I read carefully you query.
I think that diagnosis which is suspected is a radiologic diagnosis and you should not disturb about the low fat bone marrow
The disc herniated need some pain killer and if your son will be good he should do swimming.
To be sure your son should do bone marrow biopsy
which is not emergent but he should do because after that you all will be sure for diagnosis.
Wishing you and your son all best.