Diagnosing Brain Aneurysms

A brain aneurysm is a sac-like protrusion of a weak segment on an artery in the brain. While many brain aneurysms can go undiagnosed, some may produce severe symptoms. The diagnostic workup of a brain aneurysm can include several imaging tests. In this article, we discuss how the diagnosis of a brain aneurysm is confirmed and what each test entails. 

Typically, a brain aneurysm looks like a bubble filled with blood. Unlike healthy arteries that have a pinkish color, an aneurysm appears more reddish because of thinning of the artery. 

There are 5 types of brain aneurysms:

• Saccular aneurysms: Also called berry aneurysms, saccular aneurysms are round and extend from the sidewall of the artery. Most aneurysms diagnosed today are saccular. 
• Fusiform aneurysms: With fusiform aneurysms, the blood vessel balloons on all sides so that the bubble of the aneurysm appears wider and resembles a snake that has swallowed a rat.
• Blister aneurysms: Blister aneurysms are blister-like protrusions from the wall of an artery, making the artery prone to bleed.
• Mycotic aneurysms: An infection elsewhere in the body can cause infection and damage to a part of an artery, resulting in a mushroom-like dilation and aneurysm formation.
• Pseudoaneurysms: Pseudoaneurysms look similar on imaging to saccular aneurysms but are caused by injury through all layers of the artery, which results in a pocket of blood collected on the outside of the blood vessel.

A ruptured aneurysm is one that has burst. Thus, the most prominent imaging finding is the blood that is released into the surrounding space. This blood is usually seen on a CT scan and will prompt further testing via a CT angiogram (CTA) or diagnostic cerebral angiogram to determine the exact location of the aneurysm. A ruptured aneurysm usually shows a small projection on the dome of the aneurysm called a bleb.

Unruptured brain aneurysms rarely produce symptoms unless they burst or leak. When the aneurysm ruptures, it causes a sudden severe headache, often described as a thunderclap headache in medical circles. People who have had ruptured aneurysms say the headache is the worst they've ever experienced.

A ruptured aneurysm is a medical emergency because it causes life-threatening bleeding (subarachnoid hemorrhage). Urgent medical attention is required to prevent damage to the brain (hemorrhagic stroke) and death.

Although most unruptured aneurysms do not produce any symptoms, an incidental finding of an aneurysm should prompt a discussion with a specialist to determine if treatment is recommended. If you do not experience symptoms, the decision to treat is usually related to the cumulative risk of rupture over your lifetime.  

Computed Tomography (CT), also known as computer axial tomography (CAT) scan, is a medical imaging technique that uses X-rays and computer processing to create detailed cross-sectional images, or slices, of the body. It is relatively quick way to visualize internal structures.

During a CT scan, the patient lies on a table that moves into a ring-shaped machine called a CT scanner. The scanner emits a series of X-ray beams that pass through the body from different angles. Detectors inside the scanner measure the amount of radiation that passes through the body and creates multiple cross-sectional images, or slices, of the area being examined.

In the context of a brain aneurysm, a CT can be particularly helpful to determine if blood is present in the brain (subarachnoid hemorrhage). While there are many potential causes for a subarachnoid hemorrhage, a ruptured aneurysm is one of them. This can prompt further testing to determine if an aneurysm is present. 

A computerized tomography angiogram (CTA) is a specialized type of CT that combines the principles of conventional CT scanning with the injection of a contrast dye into the bloodstream to enhance the visibility of blood vessels. This is often one of the first tests ordered by doctors when there is concern for an aneurysm.

During a CTA, a contrast dye containing iodine is injected into a vein, usually in the arm. As the contrast dye circulates through the bloodstream, it highlights the blood vessels, making them more visible on the CT images. CTAs are particularly valuable for assessing blood flow and visualizing the location of the aneurysm. However, smaller aneurysms can sometimes go undetected through this test.

Magnetic resonance imaging (MRI) is a medical imaging technique used to produce detailed images of the inside of the body. Unlike X-rays or CT scans, which use ionizing radiation, MRI uses a powerful magnetic field and radio waves to generate images.

Like a CTA to a CT, magnetic resonance angiography (MRA) is a special type of MRI used to visualize blood vessels in the body. However, it is different from a CTA in that a contrast dye may or may not be used.

Techniques such as time-of-flight MRA or phase contrast MRA can produce images of blood flow patterns without using contrast dye. However, in some cases, a gadolinium-containing contrast agent may be used to enhance the quality of MRA images.  

MRI is typically not used in the acute setting, as it takes much longer than a CT scan to obtain. However, it can be useful for screening tests or follow-up imaging to avoid repeated exposure to ionizing radiation.

A diagnostic cerebral angiogram is the most definitive imaging method for diagnosing brain aneurysms. It is a type of X-ray image that is used to create detailed images of the blood vessels. During a diagnostic cerebral angiogram, the following steps are performed:

• Preparation: The patient is positioned on an X-ray table, typically lying flat on their back. Local anesthesia is often used to numb the area where the catheter will be inserted, usually in the groin or wrist.

• Catheter insertion: A thin, flexible tube called a catheter is inserted into a large artery, such as the femoral artery in the groin, under the guidance of fluoroscopy (real-time X-ray). The catheter is carefully advanced through the blood vessels until it reaches the arteries supplying blood to the brain.

• Contrast injection: Once the catheter is in place, a contrast dye containing iodine is injected into the bloodstream through the catheter. The contrast dye flows through the blood vessels, highlighting the cerebral arteries and veins on X-ray images.

• X-ray imaging: X-ray images are taken rapidly as the contrast dye fills the blood vessels. The X-ray machine captures images of the contrast dye passing through the cerebral vasculature at different angles. Specialized techniques, such as digital subtraction angiography (DSA), may be used to enhance the visibility of the blood vessels by subtracting background structures from the images.

• Image interpretation: The resulting images provide detailed views of the blood vessels in the brain, allowing healthcare providers to identify abnormalities such as aneurysms, arteriovenous malformations (AVMs), blockages, or other vascular conditions.


Diagnostic cerebral angiography is considered the gold standard for evaluating the cerebral vasculature due to its ability to provide high-resolution images and precise anatomical detail. It can detect small aneurysms that are missed on CTA or MRA.

While it is more invasive than other imaging techniques, such as CT or MRI angiography, it remains an essential tool in the diagnosis and treatment planning of aneurysms.

Imaging tests are the cornerstone for diagnosis of a brain aneurysm. CTA and diagnostic cerebral angiograms are most used and can help to visualize the size, location, and morphology of a brain aneurysm.

• Ruptured brain aneurysms are life-threatening with the most common symptom being that of a severe headache, often described as the worst headache in one's life
• Brain aneurysms are typically diagnosed through CT angiography and diagnostic cerebral angiograms
• MRI and MRA scans can be helpful tests for screening or monitoring of 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)