Laboratory studiesA small animal model for early cerebral aneurysm pathology

- Studies using hypertension/elastase have induced cerebral aneurysms (CA) in mice.
- Using lower dose elastase, early CA pathology was sought at arterial bifurcations.
- Pathology included endothelial change and internal elastic lamina degeneration.
- Such bifurcation changes have not been systematically/simultaneously studied before.
- A spectrum of early CA pathology permits study of factors influencing CA formation.

Prior studies, using systemic hypertension and elastase infusion, have induced cerebral aneurysm (CA) formation in mice. However, the CAs induced were rapidly formed, relatively large, and often ruptured. These features are not completely representative of human CAs. We set out to develop a mouse model representative of the early pathological features of human CA. Twenty male C57/BL6 mice were placed in a stereotactic frame. Low dose elastase solution (2 μl/min) was manually injected into the right basal cistern. Human angiotensin II (0.11 μl/h) was infused subcutaneously. Mice were observed for 2-3 weeks prior to euthanasia. Early CA histopathological features including endothelial change (EC) and internal elastic lamina degeneration (IELD) were systematically sought at major cerebral arterial bifurcations. Brains were harvested from 11 of 15 mice, yielding 27 bifurcations. Sub-arachnoid haemorrhage (SAH) without CA formation was observed in one brain. Macroscopic CA without SAH was observed in another brain. Early CA features were observed in 8/11 (73%) brains. All bifurcations with IELD demonstrated EC: where EC was absent, IELD was also absent. EC severity appeared to correlate with IELD severity. EC and IELD were both severe within the CA. Using lower dose elastase solution than previously employed, we developed a model of early CA pathology. Our model demonstrated that the spectrum of known early CA pathology can be created at multiple bifurcations in mice, with EC severity appearing to correlate with IELD severity. This model permits the study of factors which potentially advance or retard the progression of CA formation.