Intracranial aneurysms (IAs) are persistent, localised dilatations of the arterial
wall that are found in approximately 3% of the general population. The most severe
complication of IAs is rupture, which results in devastating consequences such as
subarachnoid haemorrhage and brain damage with serious neurological sequelae. Numerous
studies have characterised the mechanisms underlying IA development and growth and
identified a number of environmental modifiable (smoking, hypertension) and nonmodifiable
risk factors (related to the histology of cerebral arteries and genetic factors) in
its pathogenesis. Haemodynamic stress also likely plays a crucial role in the formation
of IAs and is conditioned by the geometry and morphology of the vessel tree, but its
role in the natural history of unruptured IAs remains poorly understood; it is believed
that changes in blood flow might generate the haemodynamic forces that are responsible
for damage to the vascular wall and vessel remodelling that lead to IA formation.
This review summarises the most relevant data on the current theories on the formation
of IAs, with particular emphasis on the roles of special conditions resulting from
the microscopic anatomy of intracranial arteries, haemodynamic factors, bifurcation
morphometry, inflammatory pathways, and the genetic factors involved in IA formation.
