The High‐Intensity Zone: A Dynamic Inflammatory Hub in Lumbar Disc Degeneration

ABSTRACT

The lumbar intervertebral disc high‐intensity zone (HIZ), a focal hyperintensity within the annulus fibrosus on T2‐weighted magnetic resonance imaging, has garnered significant attention as a critical imaging biomarker in the pathological cascade of lumbar disc degeneration (LDD). This review systematically delineates the pathological basis of the HIZ and provides a comprehensive dissection of the molecular pathways it shares with LDD. while also summarizing recent advancements in artificial intelligence and multimodal imaging for enhancing HIZ detection and characterization. The HIZ is positioned as a “dynamic inflammatory hub” characterized by vascularized granulation tissue infiltration, nerve ingrowth, and a localized chronic inflammatory response following annular fissures. The molecular pathology involves a self‐perpetuating “inflammation‐matrix degradation” vicious cycle driven by cytokines (e.g., TNF‐α, IL‐1β) and matrix‐degrading enzymes (e.g., MMPs, ADAMTS), underscoring its central role in the chronicization of discogenic low back pain (DLBP). Although the HIZ exhibits high specificity for diagnosing DLBP, its utility is constrained by limited sensitivity, false positives, and a notable dissociation from clinical symptoms. Furthermore, a stratified and diversified therapeutic blueprint is outlined, ranging from physical ablation and nucleus pulposus replacement to biologic agents (e.g., platelet‐rich plasma), regenerative medicine (e.g., stem cell therapy), and cutting‐edge nanotechnologies. Moving beyond conventional morphology to integrate advanced diagnostic technologies is imperative. Looking forward, integrating molecular imaging, single‐cell omics, and precision medicine strategies to target the HIZ microenvironment offers a promising new paradigm for disrupting the “inflammation‐degeneration‐pain” cycle, restoring disc homeostasis, and achieving precise diagnosis and treatment of DLBP.

The HIZ, a dynamic inflammatory hub in lumbar disc degeneration, links inflammation‐degeneration‐pain; integrating advanced diagnostics and targeted therapies offers precise management for discogenic low back pain.

1. Introduction

The high‐intensity zone (HIZ), an imaging hallmark in the assessment of lumbar intervertebral disc degeneration, has garnered significant attention due to its potential association with discogenic low back pain. First systematically characterized by Aprill and Bogduk in 1992, the HIZ is defined as a focal area of high signal intensity within the annulus fibrosus on T2‐weighted MRI, typically exhibiting higher signal than the nucleus pulposus and being demarcated from it by a surrounding low‐signal rim [1]. Pathologically, the HIZ represents a fissure in the annulus fibrosus, through which nuclear material extrudes, inciting a localized inflammatory response accompanied by the ingrowth of vascularized granulation tissue and nerve endings [2]. However, HIZs are not exclusive to markedly degenerated discs; they can also be observed in discs with relatively preserved morphology. Bogduk postulated that low‐intensity zones might represent asymptomatic fissures that require activation to evolve into symptomatic HIZs, suggesting that the HIZ may serve as a sensitive marker for early annular injury. Epidemiological data further elucidate its distribution pattern: the reported prevalence of HIZ in the general population ranges from 28% to 59%, with a notable positional predilection [3, 4]. Posterior HIZs are far more common than anterior HIZs, and their preferred spinal levels differ distinctly. Anterior HIZs predominantly occur in the upper lumbar spine (L2/3–L3/4), whereas posterior HIZs are highly concentrated at the lower lumbar segments (L4/5–L5/S1), which bear the greatest biomechanical load. This distribution pattern clearly mirrors the gradient of biomechanical stress across the lumbar spine. Furthermore, the detection rate of HIZ demonstrates a significant age‐dependent trend, peaking in the 40–49 age group (approximately 24.2%) and showing a statistically significant correlation with the degree of disc degeneration [5, 6].

Lumbar disc degeneration (LDD) constitutes the core pathological process of spinal degenerative disorders, characterized by the loss of structural integrity and biomechanical failure of the intervertebral disc. Under physiological conditions, the disc maintains its shock‐absorbing capacity through the hydration of the nucleus pulposus. During degeneration [7, 8], however, the degradation of proteoglycans and subsequent water loss in the nucleus lead to diminished elasticity, coupled with the appearance of lamellar disruptions or fissures in the annulus fibrosus (Figure 1). This process is highly prevalent in the population and exhibits distinct patterns [9, 10]: high prevalence with a trend towards onset at younger ages, a highly segment‐specific distribution (primarily affecting the lumbar spine, especially the load‐bearing L4–L5 level), and modulation by risk factors such as obesity and occupational stressors [11, 12, 13]. LDD is not merely a morphological alteration but also an active molecular cascade [14]. The aberrant upregulation of inflammatory mediators (e.g., TNF‐α, IL‐1β) sensitizes nerve endings and activates matrix‐degrading enzymes, establishing a self‐perpetuating “inflammation‐degeneration‐pain” cycle. Consequently, LDD represents both an age‐related physiological phenomenon and a central driver of pathological low back pain.

FIGURE 1.

Representative MRI appearance of lumbar disc high‐intensity zone (HIZ). (A–C) Sagittal T2‐weighted MRI demonstrating a focal hyperintense signal within the posterior annulus fibrosus (arrow). (D) Axial T2‐weighted MRI confirming the localized high‐signal region in the posterior annulus (arrow).

The HIZ is not an isolated imaging phenomenon but rather a manifestation within the broader pathological continuum of LDD, with both entities exhibiting significant correlations across anatomical, pathological, and molecular dimensions. Radiographically, the presence of an HIZ is associated with key degenerative parameters, including nucleus pulposus degeneration (OR = 3.0), disc herniation/bulging (OR = 6.4), and increased disc angle [15]. Moreover, the predilection of HIZ for the L4/5–L5/S1 levels closely coincides with the regions most frequently affected by LDD. At the pathological and molecular levels, the infiltration of vascularized granulation tissue, aggregation of inflammatory cells, and disorganization of the collagen framework within the HIZ are intimately linked to annular fissures in the degenerative process [2, 14]. This local active lesion is characterized by a chronic inflammatory microenvironment (predominantly driven by TNF‐α, IL‐1β, IL‐6) and progressive matrix degradation (mediated by MMP‐3, MMP‐13, ADAMTS‐4/5, among others). These features position the HIZ as a unique “window” for investigating the molecular mechanisms underpinning LDD.

Therefore, this study will focus on the HIZ as an “active pathological locus” within LDD, aiming to systematically characterize its distinct molecular microenvironment. Our goal is to bridge fundamental pathological mechanisms of LDD with clinical precision medicine, thereby providing novel strategies for the early identification and targeted intervention of discogenic low back pain.

2. Literature Search and Selection Strategy

A structured literature search was conducted to identify studies relevant to the HIZ of lumbar intervertebral discs and its relationship with LDD, discogenic low back pain, inflammatory mechanisms, imaging diagnosis, and emerging therapeutic strategies. The PubMed database was searched from inception to October 2025, with the language restricted to English. Gray literature, including conference abstracts, dissertations, preprints, and non‐peer‐reviewed materials, was not included. To avoid missing seminal or cross‐disciplinary studies that were not captured by a single search formula, the electronic search was supplemented by manual screening of the reference lists of relevant reviews and included articles.

The search strategy was constructed around five thematic modules: (1) lumbar disc HIZ and annular fissure; (2) LDD and inflammatory microenvironment; (3) discogenic low back pain and diagnostic value; (4) MRI, multimodal imaging, radiomics, and artificial intelligence; and (5) conservative, minimally invasive, biologic, regenerative, and nanotechnology‐based treatments. The core PubMed search strategy is provided in the Supporting Information.

Two reviewers independently screened titles and abstracts, followed by full‐text assessment of potentially eligible articles. Disagreements were resolved by discussion or consultation with a third reviewer. Studies were considered eligible if they met one or more of the following criteria: (1) they investigated the definition, prevalence, classification, or imaging characteristics of lumbar disc HIZ; (2) they addressed the pathological basis of HIZ, including annular fissure, granulation tissue, neovascularization, nerve ingrowth, or inflammatory mediators; (3) they examined the association between HIZ, LDD, Modic changes, endplate defects, disc herniation, or discogenic low back pain; (4) they evaluated diagnostic techniques, including MRI, discography, quantitative imaging, multimodal imaging, radiomics, or artificial intelligence; or (5) they discussed therapeutic approaches relevant to HIZ‐associated disc degeneration or discogenic pain. Reviews, meta‐analyses, clinical studies, experimental studies, and key mechanistic studies were eligible.

The exclusion criteria were as follows: (1) studies unrelated to lumbar disc HIZ, LDD, discogenic low back pain, or relevant diagnostic and therapeutic strategies; (2) case reports with limited generalizability, unless they provided unique mechanistic or imaging evidence directly relevant to the review; (3) conference abstracts, dissertations, preprints, editorials without substantive data, and non‐peer‐reviewed literature; (4) articles with insufficient methodological or outcome information; and (5) non‐English articles.

In the initial PubMed search, 5599 records were identified. After title and abstract screening, 5385 records were excluded because they were unrelated to the topic, focused on non‐lumbar spinal disorders, or lacked relevance to HIZ/LDD mechanisms, diagnosis, or treatment. A total of 214 full‐text articles were assessed for eligibility, of which 164 were excluded because they were case reports with limited relevance, conference abstracts, non‐English articles, inaccessible full texts, or studies with insufficient methodological information. Finally, 87 articles were included in this narrative review, including 37 articles identified through manual reference screening (Figure 2).

FIGURE 2.

Literature search and selection flow diagram.

3. Dynamic Inflammatory Mechanisms in Disc Degeneration and HIZ: From Initiating Factors to Pain Chronicization

3.1. Initiating Factors and the Onset of Disc Degeneration

The extracellular matrix (ECM) of a healthy intervertebral disc, composed primarily of proteoglycans and collagen fibers, maintains a dynamic equilibrium between anabolism and catabolism. However, with advancing age and under the influence of various environmental stressors—such as smoking, abnormal mechanical loading, injury, and infection—disc cells mount a multifaceted cytokine response that initiates the degenerative cascade [10, 16, 17]. These factors first impinge upon the ECM, precipitating its structural disintegration [18, 19, 20, 21]: Nucleus pulposus cells exhibit diminished synthetic capacity (evidenced by suppressed SOX9 expression and downregulated proteoglycan [PG] synthesis), concurrently with a marked upsurge in catabolic activity. Enzymes including matrix metalloproteinases (MMP‐3/13), tissue inhibitors of metalloproteinases (TIMP), and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS‐4/5) are robustly activated, driving the degradation of collagen and proteoglycans [22, 23]. The ensuing loss of proteoglycans leads to nucleus pulposus dehydration [24], directly impairing its shock‐absorbing capacity and thereby shifting greater mechanical loads onto the annulus fibrosus. Subsequent disc height collapse can further exacerbate this aberrant biomechanical stress [25]. Concurrently, the collagen network becomes disorganized: the predominant elastic type II collagen is progressively replaced by rigid type I collagen, reducing the annulus fibrosus's toughness [26]. Supplementing this, MMP‐mediated degradation of collagen cross‐links disrupts the lamellar architecture of the annulus, culminating in the formation of radial micro‐tears.

These micro‐tears can propagate through the full thickness of the annulus fibrosus under continued mechanical stress. When a tear extends to the outer annulus, degraded materials from the nucleus pulposus (e.g., aggrecan fragments, collagen fragments) act as damage‐associated molecular patterns (DAMPs) [25]. By activating NF‐κB and MAPK signaling pathways within nucleus pulposus and annulus fibrosus cells, they spark a sterile inflammatory response. Disc cells subsequently secrete inflammatory mediators such as IL‐6 and PGE₂, and stimulate the production of chemokines [27, 28], which recruit immune cells—including M1 macrophages, neutrophils, and T lymphocytes—from the surrounding vascularized zones. Driven by Toll‐like receptor (TLR) and interferon signaling pathways, these infiltrating cells produce high levels of inflammatory cytokines, triggering a cascading inflammatory reaction [27, 29, 30]. Specifically, factors like TNF‐α and IL‐1β, released by macrophages and neutrophils, reciprocally activate disc cells: TNF‐α stimulates nucleus pulposus cells to overexpress MMP‐3/13, accelerating matrix dissolution [31], while IL‐1β drives annulus fibrosus cells to produce vascular endothelial growth factor (VEGF), promoting vascular ingrowth. Simultaneously, IFN‐γ secreted by T cells further amplifies the inflammatory signaling. The persistent stimulation by inflammatory cytokines leads to the excessive secretion of MMP‐3/13 and ADAMTS [32], resulting in the breakdown of collagen and proteoglycans. The resulting fragments, in turn, attract more immune cell infiltration, thereby establishing a vicious “inflammation‐matrix degradation” cycle that impedes tissue repair and collectively fosters a pathological repair microenvironment (Figure 3).

FIGURE 3.

The catabolic shift in intervertebral disc degeneration. A healthy disc maintains extracellular matrix (ECM) homeostasis. During degeneration, catabolic enzymes (MMPs, ADAMTS) are upregulated, leading to excessive degradation of key ECM components (e.g., collagen, proteoglycans). This results in loss of disc integrity and function, initiating the degenerative cascade.

3.2. Granulation Tissue Ingrowth and HIZ Formation

The intervertebral disc is inherently avascular, relying primarily on limited tissue diffusion for metabolite exchange. During degeneration, tissue injury and cellular proliferation exacerbate local hypoxia [33]. Hypoxia‐inducible factor‐1α (HIF‐1α), a master regulator of oxygen sensing, accumulates stably under low oxygen tension and activates downstream target genes, among which VEGF is one of the most critical effectors [1, 34]. In this context [35], VEGF binds to VEGFR‐2 on the surfaces of endothelial cells from the external annular vascular plexus and at the fissure site, inducing endothelial cell differentiation into tip cells. These tip cells extend filopodia to penetrate the ECM and secrete platelet‐derived growth factor‐B (PDGF‐B), recruiting pericytes to adhere to the nascent vessel walls, thereby forming a structurally initial vascular network [36].

Concomitantly, fibroblasts, guided by inflammatory chemokines such as transforming growth factor‐β (TGF‐β) and IL‐8, migrate to the injury site. Together with the neovessels, they constitute vascular‐rich granulation tissue [2]. The inflamed tear becomes filled with fluid or mucoid material [24], causing it to appear hyperintense on T2‐weighted MRI—this constitutes the pathological basis of the HIZ (Figure 4).

FIGURE 4.

Inflammatory signaling and immune cell recruitment in HIZ. Damage‐associated molecular patterns (DAMPs) activate Toll‐like receptors (TLRs), triggering intracellular signaling cascades (e.g., NF‐κB, MAPK) that drive the production of pro‐inflammatory cytokines (e.g., TNF‐α, IL‐1β). These cytokines amplify the local inflammatory response and recruit immune cells (e.g., macrophages, T cells), characterizing the inflammatory microenvironment of the HIZ.

3.3. Nerve Ingrowth and Aberrant Pain Mechanisms

Driven jointly by inflammation and vascularization, ECM degradation products (e.g., hyaluronan fragments) and inflammatory cytokines (e.g., IL‐1, IL‐6, TNF‐α) within the degenerated disc persistently activate resident immune cells (e.g., macrophages) [13, 37, 38]. This induces the upregulated expression of neurotrophic factors such as nerve growth factor (NGF) and brain‐derived neurotrophic factor (BDNF) in the disc. These factors bind to tyrosine kinase receptor TrkA and the p75 neurotrophin receptor (p75NTR) on nerve fiber surfaces, stimulating the expression of pain‐associated ion channels in dorsal root ganglia [36, 39] and promoting the ingrowth of sensory nerve axons (e.g., unmyelinated fibers expressing GAP‐43) along the paths of neovessels into the deeper layers of the disc [40]. In advanced stages of degeneration [41], nerve terminals formed within the nucleus pulposus or inner annulus fibrosus interact with locally aggregated mast cells and T lymphocytes (Figure 5).

FIGURE 5.

Hypoxia‐driven neurovascular ingrowth in disc degeneration. Disc degeneration creates a hypoxic microenvironment, stabilizing hypoxia‐inducible factor‐1α (HIF‐1α). HIF‐1α upregulates vascular endothelial growth factor (VEGF) expression. VEGF binding to its receptor (VEGFR) on endothelial cells promotes pathological neovascularization, which concurrently facilitates the ingrowth of sensory nerves, linking hypoxia to pain sensitization.

Through the release of algogenic substances like substance P (SP) and calcitonin gene‐related peptide (CGRP), they activate cation channels such as acid‐sensing ion channels (ASICs) and the transient receptor potential vanilloid 1 (TRPV1) [42]. Furthermore, NGF promotes the expression of neuropeptides like SP and CGRP, as well as acid‐sensitive nociceptive ASIC receptors, thereby lowering pain thresholds and enhancing nociceptive signal transmission [43]. Additionally, neovessels, granulation tissue, and macrophage infiltrates [2] can release inflammatory factors like PGE₂ and NO, directly activating the nerve endings of the sinuvertebral nerve outside the annulus fibrosus, initiating pain. Studies have further confirmed that TNF‐α expression levels are significantly higher in HIZ areas compared to normal annulus fibrosus, exacerbating pain transmission by sensitizing nerve endings. Consequently, the hyperintense HIZ region observed on MRI is not merely a marker of neovascularization and inflammation; it represents a “pain amplifier” where neurogenic inflammation and mechanical stimulation interact, ultimately leading to the persistence of chronic low back pain.

4. Association Between HIZ and Disc Pathology

The HIZ, an imaging marker for annular fissures, is intimately linked to the pathological progression of LDD. Histological studies confirm that HIZ regions correspond to areas of inflammatory granulation tissue infiltration, neovascularization, and nerve ingrowth within annular tears [44]. Their prevalence is significantly higher in severely degenerated discs, particularly those with Dallas Grade 3–5 fissures (according to the 1987 Dallas Discogram Description grading system [45], a Grade 3 or higher is considered abnormal). Meta‐analyses further demonstrate a statistically significant association between a positive HIZ and morphologically abnormal discs on discography (OR = 28.15, 95% CI: 7.38–107.46) [46, 47]. Furthermore, the extent of the tear correlates with the severity of pain. When a tear involves the outer one‐third of the annulus fibrosus (Dallas Grade 4), the presence of an HIZ shows high specificity (89%) for diagnosing a painful Grade 4 rupture, indicating that the HIZ is not merely a marker of structural damage but also a crucial indicator for identifying the source of pain [1]. This HIZ‐represented annular weakness or rupture forms the pathological basis for the extrusion of nuclear material. A multicenter cross‐sectional study by Teraguchi et al. revealed that the prevalence of extrusion‐type herniation was significantly higher in HIZ‐positive discs (37.9%) compared to HIZ‐negative discs (29.3%), confirming a significant association between HIZ and disc protrusion/extrusion (p < 0.01) [4, 15]. Other studies have observed a similar trend, with HIZ detected in approximately 38.8% of patients with disc herniation [48].

Beyond being a marker for annular tears, lumbar disc HIZ exhibits a distinct spatial relationship with endplate pathology. Studies indicate a significant spatial co‐occurrence between HIZ and endplate defects [49]. Notably, approximately 17.8% of endplate defects are accompanied by Modic changes (MC), and the dimensional measurements of these MC‐associated defects are significantly larger (p < 0.01) [50]. Within the dynamic process of disc degeneration, HIZ and MC demonstrate a specific evolutionary relationship: HIZ, as a typical manifestation of annular fissures, is often observed in earlier stages of degeneration, whereas MC is more closely associated with extensive disc fissures and advanced endplate damage [51]. Intriguingly, they often exhibit a “mutually exclusive” pattern at the disc level—although a correlation exists between HIZ and Modic type II changes, their actual co‐occurrence rate is relatively low, suggesting they may represent distinct phases of the degenerative cascade. HIZ, endplate defects, and MC (especially type II) frequently co‐localize within the same motion segment, collectively contributing to the pathological process of low back pain [49].

Furthermore, HIZ and MC act synergistically to exacerbate disc space narrowing through multiple pathways. On one hand, discs with HIZ exhibit a 42% reduction in T2 relaxation time, indicating substantial water loss and diminished load‐bearing capacity, leading to abnormal stress transmission to the endplates. On the other hand, MC‐associated pathological changes, such as ligamentum flavum hypertrophy, facet joint hyperplasia, and disc herniation (p < 0.05), contribute to secondary stenosis. Supporting this, the detection rate of Modic changes is significantly higher in stenotic segments (22.6%) compared to non‐stenotic segments (6.2%) (p < 0.001) [52], further validating their synergistic role. More importantly, endplate defects alter the mechanical microenvironment of the disc (e.g., causing aberrant stress distribution), inducing the upregulation of BMP2 expression and subsequently promoting calcification [53, 54].

5. Diagnostic Value and Controversies of HIZ in Discogenic Low Back Pain

The diagnostic utility of the HIZ as an imaging biomarker for discogenic low back pain (DLBP) is notably complex. A recent meta‐analysis [55] reported that HIZ has a sensitivity of 49% (95% CI: 0.37–0.61) and a high specificity of 89% (95% CI: 0.85–0.93) for diagnosing DLBP, with a positive likelihood ratio of 4.52 and a summary area under the curve (AUC) of 0.82. These findings indicate that while the low sensitivity limits its utility as a screening tool, the high specificity renders it clinically valuable for ruling out non‐painful degenerative disc changes. However, the positive predictive value of HIZ must be interpreted in the context of population baseline characteristics. A multicenter study (n = 637) [56] found that although the incidence of DLBP was significantly higher in the HIZ‐positive group (36.16%) than in the HIZ‐negative group (26.96%), nearly one‐third of individuals with a positive HIZ were asymptomatic. This underscores a central paradox: the HIZ primarily represents an imaging manifestation of Grade III or higher disc degeneration, rather than being directly equivalent to the pain generator responsible for LBP, suggesting that its association with LBP is likely indirect.

This indirect association underlies the core controversies regarding the diagnostic reliability of HIZ. The primary issue is false positives. Carragee et al. [57] reported a HIZ prevalence of 24% in asymptomatic individuals, while 24% of discs without HIZ showed a positive response on provocative discography. We hypothesize that this discrepancy may stem from the dynamic nature of HIZ formation: early annular tears that are not yet sufficiently vascularized may appear as false negatives on MRI, whereas HIZ formed during the repair phase due to granulation tissue hyperplasia might no longer be associated with active inflammation, leading to false positives.

The second controversy involves the ambiguous pathological significance of dual HIZ. A dual HIZ (hyperintense on both T1‐ and T2‐weighted images) often corresponds to annular calcification or endplate osteophytes, rather than the inflammatory granulation tissue characteristic of a single HIZ [58]. Calcified foci typically induce lower limb radicular pain (e.g., sciatica) via mechanical nerve root compression, contrasting with the characteristic chemical axial pain associated with a single HIZ. This distinction means that reliance solely on T2 hyperintensity can lead to misinterpretation of the pain mechanism, potentially impacting subsequent treatment strategies—for instance, a calcified HIZ may require neural decompression rather than anti‐inflammatory therapy.

The third controversy pertains to the spatiotemporal dissociation between imaging findings and clinical symptoms. Provocative discography, often considered the diagnostic “gold standard” for DLBP, further highlights the limitations of HIZ. Studies indicate that the pain reproduction rate in HIZ‐positive discs increases significantly only when the Dallas discogram grade is ≥ 3 (indicating a full‐thickness annular tear), whereas the mere presence of an HIZ does not reliably predict the source of pain [5, 59]. Furthermore, a subset of discs without HIZ can still elicit concordant pain on discography [60], emphasizing that a negative HIZ does not exclude DLBP.

Given these controversies, a nuanced understanding of HIZ morphological features is crucial for enhancing its diagnostic value. First, location matters: posterior HIZs (approximately 95% concentrated in the high‐stress regions L4/5 and L5/S1) show a significantly stronger association with DLBP (OR = 2.18) than anterior HIZs, likely due to their proximity to neural structures. Second, regarding morphological subtypes, the round shape is the most prevalent (anterior: 3.6%, posterior: 3.7%), far exceeding other forms like the vertical type (posterior: 1.6%) [4]. Finally, HIZ continuity reflects the extent of tissue damage and inflammatory activity: continuous multi‐slice HIZ (appearing on ≥ 2 consecutive sagittal slices) suggests more extensive annular injury and is associated with a significantly higher DLBP positive rate (58%) compared to single‐slice HIZ (48.6%), with a specificity reaching 89.1% [3] (Table 1).

TABLE 1.

Summary of epidemiological studies on the prevalence of lumbar high‐intensity zone (HIZ) and its clinical associations.

Authors	Years	Study designs	Sample sizes	Overall HIZ prevalence	Key findings from included studies
Sima et al. [15]	2024	Retrospective study	136 participants	41.9%	A high prevalence of HIZ (41.9%) was observed in patients with lumbar degeneration, where it was independently associated with disc herniation and nucleus pulposus degeneration. HIZ significantly increased the risk of low back pain, supporting its utility as an auxiliary indicator for assessing degeneration severity.
Yang et al. [46]	2023	Systematic review and meta‐analysis	5889 discs	28.6%	A positive HIZ indicates disc degeneration and annular fissures, showing a significant correlation with low back pain risk. However, its limited sensitivity precludes its use as a standalone diagnostic marker, necessitating multimodal assessment.
Wang and Hu [3]	2021	Retrospective cross‐sectional study	1188 participants	48.4%	HIZ serves as a sensitive marker for internal disc disruption (IDD). The presence of a continuous multi‐slice HIZ may be a reliable indicator for discogenic pain, requiring comprehensive evaluation that incorporates morphology (e.g., round/vertical type) and location (e.g., posterior).
Teraguchi et al. [61]	2020	Cross‐sectional study	1214 participants	59.1%	HIZ is a significant imaging hallmark of disc degeneration. Multi‐level posterior HIZs are strongly associated with severe low back pain and sciatica, supporting its role as a supplementary tool in clinical pain assessment.
Wang and Hu [56]	2018	Retrospective study	637 participants	31.55%	HIZ is a common imaging finding in lumbar degeneration, significantly correlated with age, body weight, and low back pain symptoms. However, its clinical value as a specific pain marker is limited. Future studies with larger samples and discography data are warranted to clarify its role in discogenic pain.
Tsuchiya et al. [4]	2016	Cross‐sectional study	814 participants	38.0%	This study was among the first to systematically classify HIZ in a large population and reveal its significant relationships with disc degeneration and Modic changes. Posterior HIZ may be an imaging marker of progressive degeneration, whereas anterior HIZ might reflect a distinct pathological mechanism.

In summary, the core diagnostic value of HIZ in discogenic low back pain lies in its high specificity (89%). This value is enhanced when the HIZ exhibits posterior location and continuous features, strengthening its correlation with patient symptoms. However, significant limitations remain, including its low sensitivity (49%), substantial false‐positive rate, and the observed dissociation between imaging findings and clinical manifestations. Therefore, HIZ cannot serve as a standalone definitive diagnostic criterion for DLBP [62]. Future research should focus on integrating detailed morphological assessment, inflammatory biomarker detection, and comprehensive clinical profiling to develop multimodal diagnostic models, thereby advancing towards precise diagnosis and personalized treatment for DLBP.

6. Advances in Diagnostic Techniques for HIZ

Conventional magnetic resonance imaging (MRI), particularly T2‐weighted imaging, exhibits limited sensitivity for detecting early‐stage HIZs, often failing to identify subtle lesions within the inner annulus fibrosus due to insufficient signal contrast on standard sequences. Notably, the detection rate of HIZ may be influenced by the magnetic field strength of the MRI system. Theoretically, low‐field‐strength MRI, characterized by reduced signal‐to‐noise ratio, poses challenges to spatial resolution and tissue contrast on T2‐weighted images; moreover, prolonged scan times increase susceptibility to motion artifacts, potentially compromising the identification of fine annular structures [63, 64]. A recent study by Lavrova and colleagues comparing image quality between 0.55 T and 1.5/3 T MRI for lumbar spine imaging demonstrated that although low‐field images generally met diagnostic criteria, the image quality scores for T2‐weighted sequences—the cornerstone sequence for HIZ diagnosis—were significantly lower than those obtained with high‐field MRI, particularly with respect to visualization of intervertebral discs and neural foramina [65]. Conversely, ultra‐high‐field (9.4 T) studies have indicated that higher field strengths improve interobserver agreement for disc degeneration grading, whereas 3 T MRI may carry a risk of overestimating the degree of degeneration [66]. Collectively, the ability to detect degenerative disc changes varies across magnetic field strengths, potentially affecting HIZ detection sensitivity. Accordingly, magnetic field strength should be considered a potential confounding factor when comparing epidemiological data across studies.

Beyond these technical factors, the HIZ appears on T2‐weighted MRI as a focal hyperintensity in the posterior annulus fibrosus, pathologically corresponding to infiltrating vascularized granulation tissue and associated inflammatory responses. Traditional diagnosis relies on visual assessment by radiologists, which is inherently subjective and carries a high risk of missed diagnoses. Although dynamic load‐bearing MRI (e.g., axial loading) can provoke the visualization of occult HIZs by simulating physiological load conditions, its clinical adoption remains limited due to procedural complexity and a lack of standardized protocols. With advances in radiomics and regenerative medicine, the precise diagnosis and targeted therapy of HIZ have emerged as key research foci.

6.1. Application of Deep Learning and Artificial Intelligence in Automated HIZ Detection

Deep learning and artificial intelligence are increasingly applied in medical image analysis, demonstrating significant potential for the automated identification and grading of HIZ. An improved YOLOv5 framework has been implemented for automated HIZ detection [67]. This model incorporates an attention mechanism (CSP module) and a residual structure (SPPF module), enhancing its ability to capture complex morphological features. Its strength lies in simultaneously identifying HIZs, grading disc degeneration, and detecting herniation from a single lumbar MRI scan, covering all common HIZ types. The model demonstrates excellent performance in both accuracy and recall for HIZ detection. This technology effectively addresses the challenge of detecting morphologically variable HIZs, providing clinicians with an efficient, standardized diagnostic tool that aids in identifying easily overlooked small lesions (e.g., HIZs in the axial plane), thereby promoting the evolution of disc degeneration assessment towards integrated multi‐task analysis [68].

Furthermore, since the HIZ serves as an indirect marker for annular fissures with limited sensitivity, it cannot fully represent the actual presence or location of a tear. Recent AI strategies have focused on extracting deeper information from conventional MRI to diagnose and localize the fissures themselves. Waldenberg et al. [10] developed a texture‐based AI approach validated against CT discography as the reference standard using 10‐fold cross‐validation. Their model achieved 100% sensitivity (94/94 fissured discs) and 97% specificity (28/29 non‐fissured discs) for detecting fissure presence, with 87% localization accuracy (90/104 discs). Critically, this performance was demonstrated on a clinically relevant cohort of 123 discs from 43 patients with discogenic pain—not on synthetic or simplified phantom datasets. This represents an important advancement: moving beyond HIZ as a surrogate marker to direct fissure mapping, enabling precision interventions targeting the true pain generator.

6.2. Integrated Application of Multimodal Imaging Techniques

With the progression of emerging imaging technologies in diagnostics, the application of multimodal imaging for the early detection and precise management of disc degeneration is gradually expanding [69]. Multimodal imaging techniques—such as PET/CT, PET/MRI, and quantitative MRI—overcome the limitations of single‐modality imaging by integrating anatomical, functional, metabolic, and quantitative biochemical information. PET/CT, combining glucose metabolism (FDG) and calcification activity (NaF) imaging, sensitively captures early inflammation and degenerative activity. Quantitative MRI techniques (e.g., T2 mapping, sodium MRI) non‐invasively quantify biochemical changes within the disc (e.g., proteoglycan loss, hydration status), providing objective diagnostic evidence for HIZ and early degeneration. The emerging PET/MRI synchronously combines metabolic (PET) and anatomical (MRI) information, significantly improving the precision of disc lesion classification and pain generator localization. This multi‐dimensional integrated strategy effectively addresses the diagnostic challenge of “non‐specific low back pain,” provides a comprehensive basis for targeted treatment decisions, and promotes the evolution of HIZ and intervertebral disc degeneration diagnosis towards a precision model integrating ‘structural‐functional‐molecular’ synergistic assessment.

7. Therapeutic Strategies for Disc Degeneration and HIZ

In recent years, a stratified and diversified therapeutic framework for managing discogenic low back pain associated with HIZ has begun to crystallize, encompassing strategies ranging from conservative treatment to regenerative medicine (Table 2).

TABLE 2.

Key therapeutic strategies for disc degeneration associated with High‐Intensity Zone (HIZ).

Therapeutic strategies	Core mechanisms/technical features	Key advantages/clinical values
1Basal anti‐inflammatory and conservative management	Multimodal analgesic regimen: COX‐2 inhibitors as first‐line, with neuromodulators for chronic pain. Biomechanical optimization: Core strengthening, postural control, and spinal stabilization exercises to reduce aberrant loading on annular fissures. Integrated non‐pharmacological interventions: Lifestyle modifications (weight control, activity modification, smoking cessation) combined with cognitive behavioral therapy.	Serves as the foundational tier of a stepped‐care paradigm. Provides symptom relief while improving biomechanical profiles; helps identify patients who may avoid immediate invasive interventions and establishes a baseline upon which escalated therapies can be built.
2Physical and minimally invasive interventions	Percutaneous endoscopic lumbar discectomy (PELD): Precisely removes herniated nucleus pulposus and clears inflammatory mediators/granulation tissue. Intradiscal radiofrequency ablation (RFA): Ablates nociceptive nerve endings and neovessels within annular fissures. Thermal annuloplasty: electrocoagulation promotes collagen contraction, stabilizing the damaged area.	Provides rapid analgesia by relieving nerve compression, eliminating inflammatory foci, and disrupting pain signaling pathways, enabling prompt symptomatic relief and structural stabilization.
3Nucleus pulposus replacement	Pre‐formed prostheses (e.g., PDN SOLO): Implants restore disc height and biomechanical function via hydration and swelling. Injectable substitutes (e.g., DASCOR): In situ curing seals annular fissures and prevents implant migration. Bioactive scaffolds (e.g., loaded with TGF‐β): Induce regeneration of nucleus pulposus‐like cells and promote matrix synthesis.	Achieves a combination of immediate mechanical support and long‐term biological repair, aiming for functional restoration beyond mere structural reconstruction.
4Biologic injection therapy	Platelet‐rich plasma (PRP): Rich in growth factors (PDGF, TGF‐β, VEGF); promotes tissue repair, modulates macrophage polarization, inhibits MMPs, and mitigates chronic inflammation.	Most studies report significant pain reduction (VAS scores) and positive effects on nerve healing, offering an effective alternative for patients unsuitable for surgery or pharmacotherapy.
5Regenerative and advanced therapies	Mesenchymal stem cells (MSCs): Promote repair via multiple mechanisms: differentiation into NP‐like cells, secretion of anti‐inflammatory factors (IL‐10, TGF‐β), and suppression of nerve ingrowth. Structured biomimetic nanoparticles (e.g., TMNP@SR): Macrophage membrane shell adsorbs inflammatory factors; rapamycin payload promotes M1‐to‐M2 polarization, concurrently suppressing inflammation and nerve sensitization.	Demonstrates profound potential for structural regeneration. Animal models show significant pain relief, reduced ECM degradation, and diminished inflammation, offering innovative strategies to disrupt the “inflammation‐degeneration‐pain” cycle.

7.1. Conservative Management and Basal Anti‐Inflammatory Therapy

For patients not requiring immediate interventional procedures, conservative management remains the cornerstone of initial treatment, focusing on symptom control and biomechanical optimization. Nonsteroidal anti‐inflammatory drugs (NSAIDs) are the most commonly utilized agents for acute low back pain. However, evidence indicates they confer only a modest reduction in pain intensity relative to placebo [70]. Cyclooxygenase‐2 (COX‐2) inhibitors are often preferred due to their theoretical gastrointestinal safety advantage over non‐selective NSAIDs, although the clinical significance of this difference remains debated.

Simultaneously, non‐pharmacological approaches encompass physical therapy and rehabilitation, comprising core muscle strengthening, postural control training, and spinal stabilization exercises. According to Hayden et al. (2021), these specific exercise modalities (such as Pilates and McKenzie therapy) are proven to be highly effective in alleviating pain and functional limitations [71]. Furthermore, lifestyle modifications—including weight management, avoidance of high‐impact activities, and smoking cessation—alongside cognitive behavioral therapy, contribute to functional recovery and enhanced quality of life [72].

7.2. Physical Ablation and Structural Stabilization Techniques

For cases requiring intervention, physical ablation techniques achieve rapid analgesia by precisely modulating the inflammatory microenvironment. Depending on the clinical presentation and the predominant pathoanatomical features, two main approaches can be considered either independently or in combination. Percutaneous endoscopic lumbar discectomy (PELD) [73] is employed to address mechanical compression and remove inflammatory foci; it utilizes a minimal incision to endoscopically resect herniated nucleus pulposus tissue, thereby relieving mechanical neural compression while concurrently and thoroughly removing inflammatory mediators, free nuclear fragments, and vascularized granulation tissue from the annular tear. Intraoperative bipolar electrocoagulation may be applied to the fissure for thermal annular sealing and hemostasis [74], promoting local collagen contraction to stabilize the damaged area.

Alternatively, or additionally, intradiscal radiofrequency ablation (RFA) [44] utilizes a bipolar radiofrequency probe to precisely ablate aberrant nociceptive nerve endings and residual neovessels that have grown into the fissure. When performed as a stand‐alone procedure, RFA offers a minimally invasive option for patients whose symptoms are predominantly driven by nociceptive nerve sensitization without significant mechanical compression. The therapeutic efficacy of such interventional approaches can be further substantiated by postprocedural imaging. As illustrated in Figure 6, a representative case undergoing intradiscal ablation demonstrated stable HIZ signal intensity on postoperative MRI, reflecting absence of further annular fissure progression and indirectly confirming maintained intradiscal pressure homeostasis without disease exacerbation, along with resolution of surrounding inflammatory changes. These imaging findings provide direct evidence of the intervention's ability to modulate the inflammatory microenvironment and restore disc homeostasis. These techniques work synergistically to repair the damaged structure and disrupt pain signaling pathways.

FIGURE 6.

Dynamic imaging changes throughout the disease course and treatment in a patient with degenerative disc disease accompanied by high‐intensity zone (HIZ) and Modic changes. (A) Preoperative T2‐weighted imaging shows disc degeneration at the L4/5 level, with a high‐intensity zone (HIZ) classified as type E in the posterior annulus fibrosus. During the phase of symptom exacerbation: (B) Modic changes have increased in extent; STIR imaging reveals extensive active inflammation at the inferior endplate of L4, which was identified as the primary source of pain and guided the decision to perform percutaneous disc ablation. (C) T2‐weighted imaging shows transformation of the HIZ to type A with increased signal intensity. (D) T2‐weighted imaging obtained 1 month postoperatively shows the HIZ has returned to type E. (E) At 1‐year follow‐up, T2‐weighted imaging demonstrates the HIZ remains type E with stable size, indicating sustained reduction in intradiscal pressure and favorable long‐term decompression outcomes.

7.3. Nucleus Pulposus Replacement and Structural‐Functional

Reconstruction Building upon ablation therapy, nucleus pulposus replacement (NPR) technologies focus on restoring disc structure and function. This approach involves the minimally invasive implantation of synthetic hydrogels or biocompatible materials to precisely fill the cavity left after nucleotomy, aiming to restore disc height and re‐establish normal biomechanical function. For instance, pre‐formed nucleus prostheses (e.g., PDN SOLO) can achieve mechanical integration with surrounding tissues post‐implantation via water absorption and swelling, and their viscoelastic properties mimic the load‐bearing and shock‐absorbing functions of the native nucleus [75]. Furthermore, injectable, in situ curing polyurethane nucleus substitutes (e.g., DASCOR) are delivered via a balloon catheter and solidify within the cavity, thereby sealing the annular fissure and preventing implant migration [76]. Additionally, the application of biodegradable scaffolds loaded with growth factors like transforming growth factor‐β (TGF‐β) can further induce the regeneration of nucleus pulposus‐like cells, promote proteoglycan synthesis, and restore matrix osmotic pressure and biological activity [77]. Such integrated interventional strategies not only provide immediate mechanical support and fissure sealing but also aim for long‐term biological repair, collectively advancing the therapeutic goal from structural reconstruction to functional restoration.

7.4. Biologic Injections and Regenerative Medicine Therapies

Within biologic injection therapies, platelet‐rich plasma (PRP) therapy, in particular, offers a biological pathway for disc repair. PRP is rich in various growth factors (e.g., PDGF, TGF‐β, VEGF) that can promote annulus fibrosus repair and stimulate the synthesis of key ECM components. Simultaneously, it modulates macrophage polarization, suppresses the expression of matrix metalloproteinases (MMP‐1/3), thereby mitigating chronic inflammation, and exerts positive effects on nerve healing, ultimately alleviating discogenic pain [78, 79]. Most studies report [80, 81, 82, 83] significant improvement in patient pain scores (VAS) following PRP injection, with some demonstrating sustained efficacy at long‐term follow‐up. Consequently, PRP can be considered an effective alternative therapy for lumbar degenerative conditions (especially discogenic pain), particularly suitable for patients reluctant to undergo surgery or those experiencing significant side effects from medications.

At the frontier of regenerative medicine, stem cell therapy demonstrates profound therapeutic potential for disc regeneration, leveraging its multidirectional differentiation capacity and sustained paracrine activity [84, 85, 86]. Mesenchymal stem cells (MSCs), as the core therapeutic vehicle, operate through a tripartite synergistic mechanism: differentiating into nucleus pulposus‐like cells to rebuild the ECM; secreting factors like IL‐10 and TGF‐β to suppress pain signaling and reduce nerve fiber ingrowth; and activating endogenous repair processes. Clinical studies confirm that stem cell transplantation can significantly improve patient pain (VAS) and functional disability (ODI). Future integration with genetic engineering, biomaterials, and precision medicine holds promise for overcoming current limitations and facilitating the broader application of stem cell therapies.

7.5. Advanced Nanotechnology Intervention Strategies

Even more groundbreaking progress stems from the application of structured nanotechnologies. For example, the advent of biomimetic nanoparticles (e.g., TMNP@SR) opens a new dimension for disease intervention [29]. This composite structure utilizes a macrophage membrane overexpressing TrkA as its shell, enabling specific adsorption of inflammatory cytokines and nerve growth factor. Concurrently, its rapamycin payload acts as an autophagy modulator, promoting the transition of macrophages from the M1 to the M2 phenotype. This regulatory mechanism not only suppresses peripheral inflammation but also blocks the processes of peripheral and central sensitization. Animal model studies show that the TMNP@SR treatment group exhibited significant recovery in mechanical and thermal pain thresholds, alongside reduced ECM degradation and inflammatory cell infiltration, offering a novel strategy for mitigating disc degeneration. Although this technology is currently validated only in animal models and its long‐term safety requires comprehensive evaluation, it undoubtedly provides an innovative perspective and strategy for treating lumbar disc degenerative diseases.

8. Conclusion

Future HIZ research must transcend the static morphological framework and focus on its role as a “dynamic inflammatory hub.” This entails deciphering the spatiotemporal evolution of its microenvironment—for instance, using single‐cell transcriptomics to unravel the cascade of macrophage polarization and neuro‐immune synaptic interactions within this niche. Diagnostically, challenges remain, such as the lack of real‐time inflammatory biomarker tracers for PET and the need for improved accuracy in quantitative MRI. On the therapeutic front, bottlenecks including the heterogeneous efficacy of PRP, the low survival rate of stem cells in the disc microenvironment, and the clinical translation of nanoparticles must be overcome. The ultimate goal is to disrupt the self‐perpetuating “inflammation‐degeneration‐pain” cycle and achieve the restoration of disc biomechanical homeostasis.

Author Contributions

Jingyi Cai: writing – review and editing. Sirui Zhou: investigation, supervision, resources, project administration. Qi Zhou: writing – original draft, writing – review and editing. Gang Wu: writing – review and editing. Yiyao Pei: methodology, conceptualization. Weijian Zhu: conceptualization, methodology. Liling Zhou: writing – review and editing.

Funding

The authors have nothing to report.

Disclosure

The authors have nothing to report.

Ethics Statement

Ethical approval was not required for this study because it only used publicly available, de‐identified datasets.

Consent

Consent for publication was not required for this study, as it did not involve any identifiable personal data, clinical images, or case details of individual participants.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Data S1: Supporting Information.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.