• in each patient with a subarachnoid hemorrhage (SAH), it is necessary to identify the source by examining the arterial circulation
  • CT angiography (as part of the usual baseline imaging) serves as the primary diagnostic modality for aneurysm detection in the acute setting; if negative, DSA is usually performed
    • in isolated perimesencephalic SAH (PMSAH), the cost-effectiveness of subsequent DSA is questionable  [Kalra, 2015]
  • a potential source of bleeding in the spinal cord should be excluded when SAH is localized to the posterior fossa
Clinical manifestation
  • asymptomatic
  • symptomatic
  • small: <12 mm (baby aneurysms < 3 mm)
  • large: 13-24 mm
  • giant: >25 mm    Giant aneurysm (27 mm)  Giant aneurysm of the carotid siphon (FLAIR and MRA)  Giant aneurysm of the carotid siphon
    • account for ~5% of all intracranial aneurysms; occur in the 5th-7th decade of life
    • typically cause mass effect and SAH
    • most commonly saccular in shape but can also be fusiform
    • increased incidence in the posterior circulation compared to non-giant aneurysms
Neck width
  • narrow neck: < 4 mm, or a pouch width to neck width ratio < 1
  • wide neck: > 4 mm, or a pouch width to neck width ratio >1
  • blister-like a broad-based bulge on a non-branching segment of a vessel Blister-like aneurysm on ICA
  • saccular (berry) Saccular aneurysm on AComA (CTA) Saccular aneurysm in the middle cerebral artery (MCA)
  • fusiform  Basilar artery fusiform aneurysm (CTA)  A fusiform aneurysm
    • dilated, tortuous arteries, often with atherosclerotic changes in the wall
    • may cause compression of surrounding structures (mass effect)
    • may contain intraluminal thrombi (risk of embolization or occlusion of distal arteries)
  • dissecting (false aneurysms)   A traumatic dissecting pseudoaneurysm of the ICA filled with emboli  Dissecting aneurysm in a patient with Ehlers-Danlos syndrome  Post-PTA dissecting aneurysm

    • usually the result of a wall disruption (dissection) with the formation of a false lumen
Localization Typical localizations of cerebral aneurysms
  • AComA (30 – 35%)
  • TICA (7.5%)
  • PComA (25%)
  • MCA bifurcation (20%)
  • basilar artery (5-7%)
  • posterior circulation arteries (5%)
  • atherosclerotic
  • non-atherosclerotic
    • congenital
    • hypertension
    • vasculitis/ vasculopathy
    • hereditary connective tissue disorders  (Ehlers-Danlos syndrome, Marfan syndrome)
    • trauma
    • iatrogenic (more common is a dissection with pseudoaneurysm formation)
    • flow-related (in the feeding arteries of an AVM)
SAH caused by rupture of a basilar apex aneurysm

CT Angiography

  • CTA sensitivity is ~ 95% for aneurysms > 5mm
    • sensitivity decreases with smaller aneurysms (< 5mm ~ 64-83%)
  • always evaluate MIP projections, 3D reconstructions, and source images
  • evaluation near the skull base (e.g., intraosseous part of the ICA) can be tricky
    • adjust the window parameters (width/level) accordingly
    • utilize methods to remove bone, such as subtraction (matched mask bone elimination) ) and manual or automated bone editing
  • CTA is suitable for screening at-risk groups and for monitoring asymptomatic or treated aneurysms  (AHA guidelines 2020)
  • in diffuse SAH with negative CTA, always proceed with DSA
    • with negative CTA, aneurysm detection on subsequent DSA is reported in 5% of cases
    • according to some reports, false-negative findings on CTA occur in up to 20% of cases  [Agid, 2009]
  • in convexial SAH, search for signs of vasculitis and perform DSA if CTA is negative
Fusiform aneurysm on basilar artery (CTA)

Aneurysm of the right MCA

A partially thrombosed aneurysm of the top ICA (CTA)
CTA - source images (SI) on the left, reconstruction (MIP) on the right

MRI and MR Angiography

  • intracranial MRA uses the time-of-flight (TOF) method;  3T scanners have higher sensitivity
    • sensitivity 85-100% for aneurysms > 5mm  [Sailer, 2013]
    • sensitivity decreases with aneurysms < 5mm (56%)
  • MRA is a suitable method for screening and follow-up (though, compared to CTA and DSA, MRA is less sensitive for detecting subtle changes in aneurysm size)
  • MRI + MRA can identify thrombosed aneurysms that DSA may miss and can help to assess the extent of thrombosis)
Aneurysm of the intracranial ICA segment

ICA aneurysm on MRA
ICA aneurysm on MRA

Digital Subtraction Angiography (DSA)


Content available only for logged-in subscribers (registration will be available soon)
Aneurysm of the ICA siphon

SAH caused by a PComA aneurysm
Aneurysm of the distal segment of the ICA

Images assessment

  • look for aneurysm(s) or other sources of bleeding
  • assess the type and location of the aneurysm (shape and size of the sac, type and width of the neck, vessel geometry, and relationship to the parent artery and surrounding branches)
  • exclude multiple aneurysms and other concomitant vascular malformations Vascular malformations
  • with multiple aneurysms (present in up to 15% of cases), estimate which aneurysm was the probable source of the current bleeding
    • location of the blood and shape of the aneurysm may help
      • GRE sequence may be helpful in SAH with negative CT (small or old SAH)  Subtle convexal SAH on MR GRE sequence
    • the most common findings in ruptured aneurysms are:
      • multilobular aneurysm
      • sac with irregular contour
      • aneurysm with a daughter sac
  • assess the overall intracranial vascular status:
    • the presence of vasospasms
    • the patency of the circle of Willis  (is the collateral circulation sufficient if occlusion of the feeding artery is required?)
    • the general condition of the intracranial circulation (atherosclerotic changes and stenoses in the access route and the feeding artery)
  • if occlusion of the feeding artery is considered, add functional tests
    • Matas test – manual compression of the artery with simultaneous injection of the contralateral ICA or ipsilateral vertebral artery to assess the functionality of the collateral circulation
    • Balloon Test Occlusion  (BTO) is more reliable because manual external compression is usually inadequate
      • should not be performed in acute SAH as heparinization is required during the procedure

Further procedures after negative initial examination

Perimesencephalic SAH

  • if CTA and DSA are negative, then repeat DSA is not needed Perimesencephalic subarachnoid hemorrhage (PMSAH)   [Huttner,2006]

Non-perimesencephalic SAH

  • source of bleeding is not found in 15-30% of SAH patients
  • in Sylvian and interhemispheric fissure SAH, the presence of an aneurysm is highly probable – false-negative initial examination may have the following reasons:
    • poor imaging quality, motion artifacts
    • incomplete examination
    • failure to detect aneurysm on standard projections
    • thrombotic occlusion of the aneurysm
    • vasospasms (VSP)
    • human error
  • indication and number of DSA examinations are discussed
    • the rate of aneurysm detection on repeat DSA is about 4-20%, and it is higher in cases with VSP on initial DSA  [Yu, 2012]   [Ringelstein, 2013]
    • the risk of false-negative DSA can be reduced using 3D DSA and oblique projections
  • indications for repeat DSA:
    • detection of vasospasms on the initial DSA or poor quality of the initial study
    • second DSA should be performed after 2-6 weeks (use TCD/TCCD to rule out vasospasms before DSA)
    • perform CTA/MRA (+ GRE sequence) instead of the third DSA
    • consider the potential source of bleeding in the spinal canal (in posterior fossa SAH cases)
Initially negative DSA (left), repeated DSA showing ACoA aneurysm (middle), post-embolization status (right).

You cannot copy content of this page

Send this to a friend
you may find this topic useful:

Brain aneurysm diagnosis
link: https://www.stroke-manual.com/brain-aneurysm-diagnosis/