What is the CSF-filled space between the arachnoid mater and pia mater that is continuous between the brain and spinal cord?

• A. Subdural space
• B. Epidural space
• C. Arachnoid mater
• D. Subarachnoid space

Answer: (D)

The space between the arachnoid and the pia that is filled with CSF is the subarachnoid space. This space forms a continuous sleeve around the brain and spinal cord, extending from the cranial cavity down through the spinal canal, so CSF can circulate around the entire central nervous system. It houses the CSF itself and the blood vessels on the brain and spinal cord surfaces. CSF moves from the ventricular system into this space through openings in the fourth ventricle and then is reabsorbed into the venous system via arachnoid granulations. The other two options aren’t spaces with CSF in normal anatomy: the subdural space lies between the dura and arachnoid and is a potential space; the epidural space lies outside the dura; and the arachnoid mater is a membrane, not a space.