Aneurysm
- IWBCA
- Feb 6
- 16 min read
An aneurysm is a weakened, stretched area of an artery that balloons outward. Many aneurysms are asymptomatic until they enlarge, leak, or rupture. A rupture can cause sudden internal bleeding, and some aneurysms can also form clots that reduce or block blood flow, depending on where they are located.
Overview
What is an aneurysm?
An aneurysm is a localized weakening of an artery wall that allows the vessel to widen and bulge. Arteries carry oxygen-rich blood under pressure, so when a small section of the wall becomes less strong, each heartbeat can gradually push that area outward. Over time, an aneurysm can enlarge, and the risk generally increases as it grows or changes shape.
Many aneurysms are silent. People often feel completely well and only learn they have an aneurysm after imaging for another reason. When symptoms occur, they depend on the aneurysm's location and on whether it is compressing nearby structures, leaking, or rupturing.
Categorization
Are there different types of aneurysms?
Types are usually described by location because location shapes the risk profile, the symptoms that appear, and the way clinicians monitor and treat the condition.
Aortic aneurysms involve the aorta, the body’s largest artery, and are grouped by the segment affected.
Abdominal Aortic Aneurysm (AAA): AAAs develop in the portion of the aorta that runs through the abdomen, often below the arteries that supply the kidneys. Most are silent and discovered during a screening ultrasound or imaging performed for another reason. Clinical decision-making centers on diameter, growth rate, and wall features observed on imaging, as these factors help estimate the risk of rupture. Some AAAs also contain a clot within the aneurysm sac, which can contribute to circulation problems in the legs or increase concern for embolic complications.
Thoracic Aortic Aneurysm: Thoracic aneurysms involve the chest portion of the aorta and may occur in the ascending aorta, the arch, or the descending thoracic segment. Causes include long-standing high blood pressure, age-related vascular changes, bicuspid aortic valve disease, and inherited connective tissue disorders that weaken the aortic wall. When present, symptoms may reflect pressure on adjacent structures and may include chest or upper back pain, shortness of breath, hoarseness, cough, or difficulty swallowing. Management typically includes strict blood pressure control and scheduled imaging, with repair considered when size, growth, or anatomy indicate higher risk.
Intracranial aneurysms occur within the arteries of the brain and are often characterized by both location and shape, as these features influence the risk of rupture.
Cerebral Aneurysm: Many cerebral aneurysms are saccular, forming a pouch that arises near vessel branch points where blood-flow forces are higher. Most remain unruptured, but risk varies with size, location within the brain’s circulation, irregular shape features, and documented growth over time. Even without rupture, an aneurysm can sometimes affect nearby nerves and cause warning symptoms such as a new pattern of headache, double vision, drooping eyelid, or changes in pupil size. Rupture leads to bleeding around the brain and is a medical emergency.
Peripheral aneurysms involve arteries outside the aorta and brain, and their risks often relate to clot formation and downstream blockage.
Peripheral Aneurysm: These can develop in arteries such as the carotid artery in the neck, the popliteal artery behind the knee, the mesenteric arteries supplying the intestines, or the splenic artery. A key concern is the development of a clot within the aneurysm that breaks off, potentially causing a sudden reduction in blood flow to a limb or organ. Symptoms may include sudden leg pain, numbness, weakness, coolness, or changes in color. Some aneurysms also cause swelling or nerve symptoms if they compress nearby veins or nerves. Treatment is tailored to the involved artery and may prioritize preventing embolic events, preserving blood flow, and reducing the risk of rupture in high-risk locations.
Prevalance
How common are aneurysms?
Unruptured brain aneurysms are relatively common in adults, with large population studies using modern imaging repeatedly landing in the low single digits overall, often cited around 3 percent. In female populations, unruptured intracranial aneurysms are detected more frequently than in males, and the difference becomes clearer after midlife. Clinical datasets of patients diagnosed with unruptured aneurysms frequently show women representing the majority, and women also account for a substantial share of aneurysmal subarachnoid hemorrhage cases. Detection has risen over time for both sexes because CT and MRI of the head and neck are now used routinely for headaches, dizziness, trauma, and stroke evaluation, which increases incidental findings.
Aortic aneurysms also track strongly with age, but prevalence differs sharply by sex and smoking history. Abdominal aortic aneurysm remains far less common in women overall than in men, which is why routine screening is not recommended for women who have never smoked and have no family history. In contemporary screening-era data, the prevalence in older women is generally under 1 percent in broad populations, but it rises with age and tobacco exposure. In women older than 70, prevalence often reaches or exceeds 1 percent, and in current smokers, it can rise into the low single digits in some cohorts. The practical takeaway is that abdominal aortic aneurysm is uncommon in women as a whole, but it becomes meaningfully more relevant in women who are older and who have ever smoked or have a first-degree family history, which is the subgroup clinicians watch most closely.
High-Risk Populations
What populations are most at risk for aneurysm?
Risk depends on the aneurysm’s location, but several patterns are consistent across types.
For abdominal aortic aneurysm, risk is higher in people who are:
Male and older, especially those aged 65 and up.
Current or former smokers, because tobacco exposure is one of the strongest drivers of AAA formation and growth.
Living with a close family history of AAA, since risk increases when a first-degree relative is affected.
Managing long-standing high blood pressure, high cholesterol, or atherosclerosis.
For a brain aneurysm, the risk is higher in people who are:
Female, since unruptured aneurysms are detected more often in women in population estimates.
Living with high blood pressure or a history of smoking cigarettes or other nicotine use, both of which are associated with a higher rupture risk over time.
For a thoracic aortic aneurysm, the risk is higher in people who have:
Long-standing high blood pressure.
A bicuspid aortic valve.
A connective tissue disorder or a strong family history of thoracic aortic disease, which can raise risk at smaller diameters than in typical age-related aneurysms.
Symptoms
What are the most common symptoms of an aneurysm?
Many aneurysms cause no symptoms. They are often identified incidentally during imaging for another condition. Symptoms typically manifest when an aneurysm enlarges sufficiently to irritate adjacent tissue, leak, form a clot, or rupture.
A ruptured aneurysm is a medical emergency. Symptoms typically onset suddenly and can worsen rapidly. Call 911 if anyone has signs that could suggest a rupture, especially if symptoms start abruptly and feel severe.
Common warning signs of a possible rupture include:
Lightheadedness or fainting.
A very fast heartbeat.
Sudden, intense pain in the head, chest, abdomen, back, or flank.
Sudden collapse or loss of consciousness, especially after a severe headache.
Depending on where the aneurysm is located, an aneurysm that is not ruptured can still cause symptoms by pressing on nearby nerves or organs, affecting blood flow, or sending small clots downstream.
Symptoms can include:
Confusion, dizziness, or feeling disoriented.
Trouble swallowing or a sensation of pressure in the throat.
Unusual fatigue or weakness.
Headache, especially if new, persistent, or different from prior headaches.
Nausea or vomiting.
Pain in the abdomen, chest, back, or groin that is persistent, deep, or difficult to explain.
A pulsing sensation in the abdomen, or a noticeable throbbing mass.
Swelling or a pulsating lump in the neck.
Rapid heart rate or a pounding sensation in the chest.
Vision changes, including double vision, drooping eyelid, or a change in pupil size.
Some symptoms reflect the body’s response to major internal bleeding and falling blood pressure. These can include feeling cold, clammy, intensely weak, unusually anxious, or “not fully present,” along with a racing heart.
Complications
What are the most common complications associated with an aneurysm?
Complications depend on the aneurysm’s location and whether it ruptures or forms a clot.
A rupture causes internal bleeding. In the chest or abdomen, this can lead to rapid blood loss and shock. In the brain, rupture causes bleeding around the brain, which can quickly become life-threatening and can injure brain tissue.
Aneurysms can also cause complications without rupturing. Blood can swirl and stagnate inside the bulge, which increases the chance of clot formation. A clot can reduce blood flow at the aneurysm site or dislodge and travel downstream, obstructing smaller arteries.
Key complications include:
Severe internal bleeding after rupture.
Shock from rapid blood loss, which can lead to organ failure.
Stroke if a clot forms and travels to the brain, or if blood flow is reduced in critical arteries.
Brain bleeding after a ruptured cerebral aneurysm is often marked by a sudden, severe headache followed by symptoms such as weakness, confusion, trouble speaking, or loss of consciousness.
Reduced blood flow to organs or limbs if clots block circulation, which may cause sudden pain, numbness, weakness, coolness, or color change in an arm or leg.
Causes
What causes an aneurysm?
An aneurysm forms when a segment of an artery wall loses strength and stretches beyond its normal diameter under blood pressure. In some people, this reflects inherited traits in the structure of blood vessels. In others, it develops gradually through a combination of wear, inflammation, injury, and long-term strain on the circulation.
In many cases, no single cause is identified. Several factors often act together over time to weaken the vessel wall and increase the risk of aneurysm formation.
Common causes and contributors include:
Atherosclerosis and Arterial Degeneration: Atherosclerosis is characterized by the accumulation of plaque within the artery, along with local inflammation and scarring. Over time, this process can thin or fragment the elastic and muscular layers that give the wall strength and flexibility. The weakened segment can then dilate under normal blood pressure, especially in large and medium-sized arteries such as the aorta, iliac arteries, femoral arteries, and popliteal arteries.
High Blood Pressure and Hemodynamic Stress: Chronic high blood pressure increases the force of each pulse on the artery wall. Repeated exposure to elevated pressure accelerates microscopic damage, promotes loss of elastic fibers, and amplifies the effects of atherosclerosis and aging. Sudden surges in pressure, such as during heavy exertion or intense emotional stress, can add further strain to already vulnerable segments.
Age-Related Changes in Arterial Structure: As people age, the composition of artery walls shifts. Elastic fibers gradually break down, smooth muscle cells decline, and collagen becomes stiffer. These changes render vessels less resilient and more prone to dilation under sustained pressure. This age-related remodeling helps explain why many aneurysms are first detected later in life, even when other risk factors are modest.
Family History and Inherited Vessel Traits: A family history of aneurysm, arterial dissection, or sudden unexplained death suggests a shared structural tendency in the vessel wall. Even when no specific genetic syndrome is identified, first-degree relatives often have a higher baseline risk. This inherited vulnerability can lower the threshold at which common factors such as blood pressure, smoking, or atherosclerosis lead to aneurysm formation.
Inherited Connective Tissue Disorders: Certain genetic conditions affect the proteins that give artery walls strength and elasticity. Examples include Marfan syndrome, vascular Ehlers-Danlos syndrome, Loeys-Dietz syndrome, and some familial aneurysm syndromes. In these conditions, abnormalities in collagen, fibrillin, or related pathways leave arteries more fragile and more likely to dilate or tear, sometimes at younger ages and at smaller diameters than usual.
Inflammatory and Autoimmune Vascular Disease: Vasculitides and other inflammatory conditions can directly attack the arterial wall. Diseases such as giant cell arteritis, Takayasu arteritis, polyarteritis nodosa, and certain autoimmune diseases can cause immune cells to infiltrate the vessel wall, damage normal tissue layers, and trigger scarring and remodeling. These changes can result in segments that are irregularly narrowed and dilated, with aneurysm formation in affected regions.
Infections Of The Arterial Wall (Mycotic Aneurysms): Certain bacteria and other pathogens can lodge in the artery wall or in pre-existing plaque and cause a localized infection. The resulting inflammation and tissue destruction weaken the wall and can lead to a rapidly expanding infected aneurysm. These aneurysms are less common than atherosclerotic aneurysms but carry a high risk of rupture and usually require urgent specialist care.
Structural and Developmental Vessel Differences: Some aneurysms arise at natural weak points in the arterial tree, such as branch points where vessels divide. Intracranial “berry” aneurysms, for example, often occur at arterial bifurcations in the circle of Willis. Other structural differences, such as certain congenital heart and vascular abnormalities, can alter the distribution of blood flow and pressure, creating focal areas of increased mechanical stress that are more prone to dilation over time.
Injury or Trauma to Arteries: Direct injury can damage one or more layers of an arterial wall and leave behind a structurally weakened segment. This can occur after high-speed accidents, penetrating injuries, or rare complications of medical procedures that involve catheters, wires, or surgical instruments. Even when the immediate injury heals, the affected area may slowly dilate and form a true aneurysm or a pseudoaneurysm.
Lifestyle and Cardiometabolic Factors: Smoking, high cholesterol, diabetes, and long-term metabolic strain contribute to widespread arterial injury and remodeling. These factors magnify the impact of atherosclerosis and hypertension on the vessel wall, making aneurysm formation and progression more likely in people who already carry inherited or structural vulnerabilities.
When a person has a strong family history of aneurysm, an aneurysm at a younger age, aneurysms in more than one location, or aneurysms that behave unusually, clinicians often consider whether an inherited or systemic condition may be contributing and whether relatives could benefit from assessment or imaging.
Diagnosis and Testing
How is an aneurysm diagnosed?
Many aneurysms develop without symptoms and are found incidentally during imaging for another concern. Some are detected during routine screening in higher-risk groups, such as abdominal aortic aneurysm screening in certain older adults with a smoking history.
If symptoms suggest an aneurysm, or if risk factors make an aneurysm more likely, clinicians typically confirm the diagnosis with imaging. The goal is to identify the aneurysm’s location, size, and shape, and to look for urgent complications such as leakage, rupture, or clot.
Imaging tests that can help diagnose an aneurysm include:
CT Scan: This is often the fastest and most detailed option in urgent situations, particularly for chest or abdominal pain that may indicate a leak or rupture. It can show the aneurysm’s size, surrounding anatomy, and signs of bleeding.
CT or MRI Angiography: These are specialized scans that highlight blood vessels using contrast. They help clinicians map the aneurysm precisely and plan treatment, particularly for aneurysms in the aorta, brain, neck, or limbs. MRI may be preferred when radiation exposure avoidance is important or when clinicians require detailed vessel-wall and soft-tissue information.
Ultrasound: This is commonly used to screen for and monitor abdominal aortic aneurysms. It is painless, does not involve radiation, and can reliably measure aneurysm diameter over time. In some settings, Doppler ultrasound can also evaluate blood flow patterns and clot risk in peripheral aneurysms.
Imaging not only confirms the presence of an aneurysm but also provides information on its morphology. It also addresses the questions that inform next steps, including whether the aneurysm is stable, growing, irregularly shaped, or associated with a clot or vessel dissection.
Patient-Provider Communication
How will my provider classify an aneurysm?
Clinicians classify aneurysms based on size, shape, location, and how the vessel wall is involved. This classification helps estimate risk and guides monitoring frequency and treatment decisions.
Your provider will classify an aneurysm by its size and mode of formation. The different classifications include:
Fusiform Aneurysm: This bulges outward on all sides of the artery, creating a widened segment of vessel. Fusiform aneurysms are common in the aorta and are often related to long-term vessel-wall degeneration from aging, high blood pressure, and atherosclerosis.
Saccular Aneurysm: This forms a pouch on one side of the artery, often with a defined “neck.” Saccular aneurysms are frequently discussed in the brain, but they can occur elsewhere. Their shape can matter because uneven wall stress and blood flow patterns may affect the risk of rupture or thrombosis.
Mycotic Aneurysm: This develops when infection weakens an artery wall. Despite the name, it is usually caused by bacteria, not fungi. It can occur when an infection in the bloodstream or in heart valves damages the vessel wall, creating a weakened area that can enlarge quickly.
Pseudoaneurysm or False Aneurysm: This occurs when the artery wall is injured, and blood escapes the inner layers but is contained by the outer layer or surrounding tissue, creating a sac outside the normal vessel wall structure. It can happen after trauma, medical procedures, or an arterial dissection. Pseudoaneurysms can behave differently from true aneurysms and may require different treatment urgency depending on size, location, and symptoms.
In addition to shape-based labels, clinicians often describe aneurysms using practical risk features, including the aneurysm’s diameter, growth rate over time, and whether it has irregular contours, inflammation, a clot within the sac, or associated dissection.
Management and Treatment
How is an aneurysm treated?
Treatment depends on whether the aneurysm is ruptured, leaking, symptomatic, or at high risk of rupture. For unruptured aneurysms, the core goal is prevention, meaning reducing stress on the artery wall, slowing growth, and intervening before the risk becomes unacceptable.
If your provider discovers that you have an unruptured aneurysm, they will monitor it closely. Monitoring typically involves repeat imaging to measure size and detect growth. Follow-up timing is based on location and diameter, because the risk profile is different for a small abdominal aortic aneurysm than for a brain aneurysm or a rapidly enlarging thoracic aneurysm.
Depending on the aneurysm’s type, location, and size, treatment can include medication or surgery.
Medication and Risk Factor Control: Medications do not make an aneurysm disappear, but they can reduce the forces that contribute to growth or rupture. Treatment often focuses on controlling blood pressure, improving cholesterol and vascular health, and lowering the overall strain on arteries. If there is a risk of thromboembolism at certain sites, clinicians may also consider therapies to reduce embolic complications, based on the specific aneurysm and the patient’s overall risk profile.
Procedural or Surgical Repair: Repair is indicated when an aneurysm reaches a size at which the risk of rupture increases, when it grows rapidly, when it causes symptoms, or when its shape suggests instability. Ruptured aneurysms require emergency treatment.
Types of procedures and surgery may include:
Endovascular Aneurysm Repair (EVAR): During endovascular repair, a clinician guides a catheter through the arteries to the aneurysm and places a stent graft to reinforce the weakened segment from the inside. This is often used for abdominal aortic aneurysms when anatomy allows. For thoracic aortic aneurysms, this approach is known as TEVAR. In complex cases involving branch vessels, a specialized graft, sometimes referred to as FEVAR, may be usedto preserve blood flow to critical arteries while sealing the aneurysm.
Open Surgery: In open repair, a surgeon accesses the aneurysm through an incision and replaces or reinforces the affected artery segment with a graft. This may be necessary when anatomy is unsuitable for an endovascular approach or when long-term durability considerations favor open repair. Recovery is typically longer than with endovascular techniques.
Endovascular Coiling: This is commonly used for certain cerebral aneurysms. A catheter is advanced into the aneurysm, and soft coils are deployed within the sac to reduce blood flow and promote clot formation, thereby lowering the risk of rupture.
Microvascular Clipping: This is an open brain surgery option for some cerebral aneurysms. A surgeon places a clip at the aneurysm’s base to stop blood flow into the aneurysm while preserving normal flow through the artery.
Catheter Embolization: This approach occludes blood flow to the aneurysm by delivering embolic agents via a catheter. It is used in selected aneurysms depending on location and vessel anatomy. The goal is to prevent bleeding or rupture by excluding the aneurysm from circulation.
Across treatment types, decisions are individualized. Clinicians weigh aneurysm size, growth, location, symptoms, overall health, age, and the risks of intervention. A small aneurysm in a high-risk location may warrant a different approach than a larger aneurysm in a location where monitoring is safer.
Outlook and Prognosis
What is the prognosis for people with an aneurysm?
Prognosis depends on the aneurysm’s location, size, growth rate, and whether it has ruptured.
A ruptured aneurysm is a life-threatening emergency. Bleeding can be rapid and severe, and the first minutes and hours matter. A rupture in the brain causes bleeding around the brain, which is a type of stroke that can lead to coma or death without immediate treatment. Even with fast care, recovery can take time and may involve rehabilitation for headaches, fatigue, weakness, speech changes, memory problems, or balance issues.
Unruptured aneurysms often have a much better outlook. Many remain stable for years. When an aneurysm is small and not growing, clinicians usually focus on monitoring and risk reduction. The goal is to prevent rupture and clot-related complications by reducing stress on the arterial wall and monitoring for changes on repeat imaging.
Treatment improves prognosis when it is matched to the specific aneurysm and the person’s risk profile.
Monitoring: Regular imaging can detect growth early, before the aneurysm reaches a higher-risk stage.
Medical management: Controlling blood pressure and reducing vascular inflammation and plaque burden can slow progression in some aneurysms.
Procedures or surgery: Repair can prevent rupture when the risk rises, and emergency treatment can be lifesaving after rupture.
Prevention
How can I prevent an aneurysm?
Not every aneurysm is preventable. Some are associated with inherited vessel-wall traits or conditions that cannot be modified. Prevention is still meaningful because it targets the factors that most often drive aneurysm formation, growth, and rupture risk over time, especially smoking exposure, uncontrolled blood pressure, and atherosclerosis.
Steps that reduce risk and support artery health include:
Eat A Heart-Healthy Diet: Prioritize vegetables, fruits, legumes, whole grains, nuts, and unsaturated fats, and limit ultra-processed foods, added sugars, and excess sodium to support healthier blood pressure and vascular function.
Exercise Regularly: Aim for steady, moderate-intensity aerobic activity on most days of the week, and incorporate strength training on a regular schedule, with a plan tailored to existing diagnoses and clinician guidance.
Maintain A Healthy Weight: Aim for a weight range that supports healthy blood pressure and blood glucose, as both hypertension and diabetes-related vascular damage can accelerate vessel-wall injury.
Avoid or Quit Smoking: Eliminate tobacco exposure completely, including cigarettes and other nicotine products when possible, because smoking is one of the strongest predictors of abdominal aortic aneurysm development and faster aneurysm growth.
Control Blood Pressure: Monitor blood pressure at home when appropriate and follow a treatment plan that reliably keeps readings within a safe range, because elevated pressure increases mechanical stress on weakened arterial walls.
Manage Cholesterol and Atherosclerosis: Treat high LDL cholesterol and known plaque disease with lifestyle modifications and medications when indicated, because atherosclerosis contributes to vessel-wall weakening and increases overall vascular risk.
Know Your Family History: Tell clinicians if a first-degree relative has had an aortic aneurysm, brain aneurysm, dissection, or sudden unexplained death, because this can change screening decisions and the threshold for closer surveillance.
Follow Screening and Monitoring When Eligible: Complete recommended aneurysm screening if you fall into a higher-risk group and attend scheduled follow-up imaging if an aneurysm has already been found, because growth over time is a key driver of risk.
Patient-Provider Communication
When should you call your provider?
Call 911 immediately if symptoms start suddenly or feel severe, especially if they involve intense headache, collapse, or severe chest, back, or abdominal pain.
Call your healthcare provider promptly if you experience:
Lightheadedness: This may indicate low blood pressure, reduced blood flow, or internal bleeding when accompanied by other symptoms.
Rapid Heart Rate: A racing heart can be a sign of shock or the body compensating for blood loss.
Sudden, Severe Pain In Your Head, Chest, Abdomen, or Back: Sudden severe pain can signal leak, rupture, or compromised blood flow and should be treated as urgent.
If you have a known aneurysm, contact your clinician sooner rather than later for any new symptom pattern, especially new neurologic symptoms, fainting, severe pain, or sudden changes in vision.
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