Non-aneurysmal subarachnoid hemorrage with right A1 hypoplasia of the circle of Willis

Case contributed by Roberto Pais


Male patient with severe sudden-onset headache associated with nausea and vomiting, started 12 hours earlier. No head trauma history.

Patient Data

Age: 40 years
Gender: Male

Axial cerebral CT without contrast enhancement shows unenhanced hyperdensity in the subarachnoid spaces affecting the interhemispheric fissure without flooding of the ventricles and without involving the basal cisternae.

T2 FLAIR shows hyperintense signal in the frontal and parietal sulci as well as in the anterior portion of the interhemispheric fissure.

In the DWI b1000 there's no evidence of ischemic or hemorrhagic pathology.

T2* shows no evidence of susceptibility inducing vascular lesions.

3D Time-of-Flight (TOF) angiography demonstrates a right A1 hypoplasia of the circle of Willis, but no other significant vascular abnormalities.

3D Phase Contraste (PC) venography shows no significant vascular abnormalities.

Case Discussion

These CT and MRI studies demonstrate a subarachnoid hemorrhage (SAH) with apparent involvement of the left cavernous sinus in CT (but apparently not reflected in the MRI), parietal and frontal sulci and interhemispheric fissure.

Also visible a right A1 hypoplasia of the circle of Willis, but no other significant vascular abnormalities were found in the arterial study (Time-of-Flight (TOF)) and venous study (Phase Contrast (PC)). 

85% of non-traumatic SAH are caused by aneurismal rupture and with basal cisternae involvement. 7% are caused by non-aneurysmal cause.

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