Extradural neural axis compartment
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At the time the article was created Frank Gaillard had no recorded disclosures.View Frank Gaillard's current disclosures
At the time the article was last revised Frank Gaillard had the following disclosures:
- Radiopaedia Australia Pty Ltd and Radiopaedia Events Pty Ltd, Director, Founder and CEO (Radiopaedia) (ongoing)
- Biogen Australia Pty Ltd, Investigator-Initiated Research Grant for CAD software in multiple sclerosis: finished Oct 2021 (past)
These were assessed during peer review and were determined to not be relevant to the changes that were made.View Frank Gaillard's current disclosures
Extradural neural axis compartment (EDNAC) exists from the tip of the coccyx all the way to the back of the globe, and yet it is relatively unknown as a concept. It is bounded externally by the periosteum of the vertebrae and sacrum inferiorly and the skull superiorly, and the visceral (meningeal) layer of the dura (dura propria/theca) internally.
The space contains veins (without valves), nerves and adipose tissue. The size of this space varies depending on the location. In the spine, the EDNAC is known as the epidural space and is capacious, filled with ample fat and epidural veins. Intracranially it is essentially non-existent in most parts as the two layers are closely apposed/fused. Where they separate the space is predominantly filled with veins forming the dural venous sinuses, including the cavernous sinus.
Anteriorly the space continues into the orbit with the dura propria forming the optic nerve sheath, and the periosteum flowing over the inner surface of the bones 1,2.
Understanding the relationship of the two layers of the dura is important:
- spinal epidural hematomas are within the EDNAC, whereas intracranial extradural hematomas are external to it (actually subperiosteal hematomas); note that intracranial hemorrhage within the EDNAC is exceedingly rare, sometimes known as intralaminar dural hematoma
- fat can be found anywhere in this space, accounting not only for the normal fatty epidural space in the spine and the orbital fat, but also not infrequent fatty falx and the presence of fat in the cavernous sinus