Three-Dimensional Fusion Angiography of a Giant Basilar Aneurysm for Coil Embolization

Conventional angiography is essential to assess intraluminal flow and define aneurysm neck and angio-architecture in treatment planning. However, when giant aneurysms are supplied by more than one parent artery, the precise relationship of the aneurysm to adjacent arterial structures might not be clearly demonstrated even with three-dimensional (3D) rotational angiography, because of the preferential flow to the giant aneurysmal sac (1). We present a case in which each rotational angiogram with 3D reconstruction of both parent arteries was fused with each other to guide the treatment strategy for a giant, partially calcified, lower basilar trunk aneurysm.

A 54-year-old female was referred to our neurointervention clinic for a giant aneurysm of the basilar top. The aneurysm had been previously detected during an evaluation for a lateral neck mass. The mass was resected and was ultimately proven to be a thoracic duct cyst. The patient reported no past medical history, except for hyperlipidemia. Neurologic examination and primary laboratory investigations were all within the normal limits. Contrast-enhanced computed tomography angiography revealed a 25-mm, partially calcified, intracranial aneurysm in the ventral aspect of the lower basilar trunk (Fig. 1A). Conventional and rotational angiograms obtained using digital biplane angiography with an AXI-OM Artis Zee apparatus (Siemens Medical Solution, Erlangen, Germany) showed the large basilar trunk aneurysm above the level of the anterior inferior cerebellar artery (AICA). However, the angiograms obtained from each vertebral artery showed incomplete filling in both of the aneurysmal sac and the basilar artery above the aneurysm because of the preferential flow from equally developed, balanced vertebral arteries on both sides. There were also uncertainties regarding the aneurysm neck and the angled basilar trunk due to the ventrally-located, giant aneurysm at the basilar artery. Moreover, it was difficult to define the precise relationship of the aneurysmal sac to the origin of the adjacent branches (Fig. 1B), which necessitated further study to develop a treatment plan. The main focus was to define the detailed angio-architecture of the aneurysm and the basilar artery, and to demonstrate the precise relationship of the origin of the AICA to the aneurysm neck. Fusion images were obtained using the VB21C fusion application software of a Syngo X Workplace apparatus (Siemens Medical Solution) to reconstruct the aneurysm and the adjacent segment of the vertebra-basilar system. The full dimension of the aneurysm sac and the basilar artery was demonstrated in 3D fusion images using different color coding according to the orientation of the vertebral artery (Fig. 1C). The origin of the right AICA arose just proximal to the aneurysmal sac on the right side (Fig. 1C). Based on the 3D fusion images, the giant aneurysm was safely treated with coil embolization using the double-catheter technique. Post-procedural angiography revealed dysplastic changes of the distal basilar artery (Fig. 1D), which might not be directly related to the giant aneurysm and were not clearly seen before coiling due to incomplete filling of the contrast agent to the basilar artery distal to the aneurysm. There was no adverse event during the peri-procedural period or after the procedure and a 3D time-of-flight magnetic resonance angiogram obtained 8 months following the procedure showed successful coiling of the basilar aneurysm.

Fig. 1
A 54-year-old female with giant aneurysm of basilar artery.
A. Sagittal CT angiogram shows a partially calcified, saccular aneurysm (arrow) at the ventral aspect of the lower basilar trunk with 2.5-cm in maximal diameter.

B. Vertebral angiogram shows the giant basilar trunk aneurysm, however, the aneurysmal sac is not completely filled, which hinder our accurate assessment of the relationship between the aneurysmal sac and the origin of the branches in vicinity.

C. 3D-fusion image obtained from the right vertebral (grey color) and left vertebral (red color) arteries shows the different-colored filling of each part of the aneurysm and the basilar trunk beyond the aneurysm.

D. Post-embolization vertebral angiogram shows a dysplastic distal basilar artery is clearly seen in the left vertebral angiogram. It was not demonstrated on pre-procedural angiogram because of an incomplete filling of contrast media to the basilar artery distal to the aneurysm, although this morphological change was not directly related to the giant saccular aneurysm.

3D = three-dimensional

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A giant intracranial aneurysm is diagnosed when the aneurysmal sac is larger than 2.5 cm in size and represents approximately 5-8% of the intracranial aneurysm (2). A giant aneurysm at the top of the basilar trunk accounts for approximately 15% of all giant intracranial aneurysms and the vertebral artery accounts for approximately 5% of the lesions. Giant aneurysms notoriously remain one of the most difficult to treat intracranial vascular lesions, and can have a dramatic clinical presentation including subarachnoid hemorrhage (25%), intra-aneurysmal thrombosis, subsequent stroke and distant emboli (2-5%) and mass effects that include visual disturbance, cranial nerve dysfunction, seizure, headache and hemiparesis (2). Surgical management of giant aneurysms has been associated with a higher morbidity and mortality (20-30%) than those of smaller lesions (3) and no single technique is effective for treating all giant aneurysms. Current treatment options for these lesions include direct surgical techniques, endovascular techniques and combined approaches (2). Therefore, it is important to determine the precise angio-architecture as a treatment planning for every kind of the treatment modalities, especially for complex vascular lesions, such as giant aneurysms.

Attempts to classify giant aneurysms have included morphology and the location (4) and fourth-dimension magnetic resonance imaging to demonstrate the influence of lesion size and morphology on aneurysm hemodynamics (5). Our pre-procedural planning was feasible based on the 3D fusion images that revealed the detailed angio-architecture, especially the aneurysm and its major branch arising from the parent artery. We were able to clarify the origin of the AICA arising from the dorsally displaced, lower basilar trunk secondary to the giant aneurysm, which otherwise was not possible using only 3D rotational cerebral angiography. Additional roles of fusion images based on 3D rotational angiography could be to simultaneously determine the relationship between vascular and osseous structures, especially near the skull base, and to detect calcified tissue near the aneurysmal neck, neither of which is otherwise possible using only 3D rotational cerebral angiography (1, 6). Moreover, increasing attention is being given to the use of computational fluid dynamics to ascertain the association between some specific intra-aneurysmal hemodynamics that can increase the risk of aneurysmal rupture (7).

The 3D rotational angiography fusion technique has some limitations. First, considering the deterministic and random effects of the radiation, it is necessary to reduce the radiation dose in additional 3D rotational angiography scans. Second, an inherent limitation of the volume-rendering technique used in 3D fusion can be that it overestimates the aneurysmal neck size compared with two-dimensional digital subtraction angiography images (8). Last, the additional fusion imaging technique requires more processing time, although it cannot impede the subsequent procedure.

In conclusion, the fusion technique of 3D rotational angiography revealed the complete filling of a giant aneurysm near the confluent junction area of the lower basilar trunk, which was filling from both sides of the vertebral artery. Complete understanding of the angio-architecture of an aneurysm as well as the neck, including the relationship between the origin of the branching artery and the aneurysmal sac, assisted us in performing the neuro-interventional procedure accurately and safely.