Introduction 

   Unruptured intracranial aneurysms are diagnosed with greater frequency as imaging technique improve and the finding of unruptured aneurysms in a patient allows the opportunity of providing preventive treatment. Although either neurosurgically and endovascularly treatment may be advocated because of the devastating effects of aneurysm ruptured, the natural history of unruptured intracranial aneurysm is still a matter of debate. The treatment is only justified if the morbidity and mortality is less than the risk that the untreated aneurysm poses to the patient. Most studies, defining the long-term natural history of unruptured intracranial aneurysms, found a 0.05% to 2.3% annual risk of rupture with a 50% mortality incidence associated with each episode of aneurysm rupture^2)7)17)18) In the study presented by Johnston et al,⁹⁾ comparing surgical occlusion verse coil embolization of unruptured intracranial aneurysms, a morbidity rate of 18.5% was found in the surgical group, 10.6% in the endovascular group, and mortality rates of 2.3% and 0.4%, respectively. The risk associated with surgical treatment depends on following features: patient age, aneurysm size, aneurysm location⁸⁾¹⁷⁾ Successful treatment by Guglielmi Detachable Coil(GDC) embolization depends on endovascular access, aneurysm neck size and overall aneurysm size¹⁴⁾ When aneurysm treatment is warranted, which modality should be used. To identify the factors that determine whether a patient with an unruptured intracranial aneurysm is treated by endovascular coil embolization or surgical clipping, we reviewed 74 consecutive unruptured intracranial aneurysms in patients who present at our institutions. 

Materials and Methods 

   This is a retrospective review of 68 patients with 74 unruptured intracranial aneurysms who underwent embolization with GDCs and surgical clip occlusion between April 1990 and December 2005 at our institution. Surgical clip occlusion was administered 58 consecutive patients (16 male and 42 female patients) with a total of 63 unruptured intracranial aneurysms and GDC embolization was a administered 10 consecutive patients (4 male and 6 female patients) with a total of 11 unruptured intracranial aneurysms. There were no standard selection criteria, whether the patient was treated with GDC embolization or with surgical clip occlusion. Treatment was jointly discussed in an interdisciplinary manner between neuroradiologist and neurosurgeons. In patients with aneurysm in the posterior circulation and in patients with infraclinoidal aneurysms, we favored endovascular techniques because of the more complicated or impossible surgical approach. Twenty-four patients had experienced previous subarachnoid hemorrhage from other aneurysms and were treated electively after complete rehabilitation. The 74 unruptured intracranial aneurysms reported in this series were divided into two groups. Group A consisted of aneurysms that were treated with surgical clip occlusion. Group B consisted of those aneurysms in which attempts at GDC embolization. The patient's outcome was recorded at the last follow-up and categorized into four groups: excellent; no neurological deficit remained; good; mild neurological deficits like mild hemiparesis, third nerve palsy remained; fair; severe disability remained; and death. 

Results 

   The characteristics of 68 patients with 74 unruptured intracranial aneurysms are detailed in Table 1. 

Group A 
   Fifty-eight patients underwent surgical clip occlusion: 42 women and 16 men. Age varied from 35 to 75 years (mean age 55.6 years). Five patients had multiple lesions. Seven patients had neurological symptoms, including third nerve palsy, visual disturbance due to the mass effect of the aneurysm itself. Twenty-two patients had experienced previous subarachnoid hemorrhage from other aneurysms. Nineteen patients were examined because of headache (n=9) and dizziness (n=10). The aneurysm was an incidental finding in ten patients: benign intracranial tumor (n=1), intracranial hemorrhage (n=2), head trauma (n=2), previous infarction (n=5). Aneurysms were encountered in the following location: eight arising from the anterior communicating artery (ACoA); two from pericallosal artery; thirty three from the middle cerebral artery (MCA); thirteen from the posterior communicating artery; and seven from the internal carotid artery. 45 aneurysms were small (<10mm), 17 were large (10~24mm), 1 were giant (25mm). Of 63 unruptured intracranial aneurysms, 61 were clipped and two were wrapped. Out of 58 patients with surgical clip, 3(5.2%) had fair outcome (Table 2). One patient with calcification presented frontal infarction by left A2 artery clip, leading to right hemiparesis. Another patient treated for a wide neck pericallosal aneurysm presented right hemiparesis and aphasia. A third patient, treated for a thrombosed giant MCA aneurysm, presented right hemiparesis and seizure. 

Group B 
   Ten patients with 11 unruptured intracranial aneurysms underwent GDC: 6 women and 4 men. Age varied from 37 to 69 years (mean age 59 years). Two patients had experienced previous subarachnoid hemorrhage from other aneurysms. Five patients were examined because of headache (n=2) and dizziness (n=3). The aneurysm was an incidental finding in two patients: benign intracranial tumor (n=1), hemifacial spasm (n=1). One patient had third nerve palsy. Aneurysms were encountered in the following location: one from pericallosal artery; one from the middle cerebral artery; two from the posterior communicating artery; three from the cavernous part of internal carotid artery; and four from the apex of basilar artery. Nine aneurysms were small (10mm) and two were large (10~24mm). One patient(10%) treated for a left pericallosal artery aneurysm occurred thromboembolic incident (Table 2). The patient had a left anterior cerebral artery(ACA) territory infarction that was treated by local injection of urokinase with right hemiparesis. 

Discussion 

   The natural history of the unruptured intracranial aneurysm varied with characteristics of lesion. The mortality and morbidity from surgery for those which were varied with characteristics of lesion.^11)16)17) More recent series reporting outcome following surgery for unruptured intracranial aneurysms have found 0% to 3% mortality and 4% to 17.5% morbidity.^{1)5)11)17)20)} 

Aneurysm size 
   Orz et al.¹¹⁾ reported that for aneurysms less than 16mm, there was no difference between the results for aneurysms less 6mm and for those between 6 to 15mm in diameter but aneurysms greater than 25mm in size carried 18% risk of severe disability or death.¹¹⁾ Solomon et al.¹⁹⁾ found that morbidity and mortality were 1% for aneurysms smaller than 10mm, 5% for those between 11 and 25mm, and 20% for those larger than 25mm. In another study it was demonstrated that aneurysm size influences surgical outcome, regardless of the location and 25mm aneurysm had a fourfold higher risk of a poor outcome after surgery compared to a 5mm aneurysm.⁸⁾ In ISUIA series,¹⁶⁾ aneurysms greater than 12mm in size carried a 2.6 relative risk of poor surgical outcome. 

Aneurysm location 
   The location of an aneurysm in the posterior circulation was associated with an increased incidence of poor outcome independent of the aneurysm size.^4)8)11)16) This difference may be attributed to the complicated surgery required for access to the posterior circulation and the number of perforators that supply vital structures arising from posterior circulation vessels. Solomon, et al., observed a 50% morbidity and mortality rate with surgery of unruptured giant basilar aneurysms compared to a 13% rate for anterior circulation giant aneurysms.¹⁵⁾ Other locations such as aneurysms in the anterior communicating artery with a posterosuperior projection and cavernous portion of internal carotid artery are also associated with higher levels of morbidity and mortality due to technical difficulties. Mizoi et al.¹⁰⁾ felt that a giant unruptured aneurysm located on the paraclinoid portion of the internal carotid artery or on the basilar artery contraindicated surgery because of the high probability of operative morbidity. In these cases, they recommended other forms of treatment like endovascular treatment.¹⁰⁾ 

Patient age 
   Older individuals are more likely to have an increased incidence of atherosclerotic or calcified aneurysm neck and dome, making surgical clipping difficult. Khanna, et al.⁸⁾ showed that a 70-year-old patient undergoing surgery for unruptured aneurysm has a six fold higher risk of poor outcome compared to a 30-year-old patient, keeping aneurysm size and location constant. Mizoi et al.¹⁰⁾ recommended that surgical treatment is indicated for patients under 70 years of age. The ISUIA part2, a prospective study, was published in 2003. In this study, an increase of 2.4 in relative risk was observed in patients who were older than 50 years of age.¹⁶⁾ 

Conditions influencing endovascular outcome 
   Since its introduction by Guglielmi and colleagues in 1991, there has been a steady increase in coil emboilzation of unruptured intracranial aneurysms. A meta-analysis involving a total of 1383 patients treated with endovascular coils for ruptured and unruptured intracranial aneurysms found a low permanent complication rate (3.7%) but a high rate of incomplete obliteration (46%).³⁾ In the ISUIA,¹⁶⁾ investigators revealed that 451 unruptured intracranial aneurysms were treated with endovascular therapy, occlusion rate were documented (obliteration was complete in 55% of patients and incomplete in 24%; in 18% there was no obliteration and in 3% the status was unknown). Endovascular treatment is a very attractive option, for both patient and physicians but it is not clear whether incomplete coil embolization affects the bleeding rate of unruptured intracranial aneurysms. Consequently, it is premature to evaluate the effectiveness of endovascular therapy for unruptured intracranial aneurysms. In the ISUIA,¹⁶⁾ investigators revealed a 2.4 relative risk of poor endovascular outcome for aneurysms larger than 12mm in diameter and location in the posterior circulation (2.25 relative risk). Regli L et al.⁹⁾ Recommended an angioanatomical features contraindicate endovascular coil placement for patient presenting with unruptured intracranial aneurysm: neck width 4mm, dome/neck ratio 1.5, inadequate endovascular access, unstable intraluminal thrombus, arterial branch origin incorporated with aneurysm neck. Endovascular treatment could be more suitable for older patient, because age wasn't associated with higher morbidity and mortality rate after coil occlusion.¹⁶⁾ Although endovascular procedure might be associated with less immediate risk, long-term risk and durability of treatment is not known and long-term follow-up review of treated patient is necessary. 

Management recommendation 
   For patients who require interventions, factors such as its location, surgical or endovascular accessibility, dome and neck size, the patient age, the patient's general medical condition, and the individual's treatment preference should be taken into account to determine the choice of therapies (Table 3). Patients' age was a strong predictor of surgical outcome, and the size and location of an aneurysm predict both surgical and endovascular outcomes. Zipfel et al.¹⁹⁾ are much more likely to recommend endovascular therapy for patients with aneurysms who are older than 60 years of age. On the other hand, they more commonly advocate surgery for patients who are younger than 50 years of age, because concerns regarding long-term durability of the occlusion after endovascular therapy still exist.¹⁹⁾ Proust et al.¹²⁾ propose surgical clip application for ACoA aneurysms that have an anterior projection and endovascular coil embolization for those with a posterior projection. In general, aneurysms that are located along the basilar artery or basilar apex are more commonly treated with endovascular therapy, whereas lesion along the MCA and distal ACA are typically treated with surgery. Regarding other aneurysm locations, aneurysm characteristics are considered during the decision making process. For example, larger lesions are more likely to be treated with surgery because of the rather poor initial and long-term angiographic results following platinum coil therapy. Similarly, wide-necked aneurysms are more commonly treated with surgery, because endovascular therapy for such lesions often mandates the use of higherrisk techniques such as balloon remodeling or stent placement. Finally, aneurysm complexity must be carefully assessed, because the presence of calcification and/or atheroma would make endovascular therapy more attractive, whereas the presence of intraluminal thrombus would make surgical treatment more likely. 

Conclusion 

   Unruptured intracranial aneurysms are diagnosed with greater frequency as imaging technique improve such as Magnetic resonance angiography and Computed tomography angiography. Endovascular therapy with platinum coils has been accepted a valuable alternative treatment to surgical clip occlusion. These changes have led to an ongoing debate about the optimal management strategy for patients harboring unruptured intracranial aneurysms. Currently, management decisions in patients with unruptured intracranial aneurysms require accurate assessment of the risk factors. A collaboration by vascular neurosurgeons and interventional neuroradiologists is recommended to evaluate each patient and to tailor the best treatment plan. 

REFERENCES

1. Ahn JS, Kwun BD. Management of unruptured intracranial aneurysms -natural course & surgical outcome. J Kor Neuro Soc 30:813-8, 2001 

2. Asari S, Ohmoto T. Natural history and risk factors of unruptured cerebral aneurysms. Clin Neurol Neurosurg 95:205-14, 1993 

3. Brilstra EH, Rinkel GJE, van der Graaf Y, van Rooij Wjj, Algra A. Treatment of intracranial aneurysms by emboilzation with coils: a systematic review. Stroke 30:470-6, 1999 

4. Chen PR, Ferrichs K, Spetzler R. Current treatment options for unruptured intracranial aneurysms. Neurosurg Focus 17(5):E5, 2004 

5. Jeong YG, Sim JH, Jung YT, Lee SI, Kim MS. Treatment of unruptured intracranial aneurysms. Kor J cerebrovascular surgery 6:130-6, 2004 

6. Johnston SC, Dudley RA, Gless DR. Onol: Surgical and endovascular treatment of unruptured cerebral aneurysms at university hospitals. Neurology 10:1799-805, 1999 

7. Juvela S, Porras M, Heiskanen O. Natural history of unruptured intracranial aneurysms: a long-term follow-up study. J Neurosurg 79:174-82, 1993 

8. Khanna RK, Malik GM, Qureshi N. Predicting outcome following surgical treatment of unruptured intracranial aneurysms: a proposed grading system. J Neurosurg 84:49-54, 1996 

9. Legli L, Uske A, Tribolet N. Endovascular coil placement compared with surgical clipping for the treatment of unruptured middle cerebral artery aneurysms: a consecutive series. J Neurosurg 90:1025-130, 1999 

10. Mizoi K, Yoshimoto T, Nagamine Y, Kayama T, Koshu K. How to treat incidental cerebral aneurysms: A review of 139 consecutive cases. Surg Neurol 44: 114-20, 1995 

11. Orz YI, Hongo K, Tanaka Y, Nagashima H, Osawa M, Kyoshima K, et al. Risk of surgery for patients with unruptured intracranial aneurysms. Surgical Neurol 53:21-9, 2000 

12. Proust F, Debone B, Hannequin D, Gerardin E, Clavier E, Langlois O, et al. Treatment of anterior communicating artery aneurysms: complementary aspects of microsurgical & endovascular procedures. J Neurosurg 84:49-54, 1996 

13. Raaymakers TW, Rinkel GJ, Limburg M, Algra A. Mortality and morbidity of surgery for unruptured intracranial aneurysms: a meta-analysis. Stroke 29: 1531-8, 1998 

14. Rufenacht DA, Mandai S, Levrier O. Endovascular treatment of ntracranial aneurysms. AJNR 17:1658-60, 1996 

15. Solomon RA, Fink ME, Pile-Spellman J. Surgical management of unruptured intracranial aneurysms. J Neurosurg 80:440-6, 1994 

16. The International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 362:103-10, 2003 

17. The International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms-risk of rupture and risks of surgical intervention. N Eng J Med 339:1725-33, 1998 

18. Yasui N, Suzuki A, Nishimura H, SuzukiK, Abe T. Long-term follow-up study of unruptured intracranial aneurysms. Neurosurgery 40:1155-60, 1997 

19. Zipfel GJ, Dacey RG. Update on the management of unruptured intracranial aneurysms. Neurosurg Focus 17(5):E2, 2004 

20. Zuccarello M. Treatment strategy of patient with unruptured intracranial aneurysms. Neurol Med Chir(Tokyo) 41:571-5, 2001