• About 2% of the adult population have an asymptomatic cerebral aneurysm.

• Unruptured aneurysms can cause symptoms such as headache, visual acuity loss, cranial neuropathies (particularly thrid nerve palsy), pyramidal tract dysfunction, and facial pain; these are thought to be due to mass effect on the aneurysm.

• 20 to 30% of people with a cerebral aneurysm, have multiple aneurysms; Don't miss co-existing aneurysms on CTA or MRI. 

• The majority of intracranial aneurysms are located in the anterior circulation, most commonly in the Circle of Willis.

• When localizing aneurysm on CTA and MRI, common sites include: 

              ---  junction of the anterior communicating artery (ACOM) with the anterior cerebral artery (ACA)

              ---  junction of the posterior communicating artery (PCOM) with the internal carotid artery (ICA)

              ---  bifurcation of the middle cerebral artery (MCA)

References

Singer, et al. "Unruptured Intracranial Aneurysms." November 2007. UptoDate online 16.2.