Clinical Results and Pathological Findings of Stent-Assisted Coil Embolization for Basilar Artery Trunk Dissecting Aneurysms

Summary

Stent-assisted coil embolization is a new method for treating dissecting or fusiform aneurysm, especially the aneurysms arising from the basilar artery trunk or dominant vertebral artery. At present, this technique is considered as an effective treatment option to obliterate such aneurysm keeping the parent artery patent. Several authors reported the effectiveness and excellent radiological result of this treatment, but fewer reports focus on the limitations of this technique.

We treated two patients with a basilar artery trunk dissecting aneurysm with this technique. Transient ischemic symptoms were observed in one patient and haemorrhagic and thromboembolic complications were observed the other. We lost the latter patient due to postoperative complications, and the pathological finding was achieved by autopsy. We report the clinical and pathological findings in the two cases and investigate the efficacy and limitations of this technique.

Introduction

Dissecting aneurysms in the vertebrobasilar system are currently suitable lesions for interventional neuroradiological treatment. Parent artery occlusion, including aneurysmal dilatation with coils, is widely applied for treating dissecting vertebral artery (VA) aneurysms. However, simple coil obliteration of the parent artery is not possible when the dissecting aneurysm originates from the basilar artery (BA) trunk or dominant VA associated with a contralateral hypoplastic VA. The present innovation of an intravascular stent made their application possible to intracranial arteries. Higashida et Al first reported a new technique for preservation of the parent arterial circulation during and after coil obliteration of dissecting aneurysms with intravascular stent ¹. Currently, it is a trend as a treatment option for dissecting aneurysms arising from the BA trunk, and several excellent angiographical results have been reported^2-8. However, no papers describe the risk, efficacy and limitations of this technique.

In this paper, we report the clinical and pathological findings of two cases treated with this technique and investigated the efficacy and limitations of the technique.

Case Reports

Case 1

A 47-year-old woman became unconscious on november 30,1998 and was transferred to a local hospital. A computed tomography (CT) scan showed a subarachnoid haemorrhage (SAH) and an angiogram showed a small aneurysm with fusiform dilatation on the BA trunk. As neurosurgeons at the hospital considered that the protrusion would be a dissecting and pseudo-aneurysm, the dominant right VA was obliterated with clips expecting aneurysmal thrombosis by decreasing focal blood flow. After the operation, the patient recovered without any neurological deficits, but she complained of continuous headache. Follow-up angiograms taken five and ten months after the SAH attack showed progressive enlargement of the aneurysmal dilatation of the BA (figure 1). She was referred to us for further treatment.

Figure 1.

Left vertebral arteriogram at the time of onset in case 1 showing a small aneurysm with a fusiform dilatation of the BA trunk (A), and left vertebral arteriogram one year after the SAH attack showing an enlarged aneurysm arising at the fusiform dilatation of the BA (B).

The size of the aneurysm was 10 mm in diameter, and stent-assisted coil embolization was performed one year after the SAH attack. A 12 mm-long coronary stent (gfx, AVE, Minneapolis, USA) was placed at the neck of the aneurysm and the aneurysm was obliterated with Guglielmi detachable coils (GDC) (BostonScientific, Fremont, USA). After the treatment, the patient showed multiple brainstem symptoms (consciousness disturbance, bilateral abducens nerve palsy, bilateral motor paresis) which improved in a week with conservative therapy. A magnetic resonance image (MRI) showed bilateral pontine infarction just behind the aneurysm (figure 2). The patient recovered without any neurological deficits.

Figure 2.

Left vertebral arteriogram after the stent-assisted coil embolization in case 1 showing successful obliteration of the aneurysm (A). MRI demonstrated multiple pontine and cerebellar infarctions.

Case 2

This 70-year-old man suffered left hemiparesis, and BA dissection without aneurysmal dilatation was disclosed on an angiogram. He was treated conservatively and was in good condition for ten years. On february 21,2001, the patient suffered sudden onset of severe headache and visited a local hospital, where an angiogram showed two aneurysmal dilatations arising from the BA trunk. A CT scan and cerebrospinal fluid obtained by a lumbar spinal puncture showed no SAH; the headache was considered to be due to the extension of BA dissection.

Stent-assisted coil embolization was performed two months after the headache episode. An 18 mm-long coronary stent (S67O, AVE, Minneapolis, USA) was placed at the BA trunk and the aneurysm was obliterated with GDC and a detachable coil system (DCS) (COOK, Bloomington, USA) (figure 3). The patient showed no neurological deficits afterthe treatment and was maintained with systemic administration of heparin with a dose to elevate the activated coagulation time twice that before administrating heparin. One day after the treatment, the patient showed an SAH and idiopathic bleeding distant from the aneurysms was observed. Therefore, we reduced the dose of systemic heparin and finally the BA occluded at the site of stent placement five days after the treatment.

Figure 3.

Left vertebral angiogram before (A) and after (B) stent-assisted coil embolization in case 2 showing two aneurysmal dilatations are successfully obliterated with the parent artery patent.

Pathological findings at autopsy disclosed that the aneurysmal wall was covered only with thin collagenous fibers, the BA wall was extremely sclerotic with atheromatous plaques containing cholesterin crystals, and some coils had herniated into the parent artery through the strut of the stent (figure 4).

Figure 4.

Pathological findings in case 2 showing that the partially hypertrophic BA wall and a part of coil is herniated into the parent artery through the strut of the stent (A), and the aneurysmal wall is covered only with thin collagenous fibers (B).

Discussion

Dissecting aneurysms originating from the vertebrobasilar system are known as a difficult pathology for microsurgical treatment. Especially, dissecting aneurysm arising from the BA trunk or dominant VA associated with contralateral hypoplastic VA is one of the most difficult lesions in the neurosurgical field. Dissecting aneurysm arising from the unilateral VA has been treated by proximal clip occlusion or trapping of the parent artery⁹. Since the introduction of interventional neuroradiology, the treatment option for dissecting aneurysms arising from VA has shifted to interventional treatment ¹⁰). However, treatment for dissecting aneurysm located in the BA trunk or contralateral hypoplastic VA was difficult. Parent artery trapping associated with bypass surgery was reported as preliminary¹¹). In 1997, Higashida et A1 introduced a stent-assisted coil embolization technique for treating dissecting or fusiform aneurysm with a parent artery patent¹). After this first technical report was published, several series of successful result were reported, and this technique has become a trend for treating the BA trunk or dominant VA aneurysm^2-8).

In our first case, we achieved clinically and angiographically successful results; the size and shape of the aneurysm remained unchanged for two years. However, the clinical course and postoperative MRI after treatment suggest the possibility of perforating artery obliteration due to the stent and coil placement. Indeed, the contralateral VA was obliterated surgically, and consequently, the vertebro-basilar circulation may be reduced during the procedure. This is one possible reason for brainstem infarctions in this case. However, the distribution of the infarct is only at the level of the stent and the possible role of stent obstructing perforating arteries is undeniable in stent-assisted coil embolization technique.

At present, recanalization caused by coil compaction is a problem of coil embolization of aneurysms, and the importance of dense coil packing is recomended to avoid coil compaction^12,13. An intravascular stent positioned at the neck of the aneurysm allows tight coil packing even in the case of wide-necked, fusiform or dissecting aneurysms. On the other hand, coils strongly press the aneurysm wall in a stent-assisted condition, and the risk of aneurysmal rupture will increase. According tothe pathological finding of our second case, the basilar artery trunk dissecting aneurysm had a quite thin and fragile wall and is thought to have a high risk of bleeding in stent-assisted condition.

The stent-assisted coil embolization technique is believed to be suitable because the coil can be placed inside the aneurysm and the parent artery can be preserved by stent. The coils placed through the stent are considered not to herniate into the parent artery between the struts of the stent. However, there have been no manuscripts published previously on the histological finding of the stent-assisted coil embolization. In our second case, the patient finally died due to basilar artery occlusion and the histological finding of the case revealed that some of the coils had herniated through the strut of stent. This may result the late thromboembolic event of the basilar artery. We emphasize that prolonged systemic heparinization is important after stent-assisted coil embolization when considering this pathological result.

Conclusions

We report two patients with basilar artery dissecting aneurysm who were treated with stent-assisted coil embolization. The technique is useful for treating dissecting aneurysm with the parent artery patent, but carries risks of occluding perforating arteries, lacerating an aneurysmal wall and inducing thromboembolic complications. We emphasize that the stent-assisted coil embolization is an effective alternative for treating basilar artery trunk or dominant vertebral artery dissecting, or fusiform aneurysms. However, physicians should know the risks.