Can you please explain brain aneurysm and what are the symptoms?

Brain aneurysm. Brain aneurysm is an abnormal swelling of a brain blood vessel. Symptoms may be none, or caused by compression of adjacent brain wherever the lesion is located. If the aneurysm ruptures, headache is fairly universal and severe.
Dilated. One of the named arteries expands size relative to the remainder of that vessel or normal size.( there are many tiny blood vessels ) expansion may press on something and create symptoms. More dangerous is leak, of blood under pressure and damage to, brain by disruption of tissue, or hematoma and pressure. Severe headache!