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Giant Cerebral Aneurysm

Last Updated: March 27, 2020

Open Table of Contents: Giant Cerebral Aneurysm

Figure 1: Axial nonenhanced CT image (top row left) through the suprasellar cistern in this 27-year old male patient demonstrates a large mildly dense parasellar mass with peripheral calcifications. The CT Angiogram (top row right) demonstrates this mass to have direct communication with the internal carotid artery (arrow) and to have an enhancement pattern identical to the opacified vessels in the brain, a characteristic that would be unusual for tumor. Conventional angiogram (middle row left) demonstrates the size and extent of this giant aneurysm and its communication with the elongated internal carotid artery. T1 (middle row right) and T2 (bottom row) weighted MRI images of this aneurysm (after pipeline stent placement) may also be easily mistaken for a mass with either hemorrhage or proteinaceous material, particularly given the T1 hyperintensity (arrow). In reality, this likely represents clotted blood within the aneurysm.


  • Cerebral aneurysms that measure > 2.5 cm
  • Typically, saccular aneurysms
  • More commonly located in the posterior circulation
  • Account for roughly 5% of all intracranial aneurysms


  • Two mechanisms of development
    • De novo at areas of defect in the internal elastic lamina
    • Evolve from smaller aneurysms that endure continued hemodynamic stress

Clinical Features

  • Symptoms
    • Depend on if ruptured at time of diagnosis
      • If ruptured: worst headache of life, meningismus, altered mental status, nausea, vomiting, and focal neurologic defects
      • If unruptured: depends on location and may include visual disturbance, headache, cranial nerve palsies and seizures
  • Age

    • Typically manifest during the fifth to seventh decades
  • Gender

    • Female > male
  • Prognosis

    • Depends on location and whether or not there is hemorrhage at the time of diagnosis
  • Associations

    • Advanced age, hypertension, tobacco use, arteriovenous malformations, connective tissue disorders (including Ehlers-Danlos, Marfan syndrome and autosomal dominant polycystic renal disease) and vasculitis


  • General
    • Well-delineated, round or lobulated mass
  • Modality specific

    • CT
      • Round or lobulated mildly hyperdense extra-axial mass
      • Peripheral calcifications
      • Often have associated subarachnoid hemorrhage
    • CTA

      • Helpful to characterize
      • Look for additional aneurysms (>20%)
      • Look for vasospasm
      • Contrast will not opacify any thrombosed portion of the aneurysm
    • MR

      • T1
        • Signal characteristics are variable with age of aneurysm thrombus and depends on the velocity/turbulence of the blood flow
      • T2/FLAIR

        • Hypointense
      • T2*/SWI/GRE

        • Hypointense
      • DWI

        • Look for restriction associated with ischemia/infarction from vasospasm related to subarachnoid hemorrhage
        • Thrombosed blood products within the aneurysm may also have restriction
      • Contrast

        • May see enhancement with slow flow
        • IRSPGR 3-D contrast images will often delineate abnormality as well as CTA or MRA
      • Conventional Angiography

        • Look for bleb at site of recent rupture or outpouching from aneurysm fundus which is concerning for focal wall weakness and increased risk of rupture
  • Imaging Recommendations

    • NECT + CTA for workup of subarachnoid hemorrhage
    • CTA for screening of high-risk population
  • Mimic

    • Depending on the origin, aneurysms most commonly mimic a meningioma or macroadenoma when located in and around the sella. Other locations of aneurysms may also mimic a tumor if the location appears parenchymal. Angiography will help identify the correct diagnosis.

For more information, please see the corresponding chapter in Radiopaedia, and the Subarachnoid Hemorrhage and Aneurysm chapter within the Cerebral Vascular Diseases sub-volume within the Neurosurgical Atlas.

Contributor: Sean Dodson, MD

DOI: https://doi.org/10.18791/nsatlas.v1.03.02.14


Hacein-Bey L and Provenzale JM. Current Imaging Assessment and Treatment of Intracranial Aneurysms. AJR. 2011; 196:32-44.

Mehta RI, et al. Giant Intracranial Aneurysm. Radiographics. 2010; 30(4):1133-38.

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