Final answer:
The term 'intrathecal' refers to procedures or substances that occur within the subarachnoid or subdural space, which is filled with CSF and cushions the central nervous system.
Step-by-step explanation:
The word intrathecal pertains to something occurring within the subarachnoid or subdural space. The subarachnoid space is an area between the brain and spinal cord filled with cerebrospinal fluid (CSF), which serves as a protective buffer for the central nervous system, aiding in its metabolic functions and providing cushioning against physical injury. By withdrawing a sample of CSF, clinicians can analyze the fluid for neuropathological and metabolic biomarkers relevant to various diseases.