The initial imaging examination in the evaluation of SAH is the noncontrast CT scan (Table 6.1, Section 3). CT scanning performed within 72 hours of SAH has a high sensitivity and specifi city for detecting blood in the subarachnoid space, whereas magnetic
Table 6.1 Guidelines for the management of aneurysmal subarachnoid hemorrhage (in press, 2008)
Section 1
Prevention of subarachnoid hemorrhage: summary and recommendations
1 The relationship between hypertension and aneurysmal SAH is uncertain. However, treatment of high blood pressure with antihypertensive medication is recommended to prevent ischemic stroke and intracerebral hemorrhage, cardiac, renal, and other end-organ injury (Class I, Level of Evidence A).
2 Cessation of smoking is reasonable to reduce the risk of SAH, although evidence for this association is indirect (Class IIa, Level of Evidence B).
3 Screening of certain high-risk populations for unruptured aneurysms is of uncertain value (Class IIb, Level of Evidence B);
advances in noninvasive imaging may be used for screening, but catheter angiography remains the “gold standard” when it is clinically imperative to know if an aneurysm exists.
Section 2
Natural history and outcome of aneurysmal SAH: summary and recommendations
1 The severity of the initial bleed should be determined rapidly as it is the most useful indicator of outcome following aneurysmal SAH, and grading scales which heavily rely on this factor are helpful in planning future care with family and other physicians (Class I, Level of Evidence B).
2 Case review and prospective cohorts have shown that for untreated, ruptured aneurysms, there is at least a 3% to 4% risk of rebleeding in the fi rst 24 hours and possibly signifi cantly higher, with a high percentage occurring immediately (within 2 to 12 hours) after the initial ictus, a 1% to 2% per day risk in the fi rst month, and a long-term risk of 3% per year after 3 months. Urgent evaluation and treatment of patients with suspected SAH are therefore recommended (Class I, Level of Evidence B).
3 In triaging patients for aneurysm repair, factors that may be considered in determining the risk of rebleeding include severity of the initial bleed, interval to admission, blood pressure, gender, aneurysm characteristics, hydrocephalus, early angiography, and the presence of a ventricular drain (Class IIb, Level of Evidence B).
Section 3
Manifestations and diagnosis of subarachnoid hemorrhage:
summary and recommendations
1 SAH is a medical emergency that is frequently misdiagnosed. A high level of suspicion for SAH should exist in patients with acute onset of severe headache (Class I, Level of Evidence B).
2 CT scanning for suspected SAH should be performed (Class I, Level of B), and lumbar puncture for analysis of cerebrospinal fl uid is recommended when the CT scan is negative (Class I, Level of Evidence B).
3 Selective cerebral angiography should be performed in patients with documented SAH to document the presence and anatomic features of aneurysms (Class I, Level of Evidence B).
4 MRA or infusion CT (CTA) may be considered when conventional angiography cannot be performed in a timely fashion (Class IIb, Level of Evidence B).
Section 4
Emergency evaluation and preoperative care: summary and recommendations
1 The degree of neurological impairment using an accepted SAH grading system can be useful for prognosis and triage (Class IIa, Level of Evidence B).
2 A standardized ED management protocol for the evaluation of patients with headaches and other symptoms of potential SAH does not currently exist and should probably be developed (Class IIa, Level of Evidence C).
Section 5
Medical measures to prevent rebleeding after SAH: summary and recommendations
1 Blood pressure should be monitored and controlled to balance the risk of strokes, hypertension-related rebleeding, and maintenance of cerebral perfusion pressure (Class I, Level of Evidence B).
2 Bed rest alone is not enough to prevent rebleeding after SAH. It may be considered as a component of a broader treatment strategy along with more defi nitive measures (Class IIb, Level of Evidence B).
3 Although older studies demonstrated an overall negative effect of antifi brinolytics, recent evidence suggests that early treatment with a short course of antifi brinolytic agents, when combined with a program of early aneurysm treatment followed by discontinuation of the antifi brinolytic and prophylaxis against hypovolemia and vasospasm may be reasonable (Class IIb, Level of Evidence B), but further research is needed. Furthermore, antifi brinolytic therapy to prevent rebleeding may be considered in certain clinical situations, e.g., patients with a low risk of vasospasm and/or a benefi cial effect of delaying surgery (Class IIb, Level of Evidence B).
Section 6
Surgical/endovascular treatment of ruptured aneurysms: summary and recommendations
1 Surgical clipping or endovascular coiling should be performed to reduce the rate of rebleeding after aneurysmal SAH (Class I, Level of Evidence B).
2 Wrapped or coated aneurysms as well as incompletely clipped or coiled aneurysms have an increased risk of rehemorrhage compared to those completely occluded, and therefore require long-term follow-up angiography. Complete obliteration of the aneurysm is recommended whenever possible (Class I, Level of Evidence B).
3 For patients with ruptured aneurysms judged by an experienced team of cerebrovascular surgeons and endovascular practitioners to be technically amenable to both endovascular coiling and neurosurgical clipping, endovascular coiling can be benefi cial (Class IIa, Level of Evidence B). Nevertheless, it is reasonable to consider individual characteristics of the patient and the aneurysm in deciding the best means of repair, and management of patients in centers offering both techniques is probably indicated (Class IIa, Level of Evidence B).
4 Although previous studies showed that overall outcome was not different for early versus delayed surgery after SAH, early treatment reduces the risk of rebleeding after SAH, and newer methods may increase the effectiveness of early aneurysm treatment. Early aneurysm treatment is reasonable and is probably indicated in the majority of cases (Class IIa, Level of Evidence B).
Section 7
Hospital characteristics and systems of care: summary and recommendations
1 Early referral to high-volume centers that have both experienced cerebrovascular surgeons and endovascular specialists is reasonable (Class IIa, Level of Evidence B).
Section 8
Anesthetic management: summary and recommendations 1 Minimizing the degree and duration of intraoperative
hypotension during aneurysm surgery is probably indicated (Class IIa, Level of Evidence B).
2 There are insuffi cient data on pharmacological strategies and induced hypertension during temporary vessel occlusion to make specifi c recommendations, but there are instances where their use may be considered reasonable (Class IIb, Level of Evidence C).
3 Induced hypothermia during aneurysm surgery may be a reasonable option in some cases but is not routinely recommended (Class III, Level of Evidence B).
Section 9
Management of cerebral vasospasm: summary and recommendations
1 Oral nimodipine is indicated to reduce poor outcome related to aneurysmal subarachnoid hemorrhage (Class I, Level of Evidence A). The value of other calcium antagonists, whether administered orally or intravenously, remains uncertain.
2 Treatment of cerebral vasospasm begins with early management of the ruptured aneurysm, and in most cases maintaining normal circulating blood volume and avoiding hypovolemia is probably indicated (Class IIa, Level of Evidence B).
3 One reasonable approach to symptomatic cerebral vasospasm is volume expansion, induction of hypertension, and hemodilution [Triple-H therapy] (Class IIa, Level of Evidence B).
4 Alternatively, cerebral angioplasty and/or selective intra-arterial vasodilator therapy may also be reasonable, either following, together with, or in the place of, Triple-H therapy depending on the clinical scenario (Class IIb, Level of Evidence B).
Section 10
Management of hydrocephalus: summary and recommendations 1 Temporary or permanent CSF diversion is recommended in
symptomatic patients with chronic hydrocephalus following SAH (Class I, Level of Evidence B).
2 Ventriculostomy can be benefi cial in patients with ventriculomegaly and diminished level of consciousness following acute SAH (Class IIa, Level of Evidence B).
Section 11
Management of seizures: summary and recommendations 1 The administration of prophylactic anticonvulsants may be
considered in the immediate posthemorrhagic period (Class IIb, Level of Evidence B).
2 The routine long-term use of anticonvulsants is not recommended (Class III, Level of Evidence B) but may be considered for patients with risk factors such as prior seizure, parenchymal hematoma, infarct, or MCA aneurysms (Class IIb, Level of Evidence B).
Section 12
Management of hyponatremia: summary and recommendations 1 Administration of large volumes of hypotonic fl uids and
intravascular volume contraction should generally be avoided following SAH (Class I, Level of Evidence B).
2 Monitoring volume status in certain patients with recent SAH using some combination of central venous pressure, pulmonary artery wedge pressure, fl uid balance, and body weight is reasonable, as is treatment of volume contraction with isotonic fl uids (Class IIa, Level of Evidence B).
Table 6.1 Continued
resonance imaging (MRI) is less accurate. The sen- sitivity of detecting SAH from a ruptured aneurysm using CT scans is dependent on the slice thickness, the scanner resolution, and the technician’s and interpreting radiologist’s expertise, as well as the interval between the hemorrhage and when the CT scan was obtained. For example, the expected sensi- tivity of 100% when a CT scan is obtained within 12 hours of rupture drops to 93% when the scan inter- val is extended to 24 hours [10]. In addition, CT scan can also show the presence of conditions that may require emergent treatment, such as intraven- tricular blood and hydrocephalus, or parenchymal hemorrhage with mass effect. The absence of sub- arachnoid blood on the CT scan does not rule out SAH, and a lumbar puncture may be indicated when the clinical suspicion is high (see further discussion) (Table 6.1, Section 3).
Diagnosis of IAs
Technological advances have been made in recent years that have improved the detection and charac- terization of IAs. The three radiological examinations used for this purpose are CT angiography (CTA), MRA, and catheter-based digital subtraction angiog-
raphy (DSA). Although standard head CT scans and brain MRI may detect aneurysms that are large, par- ticularly if they are calcifi ed or thrombosed, these are not optimal. The head CT of the example patient revealed a diffuse hemorrhage with blood in the suprasellar cistern and interhemispheric fi ssure but did not show an aneurysm (Figure 6.2a). CTA, MRA, and DSA are each excellent modalities with which to study aneurysms (Figure 6.3a–6.3e). Each has advan- tages and disadvantages, and the decision regarding which test to employ depends upon the specifi c clini- cal situation. Often, obtaining more than one of these tests is helpful and complementary.
MRA, which is an MRI with special sequences used to study the vasculature, is the least invasive modality to study aneurysms (Table 6.1, Section 3).
It is also the least sensitive, particularly for smaller aneurysms. Reports have documented a sensitivity of 0.69–0.99 and a specifi city of 1.00. The sensitivity dropped to as low as 0.38 in one series for aneurysms smaller than 3 mm in diameter [7,11–13]. A disad- vantage of MRA is that it takes longer to acquire images (30–90 minutes) as compared with CTA, making it cumbersome and often impractical in critically ill patients. Individuals with pacemakers or 3 The use of fl udrocortisone acetate and hypertonic saline is
reasonable for correcting hyponatremia (Class IIa, Level of Evidence B).
4 In some instances, it may be reasonable to reduce fl uid administration to maintain a euvolemic state (Class IIb, Level of Evidence B).
Rating levels of evidence and recommendations Quality of evidence
Class I: conditions for which there is evidence for and/or general agreement that the procedure or treatment is useful and effective.
Class II: conditions for which there is confl icting evidence and/or a divergence of opinion about the usefulness/
effi cacy of a procedure or treatment.
Class IIa: the weight of evidence or opinion is in favor of the procedure or treatment.
Class IIb: usefulness/effi cacy is less well established by evidence or opinion.
Table 6.1 Continued
Class III: conditions for which there is evidence and/or general agreement that the procedure or treatment is not useful/effective and in some cases may be harmful.
Therapeutic recommendations
Level of Evidence A: data derived from multiple randomized clinical trials.
Level of Evidence B: data derived from a single randomized trial or nonrandomized studies.
Level of Evidence C: consensus opinion of experts.
Diagnostic/prognostic recommendations
Level of Evidence A: data derived from multiple prospective cohort studies employing a reference standard applied by a masked evaluator.
Level of Evidence B: data derived from a single Grade A study or one or more case-control studies or studies employing a reference standard applied by an unmasked evaluator.
Level of Evidence C: consensus opinion of experts.
CSF, cerebrospinal fl uid; CTA, CT angiography; ED, emergency department; MCA, middle cerebral artery; MRA, magnetic resonance angiography; SAH, subarachnoid hemorrhage.
Fig. 6.1 The intracranial vasculature showing the most frequent locations of intracranial aneurysms. Percentages indicate the incidence of intracranial aneurysms. Reprinted with permission, Massachusetts Medical Society. From Brisman JL, et al. N Engl J Med.
2006;355:928–939.
other metallic implants or with severe claustropho- bia often cannot undergo MRA examination.
CTA is a CT scan obtained after an IV injection of contrast in which thin-section images are recon- structed using a computer software to optimize the imaging of blood vessels (Table 6.1, Section 3).
Images are acquired within a few minutes, and in less than a minute, a routine noncontrast head CT scan can be simultaneously obtained. CTA has the advantage of demonstrating the vasculature relative to the bones of the skull base, which is important for surgical planning (Figure 6.3a and 6.3b). Addition- ally, special commercially available software permits
manipulations of the reconstructed images in three dimensions.
Sensitivity and specifi city of CTA for the detection of IAs have been reported as 0.77–0.97 and 0.87–
1.00, respectively. As with MRA, the sensitivity drops precipitously for smaller lesions with estimated sen- sitivity rates of 0.40–0.91 for aneurysms smaller than 3 mm [12,14]. In recent years, newer generation CT scanners (16-slice and 64-slice multidetectors) have claimed increased ability to visualize IAs, and recent data demonstrate even higher sensitivity and speci- fi city [15]. The major disadvantages of CTA are the need for IV contrast, which may be harmful in
(a)
(c)
(e)
(b)
(d)
(f)
Fig. 6.2 (a) Noncontrast head CT scan shows a diffuse subarachnoid hemorrhage with blood in the interhemispheric fi ssure and suprasellar cistern. (b) CT angiography, coronal cut, clearly shows a small anterior communicating artery aneurysm. Angiography in the anteroposterior (c) and lateral projection (d) confi rms this fi nding. No residual aneurysm is apparent postcoiling (e). The coil mass is best seen on an unsubtracted anteroposterior skull radiograph (f).
(a) (b)
(c) (d)
(e)
Fig. 6.3 The three major imaging modalities for intracranial aneurysms. Saggital 2D (a) and reformatted oblique view 3D (b) CT angiography shows two different patients with basilar tip aneurysms. The associated bony anatomy is appreciated. The anteroposterior 2D digital subtraction angiography (DSA) (vertebral artery injection) (c) and 3D DSA (carotid injection) (d) show a basilar tip and anterior communicating artery aneurysms, respectively. The 3D magnetic resonance angiography shows a distal middle cerebral artery aneurysm (e).
patients with impaired renal function, an allergic reaction to the dye, and radiation exposure.
The gold-standard test for cerebral aneurysm detection and characterization is catheter-based DSA (Table 6.1, Section 3). The test has the highest sensitivity and specifi city provided that the angio- graphic equipment is capable of performing three- dimensional rotational angiography, a form of catheter-based angiography in which images are sequentially acquired as the fl uoroscopic gantry rotates 360 degrees around the patient’s head, enabling reformatted images to be manipulated in three dimensions (Figure 6.3d). This is the most expensive of the radiographic tests for aneurysms and also requires physicians trained in techniques of angiography. The procedure requires skilled opera- tors to introduce catheters into the arterial system (generally from the transfemoral route) using radio- graphic guidance. Catheters are selectively advanced into the carotid and vertebral arteries, contrast is injected, and images are obtained (Figure 6.3c and 6.3d). Increased experience has led to lower compli- cation rates; yet this remains an invasive technique.
Minor risks include groin hematoma (6.9–10.7%), arterial puncture site injury (0.05–0.55), allergic dye reaction, contrast-induced renal toxicity (1–2%), and radiation exposure. Major risks include throm- boembolic stroke or vascular dissection (less than 1% with experienced operators) [16–18].