- Diagnosis is made by the appearance of hyperdense blood in the subarachnoid space on non-contrast CT
- This may be widely distributed or more localised, which helps aid the site of a ruptured aneurysm:
Widely Distributed
Widely Distributed
- Within the basal cisterns, Sylvian and interhemispheric fissures
- Result classical "star sign" distribution with blood distributed around 'circle of Willi's and along basal vessels.
- Within the ventricular system
- Over the cortical sulci
Locally Distributed
Locally Distributed
- Sylvian fissure – suggests middle cerebral artery (MCA) aneurysm
- Interhemispheric fissure – suggests anterior communicating artery (ACA)aneurysm
- Perimesenchephalic - restricted to the interpeduncular region and not extending into the lateral Sylvian or interhemispheric fissures
- Usually not associated with an aneurysm but basilar aneurysms must be excluded