superimposed image of the radiographs, with prone shown in green, upright in blue, and supine in red. The superimposed image was created by manually aligning the skull contours across the three radiographs.

Figure 5:

Long-term follow-up demonstrating durable occlusion and posterior tilting of the coiled aneurysm after stent-assisted coiling with therapeutic right P1 occlusion. (a-c) Follow-up digital subtraction angiography at 3 months (a), 1 year (b), and 3 years (c) after treatment, demonstrating a stable neck remnant without recurrence. (d-f) Corresponding lateral non-subtracted angiographic images at 3 months (d), 1 year (e), and 3 years (f) after treatment, demonstrating progression of posterior tilting between 3 months and 1 year, with no substantial change thereafter.

DISCUSSION

In the present case, stent-assisted coiling combined with therapeutic occlusion of the non-stented P1 segment achieved durable angiographic occlusion. However, the coiled aneurysm subsequently underwent progressive posterior tilting, resulting in midbrain compression and obstructive hydrocephalus. Delayed posterior tilting with mass effect and durable angiographic occlusion represent the two central features of this case.

Recurrence after endovascular treatment is influenced by multiple factors, including aneurysm size, neck morphology, bifurcation geometry, coil packing, and hemodynamic conditions.[5,10,20] In basilar tip aneurysms, a wide PCA angle and greater aneurysmal inflow have been associated with recanalization.[10,20] These findings suggest that persistent inflow toward the aneurysm sac, maintained by the bifurcation configuration and incorporated branch vessels, may limit durable occlusion. From this perspective, strategies aimed at modifying the bifurcation flow pattern and reducing aneurysmal inflow may be beneficial. Stent-assisted coiling may contribute to such flow modification in addition to providing neck scaffolding.[3,25] This flow-modifying effect may result from stent-induced straightening of the parent artery[8] and the flow-diverting properties of low-porosity braided stents such as the LVIS stent.[13,24]

Further modification of the bifurcation flow pattern may be achieved by intentional branch occlusion, often with bypass support.[18,22] This concept, referred to as anatomical flow diversion, aims to convert a bifurcation aneurysm into a sidewall-type lesion by combining stent-assisted coiling with branch occlusion.[22] Although this approach is not routinely used at the basilar tip, it may represent a rational adjunctive option in carefully selected cases.[18,22] In the present case, a well-developed right PComA and perforators arising predominantly from the left P1 segment suggested that intentional occlusion of the right P1 segment could be tolerated while preserving critical perforators through stent placement into the left PCA. By eliminating outflow to the right PCA and redirecting the main outflow toward the left PCA, this strategy was expected to convert the aneurysm into a sidewall-type configuration and facilitate dense coil packing up to the neck, including the origin of the right P1 segment, thereby contributing to durable occlusion.

This strategy is not universally applicable, because intentional branch occlusion at the basilar tip carries a risk of ischemic complications. Careful assessment of perforator anatomy, PComA collateral capacity, and the risk of ipsilateral superior cerebellar artery (SCA) compromise is essential when considering therapeutic P1 occlusion. In selected challenging cases with favorable anatomy, this entirely endovascular strategy may avoid the added invasiveness of craniotomy and surgical bypass. In the present case, an independent microcatheter in the right PCA enabled controlled right P1 occlusion and coil deployment at the basilar tip, which may have helped preserve the ipsilateral SCA origin.

The most notable feature of this case was the delayed posterior tilting of the coiled aneurysm, which progressively increased mass effect on the midbrain and resulted in obstructive hydrocephalus despite stable angiographic occlusion. Delayed aneurysm tilting and basilar artery deformation after coiling of large basilar apex aneurysms have been reported previously, with proposed mechanisms including the weight of the coil mass and biomechanical forces exerted on the coiled aneurysm.[16,19] More specifically, the weight of the coil mass and altered local hemodynamic forces may contribute to the development of initial tilting. Once tilting begins, displacement of the coil-mass centroid away from the aneurysm neck may increase torque at the aneurysm– artery junction and promote further geometric change.[16] Further tilting after additional coiling for recurrence was also reported. In contrast, stent assistance was not significantly associated with the degree of tilting in the reported series. Aneurysms measuring ≥10 mm showed significantly greater posterior tilting than those measuring <10 mm and also had a greater total number, length, and volume of deployed coils. In a subset of the same series, the calculated coil weight was 1.9 ± 1.6 g in aneurysms measuring ≥10 mm, compared with 0.4 ± 0.2 g in those measuring <10 mm.[16] However, no validated threshold of aneurysm size or deployed coil burden for predicting posterior tilting has been established. In this giant basilar tip aneurysm, the substantial coil mass resulting from dense packing up to the neck, with an estimated total weight of 6.5 g, combined with marked flow alteration induced by unilateral P1 occlusion, may have changed the hemodynamic and biomechanical environment of the aneurysm–parent artery complex, thereby promoting postoperative posterior tilting.

Another notable finding in the present case was posture-dependent displacement of the coil mass. Skull radiographs obtained in different body positions demonstrated posterior displacement of the coil mass in the supine position and mild anterior displacement in the prone position, consistent with an influence of gravity. These findings suggest that treatment-related changes in the mechanical properties and surrounding hemodynamic environment of the aneurysm may have rendered it susceptible to passive displacement under gravity. To the best of our knowledge, posture-dependent displacement of the coil mass after treatment of a giant basilar tip aneurysm has not been previously documented.

Progressive posterior tilting of a coiled giant basilar tip aneurysm may increase mass effect on the midbrain and cerebral aqueduct, leading to Parkinsonian symptoms or obstructive hydrocephalus.[1,14,19] Careful postoperative follow-up for delayed posterior tilting is therefore warranted. In the present case, levodopa administration and ventriculoperitoneal shunting resulted in partial symptomatic improvement. Posterior tilting progressed during the 1^st postoperative year, with no substantial change thereafter. Mass effect on the brainstem is an important determinant of morbidity and mortality in giant basilar tip aneurysms.[21] Thus, microsurgical treatment may be considered when technically feasible, particularly when decompression of the brainstem is an important goal. Endovascular treatment planning should balance the goal of durable angiographic occlusion against the risk of postoperative mass effect. In this context, limiting excessive intra-aneurysmal coil burden may be important, although prevention of recurrence remains essential. Intrasaccular devices such as the Woven EndoBridge are lighter than coils of comparable treatment volume but have limited applicability to large or giant aneurysms.[16] The development of lighter intrasaccular devices suitable for such lesions may therefore be desirable. Flow-diverter treatment with limited adjunctive coiling may offer an alternative means of balancing treatment durability and intra-aneurysmal device burden.[4,7,17]

CONCLUSION

Stent-assisted coiling with therapeutic P1 occlusion may contribute to durable angiographic occlusion in selected giant basilar tip aneurysms with favorable anatomy. However, delayed posterior tilting of the coiled aneurysm may occur as a postoperative phenomenon in which gravity may play a role. This potential delayed complication, leading to mass effect, should therefore be considered in both treatment strategy and postoperative follow-up in the management of giant basilar tip aneurysms.

Ethical approval:

The Institutional Review Board approval is not required.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for their images and other clinical information to be reported in the journal. The patient understands that the patient’s names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship:

Nil.

Conflicts of interest:

Hitoshi Hasegawa has received lecture fees from Medtronic, Terumo, and Stryker. The other authors declare no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that they have used artificial intelligence (AI)-assisted technology. ChatGPT (OpenAI) was used to assist with English language editing and grammatical refinement. The authors reviewed and verified all manuscript content.

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