Understanding Cerebral Aneurysms

By Carolyn D. Brockington, MD Director of Stroke Center Institute of Neurology & Neurosurgery St. Luke's-Roosevelt Hospital, New York City Assistant Clinical Professor of Neurology at Columbia University College of Physicians and Surgeons

Understanding Cerebral Aneurysms

An aneurysm develops from a weakened or thin spot on the wall of a blood vessel. Over time, the fragile area may balloon out due to pressure changes inside of the vessel. The concern is if the “ballooning” or aneurysm gets too large, it may rupture causing blood to spill into an area of the body producing injury. Aneurysms may develop along any blood vessel in the body, but typically develop at branching points of arteries. When the aneurysm develops along the wall of a blood vessel supplying the brain it is called a cerebral aneurysm.  If a brain aneurysm ruptures, the bleeding usually occurs under one of the layers or membranes of the brain called the arachnoid layer, producing a subarachnoid hemorrhage (SAH).

Incidence and Risk Factors

The exact incidence of intracranial (brain) aneurysms is unknown, but has been estimated at 1-6% of the population. Aneurysms increase in frequency with age beyond the third decade and are approximately 1.6 times more common in women. Notably, only a small percentage of aneurysms may rupture or cause symptoms. The proper identification of risk factors is essential in the management of cerebral aneurysms.

Interestingly, the majority of cerebral aneurysms are sporadic, which means they are not related to a specific disease process or inherited trait, but occur as a congenital defect resulting from an inborn abnormality of an arterial wall. High blood pressure (hypertension) and smoking are two important risk factors for the development and rupture of brain aneurysms. Other risk factors include particular diseases that may cause blood vessel abnormalities like polycystic kidney disease, connective tissue disorders, fibromuscular dysplasia, Marfan’s syndrome, collagen vascular disorders, and coarctation of the aorta (narrowing of the aorta between the upper body branches and lower body branches). In addition, some types of head or neck trauma and infections (involving the arterial wall) may cause an aneurysm to develop. 

A minority of cerebral aneurysms are found within families. In regards to screening for an aneurysm, the general recommendation is screening should be considered for a particular individual if 2 or more first-degree relatives (e.g. sibling, parent or child) have cerebral aneurysms. The screening is typically performed with non-invasive imaging that may include a MR- angiogram or CT angiogram.

Signs and Symptoms
A large number of cerebral aneurysms will never produce symptoms and are found incidentally while evaluating a patient for another medical issue. When a brain aneurysm produces symptoms, the patient may develop neurological signs (e.g. visual disturbances or facial paralysis) from the compression of the brain due to a change in the size or shape of aneurysm, or the patient may develop symptoms from the rupture of the aneurysm that can include a sudden, severe headache, acute nausea and vomiting, stiff neck, seizures, alteration in level of consciousness or paralysis. 

The classical description of the headache associated with the rupture of a cerebral aneurysm is “the worst headache of your life." The headaches usually occur suddenly and violently. Since headaches are common in the population, it is important to be able to identify a headache that may require medical attention. The key is the headache associated with an aneurismal rupture is typically uncharacteristic of prior headaches experienced throughout one’s lifetime. A change in the nature of a headache, particularly if it occurs suddenly in association with neurological symptoms, deserves a prompt medical evaluation.

Clinical Outcome
The rupture of a cerebral aneurysm and development of subarachnoid hemorrhage (SAH) is a neurological emergency. Studies have demonstrated approximately 40% of individuals with ruptured brain aneurysms do not survive the first 24 hours. In addition, up to 25% die from complications within 6 months while others are left with permanent neurological disability. Notably, ruptured cerebral aneurysms are most likely to re-bleed within the first day (2-4%), underscoring the need for urgent evaluation and treatment. The risk of re-bleeding remains high for the first 2 weeks with estimates of approximately 25%, if the ruptured aneurysm is left untreated. Many factors influence the clinical outcome, including age, pre-morbid medical history, degree of brain injury and delay in medical attention. The rupture of the cerebral aneurysm initiates a series of events resulting in the brain injury and neurological deficits.

One key process associated with subarachnoid hemorrhage is vasospasm. Blood is an irritant and causes the muscles surrounding the walls of the blood vessels to go into spasm. The contractions of the vessels cause vascoconstriction that produces inadequate blood flow to certain areas of the brain leading to tissue death. Although variations occur, cerebral vasospasm typically appears 4-10 days after the development of a subarachnoid hemorrhage. 

The management of patients with ruptured cerebral aneurysms and vasospasm require a multi-disciplinary medical team in a closely monitored intensive-care setting. Detailed vascular imaging is required in conjunction with prompt surgical treatment (neurosurgical or endovascular intervention) and aggressive management of the vasospasm and associated medical issues.

It is vital to be able to examine the degree of brain injury and status of the cerebral vessels to determine the appropriate treatment.  On many occasions, non-invasive imaging is used initially with CT or MRI to evaluate the brain, followed by CT-angiography or MR-angiography to examine the vascular status and anatomy. Ultimately, the gold-standard for the evaluation of the cerebral aneurysm and surrounding vasculature is a conventional cerebral angiogram. A cerebral angiogram is performed in a sterile environment where a catheter (wire) is inserted into the body through a blood vessel (usually in the groin) and navigated to the area of interest. Contrast dye is injected through the catheter while x-ray technology is used to provide a roadmap of the blood vessels. The cerebral angiogram is able to provide a detailed picture of the features of the aneurysm and surrounding blood vessels.

Treatment (Unruptured vs Ruptured Aneurysms)

Not all unruptured cerebral aneurysms require treatment. Many patients with unruptured cerebral aneurysms are followed conservatively by modifying their risk factors along with routine imaging.The decision to treat an unruptured cerebral aneurysm is complex and requires a consultation with a qualified physician. Many factors are considered during the decision process, including the patient’s age, size, shape and location of the aneurysm along with family history. The risks and benefits of any surgical treatment need to be weighed against the natural history of the aneurysm and the risk/benefit profile of the proposed conservative management.

For individuals who present with ruptured cerebral aneurysms, the need for urgent intervention is vital to reduce the chances of permanent neurological injury and improve clinical outcome. The two options for treatment of a ruptured cerebral aneurysm include neurosurgical intervention (microsurgery) or endovascular treatment.

The neurosurgical approach (microsurgery) requires an open surgical procedure to expose the aneurysm for proper treatment. The goal is to place a titanium clip across the neck of the aneurysm to prevent blood from entering the aneurysm to stop re-bleeding and further injury.  Essentially, the aneurysm or “balloon” is deflated by pinching off the neck of the aneurysm, excluding the aneurysm from the surrounding circulation.

With the endovascular approach, a conventional angiogram is performed to provide a detailed assessment of the aneurysm and roadmap of the surrounding circulation. Once the aneurysm is identified, several platinum coils (spirals of platinum wire) are placed inside of the aneurysm to obstruct blood from entering the dome and cause clotting in the aneurysm to produce the obliteration of the vascular structure. Each treatment option has its own risks and benefits depending on the patient’s clinical status and type of aneurysm.

The need to treat a cerebral aneurysm requires an extensive evaluation and review of the risks and benefits associated with each treatment option. Ruptured cerebral aneurysms require an urgent evaluation and treatment to limit the degree of brain injury and improve clinical outcome. Patients with unruptured cerebral aneurysms require a consultation with an experienced physician to help decide on the appropriate management.        

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