Abstract
Background Thoracic disc herniation extruding into the dorsal epidural space is exceptionally rare and is frequently mistaken for an epidural tumor, abscess, or hematoma. We aimed to characterize its clinicoradiological features, identify imaging features that may favor a disc fragment over a neoplasm, and report surgical outcomes.
Methods We retrospectively present 2 histologically confirmed cases treated by posterior decompression at our institution. To contextualize these cases, a focused literature review was performed, limited to thoracic-only cases, excluding cervical, lumbar, and other epidural pathologies that mimic this condition. The primary outcome (neurological recovery) was prespecified using the modified Frankel grade, with “complete recovery” defined as full motor strength (5/5) plus the patient’s preinjury independent ambulation.
Results The pooled cohort comprised 16 patients (14 men, 2 women; median age 56.5 years; T10–T11 most common, 38%). All presented with thoracic myelopathy, most with rapid neurological deterioration. In this highly selected cohort, posterior decompression was followed by neurological improvement in all reported cases, with no major complications. Documented complete recovery was identified in 5 of 16 patients (31%), using a conservative proxy definition, at a median follow-up of 4.5 months (range 0.1–30 months). Contrast enhancement (rim, peripheral, or diffuse) did not reliably distinguish disc fragments from tumor; features favoring a disc fragment were continuity with a degenerated disc space, absence of a dural tail, and absence of a homogeneous markedly high T2 signal.
Conclusions Dorsal thoracic disc extrusion should be considered when a posterior thoracic epidural mass causes acute or rapidly progressive myelopathy. In the reported thoracic cases, posterior decompression was followed by neurological improvement in all patients, but complete recovery was documented in only 31% under a conservative proxy definition. These findings remain limited by short follow-up, small sample size, level 4 evidence, and significant publication and selection bias.
Clinical Relevance A high index of suspicion for dorsal disc extrusion is warranted whenever a posterior thoracic epidural mass is encountered, even when imaging suggests neoplasm. Continuity with a degenerated disc space, absence of a dural tail, and absence of homogeneous markedly high T2 signal are clues that may support early surgical decompression when the clinical presentation is consistent with compressive myelopathy.
Level of Evidence 4.
- thoracic disc herniation
- dorsal epidural extrusion
- spinal cord compression
- posterior decompression
- mimicking tumor
Introduction
Thoracic disc herniation accounts for approximately 1% of all symptomatic disc herniations.1–3 Within this rare group, posterior migration of a sequestered fragment into the dorsal epidural space is even less common because the posterior longitudinal ligament and peridural membrane normally prevent such migration.4,5 Once these barriers fail in the thoracic spine, the extruded fragment can directly compress the spinal cord, producing rapidly progressive myelopathy that mimics other epidural pathologies.3,6,7
The diagnostic challenge lies in radiological resemblance to epidural tumor, abscess, or hematoma, which often delays surgery.8,9 A 2025 systematic review by Hamid et al provides the broadest synthesis of posterior disc migration to date, but it pools thoracic and lumbar cases.10 Because thoracic-level pathology compresses the spinal cord—not the cauda equina—prognosis and management considerations diverge meaningfully from the larger lumbar majority. The questions therefore remain: does the thoracic-only experience identify reliable distinguishing imaging features, and does the recovery profile after posterior decompression differ from mixed-level cohorts?
To address these gaps, we present 2 histologically confirmed institutional cases with detailed clinical, surgical, and outcome data, and we contextualize them with a focused review of thoracic-only published cases. The novelty of this work lies less in describing the entity itself—which has been reported sporadically for decades—than in (1) providing thoracic-specific recovery rates that are otherwise diluted by lumbar data and (2) proposing suggestive imaging features that may help separate dorsal disc fragments from true neoplasms. We also use the 2 institutional cases as an illustrative clinical observation regarding when fusion should be added to decompression.
Methods
Two Illustrative Cases
We retrospectively reviewed 2 consecutive cases of histologically confirmed dorsal thoracic disc extrusion treated at our institution. These were the only histologically confirmed cases of dorsal thoracic disc extrusion treated surgically at our institution during the study period. The Institutional Review Board approved the study (No. 3642), and written informed consent was obtained from both patients for the publication of this case series and any accompanying images.
Focused Literature Review
To contextualize the institutional cases, a focused review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement and was prospectively registered (PROSPERO CRD420251082183).
We searched MEDLINE/PubMed, Scopus, the Cochrane Central Register of Controlled Trials (CENTRAL), CiNii Articles, and Medical Online for English- and Japanese-language reports published between 1 January 1971 and 31 May 2025. Search terms included combinations of “thoracic disc herniation” with “posterior,” “dorsal,” “epidural,” “extradural,” “sequestrated,” and “extruded.” Citation chasing of included articles supplemented the database search.
We included reports describing radiologically or intraoperatively confirmed thoracic disc fragments occupying the dorsal/posterior epidural space. Studies were excluded if the herniation was confined to the cervical or lumbar spine, if the fragment was strictly ventral to the dura, or if the lesion represented an alternative pathology (tumor, abscess, hematoma, synovial cyst, or arachnoid web). Two authors independently screened titles, abstracts, and full texts; disagreements were resolved by discussion (Figure 1).
Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 flow diagram summarizing the literature search and study selection process.
The same standardized form was used to extract patient demographics, herniation level, presenting symptoms and duration, magnetic resonance imaging (MRI) and computed tomography (CT) features, surgical approach (decompression method, fusion, and dural repair), follow-up duration, neurological outcome, complications, and histopathology. Methodological quality was appraised with the Joanna Briggs Institute checklists.
Outcome Definitions
Because the original reports did not use a uniform outcome scale, we reconstructed neurological outcome using a prespecified proxy based on the modified Frankel framework. “Complete recovery” required both full motor strength (manual muscle testing 5/5 in all relevant muscle groups, when reported) and return to preinjury independent ambulation; cases lacking sufficient motor or ambulatory detail were not upgraded to complete recovery. “Improvement” was defined as any 1-grade or greater gain in modified Frankel grade or an unequivocal narrative description of motor or sensory improvement. When original publications reported only narrative outcomes, the published narrative was mapped to the closest grade category by 2 authors independently, with disagreements resolved by discussion. Outcomes derived in this way are presented as proxy estimates and are subject to ascertainment bias, which is acknowledged in the Limitations.
Synthesis
A formal meta-analysis was not appropriate given heterogeneous outcome reporting. Continuous variables are summarized as median (range) and categorical variables as count (percentage). Because the sample is small and reporting biased, no inferential statistical test was applied to demographic distributions; observed proportions are reported descriptively only.
Case Presentations
Case 1: Posterior Decompression With Instrumented Fusion
A 58-year-old man developed sudden lower thoracic discomfort that progressed over 24 hours to bilateral lower-extremity paresis (manual muscle testing 1/5). T2-weighted MRI showed a dorsal epidural soft-tissue mass at T7–T8 with severe cord compression (Figure 2a and b). Because the mass extended over more than 1 segment with substantial laminar resection planned, posterior decompression with T7–T8 instrumented fusion was performed. T7 total laminectomy with T6–T7 and T7–T8 ligamentum flavum removal allowed delivery of the fragment; complete excision was confirmed intraoperatively by ultrasonography. Pedicle screws were inserted at T7 and T8 under image guidance, and postoperative radiographs demonstrated satisfactory implant position (Figure 2c and d). Postoperative T2-weighted MRI confirmed adequate decompression (Figure 2e and f). Histopathology demonstrated degenerated nucleus pulposus consistent with disc herniation (Figure 3).
Preoperative and postoperative radiological findings in case 1. (a and b) Preoperative sagittal and axial T2-weighted magnetic resonance images (MRIs) show a soft tissue mass in the dorsal epidural space at T7–T8 (arrowheads), causing severe spinal cord compression. (c and d) Postoperative anteroposterior and lateral radiographs show satisfactory T7–T8 instrumented fusion. (e and f) Postoperative sagittal T2-weighted MRIs confirm adequate decompression.
Histopathological findings in case 1. (a) Macroscopic view of the excised mass. (b) Photomicrograph showing degenerated fibrocartilaginous tissue consistent with a sequestered disc herniation (hematoxylin and eosin staining). Scale bars = 1000 μm (a) and 100 μm (b).
Motor function began to recover on postoperative day 1; standing rehabilitation was initiated by day 9. The patient was transferred to a rehabilitation facility on postoperative day 11. At 15-month follow-up, the patient ambulated independently and had returned to driving. Strength was 5/5 in iliopsoas, quadriceps, tibialis anterior, and triceps surae; mild residual deficit (extensor hallucis longus 3/5; flexor hallucis longus 4+/5) and residual sensory disturbance below T8 persisted. He reported gradual improvement in plantar sensation over the following months, maintained independent ambulation, and resumed his usual occupational activities. By the prespecified definition, this result represents “good improvement” but not “complete recovery.”
Case 2: Posterior Decompression Without Fusion
A 55-year-old man with poorly controlled diabetes (glycated hemoglobin 11.6% at admission) had a 1-month history of progressive right lower-extremity weakness that decompensated acutely into bilateral paraparesis. Glycemic control was first optimized at a regional hospital before referral. Contrast-enhanced MRI showed a strongly enhancing left posterolateral epidural mass at T7–T8 with associated intramedullary T2 hyperintensity (Figure 4a and b). On noncontrast sequences, the mass was hypointense on both T1- and T2-weighted images (Figure 4d), and CT showed a vacuum phenomenon in the degenerated T7–T8 disc continuous with the lesion (Figure 4c); no dural tail or diffusion restriction was present. In retrospect, these features—disc-space continuity, absence of a dural tail, and absence of markedly high intralesional T2 signal—favored a sequestered disc fragment over the suspected neoplasm. The lesion was preoperatively favored to be meningioma or nerve-sheath tumor. Because the mass appeared focal and discrete, with no preoperative biomechanical concern and no extensive bony resection required, T7–T8 laminectomy with left partial foraminotomy was performed without instrumentation. Intraoperatively, a 1-cm well-demarcated mass was found in the dorsal epidural space; the capsule ruptured during attempted en-bloc resection, revealing atheromatous “gruel-like” contents typical of degenerated disc material. No instrumentation was used. Histopathology confirmed a sequestered intervertebral disc fragment, with negative S100, SOX10, and SSTR2 immunohistochemistry excluding nerve-sheath tumor and meningioma (Figure 5).
Radiological findings in case 2. (a and b) Preoperative sagittal and axial contrast-enhanced T1-weighted magnetic resonance imags (MRIs) show a strongly enhancing epidural mass in the left posterolateral spinal canal at T7–T8 (arrowheads); no enhancing dural tail is present. (c) Preoperative sagittal computed tomography shows a vacuum phenomenon within the degenerated T7–T8 disc. (d) Preoperative sagittal T2-weighted MRI shows the mass to be hypointense (arrowhead). (e and f) Postoperative sagittal and axial T2-weighted MRIs confirm adequate cord decompression at the operative level (arrowheads), with residual intramedullary signal change.
Histopathological findings in case 2. (a) Macroscopic view of the excised mass. (b) Photomicrograph showing degenerated fibrocartilaginous tissue, confirming a sequestered intervertebral disc (hematoxylin-eosin staining). Scale bars = 1000 μm (a) and 100 μm (b).
Bilateral lower-limb pain improved immediately after surgery. At 6-month follow-up, the patient ambulated with a walker; strength was IP 5−/4+, QF 5−/4+, TA 5/5−, and EHL/TS/FHL 5/5; severe loss of pain and temperature sensation persisted below T6/T7, although light touch was preserved. He had no urinary incontinence. At the most recent follow-up, approximately 11 months postoperatively, motor strength had improved further (IP 5/5−, QF 5/5, and TA 5/5), and daily function had gradually improved, although the patient remained dependent on a walking aid and residual loss of pain and temperature sensation below T6/T7 with gait instability persisted. Standing thoracic radiographs showed no kyphotic deformity or instability despite the noninstrumented decompression, and follow-up MRI confirmed durable cord decompression with a residual cranial disc protrusion and persistent intramedullary signal change (Figure 4e and f). By the prespecified definition, this represents “improvement” but not “complete recovery.”
Why the 2 Surgical Approaches Differed
The 2 cases illustrate that the decision to add instrumented fusion is driven by the extent of bony decompression and segmental stability concerns, not by the disc pathology itself. In case 1, total laminectomy at the apex of a multisegment thoracic kyphosis raised concern for iatrogenic instability, prompting fusion. In case 2, focal hemilaminectomy with partial facetectomy removed less than 30% of the facet and was judged biomechanically tolerable without fusion. Neither approach was chosen for, or constrained by, the disc pathology per se.
Results
Cohort
Database screening and citation chasing identified 14 eligible patients in 14 published reports; combined with our 2 cases, the analytic cohort comprised 16 patients (Figure 1).
Demographic and Clinical Features
Men accounted for 14 of 16 reported patients (87.5%), suggesting male predominance in the published cases; however, this estimate is vulnerable to reporting and selection bias. The median age was 56.5 years (range 47–81). All patients presented with thoracic myelopathy, usually with rapid neurological deterioration culminating in severe paraparesis or paraplegia. Symptom duration varied widely (range 0–150 days), but onset was acute in 9 patients (56%) who presented within 1 week. Herniations clustered at the lower thoracic level: T10 to T11 (n = 6, 38%), T7 to T8 (n = 4), T9 to T10 and T11 to T12 (n = 2 each), and T6 to T7 and T12 to L1 (n = 1 each; Figure 6).
Bar chart of the anatomical distribution of herniation levels in the 16-patient cohort, with T10–T11 being the most frequent level (38%, n = 6).
Imaging
On MRI, lesions were hypointense (n = 9 of 14) or isointense (n = 5 of 14) on T1-weighted imaging. T2 signal was variable and was reported as hyperintense in 11 of 16 cases; however, the available descriptions generally did not permit reliable grading of signal intensity relative to cerebrospinal fluid, tumor, or the adjacent disc space. Gadolinium enhancement was reported in all 10 contrast-enhanced cases: rim (n = 4), peripheral (n = 4), and diffuse (n = 2). CT (n = 9) detected no calcification. Three radiological features clustered in the disc-fragment cases and may raise suspicion for a disc fragment rather than a true neoplasm: (i) continuity with a degenerated disc space, evident on either MRI or thin-section CT; (ii) absence of an osseous- or dural-attachment “tail” (in contrast to meningiomas); and (iii) relative T1 isointensity to the disc space and absence of homogeneous, markedly high T2 signal disproportionate to the adjacent disc space (in contrast to most schwannomas; Table 1).
Baseline demographics and preoperative findings in the included cases.
Treatment and Outcome
All 16 patients underwent posterior decompression; none received conservative treatment. The standard procedure was laminectomy or laminotomy with discectomy, with partial facetectomy in 3 cases and instrumented fusion in 3 cases (19%). No major complications occurred. In this highly selected published cohort, neurological improvement was uniformly observed (16/16). Documented complete recovery was identified in 5 of 16 patients (31%) using our conservative proxy definition, and the remaining 11 (69%) showed partial or good recovery. The median follow-up duration for the 12 patients with available data was 4.5 months (range 0.1–30; Table 2).
Summary of treatment details and postoperative outcomes by study.
Risk of Bias
All included studies were case reports or small case series (level 4 evidence); therefore, the synthesis carries inherent publication and selection bias risks that are addressed in the Discussion.
Discussion
Key Contributions
This focused analysis adds 2 elements not directly available from prior mixed-level reviews: a thoracic-only recovery profile and suggestive imaging features that may help separate dorsal disc fragments from epidural tumors preoperatively; the 2 institutional cases additionally illustrate when fusion is added to decompression. Because the entity has been recognized for decades, the contribution is the thoracic-specific outcome estimate and the imaging clues, both based on level 4 evidence and requiring prospective validation.
Why the Recovery Rate Matters and Why It Must Be Cautiously Interpreted
A recent comprehensive systematic review reported a 74.9% complete-recovery rate for posterior disc migration overall.10 That figure was driven by predominantly lumbar pathology with only 10 thoracic cases; we observed 31% complete recovery in 16 thoracic patients (all 16 had at least some improvement). The most plausible explanation is that direct spinal-cord compression—as opposed to cauda-equina compression—imposes a lower ceiling on recovery, even when adequate decompression is achieved early. The lower thoracic-specific rate therefore reflects underlying biology, not inadequate surgery. We note that the universal-improvement rate observed across published thoracic cases is almost certainly inflated by positive-outcome publication bias inherent to the case-report literature, and the “100% improvement” signal should not be read as a precision estimate of biological efficacy.
That said, this estimate must be read with substantial caveats. Median follow-up was only 4.5 months (range 0.1–30 months). Recovery from spinal cord compression frequently continues for 12 months or more, and the 31% figure will likely increase with longer observation. Consistent with this, both of our institutional cases—now followed for 15 and approximately 11 months—continued to gain motor strength beyond the early postoperative period, yet neither reached complete recovery under the prespecified definition, in keeping with a lower recovery ceiling after direct spinal-cord compression. The “complete recovery” bar is also not used uniformly across the literature; we attempted to mitigate this variability by prespecifying a single definition and remapping narrative outcomes, but residual ascertainment bias remains. Finally, the available cases are by definition the operated cases. The denominator—the unknown number of dorsal disc fragments mistaken for tumor and treated by other means or never operated—is inaccessible to retrospective synthesis. Pooled rates of “improvement after surgery” therefore cannot be extrapolated to “improvement after a posterior thoracic epidural mass.”
Imaging Features That May Raise Suspicion for a Disc Fragment
Rim enhancement is the radiological feature most often emphasized in case reports and was indeed present in 4 of the 10 contrast-enhanced cases. However, rim enhancement also occurs in abscess, neoplasm, and resolving hematoma, so it is not specific. The 3 additional features noted above—disc-space continuity, absence of a dural tail, and absence of markedly high intralesional T2 signal—are not pathognomonic and lack a formal neoplasm control cohort here; they are therefore hypothesis generating, intended to support suspicion rather than replace tissue diagnosis. Their joint presence in a dorsal thoracic epidural mass with rapidly progressive myelopathy may, however, favor early decompression over biopsy, as case 2 illustrates in retrospect. CT was insensitive to microscopic calcification in 1 published case15; therefore, CT cannot reliably exclude a calcified disc fragment.
Surgical Strategy: When to Add Fusion
Among 16 patients, only 3 (19%) received instrumented fusion. The 2 institutional cases illustrate the decision criteria: instrumented fusion was added when total laminectomy at the apex of a thoracic kyphosis raised concern for postoperative kyphotic decompensation (case 1), whereas hemilaminectomy with limited facet violation (<30%) was deemed biomechanically tolerable without fusion (case 2). The available cases support, at most, a selective approach to fusion: instrumentation appears most defensible when the extent of bony decompression, kyphotic alignment, or pre-existing instability raises concern for postoperative instability. The pathology itself does not require fusion.
Implications and Future Directions
First, dorsal disc extrusion belongs on the differential for any posterior thoracic epidural mass; misdiagnosis rates as high as 60% have been reported.9,24 Second, the posterior approach is appropriate; broader evidence likewise supports posterolateral over anterior approaches for thoracic disc disease in general.25 For lesions that are clearly adherent to the dura or calcified, laminectomy without forced fragment removal may mitigate the risk of dural injury or cord manipulation.26 Third, prospective registries with standardized outcome measures (e.g., modified Frankel grade), minimum 12-month follow-up, and explicit reporting of misdiagnosed cases would substantially advance the field. Finally, the role of full-endoscopic and tubular techniques warrants formal evaluation.19
Limitations
This study has several limitations beyond the inherent constraints of pooled case-level data. First, no standardized outcome measure was used in the original reports; we partially mitigated this by prespecifying a single definition of complete recovery, but residual misclassification cannot be excluded. Second, the median follow-up of 4.5 months is short relative to the trajectory of myelopathy recovery; the reported 31% complete-recovery rate is therefore an underestimate. Third, we cannot define the denominator: cases of dorsal disc fragment misdiagnosed as tumor and managed differently—or never operated—are not captured in any published case-level synthesis. Fourth, the 2 institutional cases used different surgical strategies (laminectomy with fusion vs without) and were pooled with the literature for descriptive purposes; we have explicitly addressed the biomechanical rationale for that difference in the Case Presentations and Discussion. Fifth, the proposed distinguishing imaging features are derived from a small, retrospective cohort and require prospective validation.
Conclusion
Dorsal thoracic disc extrusion is rare, has been followed by neurological improvement after posterior decompression in the reported literature, and most often presented in middle-aged to older men in the available reports. Although the entity itself is well known, this thoracic-only synthesis clarifies that (1) documented complete-recovery rates after spinal-cord compression appear substantially lower than those reported for the predominantly lumbar mixed-level literature, (2) continuity with a degenerated disc space, absence of a dural tail, and absence of homogeneous markedly high T2 signal are suggestive features that may favor a disc fragment over an epidural neoplasm, and (3) the decision to add instrumented fusion should probably be individualized according to the extent of bony decompression, alignment, and segmental stability rather than the diagnosis of disc extrusion alone. These findings derive from level 4 evidence; longer prospective follow-up with standardized outcome measures and explicit reporting of misdiagnosed cases is required to refine the recovery estimate and validate the proposed imaging features.
Acknowledgments
The authors would like to thank Dr. Junzo Fujitani for his valuable suggestions and critical review of the manuscript. During the preparation of this work, the authors used Gemini (Google LLC) to assist with English language editing prior to final review by a professional human editor. The authors reviewed and edited the content as needed and take full responsibility for the content of the published article.
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
Patient Consent Statement Written informed consent was obtained from the patients for the publication of this case series and any accompanying images.
Ethics Approval The study protocol was approved by the Institutional Review Board of Tokushima University (No. 3642).
Data Availability Statement The data that support the findings of this study are available from the corresponding author, Masatoshi Morimoto, upon reasonable request.
Clinical Trial Registration The protocol for the systematic review component of this study was registered with PROSPERO under registration no. CRD420251082183.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2026 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
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