Which space lies between the arachnoid mater and pia mater and contains circulating CSF?

• A. Epidural space
• B. Subarachnoid space
• C. Subdural space
• D. Interventricular space

Answer: (B)

The space between the arachnoid and pia mater that contains circulating CSF is the subarachnoid space. This layer of meninges forms a real gap around the brain and spinal cord in which cerebrospinal fluid circulates, providing cushioning and helping transport nutrients and waste. CSF is produced in the ventricles, flows into the subarachnoid space through openings of the fourth ventricle, and is reabsorbed into the venous system via arachnoid granulations. The other spaces—epidural (between bone and dura), subdural (between dura and arachnoid), and the intraventricular spaces within the ventricles—do not fit the description of a CSF-filled space between arachnoid and pia.