NBME 2 question

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There's a question about bilateral renal vein thrombosis with sparing of the left kidney. It asks for the collateral that allowed survival.

a. Left ovarian
b. Left 3rd Lumbar
c. SMV
d. IMV

From what I could find in similar discussions, most people are saying that the left ovarian "accomodates" the built up blood and prevents infarction of the kidney. I don't quite understand, given that 12.5% of CO is flowing through each kidney, how much blood will the varicose gonadal vein accumulate, and for how long? Is there some minor outflow from the gonadal plexus that is sufficient to maintain circulation?

I picked the left 3rd lumbar vein. Of course, this is an "offline" NBME, so I have no way of knowing what the real correct answer is. I was actually looking for the suprarenal vein/inferior phrenic vein option.

I know for a fact that lumbar veins can form collaterals between the renal veins and the hemiazygos vein. However wikipedia says it's the 2nd lumbar vein, so it comes back to the left ovarian theory.

This is what I could find:
http://forums.studentdoctor.net/arch.../t-189031.html (seems to say lumbar vein)
http://roentgenrayreader.blogspot.in...-pathways.html (says both lumbar and gonadal)
http://www.ncbi.nlm.nih.gov/pubmed/1940695 (says lumbar could be a normal variant)