When we think about the meninges, we also have to be aware of meningeal spaces.
One of these meningeal spaces is real. Two of these spaces are potential or pathologic
in nature. So, let’s take a look at the real meningeal space first. I've mentioned this earlier
to you. This is going to be the subarachnoid space which is highlighted in green and also
labelled for you. This space exists between the arachnoid and the pia mater. This is the
space that contains cerebrospinal fluid. Potential spaces form pathologically. We can have
an epidural space. This space would exist between the skull and the periosteal layer
if it happened to form. The other space would cause a separation of the arachnoid from the
meningeal layer of the dura mater. So that would be occurring in this area for example
right in through here where we have the arachnoid adherent to the darker gray dura mater.
If space developed between those areas, that would be subdural in nature. These spaces
will develop during a cranial hemorrhage for example. If there is an arterial bleed, you could
have an epidural hematoma. If there is a venous bleed, you could then have a subdural hematoma.