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

Key Features

Essentials of Diagnosis

  • Subarachnoid hemorrhage or focal deficit

  • Abnormal imaging studies

General Considerations

  • Most aneurysms are located

    • On the anterior part of the circle of Willis, particularly on the anterior or posterior communicating arteries

    • At the bifurcation of the middle cerebral artery

    • At the bifurcation of the internal carotid artery

  • Saccular aneurysms ("berry" aneurysms)

    • Occur at arterial bifurcations

    • Are frequently multiple (20% of cases)

    • Are usually asymptomatic

    • Are associated with polycystic kidney disease, moyamoya disease, familial aldosteronism type 1, and coarctation of the aorta

  • Mycotic aneurysms resulting from septic embolism occur in more distal vessels and often at the cortical surface


  • Risk factors for aneurysm formation include cigarette smoking, hypertension, and female sex

Clinical Findings

Symptoms and Signs

  • May cause a focal neurologic deficit by compressing adjacent structures

  • Most are asymptomatic or produce only nonspecific symptoms until they rupture, causing a subarachnoid hemorrhage (see Subarachnoid Hemorrhage)

  • "Warning leaks" of a small amount of blood from the aneurysm sometimes precede the major hemorrhage by a few hours or days, leading to headaches, nausea, and neck stiffness

  • Focal neurologic signs may be absent in subarachnoid hemorrhage and secondary to a focal hematoma or ischemia in the territory of the vessel with the ruptured aneurysm

  • Focal arterial spasm in the area of the ruptured aneurysm may occur after 4–14 days, causing hemiplegia or other focal deficits

  • Cause of vasospasm is unknown and likely multifactorial

  • Vasospasm may lead to significant cerebral ischemia or infarction and increase in intracranial pressure

  • Subacute hydrocephalus due to interference with the flow of cerebrospinal fluid may occur after 2 or more weeks; leads to a delayed clinical deterioration and is relieved by shunting

Differential Diagnosis

  • Meningitis or meningoencephalitis

  • Ischemic stroke

  • Space-occupying lesion, eg, brain tumor

  • Subdural hemorrhage

  • Epidural hemorrhage

  • Migraine


Imaging Studies

  • Digital subtraction angiography (bilateral carotid and vertebral studies)

    • Definitive evaluation

    • Generally indicates the size and site of the lesion

    • Sometimes reveals multiple aneurysms

    • May show arterial spasm if rupture has occurred

  • Visualization by CT or MR angiography

    • Not usually adequate if operative treatment is under consideration because lesions may be multiple and small lesions are sometimes missed

    • Can be used to screen patients who have two or more first-degree relatives with intracranial aneurysms



  • Medical management as outlined for subarachnoid hemorrhage is continued for about 6 weeks and followed by gradual mobilization


  • Definitive treatment requires surgery and clipping of the aneurysm base, or endovascular treatment ...

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