Presentation
Sudden onset of headache.
Patient Data
Non-contrast CT brain followed by volume acquisition from the vertex to the aortic arch with dynamic administration of intravenous contrast.
Subarachnoid hemorrhage is demonstrated in the perimesencephalic cistern and extending into both sylvian fissures and the anterior interhemispheric fissure. No other areas of intracranial hemorrhage. No intracranial mass. Ventricles and sulci are age-appropriate.
A bilobed saccular aneurysm projects 4 mm anteriorly from the anterior communicating artery, measuring 2 mm across the neck and 4 mm across the dome. The remainder of the intracranial arterial circle of Willis is unremarkable, with no further aneurysms or vascular formation is detected.
Case Discussion
Although the pattern of blood in the cisterns is often helpful, it does not always accurately predict the location of the responsible aneurysm. In this case the prominent left sylvian fissure may make you favor a left MCA aneurysm rather than the discovered ACOM.
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