Subarachnoid space. Remember back to the spinal cord - when taking cerebrospinal fluid for a spinal tap, you are removing fluid from the subarachnoid space. The subarachnoid space of the spinal cord is continuous with the subarachnoid space around the brain, so you know that the patient must have had a subarachnoid hemorrhage. Subarachnoid hemorrhages are acute events, often caused by an aneurysm or a closed head injury. In the spinal cord, the epidural space is filled with fat, and the subdural space is really a potential space only - there is no fluid in this area. The cavernous sinus is a venous sinus of the brain, on the lateral surface of the body of the sphenoid bone.
