Hi origamidreams.
Well this is my take on this:
The patch of inflamed veins could be part of the increased blood supply
along with the growth of neurons in the explored area, in a process known as Neurongiogenesis- which is consistent with Endometriosis.
Endometriotic growths can create their own blood and nerve supply, providing the basis for an additional set of pain symptoms, independent of the main symptoms of Endometriosis.
When the Endometriotic growths are not detectable by Laparoscopy, a biopsy would be the only way to rule out Endometriosis 100%.
I suggest you look into this possibility, before moving to other investigations.
Now, in the event that a biopsy was indeed taken, which was not mentioned
in your post, please ignore my post at its entirety.
Let us know how things develop.
Best wishes,
Niko