Catheter venography measured transverse venous sinus pressure gradients as very high & stenosis. almost 30 in each. offered a stent. without a stent, where does this backed up blood go? how does it leave the head?

It can lead to brain swelling as the pressure forces blood to leave blood vessels(veins are thin wall and fluid can leak out of them, which is different from arteries where leaks really only happen with the artery wall ruptures.) It causes increased pressure in other veins and dilate them too as that blood attempts to flow elsewhere(collateral)