STUDY DESIGN. Consecutive study. OBJECTIVE. To investigate the changes of disc signal in intradiscal vacuum phenomenon during prolonged supine MR imaging. SUMMARY OF BACKGROUND DATA. Increased T2 signal on MR imaging in intravertebral vacuum cleft during prolonged supine positioning has been described, but no sequential observation of the intervertebral discal signal change in intervertebral disc vacuum. METHODS. Six women and 4 men (age range, 49-89 years; mean, 77 years) with low back pain and more than one level of intradiscal vacuum phenomenon underwent MR examinations at 0 minute, 1 hour, and 2 hours while remaining continuously supine. We recorded the original T2 signal intensity in the vacuum disc and subsequent alterations in the disc signals; they were scored 0 for signal void, 1 for equivocal or mild fluid intensity, or 2 for fluid signal intensity. RESULTS. Vacuum phenomena affected 31 of 60 intervertebral discs (T11-T12 to L5-S1). In 9 patients, the signal intensity of the vacuum content progressively replaced by hyperintense fluid occurred in 25 discs (81%) after prolonged supine positioning, mostly from L3 to S1 levels. The location of fluid signal was central in 20 discs (65%), anterior in 4 (13%), and posterior in 1 (3%). Signal intensity was unchanged in 6 discs (19%). Fluid signal intensity was linear shape in 9 discs (29%), homogeneous in 5 (16%), and mixed in 11 (35%). Overall scores were 8, 26, and 38 at 0, 71, and 161 minutes, respectively. CONCLUSION. After prolonged supine positioning, fluid-like signal could be identified among the intradiscal vacuum by using T2 MR images. This in vivo observation suggested the possible pathway of fluid diffusion from surrounding tissues into degenerative discs.
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