Types of Brain Aneurysms

Medically Reviewed By William C. Lloyd III, MD, FACS
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Male doctor's hand examining sheet of brain MRI scans

A brain aneurysm is an abnormal bulge in the wall of an artery—a main blood vessel—within the brain. Another name for brain aneurysm is cerebral aneurysm. Some cerebral aneurysms are large; some are very small. The distended artery wall at the abnormal bulge is thinner than normal and is at risk of bursting. If the aneurysm doesn’t burst, it might not cause any problems or symptoms. An aneurysm that ruptures, though, is a life-threatening medical emergency.

According to the Brain Aneurysm Foundation, about 1 in 50 Americans has an unruptured aneurysm. Oftentimes, a doctor discovers the aneurysm when the individual undergoes medical testing for another health condition. If an unruptured aneurysm presses against nerves within the brain, the affected individual may experience double vision, a droopy eyelid, eye pain, a dilated pupil, or numbness or weakness on one side of the body. A person experiencing any of these symptoms should seek immediate medical attention.

About 30,000 Americans per year experience the rupture of a brain aneurysm, and many die. Healthcare providers know that some medical conditions and lifestyle habits increase the risk of aneurysm rupture. High blood pressure and smoking, for instance, are known risk factors. At present, though, physicians can’t predict which aneurysms will remain stable and which might rupture.

There are three primary types of brain aneurysms:

Saccular Aneurysm

A saccular aneurysm is sometimes called a ‘berry aneurysm.’ This type of aneurysm is rounded and hangs from the artery as a berry hangs from a vine. According to the National Institute of Neurological Disorders and Stroke, saccular aneurysms are the most common type of brain aneurysm. Approximately 90% of cerebral (brain) aneurysms are saccular aneurysms, according to the Columbia University Department of Neurology.

If a saccular aneurysm is not causing symptoms, your healthcare provider may recommend monitoring it over time. Treatment for saccular aneurysm may include surgical insertion of a coil to block blood flow to the aneurysm. Another option is the surgical application of a clip to the neck of the aneurysm to stem the flow of blood.

Fusiform Aneurysm

A fusiform aneurysm is one that bulges out on all sides of the artery. Picture a bulge at a weak spot in a garden hose, when water is running through the hose. That’s about what a fusiform aneurysm looks like.

Because fusiform aneurysms do not have a clear, simple connection to the main artery, they are more difficult to treat than saccular aneurysms, which usually feature a well-defined ‘neck.’ Doctors sometimes surgically reroute the flow of blood around these aneurysms to prevent additional stress on the walls of the artery that could cause a rupture.

Fusiform aneurysms are significantly less common than saccular aneurysms.

Mycotic Aneurysm

A mycotic aneurysm is caused by an infection. The infection weakens the artery wall, allowing it to bulge. According to a 2013 BioMed Research International article, only 0.7 to 5.4% of all brain aneurysms are mycotic.

Mycotic aneurysms can be caused by fungal or bacterial infection. Most often, bacteria are the cause of a mycotic aneurysm.

Because an infection causes this type of aneurysm, treatment with antibiotics (if the infection is caused by bacteria) or antifungal medication (if the infection is fungal) may cause the aneurysm to shrink or disappear. If the patient is not experiencing aneurysm-related symptoms (such as visual changes, eye pain, numbness or weakness), medication is usually the first line of treatment.

If symptoms are present, or the aneurysm gets larger despite treatment, invasive treatment may be necessary. Neurosurgeons use the same clipping and coiling procedures for mycotic aneurysm as they use for saccular aneurysms.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Apr 3
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  1. Brain Aneurysm. MedlinePlus, U.S. National Library of Medicine. https://medlineplus.gov/brainaneurysm.html
  2. Statistics and Facts. Brain Aneurysm Foundation. https://bafound.org/about-brain-aneurysms/brain-aneurysm-basics/brain-aneurysm-statistics-and-facts/
  3. Cerebral Aneurysms Fact Sheet. National Disorder of Neurological Disorders and Stroke https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Cerebral-Aneurysms-Fact-Sheet
  4. What You Should Know About Cerebral Aneurysms. American Stroke Association. https://www.stroke.org/en/about-stroke/types-of-stroke/hemorrhagic-strokes-bleeds/what-you-should-know-about-cerebral-aneurysms
  5. Unruptured Aneurysm Basics. Brain Aneurysm Foundation. https://bafound.org/about-brain-aneurysms/brain-aneurysm-basics/unruptured-aneurysms/
  6. Brain Aneurysm. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/brain-aneurysm/symptoms-causes/syc-20361483?p=1
  7. Cerebral Aneurysm. Columbia University Department of Neurology. http://www.columbianeurology.org/neurology/staywell/document.php?id=35871
  8. Monteith S, Tsimpas A, Dumont A, et al. Endovascular treatment of fusiform cerebral aneurysms with the Pipeline Embolization Device. Journal Of Neurosurgery. 2014;120(4): 945-954. doi:10.3171/2013.12.jns13945. Retrieved from https://thejns.org/view/journals/j-neurosurg/120/4/article-p945.xml
  9. Zanaty M, Chalouhi N, Starke R, et al. Endovascular Treatment of Cerebral Mycotic Aneurysm: A Review of the Literature and Single Center Experience. Biomed Res Int. 2013; 2013:1-8. doi:10.1155/2013/151643. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3872026/