Brain Aneurysm Basics

More than 6.5 million Americans suffer from a brain aneurysm, a potentially fatal brain condition that goes largely undiagnosed. Brain aneurysms are bulging, blood-filled sacs that form on weak spots of blood vessels in the brain. Although aneurysms are often painless and produce no symptoms, they are not completely harmless. If they rupture, the consequences can be devastating.

In this article, we will explore the basics of brain aneurysms. Each section summarizes important information about this condition. Follow the links in each section for additional details about the topic.

The vascular anatomy of the brain encompasses the network of vessels that supply blood to this vital organ. In the human body, blood vessels come in three primary types: arteries, veins, and smaller vessels known as capillaries. Arteries carry oxygen-rich blood from the heart to tissues throughout the body, while veins return deoxygenated blood from tissues back to the heart. Thin-walled capillaries link arteries and veins and facilitate the exchange of oxygen, nutrients, and metabolic waste products between the blood and surrounding tissues.

There are four main arteries that transport blood from the heart to the brain. Two internal carotid arteries and two vertebral arteries travel upwards in the neck. They join at the base of the brain to form a vascular ring called the Circle of Willis, which gives off branches to all parts of the brain. After blood has delivered its oxygen, it is taken back to the heart and lungs through superficial and deep veins, which drain the outer and inner parts of the brain, respectively.  

There are five main types of aneurysms — saccular, fusiform, pseudo, mycotic, and blister — each with its own shape, risk factors, and treatment options

• Saccular aneurysms: resemble small berries and are the most common type of brain aneurysm. They form a tiny sac that protrudes from a weak segment along a blood vessel in the brain. Saccular aneurysms may grow and rupture. They are the leading cause of nontraumatic subarachnoid hemorrhage (SAH).
• Fusiform aneurysms: develop with widening or ballooning in all parts of the blood vessel wall. It doesn't have a neck like some other aneurysms, which makes it resemble an enlarged tube. They have a lower risk of rupturing than saccular aneurysms but may still cause SAH and strokes. 
• Pseudoaneurysms: also known as false aneurysms, is a bulge in a blood vessel that occurs due to a tear in the vessel wall. Unlike a true aneurysm, where bulging occurs within the normal layers of the blood vessel wall, a pseudoaneurysm is caused by blood leaking out of the vessel and being contained by the surrounding tissue.
• Mycotic aneurysms: are rare and result from infection that weakens the blood vessel wall. A heart infection called subacute bacterial endocarditis is the primary cause of mycotic aneurysms, and severe infections may lead to multiple aneurysms.
• Blister aneurysm: is a small, fragile type of aneurysm that is named because it looks like a blister on an artery wall. These aneurysms are usually found on the internal carotid artery, which is a major artery that supplies blood to the brain. They are particularly challenging to treat because they have a thin wall and can rupture easily.

Symptoms of aneurysm can develop when they form close to crucial brain tissues and nerves. However, most unruptured aneurysms are asymptomatic. Rarely, unruptured aneurysms may cause vision changes, pupil inequality, and a droopy eyelid. Ruptured brain aneurysms present with significant symptoms such as a severe headache, stiff neck, lack of coordination, loss of consciousness, light sensitivity, dilated pupils, vision impairment, loss of balance, and confusion.  

Unfortunately, many aneurysms are discovered only upon rupture - a potentially fatal event. The odds of surviving a ruptured brain aneurysm depend on its size and location, a patient's age, overall health, underlying health issues, extent of bleeding, and time to treatment. Generally, the earlier the diagnosis and treatment, the better the overall outcome.

Diagnosing an aneurysm is typically performed through a combination of imaging tests. Most commonly, a computed tomography (CT) scan is obtained initially. This is a relatively quick scan to check for any blood surrounding the brain. A CT angiogram (CTA) may then be performed, which involves the injection of a dye into your bloodstream to make the blood vessels show up more clearly on the pictures.

A cerebral angiogram is a more invasive test where a thin tube (catheter) is inserted into a blood vessel in your arm or groin and moved up to your brain. A dye is then injected, and X-ray images are taken to visualize the blood vessels. This procedure can also be used to treat the aneurysm through delivery of special materials to the aneurysm site.

If the initial CT scan doesn't show any evidence of bleeding but your doctor still thinks that you might have had a ruptured aneurysm, a lumbar puncture may be performed. This test takes some of the fluid around your brain and spinal cord to check for microscopic signs of bleeding.

Additional tests that may be conducted, more often in the context of screening or monitoring purposes, include magnetic resonance imaging (MRI) and MRI angiography. These tests offer superior resolution compared to CT scans and do not involve radiation exposure. However, they typically require more time to complete compared to a CT scan.

The risk factors and causes of aneurysms can be categorized into two main groups: modifiable and non-modifiable. Modifiable risk factors develop after birth and are often linked to lifestyle choices. These include conditions such as high blood pressure, smoking, alcoholism, substance abuse (particularly with methamphetamine and cocaine), and traumatic brain injuries.

Non-modifiable risk factors are those that cannot be controlled and include conditions such as coarctation of the aorta, Ehlers-Danlos syndrome, polycystic kidney disease, arteriovenous malformation (AVM), Klinefelter syndrome, and Noonan syndrome.

While brain aneurysms pose a considerable health risk, they are treatable and manageable. While it may not be possible to prevent hereditary risk factors for aneurysms, early diagnosis allows for proper management.

Adopting a healthy lifestyle, including regular exercise, maintaining an optimal body weight, consuming a nutritious diet, and abstaining from drugs, tobacco, and alcohol, can aid in the prevention of brain aneurysms. Individuals at high risk for developing brain aneurysms should undergo periodic tests and check-ups to diagnose, treat, or manage the condition effectively.

• Brain aneurysms develop when the blood vessels in the brain develop weak points, forming blood-filled sacs. 
• Brain aneurysms typically do not produce symptoms until rupture.
• A sudden, severe headache is the most common symptom associated with brain aneurysm rupture.
• Doctors use different imaging techniques, including CT and MRI scans, as well as cerebral angiograms to diagnose brain aneurysms.

• National Institute of Neurological Disorders and Stroke
• American Association of Neurological Surgeons (AANS): Cerebrovascular Disease
• Brain Aneurysm Foundation
• American Association of Neurological Surgeons (AANS): Cerebral Aneurysm
• American Brain Foundation (ABF)