What can cause clumping of caudal nerve roots without any compression from discs or bones etc. infection? inflammation? what most often causes those? thank you?

You do not describe your symptoms, and thus, do not know if you have a "cauda equina syndrome". The findings could be consequences of prior back surgery, myelograms, steroid injections, all causing chronic arachnoiditis, but infections, carcinomatous meningitis, miscellaneous inflammatory disease, spinal stenosis, might be considered. Discuss with your doctors, who know you best.