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For further information, see CMDT Part 24-09: Stroke

Key Features

Essentials of Diagnosis

  • Sudden ("thunderclap") severe headache

  • Signs of meningeal irritation usually present

  • Obtundation is common

  • Focal deficits frequently absent

General Considerations

  • 5–10% of strokes are due to subarachnoid hemorrhage

  • Trauma is the most common cause

  • Frequently results from the rupture of an arterial saccular ("berry") aneurysm or from an arteriovenous malformation

  • Factors associated with a higher risk of subarachnoid hemorrhage

    • Older age

    • Female sex

    • "Non-white" ethnicity

    • Hypertension

    • Tobacco smoking

    • High alcohol consumption (exceeding 150 g per week)

    • Previous symptoms

    • Posterior circulation aneurysms

    • Larger aneurysms

  • See also Aneurysm, Intracranial

  • See Table 24–3

Clinical Findings

Symptoms and Signs

  • Sudden onset of headache with severity never experienced previously by the patient

  • May be followed by nausea and vomiting and loss or impairment of consciousness (transient, or progressing to coma and death)

  • Patient is often confused and irritable and may show other symptoms of an altered mental status

  • Nuchal rigidity and other signs of meningeal irritation are seen, except in deeply comatose patients

  • Focal neurologic deficits may be present and may suggest the site of the underlying lesion

  • See also Aneurysm, Intracranial

Differential Diagnosis

  • Meningitis

  • Migraine

  • Intracerebral hemorrhage

  • Ischemic stroke


Laboratory Findings

  • Cerebrospinal fluid demonstrates an elevated red blood cell count

  • Peripheral leukocytosis

  • Transient glycosuria

Imaging Studies

  • CT scan (preferably with CT angiography) should be performed immediately to confirm that hemorrhage has occurred and to search for its source

  • CT is faster and more sensitive in detecting hemorrhage in the first 24 hours than MRI

  • Rarely, CT is normal in patients with suspected hemorrhage

  • If CT is normal in such patients, examine cerebrospinal fluid for blood or xanthochromia before the possibility of subarachnoid hemorrhage is discounted

Diagnostic Procedures

  • Electrocardiographic evidence of arrhythmias or myocardial ischemia has been well described and probably relates to excessive sympathetic activity

  • Cerebral arteriography helps determine the source of bleeding

  • Bilateral carotid and vertebral arteriography are necessary because aneurysms are often multiple, while arteriovenous malformations may be supplied from several sources

  • CT angiography or MR angiography may also be revealing but is less sensitive than conventional arteriography



  • Phenytoin to prevent seizures; however, evidence of benefit is conflicting


  • Surgical clipping of aneurysm base or endovascular treatment by coil embolization is definitive treatment, ideally performed within 2 days of the hemorrhage

Therapeutic Procedures

  • Major aim is to prevent further hemorrhage

  • Conscious patients

    • Confine to ...

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