• in each SAH patient, it is necessary to search for the source by examining the arterial circulation
  • CT angiography (as part of the usual initial imaging) is the primary diagnostic modality for aneurysm detection; 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
SAH caused by rupture of basilar apex aneurysm
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CT Angiography

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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 (but compared to CTA and DSA, MRA is less sensitive for the detection of small changes in aneurysm size)
  • MRI + MRA can detect 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)


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Aneurysm of the ICA siphon

SAH caused by PComm aneurysm
Aneurysm of the distal segment of 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 convexial 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 in 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 [Huttner,2006]

Non-perimesencephalic SAH

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Brain aneurysm diagnosis
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