Final answer:
The subdural space exists between the dura mater and arachnoid mater but is not filled with CSF, which is found in the subarachnoid space between the arachnoid mater and pia mater.
Step-by-step explanation:
The subdural space, referred to in the question, exists between the dura mater and arachnoid mater. This space can sometimes accumulate blood in cases of subdural hematoma, but it is normally a potential space rather than an actual space filled with fluid like the subarachnoid space. The subarachnoid space is the area where cerebrospinal fluid (CSF) circulates, providing a cushion and exchanging nutrients and wastes for the central nervous system (CNS). This space exists between the arachnoid mater and the pia mater, not the dura mater and ligamentum flavum, which are not adjacent to each other. The subdural space does not contain CSF; therefore, it is not a space that provides reliable anesthesia and analgesia nor is it easily found in all patients as a clearly defined anatomical structure.