Introduction: In spontaneous subarachnoid haemorrhage (SAH) accurate determination of the bleeding source is paramount to guide treatment. Traditionally, the bleeding pattern has been used to predict the aneurysm location.

Objectives: Here, we have tested a software-based tool, which quantifies the volume of intracranial blood and stratifies it according to the regional distribution, to predict the location of the ruptured aneurysm.

Methods: A consecutive series of SAH patients admitted to a single tertiary centre between 2012 and 2018, within 72h of onset, harbouring a single intracranial aneurysm. A semi-automatized method of blood quantification, based on the relative density increase, was applied to initial non-contrast CTs. Five regions were used to define the bleeding patterns and to correlate them with aneurysm location: perimesencephalic, interhemispheric, right/left hemisphere and intraventricular.

Results: 68 patients were included for analysis. There was a strong association between the distribution of blood and the aneurysm location (p < 0.001). In particular: ACom and interhemispheric fissure (p < 0.001), MCA and ipsilateral hemisphere (p < 0.001), ICA and ipsilateral hemisphere and perimesencephalic cisterns (p < 0.001), PCom and hemispheric, perimesencephalic and intraventricular (p = 0.019), and PICA and perimesencephalic and intraventricular (p 0.900) for these locations.

Conclusions: Regional automatised volumetry seems a reliable and objective tool to quantify and describe the distribution of blood within the subarachnoid spaces. This tool accurately predicts the location of the ruptured aneurysm; its use may be prospectively considered in the emergency setting when speed and simplicity are attained.