Epidural space

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Structure of the spinal cord seen from a dorsal view.

The term "epidural space" commonly denotes the area between the dura mater, the outermost layer of the spinal meninges, and the inner surface of the vertebral canal. However, the term is also used to describe the extradural space of the cranial cavity, which typically exists as a potential space. Thus, to distinguish between the two spaces, they are sometimes referred to as the spinal epidural space and cranial epidural space for the spinal and cranial regions, respectively.

The spinal epidural space is located between the tissues that line the inner surface of vertebral canal and the dura mater. This space is not continuous with the cranial epidural space. It extends cranially to the foramen magnum and is closed where the spinal dura merges with the rim of the foramen magnum. Caudally, it reaches down to the sacral hiatus and is sealed by the posterior sacrococcygeal ligament, which covers the sacral hiatus.

The spinal epidural space contains fat and loosely packed connective tissue which cushions the dural sac, venous plexuses, small arterial branches, spinal nerve roots, lymphatics, and fibrous bands called meningovertebral ligaments that attach the dura mater to the inner lining of the vertebral canal, anchoring it. This space serves as the injection site for anesthetic agents during childbirth and surgery to alleviate pain, a procedure known as epidural anesthesia.

The cranial epidural space is also called the dura-cranial interface. It lies between the inner surfaces of the cranial bones and the outer (endosteal) layer of the dura mater. It is typically not present, but can form under certain pathological circumstances such as when high pressure arterial bleeding from damaged meningeal vessels forces the endosteal layer to detach from the cranium, forming an epidural hematoma.