The high-intensity zone (HIZ) in a lumbar intervertebral disc on T2-weighted magnetic resonance images has been associated with discogenic low back pain. However, its clinical significance remains uncertain. Histological studies reveal inflammatory changes surrounding the HIZ, suggesting a potential link to disc degeneration. Recent advancements in full-endoscopic spine surgery (FESS) have enabled more detailed intradiscal observations. The purpose of this study is to examine the characteristics of endoscopic findings in the HIZ.

Eighty-six patients who underwent FESS between January 2020 and August 2022 were investigated. We defined intradiscal bleeding and/or inflammation as “red annulus fibrosus” (RAF) and compared its occurrence between patients with HIZ and without HIZ. In 45 patients with HIZ, the ratio of the signal intensity of the HIZ to that of cerebrospinal fluid (the HIZ/CSF ratio) was compared according to RAF status.

RAF was observed in 54.7% of all patients, with a higher prevalence in those with an HIZ (73.3 vs. 34.1%, p < 0.01). The HIZ/CSF ratio was significantly higher in patients with RAF than in those without RAF (0.64 vs. 0.46, p = 0.03). The receiver-operating characteristic curve for the ability of the HIZ/CSF ratio to predict intradiscal bleeding had an area under the curve of 0.74, with a cutoff value of 0.48 providing 72.7% sensitivity and 66.7% specificity.

Intradiscal bleeding and inflammation were observed more often in patients with an HIZ, suggesting an association with degenerative changes. An HIZ/CSF ratio > 0.48 on preoperative magnetic resonance images may predict intradiscal bleeding.

Received: 13 March 2025

Accepted after revision: 30 March 2026

Accepted Manuscript online:
10 April 2026

Article published online:
13 July 2026

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