According to Dr. Reitzel at Empowher, intrathecal refers to a single injection that is administered through the spinal sack and into the cerebral spinal fluid, while epidural injections involve a catheter placed beside the spinal sack that is responsible for holding the cerebral spinal fluid. The difference lies not just in the technique implemented, but also in the length of time that the medications are administered for and can stay in the body. Intrathecal injections have a finite amount of time that they can stay in the body, whether it be for 30 minutes or over an hour; epidural catheters, by contrast, allow for the medications to be administered in a continuous manner without any disruptions.
Epidural catheters are normally placed between two vertebral disks so that the medications can flow into the extradural space. The medications administered diffuse naturally from the extradural space and through the dura mater to the cerebral spinal fluid, which is located in the intrathecal space. A lumbar puncture is typically required, and the medications are delivered by intermittent injections or by ambulatory infusion devices. Epidural ports may also be implanted subcutaneously for convenience, as these ports are portable and can limit the chances of infection.