Diagnosis: Types and Imaging Tools

Understanding your diagnosis begins with clear imaging. Doctors use specialized scans to create a “map” of your brain’s blood vessels, allowing them to determine the type, size, and location of the aneurysm ^[1]. Because most unruptured aneurysms are found incidentally, having a precise “baseline” is essential for deciding whether to monitor the aneurysm or treat it ^[2]. It is also important to confirm that the finding is a true aneurysm and not an infundibulum (a normal, funnel-shaped widening of a vessel) or an imaging artifact.

Common Types of Brain Aneurysms

Not all aneurysms look or behave the same way. Their shape and cause help doctors predict their behavior.

• Saccular (Berry) Aneurysms: These are the most common type, appearing like a small fruit or a “blister” on a stem ^[3]. They typically form at the “forks” or branches of arteries where the blood flow is most turbulent ^[4].
• Fusiform Aneurysms: Instead of a focal pouch, these involve a more uniform bulging or widening of an entire section of the artery ^[5]. They are often linked to atherosclerosis (hardening of the arteries) or a “dissection” (a tear in the vessel wall) ^[5][6].
• Infectious (Mycotic) Aneurysms: These are rare and caused by an infection—often from the heart valves (infective endocarditis) or bloodstream—that travels to the brain and weakens the arterial wall ^[7][8].
  • Actionable Step: If you have an aneurysm and experience a persistent fever, or have a history of endocarditis, tell your medical team immediately. Infectious aneurysms can change rapidly and require urgent infectious-disease and neurosurgical evaluation ^[8].

Imaging Tools: How Doctors See the Aneurysm

Different clinical situations call for different types of scans.

1. Noncontrast Head CT

If a patient arrives at the emergency room with symptoms of a ruptured aneurysm, a noncontrast head CT is generally the first scan performed. It is extremely fast and highly sensitive for detecting acute bleeding in the brain. If this scan is negative but suspicion remains high, further testing like a lumbar puncture (spinal tap) or CTA may be required to rule out a hemorrhage.

2. CTA (CT Angiography)

A CTA uses a standard CT scanner and an injection of contrast dye into your vein to evaluate the blood vessels ^[1].

• Pros: Highly accurate for most aneurysms; excellent at showing “calcification” (hardening) and relation to bone ^[1].
• Cons: Involves a small amount of radiation and requires contrast dye, which may be a concern for patients with kidney issues ^[9].

3. MRA (MR Angiography)

An MRA uses magnetic fields instead of radiation. It is often used for screening and long-term monitoring ^[10].

• Pros: No radiation; often can be done without contrast dye (using a technique called Time-of-Flight) ^[11].
• Cons: Less sensitive for very small aneurysms and can be less accurate near the bones at the base of the skull ^[11][12].

4. DSA (Digital Subtraction Angiography)

Catheter DSA is considered the “gold standard” for imaging ^[9]. A specialist inserts a thin tube (catheter) through an artery in your leg or wrist and guides it to the brain to inject dye directly into the arteries.

• Pros: Provides the highest resolution and allows for 3D views that show every angle of the aneurysm ^[10][13]. It is used when CTA/MRA are equivocal or for complex surgical planning ^[12].
• Cons: It is an invasive procedure that carries risks, including a small risk of stroke, access-site bleeding, and contrast reactions ^[14].

Checklist for Your Imaging Report

When reviewing your imaging report, these structural details help form the larger clinical picture:

1. Size: Measured in millimeters (e.g., 4mm x 5mm). Note that small measurements can differ slightly between scan types and readers ^[15].
2. Location: The specific artery (e.g., Middle Cerebral Artery) and which side of the brain it is on ^[15].
3. Morphology (Shape): Is it smooth and round, or “irregular”? Does it have a daughter sac (a smaller bump on top of the main one)? Irregularity provides risk information ^[16].
4. Dome-to-Neck Ratio: This compares the width of the main body (dome) to the opening (neck) ^[1]. This ratio is one factor (among many) used to determine if an aneurysm can be easily coiled ^[17].
5. Growth: If you have had previous scans, the report should state if the aneurysm has changed ^[16].
6. Branching: Does the aneurysm incorporate or block any nearby arterial branches? ^[1]