Intradural disk herniation (IDH) was initially reported in 1942 by Dandy, who documented a case of lumbar intradural disk rupture.1

Subsequent reports have described cervical and thoracic cases in 1959 and 1987, respectively.2,3

IDHs are infrequent and represent an unusual complication arising from disk protrusions. They account for approximately 0.3% of all disk herniation cases. On the other hand, there has been an upward trend in publications on IDH cases over recent decades, highlighting that this condition is probably underdiagnosed and underestimated (Fig. 1).

Fig. 1.

Publication trends: line graph shows increasing reporting in recent decades.

The exact pathogenesis and progression remain unclear, though adhesions between the annulus fibrosus, posterior longitudinal ligament (PLL), and anterior dura mater are believed to be contributing factors.

Preoperative diagnosis of IDH is challenging. Various neuroimaging techniques, including CT scans, MRI, myelography, and discography, have been described in the literature to evaluate the presence of an IDH.4,5 Despite this, preoperative diagnosis is rare, with most cases diagnosed intraoperatively.6,7

The treatment of IDH poses additional challenges. Literature suggests that IDH should be treated as early as possible, emphasizing the necessity for prompt surgical intervention.8

Considering its rarity and the difficulties associated with diagnosis and management, a systematic review of literature regarding cervical, thoracic and lumbar IDH reported in literature was conducted. The objective of this study is to better evaluate the clinical characteristics of this condition and to suggest optimal strategies for detection and treatment.

Intradural disk herniation (IDH), characterized by the displacement of the nucleus pulposus through the posterior longitudinal ligament (PLL) and dural sac into the intrathecal space, was first described by Walter E. Dandy in 1942. Despite its historical recognition, IDH remains exceedingly rare, accounting for an estimated 0.04–0.33% of all lumbar disk herniations. In our systematic review, IDH was reported more frequently in male patients (81.16%) than in females, with an average age of 54.5 years at diagnosis. The lumbar spine was most commonly affected (64.3%), followed by the thoracic (21.9%) and cervical (13.8%) regions. The L4–L5 level represented the most frequent site of involvement.

The precise etiology of IDH remains poorly understood. However, intraoperative findings often demonstrate adhesions between the PLL and ventral dura mater, which are considered potential contributors to the pathogenesis.164,165 These adhesions may arise from chronic inflammation, previous surgical interventions, trauma, degenerative changes, or congenital structural anomalies, all of which can obliterate the epidural space. Additionally, PLL hypertrophy and ossification may exacerbate mechanical stress on the dura mater, enhancing its vulnerability. Teng and Papatheodorou hypothesized that the absence of a “dural tent”—the typical separation formed by an intact PLL—may indicate pathological adherence between the PLL and dura, facilitating disk material migration into the intradural space.162

The predominance of IDH in the lumbar spine may reflect the substantial biomechanical forces acting in this region. Repetitive stress or acute high-energy trauma may contribute to PLL degeneration and subsequent IDH formation. Supporting this theory, the majority of IDH cases in our review involved central disk herniations, a location typically reinforced by the PLL.166,167

Although only a small proportion of patients (5.8%) had a history of acute trauma, a notable number (17.7%) had undergone previous spinal surgery—predominantly involving the lumbar spine—suggesting a potential role of iatrogenic factors in IDH development.

Clinical manifestations of IDH vary by spinal level. Cervical IDH often presents with severe neurological deficits such as Brown-Séquard syndrome or quadriparesis, occasionally with delayed onset after trauma. In our cohort, the most common symptom was radiculopathy with or without muscle weakness (58.3%), followed by bowel or bladder dysfunction (17.7%) and varying forms of paraparesis. A particularly distinctive finding was cauda equina syndrome, sometimes associated with a longstanding history of lumbar pain, suggestive of intradural involvement. Postoperative recovery was incomplete in the majority of cases; only 30.8% achieved full neurological resolution, highlighting the condition's clinical severity and potential for persistent deficits.

Radiological evaluation remains challenging. While plain radiographs may reveal degenerative changes, they do not directly visualize IDH. MRI and CT are routinely employed but may fail to distinguish IDH from other intradural extramedullary lesions such as schwannomas or meningiomas. In our review, preoperative diagnosis was achieved in only 16% of cases. These data confirm that this condition is both underdiagnosed and underestimated. Notably, among the subset of patients who underwent myelography in addition to MRI and CT, a significantly higher rate of preoperative identification (77.8%) was observed, indicating that myelography, though not widely available, may be particularly valuable in diagnostic workup.

Specific MRI and CT findings, such as discontinuity of the PLL, a poorly defined disk margin, disk material beyond the PLL, or the characteristic “Y-sign” on MRI, may raise suspicion for IDH. The “Y-sign,” described by Sasaji et al., represents a division between the dura and arachnoid when disk material intrudes between them, and may serve as a useful diagnostic marker.168,169

Surgery remains the definitive treatment for IDH, allowing both decompression and confirmatory diagnosis. Accurate preoperative recognition is essential for planning the surgical approach, particularly regarding durotomy management and the extent of laminectomy. An anterior approach, particularly in cervical IDH, offers direct access to the disk and ventral dura without requiring lateral cord retraction, thus reducing intraoperative risk. Most arachnoid defects encountered intraoperatively were repaired with grafts, fibrin glue, or other materials, and postoperative cerebrospinal fluid leakage was infrequent, although documentation was often lacking.

This systematic review is limited by the retrospective nature of the included studies and incomplete data on radiological features and postoperative outcomes. Nevertheless, the findings underscore the rarity and clinical significance of IDH. The condition predominantly affects the lumbar spine, often presents with severe neurological symptoms, and frequently results in incomplete recovery. Improved awareness and diagnostic acumen, particularly through adjunctive imaging like myelography, may enhance preoperative identification and optimize surgical planning.

Study concept: A.M. Study design: A.M. Data acquisition: E.L.B; F.B. Quality control of data and algorithms: A.M.; A.S. Data analysis and interpretation: E.L.B. Manuscript preparation: S.C.; A.P. Manuscript editing: A.M.; E.L.B. Manuscript review: M.A.; A. F.; D. G.; F. C. All authors agreed to the publication of this work.

Data or information needed to re-produce the findings presented are available from the corresponding author upon reasonable request.

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This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

The authors declare that the article and its content were composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.