Diagnosis of brain aneurysms

Medical imaging and tests used to identify brain aneurysms and related complications.

Computerised Tomography (CT Scan)

A CT scan utilises X-rays to create a detailed image of the brain. This technology is widely available, quick, and particularly effective in identifying bleeding in or around the brain, which can occur if an aneurysm ruptures. The scan may be performed with or without an iodinated ‘contrast’ dye, which helps in distinguishing different brain structures more clearly, such as the blood vessels. Although a CT scan does involve a small amount of radiation, the dosage is generally not high enough to pose a significant risk to the patient.

CT Angiography is a specialized CT scan that uses an injection of contrast dye to visualize the blood vessels, making it an effective tool in the diagnosis of brain aneurysms. It is usually possible to see the shape and size of an aneurysm, if present. The procedure is mostly non-invasive, other than the small injection required for the contrast.

CT scans involve being placed in a donut shaped machine. Scans usually take about 10 minutes.

Magnetic Resonance Imaging (MRI)

MRI and MR angiography (MRA) are techniques that generate high-resolution images of the brain and blood vessels respectively, without using X-rays. Instead, they use strong magnetic fields. These methods can can see certain aneurysms in more detail, and are used in the follow-up of embolised (but not clipped) aneurysms. However, they are generally slower, more expensive, and cannot be used on patients with certain metallic implants, due to the powerful magnets involved.

MRI scans involve being positioned in a tunnel and typically take 20-60 minutes.

Cerebral Angiography

Cerebral angiography is a more invasive diagnostic procedure that uses X-rays to produce very high-resolution images of the brain’s blood vessels, and it is the gold-standard method for identifying aneurysms. During this test, a small incision is made in the patient’s groin or wrist, through which a catheter is guided to the blood vessels in the neck. Contrast dye is then injected through the catheter to visualize the aneurysm. This procedure provides the most detailed images of an aneurysm, but it is more invasive than MRI or CT/CTA scans. The major risk is of developing a stroke during the procedure, on the order of 0.5%.

Lumbar Puncture

A lumbar puncture, often known as a spinal tap, is a medical procedure where a needle is inserted into the lower portion of the spine (the lumbar region) to extract a sample of cerebrospinal fluid (CSF). This fluid envelops your brain and spinal cord, acting as a protective layer and facilitating a stable environment.

In the context of aneurysms, it is usually performed when doctors suspect an aneurysm as having ruptured but other imaging tests, such as a CT scan, aren’t conclusive. This could be because the bleed was minimal, or the blood has already dispersed. During a lumbar puncture, the collected CSF is meticulously examined for the presence of blood or xanthochromia. The latter is a yellowish or pinkish discoloration that results from the breakdown of red blood cells in the CSF — both of these signs point towards a recent subarachnoid haemorrhage.