Aneurysmal subarachnoid hemorrhage (modified Fisher grade 4) and bihemispheric anterior cerebral artery

Case contributed by Subash Thapa


Sudden onset altered level of consciousness. No history of hypertension.

Patient Data

Age: 50 years
Gender: Female

ASNR 2016: This case was submitted as part of the American Society of Neuroradiology (ASNR 2016) Case Of The Day competition, in collaboration with 

There is a hyperdense area of blood density along the interhemispheric fissures and the posterior horn of the bilateral lateral ventricles suggestive of subarachnoid hemorrhage. 

There is an irregular hyperdense area of blood density involving the parasagittal region of bilateral frontal horn with associated effacement of the bilateral frontal horn suggestive of intracerebral bleed.

Cerebral angiography shows a saccular dilation of artery measuring approximately 6x4 mm at the level of A2 bifurcation extending anteriorly and superiorly suggestive of saccular aneurysm.

Bihemispheric ACA with dominant left ACA.

Hypoplastic right P1 segment with right PCA origination for the prominent right PCoA suggestive of fetal origin right PCA.

Annotated images demonstrating relationship of aneurysm to surrounding vessels. 

Anatomical variants of ACA

Case Discussion

A bihemispheric anterior cerebral artery (ACA) is an anatomical variant with a hypoplastic A2 segment and dominant contralateral A2 segment supplying both ACA territories. The incidence is ~4.5% (range 2-7%).

Distribution of subarachnoid hemorrhage (SAH) according to location 1:

  • ACoA aneurysms: superiorly into the intrahemispheric fissure
  • MCA bifurcation: Sylvian fissure
  • internal carotid-posterior communicating artery (ICA-PCoA): suprasellar cistern
  • vertebrobasilar: fourth ventricle, prepontine cistern, foramen of magnum

Modified Fisher scale (SAH grading) 1:

  1. equates to no visible SAH or intraventricular hemorrhage (IVH)
  2. focal or diffuse thin (<1mm) layer of subarachnoid blood without IVH
  3. IVH
  4. focal or diffuse thick (>1mm) SAH without IVH
  5. IVH with thick SAH

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