Natural cerebral aneurysm and spontaneous subarachnoid hemorrhage in mammals other than man: is there a scope for comparative medicine?

BACKGROUND: Concepts which showed substantial efficacy in animal models of subarachnoid hemorrhage (SAH), often failed improve outcome in humans with aneurysmal SAH. The concept of "comparative medicine", an open-minded comparison across species, might offer an alternative to the "constructed" animal models' approach. Naturally occurring diseases in animals might bear more similarity to human diseases than models. In this context, the question arises whether spontaneous intracranial aneurysms exist in animals or not, and whether they cause SAH or not. METHODS: A systematic literature search was performed. Only articles dealing with natural aneurysms and/or SAH of mammals other than man were included. All articles dealing with induced aneurysms and/or SAH were removed. RESULTS: Out of 2,812 screened articles, 9 articles describing natural intracranial aneurysms and/or SAH were found. In total 1,979 individual animals of 29 species were examined. Natural intracranial aneurysms were described in 7 individual animals of 6 species. Spontaneous SAH was described in 3 species. In one chimpanzee, a ruptured intracranial aneurysm caused a SAH. Histological descriptions of the aneurysms were strikingly similar to those of humans. CONCLUSION: Although interesting and innovative, the concept of "comparative medicine" seems to be impracticable due to the seemingly ultra-low incidence of natural aneurysmal SAH in mammals other than man. The answer to the question, why intracranial aneurysms are less common in animals despite the strong histological similarity of cerebral arteries, might be a key issue. Last but not least, primates likely matter in SAH-related research, as aneurysmal SAH occurs in primates.; Abbreviations: SAH: subarachnoid hemorrhage, CVS: cerebral vasospasm, AcomA: anterior communicating artery, CT: computed tomography, MCA: middle cerebral artery