What is the definition or description of: subarachnoid hemorrhage?

Bleed around brain: When blood is seen in the subarachnoid space surrounding the brain, it is termed a subarachnoid hemorrhage. Blood in this area is most commonly seen on CT or MRI imaging of the head. The biggest concern would be the possibility of bleeding due to an aneurysm, although blood due to trauma is more common. In some cases where SAH is suspected, but not seen on CT scan; a lumbar puncture may detect.