Types of and Location of Cerebral Aneurysms
Cerebral aneurysms are classified both by size and shape.
- Small aneurysms are less than 11 millimeters in diameter (about the size of a large pencil eraser)
- larger aneurysms are 11-25 millimeters (about the width of a dime)
- giant aneurysms are greater than 25 millimeters in diameter (more than the width of a quarter).
- Saccular aneurysm refers to any aneurysm with a sac shaped outpouching.
- Berry aneurysm, is a type of saccular aneurysm with a neck or stem resembling a berry.
- A fusiform aneurysm describes an aneurysm without a stem.
Most cerebral aneurysms are asymptomatic. They usually occur at the bifurcations and branches of the large arteries located at the Circle of Willis. Approximately 85% of aneurysms occur in the anterior part of the circle of Willis. About 25% of the time aneurysms occur as multiples and 20% are bilateral (Prayson R. 2001)
The most common sites include the:
- Anterior Communicating artery (30 - 35%)
- Bifurcation of the Internal Carotid and Posterior Communicating artery (30 - 35%)
- Bifurcation of Middle cerebral (20%)
- Basilar artery bifurcation (5%)
- Remaining posterior circulation arteries (5%)(Vega C. 2002)
The majority of cerebral aneurysms occur in the anterior portion of the circle of Willis.
- Prayson R. (2001) Neuropathology Review. Springer Science & Business Media, 2001.
- VEGA C., KWOON J.V., LAVINE S.D. (2002) Intracranial Aneurysms: Current Evidence and Clinical Practice. Am Fam Physician. 15;66(4):601-609. Accessed 11/29/2016 http://www.aafp.org/afp/2002/0815/p601.html