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Response to "Correlation of intracranial and aortic aneurysms"

We appreciate the interest and comments on our article which highlights the best available evidence at the time of publication on the correlation between intracranial and aortic aneurysms. The co-prevalence of intracranial aneurysms with thoracic aortic aneurysms has been reported as 4.9%–9.0%, and whilst we agree that the prospective study by Malhotra and colleagues had a larger sample size, the co-prevalence is still significant for descending thoracic aortic aneurysms notwithstanding the general limitations subject to a single-center cohort study design. A worthwhile argument is raised on the indications for screening for unruptured intracranial aneurysms in additional populations, and the criteria for the contemporary high-risk group may need to be reconsidered. The Unruptured Intracranial Aneurysm Study showed that small (<7mm) aneurysms in the anterior circulation without prior systemic arterial hypertension did not rupture during the follow-up period. However, there was an annual risk of rupture of up to 10% in giant aneurysms in the posterior circulation. One analysis reported that fusiform intracranial aneurysms are associated with aortic aneurysms and may be more prevalent in the vertebrobasilar arterial system, hence could be at greater risk of rupture. One of the limitations of the Unruptured Intracranial Aneurysm Study was selection bias because the majority of patients received treatment, and those who were followed up tended to be older and sicker. Additionally, cavernous intracranial aneurysms were also included in the analysis, and it is well-known that small cavernous aneurysms do not bleed into the subarachnoid space. Although several retrospective studies, as cited in our review, reported small aneurysms, in a prospective study of a Finnish cohort, 25% of small aneurysms (<7mm) ruptured during the follow-up period. We agree that there is a paucity of literature on aneurysm characteristics and the relationship between intracranial aneurysms and aortic aneurysms, because most studies have focused on prevalence. Indeed, several factors may increase the risk of aneurysm rupture and these include aneurysm morphology, neck size, size of aneurysm, and location, and these characteristics could necessarily influence the degree and invasiveness of screening protocols.