Cerebrovascular disease refers to disorders of the brain blood vessels or vessels that supply blood flow to the brain. Ischemic and hemorrhagic stroke affect patients of all ages and, although these forms of stroke can be quite different in their symptoms and underlying pathology, a stroke occurs when a blood vessel that brings oxygen and nutrients to the brain bursts or is clogged.
Stroke is a leading cause of serious and long-term disability. Each year about 700,000 people suffer a new or recurrent stroke in the United States. Over 150,000 of these people die, making stroke the third leading cause of death. About 5.7 million stroke survivors are alive today, many of them with permanent stroke-related disabilities.
Many advances have been made that can arrest or reverse the effects of stroke in some patients. Cerebrovascular abnormalities, including brain aneurysms, arteriovenous malformations (AVMs) and cavernous malformations, are just a few conditions that often cause stroke. These conditions require an immediate evaluation and potentially treatment by an experienced cerebrovascular team to obtain a maximal benefit to patients. Innovative approaches in interventional and surgical techniques and advancements in pharmacological strategies are helping to make a significant difference in clinical outcomes for patients. While timing still remains the key determinant, having the advanced technology and expertise are fundamental to minimize an existing and prevent further stroke damage.
What is a brain aneurysm?
A brain aneurysm is a weak bulging spot on the wall of a brain artery; very much like a thin balloon or weak spot on an inner tube. Aneurysms form silently from wear and tear on the arteries, and sometimes can form from injury, infection, or inherited tendency. Aneurysms can be discovered before rupture or after rupture. Aneurysms that are discovered before rupture are often discovered incidentally in looking at the brain for another reason; these aneurysm may or may not need to be treated depending on a variety of factors (see below). Aneurysms that have bled or ruptured all require urgent treatment.
Where is a brain aneurysm located?
A common location of cerebral (brain) aneurysms is on the arteries at the base of the brain, known as the Circle of Willis. Approximately 85% of cerebral aneurysms develop in the anterior part of the Circle of Willis and involve the internal carotid arteries and their major branches that supply the anterior and middle sections of the brain.
The most common sites include the anterior cerebral artery and anterior communicating artery (30-35%), bifurcation of the internal carotid and posterior communicating artery (30-35%), bifurcation of the middle cerebral artery (20%), bifurcation of the basilar artery, and remaining posterior circulation arteries (5%).
Causes of Brain Aneurysms
Aneurysms may result from congenital defects, pre-existing conditions, such as high blood pressure and atherosclerosis (buildup of fatty deposits in the arteries), or head trauma. Cerebral aneurysms occur more commonly in adults than children but, they may occur at any age. They are more common in women than in men by a ratio of 2 to 1.
Classification by Brain Aneurysm Size and Shape
Cerebral aneurysms are classified both by size and shape. Small aneurysms have a diameter of less than 15-mm. Larger aneurysms include those classified as large (15- to 25-mm), giant (25- to 50-mm), and super giant (greater than 50-mm). Saccular aneurysms are those with a saccular (like a small sack) outpouching and are the most common form of cerebral aneurysm. Berry aneurysms are saccular aneurysms with necks or stems resembling a berry. Fusiform aneurysms (spindle-shaped) are aneurysms without stems, and often encompass the entire wall of the blood vessel.
Symptoms of Brain Aneurysm
Often aneurysms, except for those that are very large, will remain asymptomatic (no symptoms) until rupture. Occasionally, before a larger aneurysm ruptures, the individual may experience symptoms such as a sudden and unusually severe headache, nausea, vision impairment, vomiting, and loss of consciousness. Or, the individual may be asymptomatic, experiencing no symptoms at all.
Onset of symptoms is usually sudden and without warning when an aneurysm ruptures. Rupture of a cerebral aneurysm is dangerous and usually results in bleeding into the meninges or the brain itself, leading to a subarachnoid hemorrhage (SAH) or intracranial hematoma (ICH), either of which constitutes a stroke. Rebleeding, hydrocephalus (the excessive accumulation of cerebrospinal fluid), vasospasm (spasm, or narrowing, of the blood vessels), or multiple aneurysms may also occur.
The risk of rupture from an unruptured cerebral aneurysm varies according to the size of an aneurysm, with the risk rising as the aneurysm size increases. The overall rate of aneurysm rupture is estimated at 1.3% per year, resulting in approximately 27,000 new cases of SAH in the United States each year. The risk of short-term rerupture increases dramatically after an aneurysm has bled, although, after approximately 6 weeks, the risk returns to baseline.
Classification of Ruptured Aneurysm Severity
In outlining symptoms of ruptured cerebral aneurysm, it is useful to use the Hunt and Hess scale of subarachnoid hemorrhage severity:
- Grade I: Asymptomatic; or minimal headache and slight nuchal (neck) rigidity. Approximate survival rate 70%.
- Grade II: Moderate to severe headache; nuchal rigidity; no neurologic deficit except cranial nerve palsy. 60%.
- Grade III: Drowsy; minimal neurologic deficit. 50%.
- Grade IV: Stuporous; moderate to severe hemiparesis; possibly early decerebrate rigidity and vegetative disturbances. 20%.
- Grade V: Deep coma; decerebrate rigidity; moribund. 10%.
- Grade VI: Instant Death
A complication of aneurysmal subarachnoid hemorrhage is the development of vasospasm. Approximately 1 to 2 weeks following the initial hemorrhage, patients may experience 'spasm' of the cerebral arteries, which can result in stroke.
The etiology of vasospasm is thought to be secondary to an inflammatory process that occurs as the blood in the subarachnoid space is resorbed. It appears that macrophages and neutrophils that enter the subarachnoid space to phagocytose senescent erythrocytes and clear extracorpuscular hemoglobin, remain trapped in the subarachnoid space, die and degranulate 3-4 days after their arrival, and release massive quantities of endothelins and free radicals that in turn induce vasospasm. Vascular narrowing, however, is only one component of the transient inflammatory injury, which is extensive.
Vasospasm is monitored in a variety of ways. Noninvasive methods include Transcranial Doppler. This method uses ultrasound to measure the velocity of blood in the cerebral arteries. As the vessels narrow due to vasospasm, the velocity of blood increases. The amount of blood reaching the brain can also be measured by CT, MRI, or nuclear perfusion scanning. The definitive, but invasive method of detecting vasospasm is cerebral angiography.
It is generally agreed that in order to prevent or reduce the risk of permanent neurological deficits, or even death, vasospasm should be treated aggressively. This is usually performed by early delivery of drug and fluid therapy, or 'Triple H' (hypertensive-hypervolemic-hemodilution therapy) (which elevates blood pressure, increases blood volume, and thins the blood) to drive blood flow through and around blocked arteries. For patients who are refractive (resistant) to Triple H therapy, narrowed arteries in the brain can be treated with medication delivered into the arteries that are in spasm and with balloon angioplasty to widen the arteries and increase blood flow to the brain. Although the effectiveness of these treatments is well-established, angioplasty and other treatments delivered by interventional radiologists have evolved over the past several years. It is generally recommended that aneurysms be evaluated at specialty centers which provide both neurosurgical and interventional radiology treatment and which also permit angioplasty, if needed, without transfer.
Brain Aneurysm Treatment
Emergency treatment for individuals with a ruptured cerebral aneurysm generally includes restoring deteriorating respiration and reducing intracranial pressure. Currently there are two treatment options for brain aneurysms: surgical clipping or endovascular coiling.
Surgical clipping was introduced by Walter Dandy of the Johns Hopkins Hospital in 1937. It consists of performing a craniotomy, exposing the aneurysm, and closing the base of the aneurysm with a clip. The surgical technique has been modified and improved over the years. Surgical clipping has a lower rate of aneurysm recurrence after treatment.
Endovascular coiling was introduced by Guido Guglielmi at UCLA in 1991. It consists of passing a catheter into the femoral artery in the groin, through the aorta, into the brain arteries, and finally into the aneurysm itself. Once the catheter is in the aneurysm, platinum coils are pushed into the aneurysm and released. These coils initiate a clotting or thrombotic reaction within the aneurysm that, if successful, will eliminate the aneurysm. These procedures require a small incision, through which a catheter is inserted.
In the case of broad-based aneurysms, a stent may be passed first into the parent artery to serve as a scaffold for the coils (stent-assisted coiling), although the long-term studies of patients with intracranial stents have not yet been done. If possible, either surgical clipping or endovascular coiling is usually performed within the first 24 hours after bleeding to occlude the ruptured aneurysm and reduce the risk of rebleeding.
At this point, it appears that the risks associated with surgical clipping and endovascular coiling, in terms of stroke or death from the procedure, are the similar (Raja et al., 2008). The major problem associated with endovascular coiling, however, is a higher aneurysm recurrence rate. For instance, the 2007 study by Jacques Moret and colleagues from Paris, France, (a group with one of the largest experiences in endovascular coiling) indicates that 28.6% of aneurysms recurred within one year of coiling and that the recurrence rate increased with time. These results are similar to those previously reported by other endovascular groups. For instance Jean Raymond and colleagues from Montreal, Canada, (another group with a large experience in endovascular coiling) reported that 33.6% of aneurysms recurred within one year of coiling. The most recent data from Moret's group reveals even higher aneurysm recurrence rates, namely a 36.5% recurrence rate at 9 months (which breaks down as 31.1% for small aneurysms less than 10 mm, and 56.0% for aneurysms 10 mm or larger). The long-term coiling results of one of the two prospective, randomized studies comparing surgical clipping versus endovascular coiling, namely the International Subarachnoid Aneurysm Trial (ISAT) are turning out to be similarly worrisome. In ISAT, the need for late retreatment of aneurysms was 6.9 times more likely for endovascular coiling as compared to surgical clipping.
Therefore it appears that although endovascular coiling is associated with a shorter recovery period as compared to surgical clipping, it is also associated with a significantly higher recurrence rate after treatment. Furthermore, the recently updated data from the ISAT group in March 2008 shows that the higher aneurysm rate of recurrence is associated with a higher rebleeding rate, given that the rebleed rate of coiled aneurysms appears to be 8 times higher than that of surgically treated aneurysms in the ISAT study. The long-term data for unruptured aneurysms are still being gathered.
Patients who undergo endovascular coiling need to have annual studies (such as MRI/MRA, CTA, or angiography) indefinitely to detect early recurrences. If a recurrence is identified, the aneurysm needs to be retreated with either surgery or further coiling. The risks associated with surgical clipping of previously-coiled aneurysms are very high. Ultimately, the decision to treat with surgical clipping versus endovascular coiling should be made by a cerebrovascular team with extensive experience in both modalities.
The prognosis for a patient with a ruptured cerebral aneurysm depends on the extent and location of the aneurysm, patient age, general health, and neurological condition. Some patients with a ruptured cerebral aneurysm die from the initial bleeding. Other patients with cerebral aneurysm recover with little or no neurological deficit.
The most significant factors in determining outcome are grade (see Hunt and Hess grade above) and age. Generally patients with Hunt and Hess grade I and II hemorrhage on admission to the emergency room and, patients who are younger, within the typical age range of vulnerability, can anticipate a good outcome, without death or permanent disability. Older patients, and those with poorer Hunt and Hess grades, on admission have a poor prognosis. Generally, about two-thirds of patients have a poor outcome, death, or permanent disability.
Arteriovenous Malformations (AVMs)
AVMs (or Arteriovenous Malformations) are defects of the circulatory system that consist of masses of abnormal blood vessels nidus (nest) through which arteries connect directly to veins (Figure 2). AVMs tend to enlarge, as veins cannot control the pressure of the arterial vessels and patients hemorrhage, which clinically usually presents with seizure.
Diagnosis is made using CT and MRI scans to localize the main mass effect. A selective angiography is performed to evaluate the complexity of the lesion, dominant blood supply, and collateral blood flow.
Treatment options include intra-arterial embolization, surgical reconstruction, or the newest addition to the treatment armamentarium -- and least invasive option – CyberKnife Radiosurgery. Generally, once an AVM has bleed, it must be treated.
- Brisman JL, Song JK, Newell DW (August 2006). "Cerebral aneurysms". N Engl J Med 355 (9): 928–39. doi:10.1056/NEJMra052760. PMID 16943405.
- Campi, A; Ramzi N, Molyneaux AJ, Summers, PE, Kerr, RS, Sneade, M, Yarnold, JA, Rischmiller, J, Byrne, JV (May 2007). "Retreatment of ruptured cerebral aneurysms in patients randomized by coiling or clipping in the International Subarachnoid Aneurysm Trial (ISAT).". Stroke 38 (5): 1538–44. doi:10.1161/STROKEAHA.106.466987. PMID 17395870.
- Gallo, GL; Rafael Tamargo (October 2006). "Leukocyte-endothelial cell interactions in chronic vasospasm after subarachnoid hemorrhage.". Neurol. Res 28 (7): 750–8. doi:10.1179/016164106X152025. PMID 17164038.
- Hop, Jeanette; Gabriel Rinkel, Ale Algra, Jan van Gijn (March 1997). "Case-Fatality Rates and Functional Outcome after Subarachnoid Hemorrhage: A Systematic Review.". Stroke 28 (3): 660–4. PMID 11157554.
- Ljunggren, B; Sonesson B, Säveland H, Brandt L (1985). "Cognitive impairment and adjustment in patients without neurological deficit after aneurysmal SAH and early operation.". Journal of Neurosurgery 62: 673–9. PMID 3989590.
- Mitchell P, Kerr R, Mendelow AD, Molyneux A. Could late rebleeding overturn the superiority of cranial aneurysm coil embolization over clip ligation seen in ISAT? Journal of Neurosurgery 108: 437-442, March 2008. PMID: 18312088
- Piotin, M; Spelle, L, Mounayer, C, Salles-Rezende, MT, Giansante-Abud, D, Vanzin-Santos, R, Moret, J (May 2007). "Intracranial aneurysms: treatment with bare platinum coils—aneurysm packing, complex coils, and angiographic recurrence". Radiology 243 (2): 500–8. doi:10.1148/radiol.2431060006. PMID 17293572.
- Piotin M, Spelle L, Mounayer C, Loureiros C, Ghorbani A, Moret J. Intracranial aneurysms coiling with matrix. Immediate results in 152 patients and midterm anatomic follow-up from 115 patients. Stroke, November 2008, PMID 18988913.
- Raja PV, Huang J, Germanwala AV, Gailloud P, Murphy KP, Tamargo RJ. Microsurgical clipping and endovascular coiling of intracranial aneurysms: A critical review of the literature. Neurosurgery 62: 1187-1202, June 2008, PMID 18824986.
- Raymond, J; Guilbert, F, Weill, A, Georganos, SA, Juravsky, L, Lambert, A, Lamoureux, J, Chagnon, M, Roy, D (June 2003). "Long-term angiographic recurrences after selective endovascular treatment of aneurysms with detachable coils.". Stroke 34 (6): 1398–1403. doi:10.1161/01.STR.0000073841.88563.E9. PMID 12775880.