In This Article
- Almost 35,000 brain aneurysms rupture each year. Approximately 50% of these result in poor outcomes
- While surgery is appropriate for symptomatic or high-risk cerebral aneurysms, patients with low-risk aneurysms may benefit more from observation and medical risk reduction
- Researchers at Massachusetts General Hospital are developing a computer model to predict which aneurysms are more likely to rupture
- Small animal models are used to help identify interventions that may help lower risk of brain aneurysm rupture
Patients with intracranial bleeding from an aneurysm almost always require surgery, but for non-ruptured cerebrovascular aneurysms, surgical management carries significant risk. These inherent risks include stroke or hemorrhagic complications from brain manipulation and antiplatelet use.
Doctors assess the need for surgery based on the likelihood the aneurysm will rupture, and Aman Patel, MD, director of Cerebrovascular and Endovascular Neurosurgery and director of the Neuroendovascular Program at Massachusetts General Hospital, says the current method for assessing that likelihood is imperfect.
Dr. Patel's research is helping to mitigate risk and provide better outcomes for patients while reducing pressure on doctors who decide whether surgery is necessary. He and other researchers at Mass General are developing a computer model that will help predict whether an aneurysm is at a higher risk for rupture, thereby determining the patients that require surgery for treatment of an aneurysm and those that can forego surgery and its complications.
The Puzzle of Aneurysm Diagnosis: Who Gets Surgery?
Currently, aneurysm treatment, including surgical management, is dictated by a patient's imaging results, age and physical condition. The predominant determination factor used is aneurysm size, with those larger than five to seven millimeters more likely to be treated with surgery, particularly in younger patients. However, it is not unusual for patients with a smaller aneurysm to get surgical treatment despite a lack of data supporting that approach. This is largely because while large aneurysms are more likely to burst, it does not mean smaller ones are incapable of bursting, all the more reason why Dr. Patel's model will help identify which aneurysms could benefit from surgery regardless of size.
"Diagnosing aneurysms that are likely to bleed is not an exact science," says Dr. Patel. "Some aneurysms are high-risk, some are low-risk and some patients should not be surgically treated. One of my patients has a 20-millimeter aneurysm that hasn't burst. I've also operated on patients with two or three-millimeter aneurysms that did burst. The trick is figuring out which patients with unruptured aneurysms are at high-risk for aneurysm rupture."
The team's work has the potential for a large impact. An estimated 3–5% of the United States population lives with a brain aneurysm. Each year, as many as 35,000 of these cerebral aneurysms rupture, resulting in intracranial hemorrhage and potential damage to brain tissue. While some people recover from an aneurysm rupture, almost 50% of patients have poor outcomes, including death.
Predicting Outcomes for Brain Aneurysm Surgery
Dr. Patel's team is developing a computer model that uses computational fluid dynamics to predict which patients with unruptured brain aneurysms would benefit from surgery. The program originated in the aerospace industry, and it is not yet in clinical use. However, Mass General physicians are collecting data during procedures and using data from past patients for the purpose of researching accuracy and efficacy in predicting potential rupture points on the aneurysm.
During endovascular occlusion or open brain surgery, Dr. Patel and his team use angiography and intraoperative images to collect information about cerebral blood vessels and blood flow through the aneurysm. The computer model measures the curvature of blood vessels and determines areas of high pressure and irregularity of flow in an aneurysm that may increase the risk of rupture.
When researchers compare data from the computer model to data collected during the operation, there is 80–90% agreement between the observed aneurysm and the flow prediction with the areas of high pressure corresponding to areas of aneurysm wall thinness or rupture point.
As the computer model develops, other information may be included that would help with the prediction model. This data may include:
- The number of blood vessel branches involved in the aneurysm
- Which part of the blood vessel is involved
- The shape and size of the aneurysm, especially when complex
- The curvature of the normal blood vessel
Preventing Aneurysm Rupture
Today, preventative care for aneurysms is extremely limited. Physicians focus primarily on making sure patients avoid tobacco and control blood pressure. According to Dr. Patel, "If a patient doesn't smoke, there aren't, unfortunately, a lot of other options that can reduce the risk of a burst aneurysm."
To better understand risk factors and interventions that may address them, the Mass General team is conducting research in small animal models. Researchers treat mice with elastase and feed them a high-sodium diet to induce hypertension, leading to aneurysm formation. And, then the team examines various therapies that may help reduce the possibility of aneurysm rupture.
Two therapies the team is currently investigating are anti-inflammatory medications and vagal nerve stimulation, a common device-based therapy for epilepsy. They hypothesize that stimulation of the vagus nerve causes the release of anti-inflammatory factors that may reduce the risk of a burst aneurysm. Early results support this theory.
"The aneurysms in mice that underwent the therapies didn't rupture as frequently," Dr. Patel says. "The mice also had better post-rupture outcomes compared to mice that received no such treatments. This shows us that in the future, we may be able to provide treatments for aneurysms to reduce the potential for progression. These could be noninvasive medical treatments at home."
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