Published online before print August 30, 2012, doi: 10.3174/ajnr.A3314
AJNR 2012 33: E120

R.A. Pérez Falero^a and O.L. Piloto^a
aDepartment of Neurosurgery
Hospital Hermanos Ameijeiras
La Havana, Cuba

After reading with interest “Endovascular Therapy of 500 Small Asymptomatic Unruptured Intracranial Aneurysms,”¹ we have some remarks to share with the authors and readers.

Oishi et al¹ included in their introduction the following comment, “Current evidence does not conclusively justify the conservative management of small asymptomatic UIA [unruptured intracranial aneurysms] ”; but is there any class I or II study that supports any particular treatment in patients with UIAs? Regardless of the fact that published series on this particular issue² have increasing numbers of cases and even outstanding results compared with outcomes of patients with ruptured aneurysms, they lack the best available statistical design. Therefore and despite the intrinsic limitations of the International Study of Unruptured Intracranial Aneurysms,³ this study remains as a landmark article on the natural history of intracranial aneurysms and, thus, an obligated control group.

In the article of Oishi et al,¹ most of the aneurysms (90%) were located in the anterior circulation. The authors have treated them with the following results: 20% residual aneurysms and 1% combined mortality and permanent morbidity. According to these numbers, almost 1 in 4 patients did not receive any benefit from the intervention or their conditions worsened. What would the outcome have been if observation was the chosen strategy instead? In agreement with the opinion of Molyneux⁴ on this issue and relying on the reported results, can we justify any kind of intervention for an asymptomatic lesion?

Concerning the learning curve of Oishi et al,¹ the combined complete occlusion and residual neck were 67% of the first 100 treated lesions, while they were 68% in the final group. Even if there was no significant difference between these 2 variables, residual aneurysms increased from 22% to 31%, and they said, “The reasons for decreased failure seem to be related to the practitioners’ technical advances and the development of the right devices. …” How can the authors explain this statement?

On the discussion related to the effectiveness of coiling in preventing aneurysmal SAH, the authors state, “These results suggest that endovascular therapy of UIAs, particularly that of small asymptomatic UIAs, provides sufficient protection from aneurysmal SAH in short-to-midterm periods.” However, how can we accept this suggestion if they have not included an observational group that truly reflects the incidence of SAH in UIAs? Again, the controversy about the natural history of UIAs shows up and dilutes the hidden benefits that any intervention can provide.

Regardless of the above-mentioned problems, Oishi et al¹ have displayed high proficiency and remarkable technical skills in dealing with this complex group of aneurysms.

References

1. Oishi H, Yamamoto M, Shimizu T, et al. Endovascular therapy of 500 small asymptomatic unruptured intracranial aneurysms. AJNR Am J Neuroradiol 2012; 33: 958–64 » Abstract/FREE Full Text
2. Im SH, Han MH, Kwon Ok, et al. Endovascular coil embolization of 435 small asymptomatic unruptured intracranial aneurysms: procedural morbidity and patient outcome. AJNR Am J Neuroradiol 2009; 30: 79–84 » Abstract/FREE Full Text
3. Wiebers DO, Whisnant JP, Huston J 3rd., et al., for the International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 2003; 362: 103–10 » CrossRef » Medline
4. Molyneux AJ. The treatment of unruptured cerebral aneurysms: cause for concern? AJNR Am J Neuroradiol 2011; 32: 1076–77< » FREE Full Text

Reply

Published online before print August 30, 2012, doi: 10.3174/ajnr.A3335
AJNR 2012 33: E121

H. Oishi^a
aDepartment of Neurosurgery
Juntendo University School of Medicine
Tokyo, Japan

In the International Study of Unruptured Intracranial Aneurysms (ISUIA),¹ the natural risk of bleeding in patients without a history of subarachnoid hemorrhage strongly depended on the size of the aneurysm. Aneurysms (<7 mm) located in the internal carotid artery, anterior communicating artery, middle cerebral artery, and aneurysms (<7 mm) located in the posterior circulation or the posterior communicating artery showed an annual bleeding risk of 0% and 0.5%, respectively. On the other hand, Sonobe et al³ reported that the annual bleeding risk of unruptured intracranial aneurysms (UIAs) <5 mm in the Japanese population was 0.54%. In their meta-analyses of the rupture risk of UIAs, Wermer et al³ reported that the risks of the aneurysms measuring ≤5 mm and 5–10 mm were 0.5% and 1.2%, respectively. Japanese and Finnish populations have a relatively high risk of aneurysm rupture. In the latest prospective study regarding the natural course of UIAs in the Japanese population, the annual rupture risks of UIAs measuring 3–4 mm, 5–6 mm, and 7–9 mm were 0.36%, 0.50%, and 1.69%, respectively.⁴ Therefore, the patient’s race should be taken into consideration regarding the rupture risk of asymptomatic small UIAs.

We believe that UIAs that are incompletely embolized with a coil can be protected from bleeding in short-to-midterm periods. Patients with incompletely embolized UIAs receive certain benefits from endosaccular coil embolization. However, a large-scale prospective cohort study with long-term follow-up is warranted.

With increasing experience and the development of endovascular devices, aneurysms that are difficult to treat with endosaccular coil embolization, probably resulting in failure in the early period, have become treatable, resulting in a residual neck or residual aneurysm.

We reported that the patients in our series were not representative of the whole Japanese population of patients with small asymptomatic UIAs because surgically treated or untreated UIAs were not included in this study. Therefore, a large-scale prospective cohort study is warranted. We discovered that experienced interventionalists can perform the endosaccular coil embolization of asymptomatic small UIAs with very low morbidity and mortality rates.

References

1. Unruptured intracranial aneurysms: risk of rupture and risks of surgical intervention—International Study of Unruptured Intracranial Aneurysms Investigators. N Engl J Med 1998; 339: 1725–33 » CrossRef » Medline
2. Sonobe M, Yamazaki T, Yonekura M, et al. Small unruptured intracranial aneurysm verification study: SUAVe study, Japan. Stroke 2010; 41: 1969–77 » Abstract/FREE Full Text
3. Werner MJ, van der Schaaf IC, Algra A, et al. Risk of rupture of unruptured intracranial aneurysms in relation to patient and aneurysm characteristics: an updated meta-analysis. Stroke 2007; 38: 1404–10. » Abstract/FREE Full Text
4. Morita A, Kirino T, Hashi K, et al. The natural course of unruptured cerebral aneurysms in a Japanese cohort. N Engl J Med 2012; 366: 2474–82 » CrossRef » Medline