Objectives: The aim of this study was to examine high-intensity zone (HIZ) characteristics on both T1- and T2-weighted sagittal magnetic resonance (MR) images, and to reveal their exact nature.
Materials: Seventy-three patients with low back pain and HIZs (identified on T2-weighted images) were included. Patients, aged 25-80 years (mean 51), were divided into two groups: the 'single-HIZ' group exhibited HIZs only on T2-weighted images, while the 'dual-HIZ' group exhibited HIZs on both T2-weighted and T1-weighted images. Tissue corresponding to the HIZ was harvested from surgery for analysis.
Results: Eighty-two discs were studied, from 39 patients with single HIZs, 30 with dual HIZs, and four with both in the posterior annulus. HIZ volume, volume ratio, and signal intensity on T2-weighted images from the dual-HIZ group were significantly greater. Surgery was able to successfully restore patients' ability in both groups, while conservative treatments were less effective for patients with dual HIZs. Histology revealed outer annular fissures invaded by granulation tissue in the single-HIZ group. In dual-HIZ discs, Von Kossa staining and CT scans showed more calcified or ossified lesions (94.1 vs. 0 %, P<0.001), and chemical analysis showed significantly higher calcium content.
Conclusions: HIZs on both T2- and T1-weighted images represent calcified tissue, possibly from a vertebral endplate. A new concept of dual HIZ should be defined.
Key points: • Conventional definition of an HIZ refers to T2-weighted images only. • Dual HIZs have greater HIZ volume, volume ratio, and signal intensity. • HIZs on both T2- and T1-weighted images represent calcified tissue. • Conservative treatments are less likely to be effective for patients with dual HIZs.
Keywords: Annular fissure; Calcification; Intervertebral disc; MRI; Spine.