Extradural (epidural) vascular malformations

General

Also known as the retrocorporeal arcade, since it is located behind the vertebral body

The aorta gives off paired segmental arteries (A), with a dorsal branch (B) penetrating the neural foramen to supply structures inside the spinal canal, such as the “epidural arterial arcade” (C).
These are normally seen as diamond-shaped vessels; they provide a robust anastomosis between left and right segmental arteries.
On the venous side, the ventral epidural venous plexus “D” is extensively connected up and down along the spinal canal, and communicates via multiple foraminal arteries (E) with the paraspinal veins (large vertical blue cylinders).
The spinal bridging veins “F” connect the intradural spinal surface veins (G, H) with the extradural veins of the epidural venous plexus and foraminal veins.
The bridging veins are the critical conduit between intradural and extradural venous systems.

Reflux of venous outflow into the spinal veins, as seen in the diagram below.
For whatever unknown reason, some epidural fistulas either do not have sufficient venous outflow, or this outflow becomes occluded, as seen in the figure
Here, the fistula opens into a “venous pouch”, which has insufficient outside connections via the foraminal vein (E) for the degree of venous congestion. Because the epidural venous plexus is also connected to spinal veins (G) via the bridging vein (F), spinal congestion and its associated clinical sequela can follow.

This pouch is usually seen on MRI as a clue into the possibility of a extradural fistula, and also to identify its level.

Venous anatomy: many connections between components of the epidural plexus and with paraspinal veins outside the spinal canal via the foraminal veins (F). → spinal cord surface veins (G,H), remain unaffected despite their potential connection with the epidural plexus.

Extradural fistulas very occasionally on spinal angiography are incidentally diagnosed
Due to (see figure above)

Reflux of venous outflow into the spinal veins, as seen in the diagram below.
Because the pathophysiology (cord venous congestion) is the same as for the spinal dural fistula, the clinical presentation is similar also — progressive myelopathy, bowel-bladder issues, sensory changes, etc.

Most epidural hematomas are probably spontaneous venous hemorrhages rather than spinal extradural (epidural) fistulas

Compression of nerve roots and by venous engorgement
Vascular steal phenomenon: blood supply shunted away from the spinal cord and contributing to myelopathic symptoms.
EDH can occur in paeds