Introduction

   Dolichoectasia including a giant fusiform aneurysm means the widening and elongation of blood vessels. The giant fusiform aneurysm in the case presented herein has a compatible feature to the definition of dolichoectasia. The incidence of intracranial dolichoectasia ranges from 0.06% to 5.8%.¹⁴⁾¹⁹⁾ According to angiographic and postmortem studies, the vertebro-basilar system is most frequently involved.⁶⁾¹²⁾ Surgical management for a giant fusiform aneurysm at the basilar trunk which has poor natural history remains controversial. Furthermore, there have been few reports of successfully treated cases of giant fusiform basilar trunk aneurysms with poor collateral supply from the carotid circulation and with perforating arteries from the aneurysm.²⁾⁷⁾ More recently, a combined approach using the advantages of microsurgical bypass and endovascular trapping has been reported in un-clippable intracranial aneurysm like as above.⁴⁾⁸⁾ We herein report our successfully treated case of a giant partially thrombosed fusiform aneurysm at the middle to lower basilar trunk with relatively poor collateral supply from the carotid circulation using this combined method. 

Case Report 

   A 57-year-old male with no significant medical history except hypertension visited our institute because of nonspecific headache. A giant fusiform aneurysm at the basilar trunk was discovered with multiple old lacunar infarction in both basal ganglia by the brain magnetic resonance image (MRI) incidentally. The patient had no history of connective tissue disorder or systemic vasculopathy. The patient also showed no other neurological deficits. MRI on admission showed a giant mass at the pre-pontine cistern compressing left side pons slightly. The lesion was evaluated by three dimensional-computed tomography (3D-CT) angiography and conventional 4 vessels angiography. The giant fusiform aneurysm extended from near vertebro-basilar junction to the distal one third of basilar trunk. It's diameter was 13 mm and length was 28 mm. There was no intra-luminal organized thrombus and calcified adventitia. We decided to do observation carefully and maintained antiplatelet medication. The patient was checked up by 3D-CT angiography every one year in the out patient clinic. During about three years, there were no changes to the neurological status and imaging feature of the patient. Subsequently, progressive dizziness symptom developed and the patient was brought to our emergency room and admitted. Brain MRI was performed again and we discovered a newly developed right cerebellar infarction in the posterior inferior cerebellar artery (PICA) territory. 3D-CT angiography and conventional 4 vessels angiography were performed to compare with the previous image feature. The rechecked up images revealed that intra-luminal thrombus developed partially and the size of the giant fusiform aneurysm increased (diameter : 20 mm and length : 35 mm) (Fig. 1). Both anterior inferior cerebellar artery (AICA) originated from the proximal one third of the giant fusiform aneurysm. Right posterior communicating (Pcom) artery maintained patency but it revealed weak blood flow. Left Pcom artery was not visible. Both superficial temporal arteries (STA) showed slender features. Left vertebral artery (VA) was dominant and small aneurysm that has relative wide neck was shown in the just distal of left PICA originated site. Because of relatively poor collateral supply from both Pcom arteries of the carotid circulation, we first attempted a highflow bypass through the left superficial temporal artery (STA) - radial artery (RA) - left superior cerebellar artery (SCA) anastomosis. Because of early detection of neurological change, balloon occlusion test (BOT) was performed one week after the initial bypass surgery with local anesthesia. We positioned one balloon at the just distal of the giant fusiform aneurysm and the other balloon at the just distal of left PICA originated site using double femoral sheath and balloon method. The results of BOT were as follows. Both PCA filled up with right Pcom artery and especially, left PCA also filled up with left superficial temporal artery (STA)-radial artery (RA)-left superior cerebellar artery (SCA) anastomosis (Fig. 2). Dominant left PICA supplied the most of middle and inferior cerebellar portion. During BOT, the patient showed no focal neurological deficit but moderate irritability was observed. At immediate post-BOT period, there were no newly appeared infarction lesions in the brain MRI. Endovascular coil occlusion of the giant fusiform basilar trunk aneurysm was performed one week after the BOT under local anesthesia. However, successful procedure was not achieved because it was difficult to make an initial coil mesh at the just distal of maximal fusiform dilatation portion and the patient lacked of cooperation. One week after the failed embolization, we attempted to occulsion of the giant fusiform basilar trunk aneurysm with endovascular coil embolization including the parent basilar artery, again. The procedure was initially performed under local anesthesia while carefully monitoring the neurological findings, but we changed to general anesthesia because of poor cooperation and irritability of the patient. There were many pontine supplying branches at the distal basilar artery, therefore we embolized at the just distal of the giant fusiform aneurysm for the sufficient remnant distal basilar artery stump. Because of so wide extent of the aneurysm transitional zone, we applied neuroform stent to make an initial coil mesh. After then, we embolized at the just distal of left PICA originated site in the left vertebral artery to obliterate the left VA aneurysm and to reduce intra-luminal pressure. Final conventional 4 vessels angiography revealed as followings. The flow of both PICA and AICA was maintained and the intra-luminal turbulent flow was reduced significantly (Fig. 3). After the endovascular procedure, the patient cooperated well and there was no focal neurological change compared with the initial status. The post-operative course was uneventful. About two days after endovascular flow diversion, the patient exhibited aggressive personality, dizziness and mild disorientation regarding the time. The rechecked brain MRI revealed no newly appeared lesions correlated with symptoms of the patient except non-specific multifocal small acute embolic infarctions in the cortex of both cerebral hemispheres. Recently, The patient was checked up in the out patient clinic with maintaining antiplatelet medication (four months later after endovascular flow diversion). Symptoms such as aggressive personality, dizziness and mild disorientation regarding the time were gradually improved. Most recently followed up digital subtraction MR angiography revealed more progression of intra-luminal thrombosis and slowing of intra-luminal turbulent flow. There were no change in the aneurysm size and no newly appeared infarction lesions (Fig. 4). 

Discussion 

   Ectasia, elongation, and tortuosity of the basilar artery, vertebro-basilar dolichoectasia (VBD), is a rare condition characterized by a high degree of variability in the final outcome from one patient to another, with the full spectrum of the disease ranging from benign asymptomatic nature to severe disabled nature. Clinical expression of VBD includes compression of cranial nerves or the brainstem, obstructive hydrocephalus, ischemia in vertebro-basilar arterial territory and intracranial bleeding of various kinds rarely including subarachnoid hemorrhage.⁹⁾¹¹⁾ Little is known about the natural causes of this condition. But according to current literatures, it may mainly occur as results of atherosclerosis and hypertension.⁵⁾¹⁵⁾ It also occurs in association with moyamoya disease, Ehlers-Danlos syndrome and EEC syndrome (ectrodactyly, ectodermal dysplasia, and clefting of the lip or palate).^1)10)18) These VBDs including giant fusiform aneurysms are difficult to eliminate because their morphology usually prevents maintenance or reconstruction of the parent vessel. Therefore, the parent arterial occlusion for the flow diversion is considered to be an alternative option. As fusiform giant basilar trunk aneurysms, basilar trunk occlusion may offer a potentially long-lasting cure.¹⁷⁾ Steinberg et al., Drake et al. and Pelz et al. have shown limited success with a surgical ligation for the basilar trunk aneurysm trapping, which demonstrates 65~70% patients with a good recovery and 30~35% patients with severe morbidity and mortality depending on the collateral supply from Pcom arteries.^3)13)16) Steinberg et al. showed that patients with two large (>1 mm) Pcom arteries had better outcomes than those of patients with one large and one small (<1 mm) Pcom arteries and patients with two small Pcom ateries who undergo surgical trapping for the basilar trunk.¹⁶⁾ Therefore, before occlusion of the basilar artery, taking consideration of the presence and size of both Pcom arteries is essential. For the patient who had a giant fusiform basilar trunk aneurysm with poor collateral circulation from carotid circulation, it is clear that bypass surgery is a good treatment option. However it remains unclear as to which types of bypass (namely, a high-flow bypass or a relatively low-flow bypass) and which sites of anastomosis. Continuing advancements in endovascular techniques have increased the safety and efficacy, especially, to patients at high risk for microsurgical techniques including bypass surgery alone because of involving vessels over along distance and many important perforating arteries to the brainstem. Recently, combined microsurgical including bypass surgery and endovascular strategies have been used to treat these giant fusiform basilar trunk aneurysms with poor collateral circulation from carotid circulation.⁴⁾⁸⁾ Most importantly, it seemed that combined management modality can improve the treatment result considering to the poor natural history of the untreated cases. 
   Previous reports have indicated that hemodynamic factors play an important role in the development and pathogenesis of the intracranial dolichoectatic artery. Through the combined microsurgery including bypass surgery and endovascular strategies was a good treatment modality for the controlling two major hemodynamic factors. Two major factors are the turbulent flow in the vertebro-basilar junction and essential intra-luminal hypertension those were considered to exert hemodynamic stress on the VBD. In our case, endovascular occlusions of the just distal of the giant fusiform basilar trunk aneurysm and the just distal of left PICA origin site in the left vertebral artery resulted in reduction of turbulent flow and progressive formation of intra-luminal thrombosis and those results will achieve complete occlusion of the aneurysm, although micro-emboli formation due to thrombosis might be a cause of multiple small embolic infarctions. Furthermore, endovascular occlusion of the just distal of left PICA originated site in the left vertebral artery was essential procedure in the presented case due to left VA aneurysm. Bypass surgery (superficial temporal artery-radial artery-superior cerebellar artery anastomosis) was also effective in diminishing the blood flow and the caliber of the vertebro-basilar insufficiency resulted from endovascular occlusion of the aneurysm. In conclusion, hemodynamic factors may play an important role in the development and pathogenesis of dolichoectasia. The reduction of hemodynamic stress is considered to be effective in the presented case obviously. In general, the risk of brainstem infarction cannot be avoided following basilar artery occlusion, because perforators to the midbrain and pons emerge from the basilar artery throughout its length. It is so difficult to guarantee the safety and to evaluate the risk of perforator injury. In cases of giant fusiform vertebrobasilar aneurysms, most perforators to the brainstem which are incorporated into the aneurysm sac seem to be gradually occluded with the thrombosis at the time of diagnosis.¹⁷⁾ If the brainstem is intact, then the territories of the involved perforating arteries may already be supplied by collateral supply.⁸⁾ Therefore, the strategy to preserve the developed collateral supply to the involved brainstem is the most important. It is suggested that a high-flow bypass using the RA preserved the upper perforator area and the antegrade flow to the basilar artery maintained after flow diversion also preserved the lower perforator area in presented case. We feel that it is not so important to consider preservation of the perforators from the site of the thrombosed aneurysm itself, because of the above reasons. We planed bypass surgery to maintain carotid collateral supply through anastomosis vessels. Furthermore, when endovascular occlusion for the flow diversion, we efforted to maintain the possible collateral flow to the brainstem from other major vessels in the posterior circulation, such as the PCA, SCA, AICA, PICA and VA. Therefore, it is important to preserve the normal vessels distal and proximal to the aneurysm as long as possible. 
   This is a single case presentation and it is difficult to apply this method in general practice. However, the treatment for these aneurysms is quite challenging. For these aneurysms, we should discuss the possibility of various modalities including surgical and endovascular techniques depending on the traits of each individual case. The appropriate modification of these techniques is thus expected to lead to positive treatment results. It is therefore necessary to accumulate a larger number of successful reports in order to treat this type of aneurysm, effectively. 

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