My husband is going through the same thing. He had spinal surgery and now has peripheral neuropathies and arachnoiditis. He has the tingling, numbness, weakness, etc in his legs too. Have you had an EMG and/or skin biopsy done? These 2 tests were done because the MRI's just weren't giving us enough answers. To me there was no reason why a seemingly healthy man of 45 was having these kinds of symptoms & pain
I'm not a doctor but isnt meningeal diverticula abnormal dilations of the nerves (nerve root cyst)? Its been my experience that anything impinging on the nerves, (such as a bulging disk thats flaired up) can cause your symptoms.
I also noticed you mentioned your B12 level. Have you ever had low B12? If you have, this can also be the problem. Once your B12 goes low a certain level, (subacute combined cord degeneration/pernicious anemia) the damage that is done is irreversible-even after your B12 levels come back to normal
Hope this helps or at least gives you an avenue to explore