Aneurysms are abnormal vascular pouches caused by structural weaknesses in the wall of the arteries of the brain. Their development and growth is influenced by a multitude of factors including congenital predisposition and individual tissue properties along vessel walls.
Most aneurysms are found at vascular branching points indicating that blood flow-related haemodynamic stress on the vessel walls near the bifurcation seems to generate a vulnerable site predisposed to aneurysm formation and growth.
Intracranial aneurysms have been associated with some systemic conditions like polycystic kidney disease, fibromuscular dysplasia, Marfan or Ehlers-Danlos syndrome and may also occur along feeding arteries of cerebral vascular malformations. The exact mechanisms of vessel wall weakening and aneurysm formation and growth, including the rare cases in which trauma or infections are involved, are still subjects of current research.