Final answer:
Subarachnoid haemorrhages typically result from ruptured brain arteries, visualized on CT scans as areas of high density due to blood accumulation, often accompanied by brain edema and displacement of structures like lateral ventricles.
Step-by-step explanation:
The likely origin of bleeding in subarachnoid haemorrhages is typically due to the rupture of an artery in the brain, often because of an aneurysm or trauma. The ruptured vessel leads to bleeding into the space between the brain and the surrounding membrane, specifically the subarachnoid space. This bleeding can be visualized using radiographic imaging such as a computed tomography (CT) scan, which shows areas of high density (appearing white) within the cranial vault where blood has accumulated. The bleeding may result in a hematoma, causing pressure on the brain tissue and potential displacement of brain structures, such as the lateral ventricles, as indicated by the presence of edema around the affected area.