The presence of a linear radiolucency in the disk space (vacuum phenomenon) is a typical finding of degenerative disk disease. It is often associated to other findings of degenerative disk disease such as disk space narrowing and endplate sclerosis. Gas in the disk space is rarely associated to disk space infection.
Reference
Chevalier X, Larget-Piet B: Vacuum sign in spondylodiscitis due to H aphrophilus. Ann Rheum Dis 1993 Jan;52(1):84.