It’s an honor to give a lecture to ANACP on cerebral aneurysm
An in-depth analysis from Dr. Kevin Zhao’s presentation on cerebral aneurysms provides critical insights into their formation, risks, and treatment strategies. A cerebral aneurysm is a bulge or weak spot in a brain artery. While the worldwide prevalence is about 3%, the primary danger lies in their potential to rupture, leading to a life-threatening type of stroke known as a subarachnoid hemorrhage (SAH).
The Genesis and Risk Factors of Aneurysms
The formation of intracranial aneurysms is a complex process initiated by increased hemodynamic stress on artery walls. This stress can lead to endothelial dysfunction, where the inner lining of the blood vessel is damaged. This initial damage triggers an inflammatory cascade, involving various cells and signaling molecules that ultimately degrade the vessel wall, leading to the formation of an aneurysm.
Several risk factors contribute to the development of cerebral aneurysms:
- Genetic Factors: A family history of aneurysms significantly increases risk.
- Age and Gender: They are most commonly diagnosed around the mean age of 50 and are more prevalent in females after this age. This is potentially due to decreased estrogen, which leads to a reduction in the collagen content of vascular tissue.
- Lifestyle and Medical Conditions: Arterial hypertension, cigarette smoking, high cholesterol, heavy alcohol consumption, and drug abuse are all significant risk factors.
The Critical Question of Rupture
While approximately 3% of the world’s population has a cerebral aneurysm, the annual rate of rupture is much lower, at about 10 per 100,000 people. Understanding which aneurysms are likely to rupture is a central goal of ongoing research.
Major international studies have sought to define the natural history of unruptured aneurysms. The International Study of Unruptured Intracranial Aneurysms (ISUIA) initially suggested a 0% risk of rupture for aneurysms smaller than 7mm in the anterior circulation. However, this created a discrepancy with clinical observations from trials like the Barrow Ruptured Aneurysm Trial (BRAT), which found that the majority of ruptured aneurysms were, in fact, small (around 6mm) and located in the anterior circulation.
The Japanese SUAVe study offered a potential explanation for this discrepancy. It suggested that new aneurysms can form and subsequently rupture while still small. This study proposed four patterns of aneurysm behavior:
- Type 1: The aneurysm ruptures within weeks of formation.
- Type 2: It grows slowly for years before rupturing.
- Type 3: It continues to grow slowly without ever rupturing.
- Type 4: It grows to a certain size and then remains stable.
The SUAVe study also found that having multiple aneurysms was a significant risk factor for rupture. To consolidate such findings, the PHASES risk score was developed to predict the 5-year risk of rupture based on six factors: Population (Japanese and Finnish populations have higher risk), Hypertension, Age (≥70 years), Size of the aneurysm, history of an Earlier SAH from another aneurysm, and Site of the aneurysm (posterior locations carry higher risk).
Family History and the Role of Screening
A family history of aneurysms is a potent risk factor. A community-based study from the Mayo Clinic found that first-degree relatives of a patient with a ruptured aneurysm have a fourfold increased risk of suffering an aneurysmal SAH themselves, with the highest risk for siblings.
Given this, screening for aneurysms is recommended for certain high-risk individuals. Specifically, those with two or more first-degree relatives who have had a ruptured aneurysm are considered candidates for screening. Screening for asymptomatic patients without known risk factors is not seen as beneficial.
Diagnosis and Treatment Pathways
Diagnosing a cerebral aneurysm typically involves non-invasive imaging like CT or MR angiography (CTA/MRA). The definitive gold-standard for evaluation is a digital subtraction angiogram (DSA), which provides a detailed view of the blood vessels.
Not all aneurysms require treatment. The decision is complex, weighing the risks of rupture against the risks of intervention. When treatment is necessary, options include:
- Surgical Clipping: A surgeon places a small metal clip at the base of the aneurysm to block blood flow into it.
- Endovascular Coiling: A less invasive procedure where a catheter is guided through blood vessels to the aneurysm, and tiny platinum coils are deployed to fill the sac and promote clotting.
- Stenting and Bypass: Other endovascular and surgical options like stenting or bypass surgery can be used for more complex cases.
Aneurysmal Subarachnoid Hemorrhage: A Medical Emergency
If an aneurysm ruptures, it causes a subarachnoid hemorrhage (SAH), where blood spills into the space surrounding the brain. This is a devastating event, accounting for 5-7% of all strokes.
The outcomes are often grim:
- 15% of patients die at the time of rupture.
- The overall 30-day mortality rate is 45%.
- Of those who survive, half do not return to their previous baseline level of function, and up to a quarter become dependent on others for their care.
Management of a ruptured aneurysm is a medical emergency focused on “resuscitating the brain”. A key immediate step for severe cases is placing an external ventricular drain (EVD) to relieve the buildup of pressure inside the skull. One of the most dangerous complications following an SAH is vasospasm, a narrowing of the brain’s blood vessels that can lead to further ischemic damage.
A Note on COVID-19
While the SARS-CoV-2 virus is known to cause endothelial dysfunction, a key element in aneurysm formation, there is currently no concrete link established between COVID-19 infection or vaccination and the formation of cerebral aneurysms.
In conclusion, cerebral aneurysms are a serious condition requiring careful evaluation of numerous risk factors to guide management. Understanding the natural history of the disease is crucial, and ongoing research continues to refine our ability to predict which aneurysms pose the greatest threat, allowing for more personalized and effective treatment decisions.