The scan shows the presence of water. Light is a high presence of water, dark is low.
Bones should generally be dark. You can see the problem - the fifth one up is quite white, and the disc looks a little squashed and misshapen. The 'hole' in the vertebrae under the disk is a Shmorl's node, apparently. These can form as the body grows, or as the result of an injury.
It is possible that I injured (fractured) my back, and this is the fallout.
Given that the pain is manageable, the alternatives are invasive and not without risk, and that there's little risk to leaving it for the intervening period, we decided that I should have a different type of scan shortly, and finally another MRI scan in 6 weeks to check progress.
So, no real conclusion as yet..