Saccular Aneurysm
- Article Author:
- Mohammed Faluk
- Article Editor:
- Orlando De Jesus
- Updated:
- 5/30/2020 10:10:39 AM
- For CME on this topic:
- Saccular Aneurysm CME
- PubMed Link:
- Saccular Aneurysm
Introduction
An aneurysm is an abnormal dilatation or bulging in a blood vessel due to the intrinsic weakness of the vessel wall.[1] Aneurysms can affect any blood vessel, but they are most commonly seen in arteries rather than veins. An aneurysm can be a true aneurysm or false aneurysm. A true aneurysm has all the three layers of the arterial wall (intima, media, and adventitia). A false aneurysm, also known as pseudoaneurysm, involves the outer layer of the artery (adventitia). Depending on their shape, they can be saccular or fusiform. Cerebral aneurysms are 90% saccular aneurysms (also known as berry aneurysms), unlike aortic aneurysms, which are about 94% fusiform. Aneurysms can be classified based on their location in the body. Depending on the etiology can be dissecting or mycotic aneurysms.
This review will focus on saccular cerebral and aortic aneurysms. Saccular cerebral aneurysms can also be classified by size (small: 5 mm or less, medium: 6 to 14 mm, large: 15 to 25 mm, giant: greater than 25 mm).[2] Most cerebral aneurysms are asymptomatic and small, and they are found incidentally during brain imaging or during an autopsy.[3] About 85% of cerebral aneurysms are located in the anterior circulation at the arterial bifurcations on the circle of Willis and the middle cerebral artery bifurcation.[3][4] Most of the saccular aortic aneurysms are located in the descending thoracic aorta.[5]
Etiology
Although the formation of cerebral saccular aneurysms is not completely understood, it is thought to be primarily associated with hemodynamically induced degenerative vascular changes. Inflammatory changes also play a role in their formation. Most saccular aneurysms are acquired, but they can be inherited.
Acquired risk factors of saccular aneurysm formation may include the following.[3][6]
- Advanced age
- Hypertension
- Excessive alcohol consumption
- Cigarette smoking
- Atherosclerosis of the cerebral arteries
- Trauma to the head
- Use of illicit drugs such as cocaine
- Estrogen deficiency
Inherited risk factors of saccular aneurysm formation may include the following.[3][6]
- Polycystic kidney disease
- Arteriovenous malformation
- Ehlers-Danlos syndrome
- Marfan syndrome
- Loeys-Dietz syndrome
- Fibromuscular dysplasia
- Hereditary hemorrhagic telangiectasia
- Tuberous sclerosis
- Family history of aneurysms
- Alpha-glucosidase deficiency
- Alpha 1-antitrypsin deficiency
- Coarctation of the aorta
- Klinefelter syndrome
- Noonan syndrome
- Female gender
Family history is the strongest indicator of rupture among non-modifiable risk factors. Compared to the general population, first-degree relatives of persons with cerebral aneurysms or previous subarachnoid hemorrhage (SAH) have a risk of 3 to 7 times higher.[7] Nicotine exposure promotes aneurysmal rupture through actions on vascular smooth muscle cells.[8]
The etiology of saccular aortic aneurysms is almost similar to that of saccular cerebral aneurysms. The most common risk factor of saccular aortic aneurysms is atherosclerotic disease; other less common risk factors include aortic infections, trauma, chronic inflammatory/autoimmune conditions (Behcet disease, giant cell arteritis, rheumatoid arthritis, Takayasu arteritis, systemic lupus erythematosus, ankylosing spondylitis), presence of bicuspid aortic valve or previous aortic surgeries.[5] In addition to the above genetic conditions listed under cerebral aneurysms, saccular aortic aneurysms can be associated with Turner syndrome.
Epidemiology
The prevalence of cerebral aneurysms is estimated to be 3.2% to 4% in the general population without inherited risk factors. The most common age of presentation is between 30 and 60 (mean age of 50-years-old with 1:1 gender ratio).[9] After the age of 50, the prevalence increases in women compared to male and may approach a 2:1 ratio.[9] Approximately 20% to 30% of patients with cerebral aneurysms have multiple aneurysms.[10] The incidence of cerebral aneurysm rupture causing SAH is estimated to be 6 to 16 per 100,000 population, and this accounts for 30,000 cases per year in the United States alone.[11] The risk of rupture of an unruptured cerebral aneurysm is 1% to 2% per year.[7] Approximately 10% to 30% of patients with aneurysm rupture die before reaching the hospital, and only 30% have a good outcome after appropriate treatment.[3] Cerebral aneurysms rupture account for 0.4% to 0.6% of all deaths.[3] Ruptured aneurysms have a 20% to 50% risk of rebleeding in the first two weeks if untreated. Cerebral aneurysms are uncommon in the pediatric population.
Approximately 85% of the cerebral aneurysms are located in the anterior circulation on the circle of Willis and the middle cerebral artery bifurcation. The most common sites of cerebral aneurysms are the junction of the anterior cerebral artery with the anterior communicating artery, the junction of the internal carotid artery with the posterior communicating artery and the bifurcation of the middle cerebral artery. In the posterior circulation, the most common sites often include the distal basilar bifurcation (basilar tip), the junction of the basilar artery and the superior or anterior inferior cerebellar arteries, and the junction of the vertebral artery with the posterior inferior cerebellar artery.[12]
A study of 284 patients with 322 saccular aortic aneurysms showed that 68% were found in the thoracic aorta, 24.2% in the abdominal aorta, 7.1% in the arch of the aorta, and 0.6% in the ascending aorta.[5] When aortic aneurysms are studied, aortic saccular aneurysms include 6% of them, while fusiform include 94% of them.[13] As saccular aortic aneurysms are less common than fusiform aneurysms, most epidemiological studies report data that includes any type of aortic aneurysms; therefore, the true incidence and prevalence of saccular aortic aneurysm are unknown.
Pathophysiology
The pathophysiology for the formation and growth of cerebral and aortic saccular aneurysms is believed to be a multifactorial process that leads to degenerative changes in the blood vessel wall.[3][6][7] These degenerative changes could be due to collagen deficiency or congenital weakness of the arterial wall layers. Alteration of the internal elastic lamina develops from hemodynamic shear stress, hypertension, turbulent blood flow, and atherosclerotic deposits, which is associated with focal defects, disorganization, or absence of the media layer.[14][15][7][16][17][18] As it is well known that chronic inflammation and immunologic response are key pathogenic features of atherosclerosis, inflammatory mediators like T-cell and macrophages could be linked in causing histologic changes within the arterial wall resulting in formation, progression, and rupture of cerebral aneurysms.[4][19][20][21][22][15][7][19][23][24][17] Endothelial dysfunction is considered the first step in the formation of cerebral aneurysms.[16]
History and Physical
Cerebral Aneurysms
The majority of unruptured cerebral aneurysms are asymptomatic (85% to 90%), and they are incidentally found during brain imaging fo other reasons.
Signs and symptoms of unruptured cerebral aneurysm include:[6]
- Headache
- Eye pain
- Unilateral complete third cranial nerve palsy
- Ischemic/embolic cerebrovascular disease
- Seizures
- Visual loss or hemianopsia
Signs and symptoms of ruptured cerebral aneurysm include:[25]
- Headache
- Nausea and vomiting
- Nuchal rigidity
- Altered mental status
- Eye pain
- Unilateral complete third cranial nerve palsy
- Loss of consciousness
- Photophobia
- Focal neurologic deficits
- Coma and death
Headache described as the "worst headache of my life" is the most common symptom in a ruptured cerebral aneurysm. About 10 to 43% of patients with SAH experience mild-moderate headache approximately 2 months before aneurysm rupture and 30 to 50% of patients report sudden onset headache 6 to 20 days before rupture. This headache could be a warning sign of an impending rupture. Approximately 10 to 30% of patients with aneurysm rupture die before reaching the hospital, another 30% die in the hospital or are severely disabled when discharged, and only 30% have a good recovery after appropriate treatment.[3]
The Hunt and Hess classification system is used to classify the severity of SAH based on clinical findings and to predict outcome and mortality. There are five different grades ranging in the severity of symptoms, which can correlate the overall mortality of SAH.[26]
- Grade I - Mild headache with slight nuchal rigidity. Approximately 30% of mortality.
- Grade II - Severe headache with full nuchal rigidity and no neurologic deficits other than a cranial nerve palsy. Approximately 40% of mortality.
- Grade III - Drowsiness or confusion with a mild focal deficit. Approximately 50% of mortality.
- Grade IV - Stuporous with moderate to severe hemiparesis. Approximately 80% of mortality.
- Grade V - Coma with decerebrate posturing. Approximately 90% of mortality.
The modified Fisher classification describes the amount of blood seen on a head non-contrast computed tomography (CT) scan to predict the likelihood of developing vasospasm, ischemia, and stroke.[27] It was adapted from the original Fisher classification.[28]
- Fisher 0 - No blood detected. The incidence of symptomatic vasospasm: 0%.
- Fisher 1 - Thin focal or diffuse SAH. The incidence of symptomatic vasospasm: 18%.
- Fisher 2 - Thin focal or diffuse SAH with intraventricular hemorrhage. The incidence of symptomatic vasospasm: 35%.
- Fisher 3 - Thick focal or diffuse SAH with no intraventricular hemorrhage. The incidence of symptomatic vasospasm: 31%.
- Fisher 4 - Thick focal or diffuse SAH with intraventricular hemorrhage. The incidence of symptomatic vasospasm: 68%.
Aortic Aneurysms
Most of the people with aortic aneurysms are asymptotic. Symptoms develop as the aneurysm enlarges and creates pressure on surrounding structures.
Signs and symptoms of unruptured aortic aneurysms include:
- Chest pain or tenderness
- Neck pain
- Cough
- Shortness of breath
- Wheezing
- Hoarseness
- Dysphagia
- Abdominal pain
- Back pain
- Trouble swallowing
Signs and symptoms of ruptured aortic aneurysms include:
- Sudden, intense and persistent chest pain that radiates to back or persistent upper back pain
- Sudden, intense and persistent abdominal pain
- Difficult breathing
- Low blood pressure
- Paralysis or weakness of lower extremities
- Loss of consciousness
- Trouble swallowing
- Sudden cardiac death
Evaluation
Cerebral Aneurysms
The majority of unruptured cerebral aneurysms are found incidentally during brain imaging for some other reasons. High-risk individuals like those with a family history of cerebral aneurysms or those with medical conditions associated with cerebral aneurysms may be screened with magnetic reasoning angiography (MRA), computerized tomography angiography (CTA), or digital subtraction angiography (DSA). In view of the inflammatory changes and macrophage deposition occurring at the aneurysm wall, magnetic resonance imaging with contrast may be utilized to detect those aneurysms prone to rupture as their wall may enhance.[16] Ferumoxytol is a nanoparticle cleared by macrophages and can be used as a contrast agent for the detection of inflammation.[16] A head CT scan without contrast is the initial test for a suspected ruptured cerebral aneurysm causing SAH. It is 100% sensitive for SAH if it is done within 6 hours of symptoms onset, but sensitivity decreases over time to 95% in 12 hours, 92% in 24 hours, and 50% in one week. If clinical suspicion is very high, and the head CT scan is negative, a lumbar puncture should be performed to measure the cell count and to look for xanthochromia of the cerebrospinal fluid (CSF). CSF xanthochromia due to hemoglobin breakdown products may take 4 hours to develop, but it almost 100% sensitive between 12 hours and one week. Once the diagnosis of SAH is confirmed, the source of bleeding can be identified with either CTA, MRA, or digital subtraction angiography (DSA). DSA is considered the gold standard for the diagnosis of SAH due to cerebral aneurysm rupture.
Aortic Aneurysms
Like cerebral aneurysms, they are usually found incidentally during imaging for other reasons. Chest (CXR) X-ray film is the study that most commonly identifies asymptomatic aortic aneurysms. CXR usually shows mediastinal widening, aortic knob enlargement, or tracheal deviation. It may also show the displacement of aortic calcifications, aortic kinking, and aortopulmonary window opacification. Aortic aneurysms may also be incidentally discovered with an echocardiogram, chest CT scan, or chest MRI performed for other reasons. In symptomatic patients, CTA or MRA is the imaging of choice for better characterization of aortic diameter, vessel anatomy, and to identify aortic dissection or aneurysm rupture. The choice of imaging technique depends on the clinical circumstances. In highly symptomatic patients, CTA is a better choice as it is readily available and requires much less time to perform. MRA is better than CTA in aneurysms involving aortic root sinus. It is also a more useful tool due to the lack of ionizing radiation for patients requiring repeated imaging. Transthoracic echocardiography should be performed in patients with a bicuspid aortic valve to assess the diameter of an aortic sinus. Transesophageal echocardiography is preferred over transthoracic echocardiography for the evaluation of the entire aorta.
Treatment / Management
Cerebral Aneurysms
Many factors should be considered when making decisions regarding the treatment of cerebral aneurysms. These factors include the patient's age and medical conditions, the size and location of the aneurysm, the presence or absence of symptoms, the presence or absence of other risk factors for aneurysm rupture, and if there has been a SAH. There are 3 main strategies for the management of cerebral aneurysms: observation, endovascular therapy, and surgical therapy. All ruptured aneurysms should receive endovascular or surgical therapy.
1. Observation
Patients with an unruptured cerebral aneurysm who are older than 64-years-old, aneurysm size less than 7 mm, asymptomatic, location is in the anterior circulation, no personal history of a SAH from another aneurysm or no family history of SAH can be observed with close clinically and radiological monitoring. Serial aneurysm monitoring can be achieved with CTA or MRA. Literature suggests that the annual risk of aneurysm rupture is approximately 1%.[6] Recently, some studies are evaluating the use of nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors to inhibit key inflammatory mediators involved in the growth of unruptured aneurysms.[29][30][31]
2. Endovascular Embolization
This is a minimally invasive technique in which a catheter is advanced from the femoral artery into the cerebral aneurysm, and with the use of a second microcatheter, platinum coils are inserted into the aneurysm. The coiled aneurysm forms a clot (embolization) and obliterates the aneurysm sac, thus preventing future rupture. The procedure can be performed either under local anesthesia or general anesthesia, although the latter is preferred. This procedure can be used to treat aneurysms that are difficult to approach surgically. Recently, flow diversion devices have been used to reduce the flow of blood inside the aneurysm, ultimately thrombosing the sac and creating a new endothelium at the neck. A new treatment with a flow disruption device is currently used in which the self-expanding mesh device is placed inside the aneurysm to prevent blood flow into the sac.
3. Surgical clipping
This procedure is performed in the operating room under general anesthesia and involves making an opening of the skull (craniotomy) and dissection through the brain cisterns and fissures to expose the aneurysm. Once the aneurysm is exposed, a metal clip is placed across the neck of the aneurysm to prevent blood flow into the aneurysm sac.[32][33] One disadvantage of this procedure is that it is highly invasive. The annual risk of post-surgical rebleeding ranges from 0.0 to 0.9%, unlike endovascular coiling, which is 2.6%, but the morbidity and mortality associated with the surgery are higher.[6]
Those patients with a ruptured cerebral aneurysm should be admitted to the intensive care unit for close monitoring. Endovascular coiling or surgical clipping of the ruptured aneurysm should be performed as early as possible in the majority of the cases to reduce the risk of rebleeding. Patients need to be monitored for the signs and symptoms of clinical deterioration due to vasospasm, rebleeding, seizures, cerebral edema, hydrocephalus, and hyponatremia. In the first 48 hours after a SAH, the major cause of morbidity or mortality is rebleeding. Blood pressure should be maintained near 120/80 mmHg before the definite procedure to occlude the aneurysm, but after the treatment, the mean arterial pressure should be maintained above 100 mmHg to reduce ischemic changes secondary to vasospasm. Cerebral vasospasm resulting in cerebral ischemic and neurologic deterioration starts around day 3 to 5 and peaks at day 7. Oral nimodipine at a dose of 60 mg every 4 hours is given for 21 days to improve outcomes.[34][35] Daily transcranial doppler is recommended to monitor vasospasm. After aneurysm repair, cerebrovascular imaging is generally recommended to look for remnant or recurrence of the aneurysm that may require re-intervention. This can be performed intraoperative or a few days later.
Aortic Aneurysms
Treatment modalities depend on size, symptoms, location, and other comorbidities. The most important determinant for rupture is the diameter of the aneurysm. The location of the aneurysm, presence of coronary artery disease, and aortic valve pathology dictate the type of repair to be performed.
1. Conservative management
Asymptomatic patients with aneurysm diameter <45 mm are managed with medical therapy and active surveillance.[13] Saccular aortic aneurysm enlarges at a rate of 2.9 mm/year.[5] This growth is similar to that of fusiform aneurysms. Conservative management includes an aggressive blood pressure control (goal <130/80 mmHg), screening for medical conditions associated with aortic aneurysms, avoidance of fluoroquinolones, cardiovascular risk reduction measures, serial imaging annually or biannually depending on the diameter of the aorta to evaluate changes in aortic diameter. Beta-blockers are the preferred blood pressure medications. Saccular aortic aneurysms become symptomatic/acute at smaller diameters than fusiform aneurysms, supporting the current idea that saccular aneurysms should be treated at smaller diameters than fusiform aneurysms.[13]
2. Repair management
(Open repair vs. endovascular repair)
All symptomatic unruptured or ruptured saccular aortic aneurysm should undergo repair. The exact diameter threshold for elective treatment of asymptomatic aneurysms is difficult to determine, but a diameter of 45 mm seems to be an acceptable threshold.[13] In asymptomatic patients with genetically mediated aneurysms, a smaller diameter is suggested as an indicator of repair. Asymptomatic aneurysm with expansion greater or equal to 5 mm per year should undergo repair. Patients undergoing coronary artery bypass or aortic valve surgery with ascending aorta aneurysms and diameter >45 mm should also have repair. Open repair is indicated for aneurysms that involve the aortic arch, ascending aorta, and aortic root. Endovascular aneurysm repair (EVAR) is preferred in patients with descending aortic aneurysms.
Differential Diagnosis
Cerebral Aneurysms
- Intracerebral hematoma
- Subdural hematoma
- Cerebral stroke
- Intracranial arterial dissection
- Mycotic aneurysm
- Arteriovenous malformations
- Cerebral amyloid angiopathy
- Reversible cerebral vasoconstriction syndrome
- Vasculitis
- Dural sinus thrombosis
- Cerebral venous thrombosis
Aortic Aneurysms
- Aortic dissection
- Aortic pseudoaneurysm
- Senile ectasia
- Post-stenotic dilatation
- Acute myocardial infarction
- Pneumothorax
- Superior vena cava syndrome
- Pulmonary embolism
- Hypertensive emergency
- Mediastinal mass
- Lung mass abutting aorta
- Abdominal mass
- Mesenteric ischemia
- Diverticulitis
- Pyelonephritis
Prognosis
Small unruptured cerebral aneurysms (less than 7 mm) have a low risk of rupture. Morbidity and mortality are very high once a cerebral aneurysm ruptures. SAH due to aneurysm rupture is a catastrophic event with a mortality rate ranging from 25% to 50%. Nearly 50% of the survivors will have a permanent disability.[16] Approximately one-third of patients have a good outcome after appropriate treatment. Cerebral aneurysms can also bleed into the brain parenchyma, causing intraparenchymal hemorrhage adding an extra insult to the brain. The outcome of a ruptured cerebral aneurysm depends on the extent of the bleed, the location of the bleed, the age of the patient, neurological status on presentation, the degree of vasospasm, and associated comorbidities.
The annual risk of rupture of an aortic aneurysm is low when the size is less than 45 mm. When an aneurysm ruptures, approximately 50% of patients die before they reach the emergency room. Those who survive have very high morbidity. When all locations are included, there is approximately perioperative mortality of 2% to 17%, with the arch of aorta location approaching a 25% mortality. The outcome depends on the timing of intervention, the location, the type of surgery, the experience of the surgeon, concomitant comorbidities, and if it has ruptured.
Complications
Cerebral Aneurysms
- Recurrent bleeding
- Vasospasm
- Seizures
- Cerebral salt wasting
- Syndrome of inappropriate antidiuretic hormone secretion
- Hydrocephalus
- Stunted myocardium and pulmonary edema
- Arrhythmias
- Gastrointestinal bleeding
- Infections
- Deep venous thrombosis
Aortic Aneurysms
- Aortic aneurysm rupture
- Acute myocardial infarction
- Aortic regurgitation
- Superior vena cava syndrome or thromboembolism
- Pneumonitis
- Heart failure
- Hemodiaphragm paralysis due to the phrenic nerve compression
- Aortoesophageal fistula
- Death
Postoperative and Rehabilitation Care
Cerebral Aneurysms
- After discharge, it is reasonable to refer most of the patients for a comprehensive evaluation, including cognitive, behavioral, psychosocial, physical, speech, and occupational therapy evaluation.
- Tobacco and alcohol counseling should be provided if they have these behaviors.
- Deep venous thrombosis prophylaxis if they have minimal or nonambulatory status.
- Serial imaging to monitor aneurysm complete obliteration after repair or aneurysm size if not totally occluded
Aortic Aneurysms
- Cardiac rehabilitation program
- Post-discharge close follow up
- Aggressive blood pressure control
- Cardiovascular risk reduction measures
Consultations
- Neurosurgeon
- Critical care specialist
- Interventional neuroradiologist
- Vascular interventional radiologist
- Vascular surgeon
- Cardiothoracic surgeon
- Neurologist
- Rehabilitation consultant
Deterrence and Patient Education
Patients should be educated about cerebral and aortic aneurysm and the risk associated with it.
A ruptured aneurysm is a serious and life-threatening emergency condition that needs to be treated promptly.
Approximately 10% to 30% of the patients with a cerebral aneurysm bleed die even before reaching the hospital and only about 30% recover after appropriate treatment.
Tobacco smoking and excessive alcohol consumption should be avoided as this can increase the risk of aneurysm progression or rupture.
Better blood pressure control is recommended as this is one of the risk factors for aneurysm formation, progression, and rupture.
Cardiovascular risk reduction measures should be implemented.
Pearls and Other Issues
Early treatment of ruptured aneurysms reduces the rate of rebleeding and facilitates the treatment of vasospasm.
Noninvasive studies may be indicated in patients with conditions associated with cerebral aneurysms and those with a family history of SAH.
Cardiologist consultation may be used as these patients can develop stunt myocardium and pulmonary edema.
A nephrologist may be needed as these patients are at risk for electrolyte abnormalities.
Enhancing Healthcare Team Outcomes
An interprofessional approach is vital for better clinical outcomes. Early diagnosis and referral to a neurosurgeon, vascular surgeon, or interventional radiologist have better outcomes in patients with ruptured saccular aneurysms. An interprofessional team including but not limited to a neurosurgeon, an endovascular interventional neuroradiologist, intensivist, vascular surgeon, cardiothoracic surgeon, neurologist, cardiologist, physical therapist, speech therapist, occupational therapist, nurse, pharmacist, and a nephrologist is recommended for proper care and management for better clinical outcomes and early hospital discharge.