Clinical Vignette

A 66-year-old woman suddenly experienced a terrible temporal pain radiating into her forehead. The headache was so severe that she almost lost consciousness. She became nauseated, vomited, and felt disoriented. Her family called emergency medical services and had her brought to the emergency room. There, she was noted to be arousable but sleepy and confused. She had nuchal rigidity, photophobia, but no focal motor deficit. An unenhanced head computed tomography (CT) showed subarachnoid hemorrhage centered in the right sylvian fissure but no brain parenchymal abnormalities. Angiography demonstrated a ruptured middle cerebral artery aneurysm that was successfully clipped the next morning. The patient’s postoperative course was uneventful (Figs. 57-1 and 57-2).

Figure 57-1 Right Middle Cerebral Artery Aneurysm.

Figure 57-2 Middle Cerebral Artery Aneurysm Clipping.

Clinical Vignette

A 44-year-old postal worker presented with severe headache and nuchal rigidity to an emergency room. Unenhanced head CT revealed a subarachnoid hemorrhage centered in the basal cisterns, and further evaluation with catheter angiography revealed a large aneurysm arising from the basilar artery tip. After consultation between the neurosurgeon and the interventional neuroradiologist, the decision to perform endovascular coil embolization was made and the procedure was carried out successfully. The patient recovered fully after a 3-week hospital stay but required a second procedure after 6 months when follow-up angiography demonstrated a reexpansion of the neck of the aneurysm (Figs. 57-3 and 57-4).

Figure 57-3 Basilar Artery Tip Aneurysmal Bleed.

Figure 57-4 Basilar Artery Tip Aneurysm.

Clinical Presentation

The classic symptom of SAH is the “worst headache of one’s life.” Headaches associated with aneurysm rupture are frequently sudden in onset and often described as a severe thunderclap, excruciating and unbearable. The headache peaks rapidly and is frequently associated with pain extending across the head and toward the neck. The headache is usually global, with a constant viselike ache but occasionally throbbing. Unilateral aches or a retro-orbital stab-like pain, even fleetingly, raise the suspicion of a possible posterior communicating artery aneurysm.

Nausea and vomiting, neck pain, and altered consciousness are often associated with the headache. Approximately 30% of patients are found to be confused and lethargic after the ictus. During the moment of rupture, one fourth of patients become comatose and up to 40% have transient loss of consciousness.

Seizure-like activity may be observed. The incidence of true seizure activity in patients with SAH is estimated at 20%. Seizures in SAH are most commonly associated with middle cerebral artery (MCA) and anterior communicating artery (ACA) aneurysmal rupture causing intracerebral hematomas. Unfortunately, many patients recall having a sentinel hemorrhage or warning leak with a fleeting but severe headache within the 2–3 weeks before the major ictus. This headache is somewhat milder and usually not associated with meningismus; it is often ignored until the catastrophic return of a major rupture. When evaluating patients with SAH or sudden severe headache, special attention should be focused on the level of consciousness, focal neurologic signs such as hemiparesis or cranial nerve palsies, and signs of meningismus (Fig. 57-5). Meningismus frequently occurs, associated with nuchal rigidity. Brudzinski’s maneuver is an excellent means of evaluating meningismus; the examiner flexes the patient’s neck, precipitating hip flexion, knee flexion, and hamstring pain. Diplopia (due to abducens or oculomotor nerve palsies) and visual loss (chiasmal or optic nerve involvement) are caused by either cranial nerve compression from the aneurysmal dome or aneurysmal rupture and increased intracranial pressure (Fig. 57-6).

Figure 57-5 Clinical Manifestations of Cerebral Aneurysm Rupture.

Figure 57-6 Ophthalmologic Manifestations of Cerebral Aneurysms.

Examination of the optic fundi frequently discloses retinal or preretinal hemorrhage, subhyaloid hemorrhages, and occasional papilledema. Hemorrhage into the vitreous results in Terson syndrome, with scarring and epiretinal membrane formation (macular pucker) and eventually visual loss or distortion. Terson syndrome is a frequent cause of visual loss in SAH, which often goes unnoticed until the patient regains consciousness 1–2 weeks later. It is often related with more severe subarachnoid bleeds that cause loss of consciousness and papilledema. Its association with ACA aneurysms is less clear. The long-term prognosis for vision in this situation is fairly good; however, a vitrectomy is occasionally required.

When the aneurysm ruptures and dissects into adjacent brain tissue, various focal deficits may also be found on examination.

Differential Diagnosis

Patients presenting with a sudden apoplectic-type headache with associated meningismus or altered mental status must be considered to have an SAH until proven otherwise. However, SAH symptoms are sometimes confused with other disorders, including migraine headaches, hypertension, meningitis, cervical spine disorders, vertigo, and syncope. The various vascular headache syndromes remain the most common mimics.

Although migraines are often characterized by the patient as sudden, a careful history reveals that they typically have a gradual onset, with progression over minutes to hours, at times, to the degree of excruciating pain often with nausea and vomiting. Many are preceded by a classic visual aura of fortification spectra or scintillating lights gradually evolving then regressing over minutes before the headache occurs.

Cluster headache is another benign but severe headache syndrome with a well-defined clinical presentation. These headaches typically affect men, awakening them from sleep with a terrible unilateral periorbital and frontal pain. Cluster headaches are almost always associated with unilateral conjunctival injection, excessive lacrimation, and nasal stuffiness. They have a limited time course, usually lasting 45–60 minutes. They occur nightly in a temporal cluster for 6–8 weeks but may recur several times within a day. When this pattern is established, the diagnosis is secure. However, when the patient first experiences this headache in early midlife, a careful evaluation is indicated to exclude SAH. A therapeutic response to inhalation of 100% oxygen is diagnostic.

Paroxysmal hemicrania is a related disorder with an equal sexual distribution. Its response to indomethacin is a specific therapeutic diagnostic modality.

Orgasmic postcoital or exercise-induced headaches are another group of benign headaches that occur during sexual intercourse or with significant exercise. Those related to sexual activity generally occur precipitously at the peak of orgasm. These incapacitating severe headaches mimic the onset of an acute SAH and require the same full evaluation to exclude a ruptured aneurysm as other patients presenting with spontaneous sudden first-time severe headaches. Orgasmic, postcoital, or exercise-induced headaches are essentially diagnoses of exclusion.

Diagnostic Approach

The clinical diagnosis of SAH is best confirmed with brain CT (Fig. 57-7). Its sensitivity is highest in the first 24 hours after headache onset. A mild hemorrhage may wash away within 24 hours but approximately 50% of severe SAHs are still visible on CT 1 week after the ictus, and only one third are seen after 2 weeks. CT confirms the presence of SAH and frequently highlights associated issues such as hydrocephalus, intraparenchymal hematoma, intraventricular hemorrhage, or subdural hemorrhage.

Figure 57-7 Subarachnoid Hemorrhage.

Whenever the clinical suspicion of SAH exists but CT is negative, a lumbar puncture must be performed. A nontraumatic tap is crucial. When the presence of blood in the CSF does not clear between the first and fourth tubes, this is particularly suggestive of SAH (See Fig. 57-5). However, a more sensitive indicator is CSF xanthochromia, which represents lysis of erythrocytes with degradation of heme products into bilirubin within the CSF. This frequently renders the CSF a yellowish color within 1–3 hours after an SAH, and often persists for approximately 2–3 weeks.

When SAH is confirmed by CT or lumbar puncture, the cause of the hemorrhage is best evaluated with a four-vessel cerebral arteriogram. An aneurysmal source is found in 80–85% of arteriograms preformed for suspected SAH. If arteriography is negative after SAH, a repeat study should be performed approximately 10 days later. Although reliance on CT angiography rather than catheter angiography has been increasing, cerebral arteriography remains the accepted standard for evaluating patients with SAH.

To ensure proper communication, predict outcomes, and guide management, a clinical grade for each SAH is needed. Several grading scales are available; the most widely used is the Hunt–Hess scale—a five-tiered description of the patient’s state and an indicator of prognosis (Table 57-1).

Table 57-1 Hunt–Hess Grading Scale for Berry Aneurysms

Pathophysiology

Intracranial Aneurysms

Subtypes of intracranial aneurysms include saccular or berry, fusiform, dissecting, traumatic, and infectious (mycotic) aneurysms. Frequently associated with an SAH, saccular aneurysms are by far the most common type. They are spherical in shape but frequently have asymmetric outpouching and multilobulated characteristics that are felt to be potential rupture sites for the aneurysm. The aneurysmal fundus or body is connected to the parent vessel via a small neck region, and as the aneurysm grows, this neck region may broaden and incorporate normal branching vessels.

Intracranial aneurysms characteristically occur at branch points of major cerebral arteries. Almost 85% of aneurysms are found in the anterior circulation and 15% within the posterior circulation (Fig. 57-8). Overall, the most common sites are the anterior communicating artery followed by the posterior communicating artery and the middle cerebral artery bifurcation. Within the posterior circulation, the most preponderant site is at the top of the basilar artery bifurcation into the posterior cerebral arteries.

Figure 57-8 Typical Sites of Cerebral Aneurysms.

Aneurysms are frequently classified according to size, with small being less than 10 mm, large 10–25 mm, and giant aneurysms larger than 25 mm. At presentation, most aneurysms are small, with only 2% found to be giant. Giant aneurysms are more likely to cause compressive symptoms on the optic chiasm, cranial nerves, and brainstem depending on location. Rarely involvement of tributary vessels, either due to aneurysmal expansion or cavitary clot, may lead to ischemic symptoms as well (Fig. 57-9). Although controversy remains regarding the association of size and the incidence of rupture, 7 mm seems to be the minimal size at the time of rupture. Overall, ruptured aneurysms tend to be larger than unruptured aneurysms.

Figure 57-9 Giant Cerebral Aneurysms.

Aneurysms occur in approximately 5% of the adult population, somewhat more commonly in women. The causes of intracranial aneurysm formation and rupture are not well understood; however, it is thought that intracranial aneurysms form over a relatively short period and either rupture or undergo changes resulting in a stable unruptured aneurysm. Pathologic examination of ruptured aneurysms obtained at autopsy demonstrates disorganization of normal vascular architecture with loss of the internal elastic lamina, and reduced collagen content. In contrast, unruptured aneurysms have nearly twice the collagen content of the normal arterial wall, resulting in increased thickness of the aneurysmal dome, which may be responsible for the observed relative stability and low rupture rate.

Ruptured Aneurysms

The peak incidence of aneurysmal SAH is in the sixth decade of life. Only 20% of aneurysm ruptures occur in patients aged between 15 and 45 years. No predisposing activity has been identified, and aneurysmal SAH is equally distributed in sleep, routine daily activities, and strenuous activity.

Nearly 50% of patients who have an SAH, when properly questioned, relate a history of a warning leak with headache or symptoms around 2–3 weeks before the major hemorrhage. Nearly half of these individuals die before arriving to the hospital. Many of the initial survivors succumb to a recurrent hemorrhage after presenting to the hospital. The peak incidence of subsequent hemorrhage occurs in the first 24 hours, but the subsequent daily risk continues such that approximately 20–25% have rebled within the first 2 weeks of presentation. Mortality associated with the second hemorrhage is nearly 70%.

Risk Factors

Risk factors associated with aneurysmal rupture include cigarette smoking, oral contraceptive use, alcohol consumption, pregnancy, and childbirth. Possible diurnal blood pressure variations are associated with a circadian rhythm for aneurysm rupture. Most ruptures occur early in the morning or evening, but few occur in the middle of the night. There also may be a predisposition to occur during the winter months or when there are drastic changes in barometric pressure. The most likely cause of rupture is hemodynamic stress associated with biomechanical and structural weakness within the blood vessel and aneurysmal wall.

Management

Technical Aspects of Surgical Clipping

Craniotomy and aneurysm obliteration by clipping is the most effective treatment available. Aneurysms completely obliterated using this technique almost never recur. Overall, surgical treatment of unruptured aneurysms is associated with 3% mortality and 7% morbidity. The following discussion illustrates lesions’ anatomical complexities and unique features.

The development of the surgical microscope and microsurgical instrumentation and the evolution of skull base techniques have revolutionized treatment of cerebral aneurysms. Magnification and brilliant illumination of very narrow exposure windows have allowed the preservation of small perforating vessels that are not easily visible to the naked eye and serve as strategic end arteries of eloquent brain regions. The advent of skull base techniques in which bone is removed to obviate any brain retraction and manipulation has also facilitated the treatment of aneurysms, particularly the more complex and giant variety.

Craniotomy

Different approaches are used depending on the location, size, and shape of the aneurysm. Most anterior circulation aneurysms are done via a pterional craniotomy, a fundamental approach in aneurysm surgery. As its name implies, it centers on the pterion and encompasses both the frontal and temporal bone removal to expose the sphenoid wing. After the dura is opened, the frontal and temporal lobes are seen in the region of the sylvian fissure. The surgical microscope is brought into the field to accomplish the remaining surgery with magnified vision (Fig. 57-10).

Figure 57-10 Frontotemporal Approach for Internal Carotid, Ophthalmic, Anterior Communicating, and Middle Cerebral Aneurysms.

Posterior circulation aneurysms can be approached posteriorly (Fig. 57-11), via a pterional-transsylvian route or subtemporal route, depending on the projection and height of the basilar bifurcation. Other more complex approaches such as orbito-zygomatic skull base approaches and far-lateral approaches can also be employed for posterior circulation aneurysms as needed. A detailed discussion of surgical approaches is beyond the scope of this chapter.

Figure 57-11 Posterior Approach for Vertebral and Posterior Inferior Cerebellar Aneurysms.

Intracranial Surgical Dissection

The neurosurgeon proceeds through the natural arachnoidal and cisternal compartments to expose the appropriate vessels and the parent artery. Dissection of the aneurysm, particularly its neck, as well as all branches and perforating vessels is completed before an appropriate aneurysm clip is placed across the aneurysm neck, sealing it from the parent vessel circulation. Close inspection to ensure that no perforating branch arteries are occluded or injured is completed just before clipping. Once secured, the aneurysm can be punctured to allow it to collapse and relieve mass effect if present. Adjuncts to the surgical treatment of aneurysms are beyond the scope of this text but include temporary clipping, cerebral bypasses, aneurysmorrhaphy, and, in some cases, full hypothermic cardiac arrest. With microsurgical technology and various temporary and permanent aneurysm clips available and the establishment of skull base and revascularization techniques, management of once inoperable lesions has become routine.

Endovascular Therapy

The treatment for ruptured intracranial aneurysms requires multidisciplinary efforts; the core team consists of an interventional neuroradiologist, vascular neurosurgeon, neurointensivists, and rehabilitation specialists. Recently the endovascular approach has emerged as an alternative treatment modality for selected aneurysms. In the treatment of complex large and giant aneurysms, endovascular therapy may serve as an adjunct to surgical interventions.

Although there are singular reports of aneurysm treatments from Ciniselli, Moore, and Werner in the last 150 years that resemble modern endovascular therapy, the current treatment modality was originally devised by Guglielmi in 1990 using platinum coils that were detached within the aneurysm dome using an electrolytic mechanism. Approved by the Food and Drug Administration in 1991, the device became known as Guglielmi detachable coil (GDC). Presently coils that incorporate other materials and utilize alternative detachment mechanisms are available in the United States.

The international subarachnoid aneurysm trial (ISAT) is currently the only large-scale international prospective randomized controlled trial (RCT) comparing surgical clipping with endovascular treatment of ruptured aneurysms. The authors demonstrated a 24% relative and 7.4% absolute reduction of death or dependency at 1 year in favor of coiling. A number of criticisms of this publication have been made, specifically the applicability of the findings to the practice pattern found in the United States and a perceived imbalance between the experience of the endovascular practitioners and the surgeons in the study.

Endovascular treatment for ruptured intracranial aneurysms is usually conducted under general anesthesia. Systemic heparinization during the procedure is preferred by some but is not universally accepted. A 6 or 7 French guide catheter is introduced via the femoral artery into the internal carotid artery (ICA) or vertebral artery to provide a stable platform. A microcatheter is advanced over a microguidewire coaxially through the guide catheter into the aneurysm, and a series of soft platinum coils are deployed sequentially until radiographic occlusion of the aneurysm dome is achieved. Coils used for aneurysm embolization are usually MR compatible, and MR imaging may be used for noninvasive follow-up imaging.

The shape, size, and neck diameter of the aneurysm in relation to the parent vessel determine whether or not its dome can be successfully occluded. Larger or odd-shaped aneurysms with wide necks are more difficult to occlude completely. In ISAT the proportions of completely, subtotally (with remnants at the neck), and incompletely occluded aneurysms at follow-up were 66%, 26%, and 8%, respectively. It is not clear what the risk of rebleeding is from a small neck remnant following either endovascular coil embolization or rarely surgical clipping. Post-clip angiography shows that only 4–10% of aneurysms have any major remnant while coiling achieves complete aneurysm occlusion in only 50% of cases. When near-complete occlusions are included, this level increases to 85–90%. Another limitation to endovascular procedures is an approximately 16–32% aneurysm recurrence depending on the location, degree of compaction, and morphology of the aneurysm when primarily treated (Fig. 57-12). Patients may require repeated treatment or even surgical intervention with removal of the coils.

Figure 57-12 Basilar Tip Aneurysm Re-expansion.

More recent modifications in device technology aim to achieve safer and more durable treatment of a larger proportion of aneurysms, including those with a wide neck or complex shape that were not readily amenable to occlusion with GDC platinum coils alone. These include complex coil shapes that conform better to irregular aneurysm geometries, balloon remodeling techniques (a nondetachable balloon catheter deployed across the aneurysm neck and inflated to prevent herniation of the coils into the parent vessel), stent-assisted coil embolization, bioactive coils coated with polyglycolic polylactic acid to enhance thrombus formation and organization, platinum coils coated with a polymeric hydrogel that swells when in contact with blood to achieve greater packing density, and radioactive coils. Liquid embolization systems with high-density Onyx (Ethyl-vinyl alcohol copolymer mixed with micronized tantalum powder) deliver a mass of highly viscous and cohesive material into the aneurysm, ideally leading to complete occlusion of the aneurysm and covered stents aimed to restore the parent vessel wall in its entirety. Many of these technologies have been studied in selected patients and are currently under review for approval in the United States.

Interval posttreatment angiographic follow-up, either with noninvasive CT or MR angiography or catheter angiography, is mandatory and should be performed lifelong. There are no clear guidelines regarding the most appropriate follow-up intervals, and an individualized approach may be taken.

Overall procedure-related morbidity is 6–19%, and mortality 1–2%. Procedural complications include aneurysm rupture (2–5%) potentially leading to worse outcome or death, thromboembolic events (5–9%), parent vessel occlusion (2.5%), coil migration 0.5%, and significant groin hematomas (0.6%).

Long-term complications of coil embolization include recanalization and coil compaction. Even after complete radiographic occlusion of the aneurysm, only about 25–35% of its volume consists of coils, with the rest being thrombus. About 10% of coiled aneurysms will require a second treatment after recanalization to ensure stability. The risk of rebleeding has been documented at 0.2% per patient year with a mean follow-up of 4 years, similar to the rebleeding rates after neurosurgical clipping.

The risk of postoperative epilepsy, though low in absolute terms, is lower after endovascular treatment compared to craniotomies. The relative risk reduction of coiling compared to surgery at 1 year is 47.9%, and the absolute risk reduction is 3.9%.

Embolization materials are more expensive than aneurysm clips, but health economic data emerging from the ISAT suggests that these excess costs are offset by shorter hospital stays, fewer dependent survivors, less requirement for rehabilitation, and possibly reduced neuropsychological impact. The development and clinical experience with the Guglielmi detachable coil technology is extensive, and follow-up is available beyond 10 years. In many patients, aneurysm endovascular coil occlusion is a valuable alternative to surgery. Overall, 82% of patients experience favorable outcomes.