Vascular.

Abstract

Cerebrovascular neurosurgery is a field where the highs are high and the lows are low. The successful cerebrovascular neurosurgeon gets to save lives and restore neurological function but must also to attend families and patients who are facing stroke and death. Patients generally fall into 2 categories: those who have had hemorrhagic or ischemic strokes, and those who are at risk for stroke but are so far unscathed. Patients in the first group have experienced a catastrophe. The neurosurgeon typically meets the patient and their family in the hospital. Morbidity and mortality within this group is common and can be devastating. The able neurosurgeon must be able to assess the situation and act rapidly to prevent worsening of neurological damage and decide how best to keep the patient from further harm. Those in the second group have often received a diagnosis after medical imaging for an unrelated complaint. While the vascular lesion may be asymptomatic, these patients are fearful and anxious about the possibility of experiencing a stroke. For these patients, neurosurgeons must be able to summarize the available evidence, provide comfort, and recommend the safest treatment option. Sometimes the safest course is not surgery, but instead, reassurance and medical management. Within the following 6 chapters, the authors lay out practical information all physicians should be familiar with. These chapters cover some of the more common diagnoses that we confront and should help to familiarize students with how to analyze, understand, and treat these problems. This is an exciting field and the authors share a passion for doing everything we can to care for our patients and to keep them from harm. It is hoped that these chapters will help to introduce the next generation of physicians to the satisfaction we enjoy when we are able to shepherd patients safely through the risks that they face. Institutional Review Board approval was not necessary for this study. Patient consent for the cases in each chapter was obtained directly from the patients; in instances in which consent could not be obtained, patient information has been anonymized. CHAPTER 1: MICROSURGERY FOR UNRUPTURED INTRACRANIAL ANEURYSMS Case Presentation A female in her mid-fifties without a significant past medical history presented with double vision. Her neurological examination revealed left ptosis, a dilated, nonreactive left pupil, and the inability to adduct and supraduct her left eye. Magnetic resonance imaging (MRI) and computed tomography angiography (CTA) imaging showed a large left internal carotid artery (ICA) aneurysm arising at the origin of the posterior communicating artery (Figure 1). (See discussion at end of chapter.)FIGURE 1.: Axial A, coronal B, and sagittal C CTA revealing a wide-necked, large left posterior communicating artery aneurysm.Questions The relative rupture risk of a posterior communicating artery aneurysm to a cavernous aneurysm is: The same Higher Lower No relationship Of the following aneurysms which has the highest rupture risk (refer to Figure 2): A 12-mm cavernous aneurysm A 12-mm posterior communicating artery aneurysm A 12-mm middle cerebral artery (MCA) bifurcation aneurysm A 12-mm superior hypophyseal artery aneurysm A 12-mm ophthalmic artery aneurysm Which craniotomy is most suitable for clipping a posterior communicating artery bifurcation aneurysm: Far lateral Subtemporal Interhemispheric Pterional Suboccipital A posterior communicating artery aneurysm can cause double vision related to compression of which cranial nerve: 2nd cranial nerve 3rd cranial nerve 5th cranial nerve 7th cranial nerve 8th cranial nerve FIGURE 2.: Location distributions of intracranial aneurysms across the neurovasculature. Abbreviations: Acomm = anterior communicating artery; MCA = middle cerebral artery; Pcomm = posterior communicating artery; PICA = posterior inferior cerebellar artery; SCA = superior cerebellar artery; VB = vertebral/basilar.Epidemiology Approximately 1% of adults have an intracranial aneurysm, most of which are not congenital. Aneurysms are quite rare in children and become more common with age. Perhaps those individuals with aneurysms are born with a weak area in the wall of their vessel and the aneurysm many develop later in life, but it is not fully known. For example, intracranial aneurysms occur in both sexes, but are distinctly more common in females. While most intracranial aneurysms are thought to be sporadic, about 15% run in families. We presume, therefore, there is a genetic basis for this and is inherited, but those genes have not yet been identified. Smoking, hypertension, family history of intracranial aneurysms, polycystic kidney disease, connective tissue diseases, and possibly aortic aneurysms are all correlated with the presence of an intracranial aneurysm; further, these factors also increase the risk of aneurysm rupture. The presence of multiple factors can magnify risk in a synergistic and multiplicative fashion. Patients with familial aneurysms tend to rupture a decade younger than those with sporadic aneurysms. The incidence is higher in families with genetic risk factors, including those with polycystic kidney disease and various connective tissue disorders (ie, Marfan's syndrome, Ehler-Danlos syndrome, etc). In such families where one individual has an aneurysm, the chance of another first-degree family member having an aneurysm may be as high as 30%. It is estimated that 30 000 patients suffer aneurysmal rupture each year. Approximately 50 to 75% of patients who have an aneurysm rupture reach a hospital in time to receive medical care. Of those who attain medical attention, approximately 50% die and another 25% suffer significant complications. Of those patients who receive timely medical care, 25% can have a good outcome. Due to this high mortality rate, it is reasonable to consider treatment in a patient diagnosed with an unruptured intracranial aneurysm. Morphology Ninety percent of intracranial aneurysms are saccular and 10% are fusiform. Most saccular aneurysms occur at bifurcations, but small percentages are sidewall aneurysms. Aneurysms are classified as small (<10 mm), large (10-24 mm), and giant (>24 mm). Infectious aneurysms (also known as mycotic aneurysms) tend to occur on distal intracranial vessels. Saccular aneurysms can have small or wide necks, which can influence treatment difficulty and strategy. As they enlarge, the sac may become filled with thrombosed blood, causing mass effect on surrounding neural tissue. Natural History Several studies have been published that attempted to quantify the risk of rupture of asymptomatic unruptured intracranial aneurysms. It is important that one keep in mind that these studies only address asymptomatic aneurysms. Symptomatic aneurysms almost always necessitate urgent intervention. These studies suffer from relatively short follow-up periods (typically 5 yr or less). These time periods are considered short because for most patients, the question of risk exposure to rupture is one of decades. The most prominent of the natural history studies is the International Study of Unruptured Intracranial Aneurysms (ISUIA) study (Wiebers DO, Whisnant JP, Huston J 3rd, et al. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet. 2003 Jul 12;362(9378):103-110). Table 1, which is reproduced from the ISUIA study, shows the relationship between aneurysm location, size, and risk of rupture. The study also showed that larger size, prior history of subarachnoid hemorrhage, and posterior circulation (including posterior communicating artery aneurysms) had a higher risk of rupture. While this suggests low rupture risk for anterior circulation aneurysms <7 mm in diameter, it should be noted that the median size of aneurysm rupture is about 6 mm. Pericallosal and anterior communicating artery aneurysms tend to rupture at smaller sizes than other aneurysms. The median rupture size of this type of an aneurysm is about 3 mm. Certain morphological features have been associated with the risk of rupture, including irregular dome shape and the presence of daughter sacs on the dome. TABLE 1. - Five-Year Annual Cumulative Risk of Aneurysmal Rupture According to Size and Location Within the Intracranial Vasculature (Reproduced from the ISUIA Trial) < 7 mm No Hx of SAH Hx of SAH 7–12 mm 13–24 mm ≥25 mm Cavernous carotid artery 0% 0% 0% 3.0% 6.4% Anterior circulation 0% 1.5% 2.6% 14.5% 40% Posterior circulation 2.5% 3.4% 14.5% 18.4% 50% Hx = history; SAH = subarachnoid hemorrhage. Clinical Presentation Due to the growing utilization of MRI and magnetic resonance angiography (MRA), there is an increasing number of incidentally discovered aneurysms diagnosed when patients are evaluated for unrelated symptoms. Unruptured aneurysms can cause a myriad of symptoms, including cranial neuropathies, seizures, headaches, and cognitive decline due to mass effect. Rarely, an intracranial aneurysm can cause ischemic symptoms due to emboli that result from turbulent flow within an aneurysm. Anatomy and Distribution Figure 2 outlines the location of the most common types of intracranial aneurysms. Eighty percent of aneurysms occur in the anterior circulation and 20% occur in the posterior circulation. Decision Making The decision of whether to treat an aneurysm or not can be complex. Several parameters must be considered, including age, the health of the patient, an assessment of the natural history of the aneurysm, and the technical capabilities of the treating surgeon. One of the most important determinants of the risk of a nonruptured aneurysm is the patient's age and health. Younger age and a longer life expectancy expose the patient to greater cumulative risk than a patient with a more limited life expectancy. Therefore, younger patients have a graver natural history favoring treatment while advanced age accompanied by lower rupture risk favors observation with serial imaging. Despite a growing body of literature on aneurysm behavior and natural history, aneurysm rupture remains unpredictable. Any absolute statements on aneurysm natural history are largely conjecture, and it is important to share this uncertainty with patients. Studies have suggested that outcomes tend to be better at high volume centers. The advent and evolution of endovascular options over the past several decades have increased the neurosurgeon's repertoire of aneurysm treatment modalities. More options may have made decision making more complicated, but it has also allowed a greater number of aneurysms to be treated. Microsurgical and endovascular treatments are associated with inherent benefits and disadvantages. Surgical clipping remains the most definitive way to treat intracranial aneurysms with a proven track record of durability and versatility. Almost all aneurysms can be treated surgically. Endovascular therapies have the advantage of being less invasive and for unruptured aneurysms, patients generally have shorter hospitalizations and recoveries. The disadvantages include risks of the treatment, greater risk of recurrence, and the fact that some aneurysms cannot be treated by current endovascular therapies. Factors that favor clipping as opposed to endovascular treatment include young patient age, wide aneurysm neck, incorporation of outflow branches into the dome, and larger aneurysm size. Surgical Techniques Aneurysm clipping involves exposing the aneurysm along with its inflow and outflow vessels. This technique requires a carefully planned surgical approach that minimizes brain manipulation and takes advantage of the subarachnoid space. With careful planning and positioning, a skilled microsurgeon can navigate atraumatically through the subarachnoid cisterns to first expose the inflow branch to an aneurysm, thus achieving proximal control. Establishing proximal control is an important tenet in aneurysm surgery. The surgeon then carefully exposes outflow vessels, which assures complete control of the circulation related to the aneurysm. This control is important for 3 reasons. First, if the aneurysm leaks during manipulation, flow can be arrested with temporary clips until the aneurysm can be clipped. Flow can be arrested for 20 to 30 min with special anesthetic techniques in most cases, which gives the surgeon time to complete the dissection and clip the aneurysm safely. Second, certain aneurysms with wide necks are best clipped after they are trapped and deflated. Finally, flow arrest may be needed if a bypass is required as part of the aneurysm treatment strategy. During flow arrest, anesthesiologists can give sufficient doses of anesthetic to suppress the electroencephalogram. This is referred to as “burst suppression.” This reduces the metabolic needs of neuronal cells thus increasing the tolerance to temporary flow arrest. Instruments used in aneurysm clipping are shown in Figure 3.FIGURE 3.: A, Various styles of aneurysm clip appliers. B, Different clip styles, both permanent and temporary. C, Clip applier opening a clip.Case Discussion This patient with a cranial nerve III palsy raised concern for an intracranial aneurysm; an awake patient with acute third nerve palsy with pupillary dilation should be assumed to have an aneurysm until proven otherwise. A posterior communicating artery aneurysm is the most likely aneurysm to cause compressive third nerve palsy. Diabetes can also be associated with this deficit and is the most common because of noncompressive third nerve paresis. Diabetes induced third nerve palsy, however, is usually pupil sparring (ie, the pupil is not asymmetrically dilated). In this case, the CTA revealed a wide-necked, large left posterior communicating artery aneurysm (Figure 1). Given the relatively young age of the patient, the mass effect on the third nerve, and the wide neck of the aneurysm, surgical clipping was recommended. At surgery, the wide neck of the aneurysm required trapping and deflation prior to successful clipping. The case is narrated in Video 1. Other clipping cases are discussed in Videos 2 and 3. {"href":"Single Video Player","role":"media-player-id","content-type":"play-in-place","position":"float","orientation":"portrait","label":"Video 1.","caption":"Trapping and deflation to clip a large Pcomm artery aneurysm. This video can be accessed in the HTML version of the article. Please visit www.operativeneurosurgery-online.com to view this article in HTML and play the video.","object-id":[{"pub-id-type":"doi","id":""},{"pub-id-type":"other","content-type":"media-stream-id","id":"1_xpznvs9a"},{"pub-id-type":"other","content-type":"media-source","id":"Kaltura"}]} {"href":"Single Video Player","role":"media-player-id","content-type":"play-in-place","position":"float","orientation":"portrait","label":"Video 2.","caption":"Miscrosurgical clipping of paraclinoid aneurysms in 3 patients. This video can be accessed in the HTML version of the article. Please visit www.operativeneurosurgery-online.com to view this article in HTML and play the video.","object-id":[{"pub-id-type":"doi","id":""},{"pub-id-type":"other","content-type":"media-stream-id","id":"1_rgt2vrwb"},{"pub-id-type":"other","content-type":"media-source","id":"Kaltura"}]} {"href":"Single Video Player","role":"media-player-id","content-type":"play-in-place","position":"float","orientation":"portrait","label":"Video 3.","caption":"Surgical clipping of an unruptured MCA aneurysm. This video can be accessed in the HTML version of the article. Please visit www.operativeneurosurgery-online.com to view this article in HTML and play the video.","object-id":[{"pub-id-type":"doi","id":""},{"pub-id-type":"other","content-type":"media-stream-id","id":"1_lfhih4hy"},{"pub-id-type":"other","content-type":"media-source","id":"Kaltura"}]} Answers to Questions B. The cavernous segment of the ICA is extradural and surrounded by bone and dura. These aneurysms have very low risk of subarachnoid hemorrhage. B. Posterior communicating artery aneurysms have a higher risk of hemorrhage than the other locations listed. D. The pterional or frontotemporal craniotomy is the ideal exposure used for most carotid segment aneurysms. B. The anatomic relationship of the posterior communicating artery to the oculomotor nerve makes this the most common cranial nerve compressed by an enlarging aneurysm at that site. Pearls ✓ Larger aneurysm size, location in posterior circulation (including posterior communicating artery aneurysms), family history of aneurysms, smoking, connective tissue disease, and a history of SAH increase the annual risk of rupture of intracranial aneurysms. ✓ Aneurysm rupture carries significant morbidity and mortality, thus justifying the treatment of many intracranial aneurysms. ✓ Aneurysm clipping is associated with very high rates of durability when compared with endovascular coiling. Patient selection for aneurysm clipping depends on careful analysis of anatomic features, an understanding of the natural history, and an honest appraisal of surgeon expertise. ✓ Endovascular treatment of aneurysms is a less-invasive approach to aneurysm treatment and may be preferable form select patients and select aneurysms. ✓ There are many new techniques arising for diagnosis and treatment of aneurysms, including emerging neurosurgical modalities and technological advancements to care. Care should be individualized and take aneurysm and patient characteristics into account. SUGGESTED READING Murayama Y, Takao H, Ishibashi T, et al. Risk analysis of unruptured intracranial aneurysms: prospective 10-year cohort study. Stroke. 2016;47(2):365-371. Wiebers DO, Whisnant JP, Huston J 3rd, et al. International Study of Unruptured Intracranial Aneurysms Investigators. Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet. 2003;362(9378):103-110. Juvela S, Porras M, Poussa K. Natural history of unruptured intracranial aneurysms: probability of and risk factors for aneurysm rupture. J Neurosurg. 2000;93(3):379-387. Rhoton AL Jr. Anatomy of saccular aneurysms. Surg Neurol. 1980;14(1):59-66. Samson D, Batjer HH, White J, et al. Intracranial Aneurysm Surgery: Basic Principles and Techniques. New York: Thieme; 2011. Bendok BR, Sattur MG, Welz ME, et al. Patient selection and technical nuances for microsurgical clipping of carotid-ophthalmic aneurysms: 2-dimensional operative video. Oper Neurosurg. 2018;15(2):245. CHAPTER 2: RUPTURED BRAIN ARTERIOVENOUS MALFORMATIONS Case Presentation An otherwise healthy pediatric patient slightly older than the age of 10 presented with sudden onset of severe headache, emesis, and confusion. Initial imaging demonstrated intracerebral hemorrhage (ICH) involving the mesial parietal and occipital lobes with extension into the ventricles (intraventricular hemorrhage [IVH]), and ventriculomegaly (Figure 4). CTA demonstrated an abnormal, periventricular tangle of vessels within the ICH.FIGURE 4.: A, CTA demonstrates an abnormal tangle of blood vessels (white arrow) adjacent to the ICH and IVH (*). B, DSA (lateral view, left vertebral artery). DSA demonstrates a small (1.5 cm), diffuse nidus (arrow), supplied by PCA branches, and arterial feeder has a flow-related aneurysm (arrowhead) proximal to the nidus. Venous drainage is both deep (*) and superficial. The Spetzler–Martin classification is grade II (S1E0V1). C, After embolization, the Onyx cast is demonstrated. D, The portion of the Onyx cast is seen intraoperatively. E, The main draining vein has been cauterized after disconnection of the arterial supply. F, Postoperative DSA demonstrates no residual BAVM.(See discussion at end of chapter.) Questions After stabilizing the patient, initial management would include which of the following: Emergent decompressive craniectomy Evacuation of the ICH Intracranial pressure (ICP) management with external ventricular drain (EVD) placement Diagnostic cerebral angiography After initial management, which of the following would be the next step in management? Microsurgical resection of the arteriovenous malformation (AVM) Stereotactic radiosurgery Diagnostic cerebral angiography What would be the Spetzler-Martin grade of this AVM with a 2 cm diameter, both superficial and deep venous drainage, and noneloquent location? I II III IV V Introduction A brain arteriovenous malformation (BAVM) is a high-flow vascular malformation characterized by an abnormal tangle of dysplastic arteries and veins, known as a nidus. This nidus lacks intervening capillaries and high-resistance vessels that allow the direct shunting of blood flow from the arterial to the venous circulation. BAVMs can present with hemorrhage, seizures, neurological deficits, and headache, or as incidental findings during work-up for other reasons. Patient and anatomic features of BAVMs help predict the risk of hemorrhage and risks of treatment. Treatment options include observation, microsurgical resection, endovascular embolization, stereotactic radiosurgery, or combination therapy. Controversy exists over optimal management, especially for unruptured asymptomatic BAVMs; however, treatment with microsurgical resection or stereotactic radiosurgery (SRS) is generally recommended for most ruptured BAVMs with the type of treatment dependent on patient and BAVM characteristics. Epidemiology BAVMs have a low prevalence but are an important cause of ICH. The prevalence of BAVMs has been estimated at 50 cases per 100 000 people. Based on several population studies, the incidence of BAVMs overall is 1 case per 100 000 people per year; for ruptured BAVMs, the incidence is 0.5 cases per 100 000 people per year. BAVMs can affect patients of any age, but most are detected between ages 20 and 40 yr. The most common presentation is hemorrhage (approximately 50% of cases), followed by seizure 25% and headache, neurological deficit, or incidental finding, which accounts for the remaining cases. The rupture risk of unruptured BAVMs is 1 to 2% per year, which increases to 3 to 5% per year with a history of hemorrhage. Overall, untreated BAVMs have a 2 to 4% risk of hemorrhage per year. Increasing age, history of hemorrhage, deep brain location, and exclusive deep venous drainage increase the risk of BAVM hemorrhage with annual risk of hemorrhage ranging from 0.9% for patients with none of these features to 34% for patients with all features. The presence of associated aneurysms can risk double the annual risk of BAVM hemorrhage. The impact of size, posterior fossa location, and venous abnormalities have not been demonstrated as clearly as prior hemorrhage. Pathophysiology Sporadic BAVM pathogenesis is uncertain, but they have been thought to be congenital lesions despite a lack of definitive evidence. Abnormal embryogenesis and angiogenesis as well as underlying genetic abnormalities may contribute to their formation and development. Normally, arteries and veins do not communicate directly and are separated by capillary beds, but in BAVMs high-flow shunting of blood occurs between arteries and veins, and the vessels that compose this tangle of blood vessels (the nidus) are dysplastic and prone to rupture. BAVM-associated aneurysms can form due to these high-flow conditions (ie, proximal and distal flow-related aneurysms), as well as within the abnormal intranidal vasculature (ie, intranidal aneurysms). These aneurysms may often be the source of hemorrhage. Draining veins become arterialized due to these high-flow and high-pressure conditions, and as a result they may develop an ectasia or stenosis. These venous features may not affect the risk of hemorrhage, but they are important in treatment planning and execution as premature occlusion of these veins will increase intranidal pressure and lead to hemorrhage. In addition to rupture and the effects of hemorrhage with resulting brain injury and increased ICP, unruptured BAVMs affect the surrounding brain due to local hypoperfusion and venous congestion, which can lead to cognitive decline, epilepsy, and hydrocephalus. Diagnosis and Initial Management Cases of spontaneous ICH, IVH, or SAH are generally diagnosed on noncontrast computed tomography (CT) imaging. Once discovered, CTA is performed, which often demonstrates the BAVM nidus, feeding arteries, and draining veins; it may also identify associated aneurysms. With the initial imaging, special attention is given to IVH or large ICHs with evidence of mass effect, brain herniation, and/or cistern effacement, as well as hemorrhage in the posterior fossa because these BAVMs may require emergent treatment with EVD placement or decompressive craniectomy. Importantly, the patient's examination combined with these imaging findings will dictate their immediate management. Patients with ruptured BAVMs are admitted to the neurosurgical intensive care unit (ICU) for close monitoring of their neurological status and overall medical condition. Once stabilized, diagnostic cerebral angiography (digital subtraction angiography [DSA]) is performed to further characterize the BAVM architecture. DSA will identify key anatomic features that will help determine management, including the number and location of feeding arteries, associated aneurysms (flow-related and intranidal), areas of high-flow shunting, nidal size and level of compactness (compact or diffuse), pattern of venous drainage (superficial and/or deep), and presence of venous ectasia or stenosis. ICH from a ruptured BAVM may compress or compartmentalize the nidus and alter perinidal flow patterns. MRI/MRA is typically performed during work-up of unruptured BAVMs and can assess the BAVM and perinidal brain parenchyma. Importantly, MRI can show evidence of prior hemorrhage with gradient echo imaging to detect degraded blood products, and evidence of perinidal gliosis identified with increased T2-weighted imaging. MRI, together with CTA and DSA, is also used for planning SRS treatment. Grading Systems Grading systems are important for the description of BAVMs, as well as management decision-making. The most commonly used system is the Spetzler–Martin grade (Table 2). The supplemented Spetzler–Martin grade is also used (Table 2). The modified Pollock–Flickinger score and the Virginia Radiosurgery AVM scale are used to determine risk of treatment from radiosurgery but are less commonly used during the initial management of a ruptured BAVM (Table 3). TABLE 2. - Spetzler-Martin and Supplemented Spetzler-Martin Grades Points Spetzler-Martin grade Nidus diameter <3 cm 1 3–6 cm 2 >6 cm 3 Eloquence Noneloquent location 0 Eloquent location 1 Venous drainage Superficial only 0 Any deep venous drainage 1 Total 1–5 Supplemented Spetzler-Martin grade Spetzler-Martin grade 1–5 Age <20 yr 1 20–40 yr 2 > 40 yr 3 Bleeding history Ruptured 0 Unruptured 1 Compactness of nidus Compact 0 Diffuse 1 Total 2–10 TABLE 3. - Type of Craniotomy Used for the Most Common Types of Aneurysms Anterior cerebral artery Pterional, interhemispheric Anterior communicating artery Pterional, interhemispheric Middle cerebral artery Pterional, supraorbital Posterior communicating artery Pterional, subtemporal Internal carotid artery Pterional, supraorbital TABLE 4. - The Modified Pollock-Flickinger Score and Virginia Radiosurgery AVM Scale Points Modified Pollock-Flickinger score Score = (0.1)(volume, mL) + (0.02)(age, y) + (0.5)(locationa) Virginia Radiosurgery AVM scale Volume <2 mL 0 2-4 mL 1 >4 mL 2 Eloquent location 1 History of hemorrhage 1 Total 0-4 points aHemispheric/corpus callosum/cerebellar = 0; basal ganglia/thalamus/brainstem = 1. BAVMs receive 1 to 5 points in the Spetzler–Martin grading system based on size (maximum diameter), venous drainage (superficial or deep), and eloquent location (Table 3). One point is assigned for an aneurysm size <3 cm, 2 points for a size 3 to 6 cm, and 3 points for a size >6 cm. One point is assigned for any deep venous drainage, and 1 point is assigned for eloquent location. Venous drainage is considered superficial if the BAVM drains into cortical veins and then to convexity sinuses (0 point), whereas deep venous drainage courses through the vein of Galen (1 point). Eloquence is anatomic and defined as sensorimotor cortex, language areas, visual cortex, hypothalamus, internal capsule, brainstem, cerebellar peduncles, and deep cerebellar nuclei. This grading system has been simplified into 3 tiers based on surgical morbidity and mortality (ie, classes A, B, and C for grades I/II, III, and IV/V, respectively). Surgical morbidity and mortality increase with increased grade/class such that poor outcomes occur in 8% of class A, 18% of class B, and 32% of class C patients. The supplemented Spetzler–Martin grade was based on the observation that age, hemorrhage, and compactness of the nidus also affect outcomes (Table 2). Points obtained from age, hemorrhage, and compactness are added to the Spetzler–Martin grade. Age < 20 yr, 20–40, and >40 yr are assigned 1, 2, and 3 points, respectively. Surgery on unruptured BAVMs carries more surgical risk (1 point) and has a higher likelihood of worse outcome from surgery than for ruptured BAVMs (0 point). A diffuse nidus (1 point) is more likely to have brain parenchyma within the nidus and is more challenging to define borders than a BAVM with a compact nidus (0 point). The supplemented Spetzler–Martin grade ranges from 2 to 10, and risk of surgical treatment increases with higher scores. Management Options Patients with unruptured BAVMs are mana