Vanishing vacuum disc phenomenon: A diagnostic key in spinal infection.

Objectives: Differentiating between pyogenic spondylodiscitis (SD) and degenerative disc disease (DDD) can be challenging due to overlapping clinical and radiological features. However, accurate distinction is critical to ensure timely and appropriate treatment and to avoid serious complications. This study aimed to identify imaging features that reliably distinguish pyogenic SD from DDD, including its erosive subtype, in clinical practice.

Methods: A total of 163 patients (mean age 62.43 years; 97 males) were evaluated between April 2007 and January 2024: 92 cases with SD (mean age: 67.03 years; 63 males) and 71 controls with DDD (mean age: 57.82 years; 34 males). This retrospective diagnostic accuracy study was conducted at a single centre, using pathogen-confirmed SD as the reference standard. Participants were selected from radiological and clinical databases. Imaging modalities included CT and MRI, with vanishing vacuum disc phenomenon (VVDP) assessed on CT scans obtained prior to the final diagnosis. Statistical comparisons were performed using Chi-squared and Fisher's exact tests.

Results: No significant differences were observed in the frequency of intervertebral gas between SD and DDD with or without erosive changes (27% vs. 39%, P = 0.137). 99% of SD cases had adjacent phlegmons or abscesses, but none of DDD cases (P < 0.001). Elevated C-reactive protein (CRP) and white blood cell (WBC) counts differentiated SD from DDD. In a subgroup of 19 subjects with repeated CT scans, VVDP showed 100% diagnostic accuracy in distinguishing SD (10/10) from DDD (0/9) (95% CI: 82.4-100%).

Conclusions: By integrating clinical, serological, and imaging findings, VVDP on repeated scans potentially offers a promising tool for earlier and more accurate diagnosis of infectious spinal conditions.