Outside the dura
In the head, the epidural space is known as a potential space, which means that normally it does not exist. In rare circumstances, a torn artery (e.g. the middle meningeal artery) may cause bleeding which is sufficient to create epidural space; this is an epidural hematoma.
The space between the dura and the arachnoid (in both head and spine), the subdural space, is also a potential space.
Bleeding may also occur here.
In the spine, the epidural space (from Ancient Greek ἐπί, “on, upon” + dura mater also known as “epidural cavity”, “extradural space” or “peridural space”) is an anatomic space that is the outermost part of the spinal canal. It is the space within the canal (formed by the surrounding vertebrae) lying outside the dura mater (which encloses the arachnoid mater, subarachnoid space, the cerebrospinal fluid, and the spinal cord). In humans the epidural space contains lymphatics, spinal nerve roots, loose fatty tissue, small arteries, and a network of internal vertebral venous plexuses.
The cervical region is a much smaller epidural space and as such is less prone to infection. Generally, spinal epidural abscesses are more common in the lumbar area because it has a larger epidural space with more tissue prone to infection.