Aneurysmal subarachnoid hemorrhage (modified Fisher grade 4) in a patient with bihemispheric ACA

Case contributed by Dr Subash Thapa


Sudden onset altered level of consciousness. No history of hypertension

Patient Data

Age: 50 yrs
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 s/o SAH.

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 s/o intracerebral bleed.

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

Bihemispheric ACA with dominant left ACA.

Hypoplastic right P1 segment with right PCA origination for the prominent right PCoA s/o fetal origin right PCA

Annotated images demonstrating relationship of aneurysm to surrounding vessels. 

Anatomy variants of ACA

Case Discussion

Bihemispheric ACA is the anatomy variant of ACA with hypoplastic A2 segment where contralateral A2 segment is dominant supplying both ACA territories; incidence of ~4.5% (range 2-7%) 

Distribution of SAH according to the location1

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, and foramen of magnum.

Modified fisher scale (SAH Grading) 1

0-      Equates to no visible subarachnoid or intraventricular hemorrhage

1-      Focal or diffuse thin (<1mm) layer of subarachnoid blood without IVH

2-       IVH

3-      Focal or diffuse thick (>1mm) SAH without IVH

4-      IVH with thick SAH


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Case information

rID: 40175
Published: 11th Oct 2015
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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