This chapter describes the microanatomy of the spinal cord that is relevant to intrathecal drug delivery started with covering of the spinal cord that are pierced to enter the intrathecal space. The dural sac is mostly constituted by the outer layer of dura and the inner layer called arachnoid membrane, which regulates diffusion of drugs into the intrathecal space. The pia matter surrounding the spinal cord is a permeable structure allowing the passage of drugs through intercellular spaces. The relationship between nerve roots, CSF, and subarachnoid catheters determines the passage of an intrathecal catheter which can cause damage to nerve roots and spinal cord. Multiple factors may be involved in the mechanisms of drug diffusion across the membranes of the spinal cord, as well as in their dilution with the CSF, which will lead to the final drug distribution and availability at nerve roots and the spinal cord.
Keywords: Arachnoid membrane; Cerebrospinal fluid (CSF); Drug delivery to the central nervous system; Dural sac; Intrathecal space; Nerve roots; Pia membrane; Spinal cord; Subarachnoid space.