Introduction

   Vertebral artery (VA) giant aneurysms are relatively uncommon, but the number of reported cases has increased in recent years. Because the natural course of these aneurysms is extremely poor, early intervention should be considered. Unfortunately, VA giant aneurysms can be difficult lesions to be treated surgically due to their location, size, complex structure and unique hemodynamics. Patients with VA aneurysm may present with ischemia, rupture and symptoms related to mass effect because the lesion compresses the brainstem. And all these conditions may lead patient to neurological deterioration and high morbidity and mortality.
   The authors report on a patient with a giant VA aneurysm that was initially treated endovascularly, and who subsequently experienced clinical deteriorations. And the pertinent literatures are reviewed.

Case Report

1. History
   This 32-year-old man was referred to our hospital with a 2-month history of dizziness, progressive dysarthria. Gait disturbance had been developed 1 month before the patient was admitted to our hospital.

2. Examination
   A neurological examination performed on admission revealed dysarthric speech, ataxic gait, dysdiadochokinesia, terminal dysmetria. Computerized tomography (CT) scans displayed a large left VA aneurysm compressing the brainstem. VA angiogram revealed basilar artery flow is predominantly supplied from the right vertebral artery. Left VA angiogram shows giant fusiform aneurysm involving the left distal VA and a large amount of injected contrast media into the left VA stagnated in the aneurysm. Because of the location of the aneurysm and its sole filling of left vertebral artery, endovascular proximal parent artery occlusion was selected as the initial treatment.

3. First proximal occlusion
   The patient underwent endovascular occlusion of the adjacent short segment of the left VA immediately distal to the origin of the posterior inferior cerebellar artery (PICA). At the end of the procedure, VA angiogram demonstrated that the aneurysm was not filled.

4. Clinical course after proximal occlusion
   On postembolization Day 1, the patient was noted right hemiparesis and hypesthesia. These deficits were initially interpreted as thromboembolic events, causing us to implement combined antiplatelet and heparin therapy. A course of subcutaneous administered low molecular heparin (Fraxiparine 5000 IU, two times a day) was started. Magnetic resonance image (MRI) study demonstrated a large thrombosed aneurysm compressing the brainstem, with a hyperintense area indicating the presence of a late subacute clot within the aneurysm. A T2-weighted MR image showed slight edema on the compressed brainstem (Fig. 1).
   On 18 days after embolization, Sudden neurological deterioration in the patient became evident. At this time, respiration arrest was noted (Glasgow Coma Scale score of 8), and there were sinus bradycardia (40 beats/minute) and hypotension. We intubated the patient and ventilator applied and then observed the patient at intensive care unit. A course of intravenously administered steroids (predisol 125 mg, four times a day) was started. The enhanced CT imaging visualized the small patent portion that was connected to left vertebral artery. And the highly enhanced area is located mainly on the anterolateral side of thrombosed aneurysm (Fig. 2). An improvement in his neurological examination findings became evident 9 days after that episode. He continued to improve on a daily basis. And 3 weeks after episode, he was neurologically normal except subjective weakness. But On 4 weeks after that episode, the right hemiplegia was occurred, the patient showed no recovery neurologically for a week. We assumed that the reason of recurrent neurological deterioration was brainstem compression due to growth of aneurysm. Therefore, we decided to obliterate the remnant aneurysm by embolization

5. Second embolization procedure
   Before the second intervention, left vertebral angiography showed occluded left distal vertebral artery by previous coil embolization, and patent left PICA flow. right vertebral angiography showed retrograde contrast filling in the lumen of partially thrombosed aneurysm. The remained lumen of the aneurysm was measured about 12 mm in length and 7 mm in diameter. After complete coil embolization, there was no contrast opacification into the aneurysm. Antegrade flow to the basilar artery was preserved (Fig. 3).

6. Clinical course after the second embolization
   After second embolization, the right hemiplegia was aggravated for a week, but gradually improved to mild hemiparesis. And, ventilator weaning was possible and he walked by him-self one month later. The patient was neurologically normal except mild right hemiparesis and the patient was discharged home and remained well. After 1 year later, Repeated cerebral angiography performed and documented no coil compaction or aneurysm recanalization(Fig. 4). Clinical and neuroimaging-confirmed improvement was documented during the follow-up period.

Discussion

   The present case is practical instance and helpful in discovering the cause of neurological deterioration after endovascular treatment of the VA giant aneurysm, and illustrates one of the pitfalls of coil embolization for the treatment of partially thrombosed giant aneurysms. Malisch, et al.¹³⁾ and Gruber, et al.⁶⁾ reported clinical results after coil embolization in patients with aneurysms causing mass effect. These authors suggested that in cases of worsening neurological deficit after coil placement, the deterioration occurred in a delayed fashion, presumably due to aneurysm growth and not from mechanical compression by the GDCs. The enlargement of intracranial aneurysms has been extensively studied physiologically, histopathologically, and neuroradiologically.^{2)4)5)10)13)19)} Suzuki J, et al. suggested the enlargement of intracranial aneurysms has been explained by repeated hemodynamic injury to the aneurysm wall.¹⁹⁾ And, Schubiger, et al. postulated that recurrent intramural hemorrhages at the highly vascularized wall are factors contributing to aneurysm growth.¹⁵⁾
   In our patient, the delayed neurological deterioration was occurred on 18 days after proximal VA embolization when aneurysm was partially thrombosed. Unfortunately, there is no consensus on the mechanisms underlying the increase in size of these partially thrombosed giant aneurysms in patients with mass lesions.^11)13)14) The process of thrombosis can itself cause physical expansion of an aneurysm sac by converting its contained fluid phase(circulating blood) into a solid phase composed of a lattice of cellular and extracellular products.¹⁶⁾²⁰⁾ If thrombosis is complete, clot retraction may eventually occur, in which an aneurysm undergoes involution caused by progressive fibrosis with reduction of the compressive mass.¹⁸⁾ In the event of incomplete thrombosis, however, aneurysm growth and rupture can occur, which may be fatal.¹⁷⁾¹⁸⁾ Incomplete thrombosis leading to growth and rupture of the sac may be facilitated by the presence of collateral arteries feeding a residual lumen, recanalization of the thrombus, and/or recurrent intramural hemorrhages from a vascularized aneurysmal wall.^1)8)9)14) Nagahiro, et al. reviewed the outcome in patients treated for thrombosed giant aneurysms of the VA and suggested that formation of intrathrombotic vascular channels and subsequent establishment of blood flow between the parent artery and channels may be important factors in the growth of thrombosed aneurysms.¹⁴⁾ And Koji I, et al. reported that a rich adventitial neovascularization of the parent artery occluded by coils could provide potential routes of blood supply to the aneurysm neck from surrounding dural and leptomeningeal arteries. This is important because, theoretically, endovascular trapping, unlike surgical trapping, cannot block such blood flow to the aneurysm neck beyond the occluded arterial segment through vasa vasorum on the adventitia. And adventitial neovascularization by the vasa vasorum on the VA occluded with coils may play a key role in the persistent enlargement of such aneurysms even after apparently complete endovascular occlusion.¹²⁾ This finding is applicable to our case, but it remained the possible mechanism because we could not undergo surgical exposure showing the intrathrombotic vascular channels.
   Besides, in aneurysm that have been treated by proximal parent artery occlusion, another particularly important mechanism may account for growth and rupture. This process, associated with morphological conversion of an aneurysm from lateral to terminal, involves exaggerated hemodynamic stress at the junction between retrograde filling and the intrasaccular thrombus, similar to a pulsatile water-hammer effect at this point.³⁾⁷⁾⁸⁾ In this case, we suspect that there was increased hemodynamic stress caused by opposing retrograde filling of the aneurysm from the basilar artery that contributed to a water-hammer effect causing brainstem compression-a summation of all the mass effect-related complications reported by Gruber and colleagues.⁶⁾ And this fatal complication after parent artery trapping was eliminated by endosaccular embolization to prevent the blood flow to the lumen of partially thrombosed aneurysm. Consequently, appropriate therapeutic plan of giant VA aneurysm is eliminating the aneurysm from the circulation by endovascular trapping together with endosaccular embolization-theoretically the best endovascular treatment-to prevent growth of thrombosed aneurysm if complication is anticipated.

Conclusion

   We have described neurological deterioration after endovascular treatment of VA giant aneurysm. In order to avoid complication, it is essential to determine appropriate therapy for giant aneurysm in the VA by evaluating cerebral blood flow and other factors for aneurysm growth after proximal artery embolization.

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