Posterior epidural migration of herniated disc: A case series and literature review

Study setting and design

A systematic literature review based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines [Figure 1] was performed in the present study.

Inclusion and exclusion criteria

In this review, the full–text articles reporting clinical and radiological characteristics of patients with posterior epidural migration of herniated disc fragments were considered eligible. Only English-language articles were included. No date range for publication was set. Letters to the editors, unpublished reports, in vitro and on animal studies, abstracts from Congress, and book chapters were excluded from the review.

Search strategy and study selection

Scopus, MEDLINE via PubMed, Cochrane Library database, and Embase, were searched using the keywords: “Posterior epidural space,” “herniated disc,” “disc migration,” “discal hernia,” “dorsal migration,” “sequestered lumbar disc” and their medical subject headings (MeSH) terms in any possible combinations using the logical operators “AND” and “OR.” The reference lists of relevant studies were forward-screened to identify other studies of interest. The search was reiterated until January 30, 2024.

The PRISMA was followed as reported in Figure 1.

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Figure 1:

Preferred reporting items for systematic reviews and meta–analyses flow–chart.

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After the screening of 474 titles and abstracts, (243 after screening duplicates), 56 papers were considered fit for selection for the full–text analysis. Ultimately, fifty–one studies that met the inclusion criteria were included in the review. In summary, including our report, 108 patients affected by posterior epidural migration of herniated discs were analyzed in this systematic review [Supplementary Table 1].^[5,6,9-57]

Data extraction and analysis

Two independent authors (M.I.B. and A.P.) conducted the search and collected data from the included studies. Any discrepancies were resolved through consensus with a third author (D.A.S.). The following data were extracted: Demographic information, affected discal level, surgical treatment, radiological diagnosis, and radiological description. Numbers software (Apple Inc., Cupertino, CA) was used to collect and categorize the obtained data. Categorical variables are presented as frequencies and percentages, while continuous variables are presented as means and standard deviations. Only one decimal place was reported and rounded accordingly.

Case 1

A 76-year-old male affected by non–Hodgkin’s lymphoma was transferred to our emergency unit for lower back pain for 3 days, left leg iposteny, and weakness in both legs. He had a history of colon adenocarcinoma, non-Hodgkin’s lymphoma, and multiple percutaneous coronary interventions (PCI). A neurologic examination revealed plegia of the left leg, and the power in hip flexion was 3/5. Reflexes were absent in both legs, and hyporeflexia was present in both arms. X–rays showed no sign of fractures. Magnetic resonance imaging (MRI) showed a disc protrusion L1–L2 [Figure 2], and at the same level, an epidural mass, isointense on T1– T1-weighted images, hyperintense on T2–weighted images. The imaging was consistent with the epidural abscess. L1– L2 left laminotomy was performed. After removing the ligamentum flavum, a disc fragment was identified on the left lateral and posterior aspect of the dural sac [Figure 3], we proceeded with the herniotomy. At the end of the procedure, the dural sac appeared loose of compressions. Pathologic analysis confirmed intraoperative findings. Microbiological analysis was carried out on the presence of Staphylococcus Epidermidis in 1 sample of 6, which was considered, according to specialists in infectious disease, a contaminant. A few days after surgery, we observed pain relief and an improvement in both leg’s strength. Due to his cardiologic history, he was undergoing antiaggregant and anticoagulant therapy that caused an important hematoma, which slowed rehabilitation.

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Figure 2:

T2–weighted images, showing (a) herniated disc that compresses dural sac, moreover an hyperintense lesion posterior to the vertebral canal, (b) intraoperative findings.

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Figure 3:

Disc fragment after removal.

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Case 2

A 47-year-old man was admitted to our emergency unit for lower radiculopathies [visual analogue scale (VAS) leg 8], and urinary and fecal retention. A neurologic examination was performed. The motor power in knee flexion bilaterally was 3/5. Hypoesthesia was found in the L4–L5 region bilaterally. In a blood test, no alterations in erythrocyte sedimentation rate, leukocyte, and activated protein C were found. A preoperative MRI of the lumbosacral spine was performed. A big fragment of the intervertebral disc was expelled posteriorly to the dural sac causing compression of the nerves of the cauda equina. A huge bladder for urinary retention is clearly evident, as an incidental feature, on wide MRI sagittal view. The diagnosis was compatible with acute onset of cauda equina syndrome (CES) due to L4–L5 disc herniated disc disease. The operation was performed 12 h after admission. We used a left hemi-laminectomy at the L3 level with the posterior approach. After the removal of the ligamentum flavum, a big disc herniation migrates in the dorsal epidural space was found. We proceeded with the herniotomy. At the end of the procedure, the dural sac appeared loose of compressions. The day after the operation, we observed substantial pain relief (Vas leg 4). The motor power in knee flexion was 4/5 on the right side and 3/5 on the left side. Fifteen days after the operation, urinary retention was resolved. At the one-month follow-up evaluation, the motor power in left knee flexion was 4/5; no other deficit was found.

Case 3

A 45-year-old man was admitted to our emergency unit for acute right sciatica with hypoesthesia in the L4–L5 right region. At the admission, the VAS leg was 8. The patient was a workman affected by chronic lower back pain. Acute sciatica was presented after moving a heavy object during work. A neurologic examination was performed. No deficit was found. In a blood test, no alterations in erythrocyte sedimentation rate, leukocyte, and activated protein C were found. An MRI of the lumbosacral spine was performed. A big fragment of the intervertebral disc was expelled in the right side of the posterior epidural space from the L4 to L5 disc. In the axial section of the MRI, the disk fragment compressed and dislocated the dural sac. The operation was performed 48 h after admission. We used right hemilaminectomy at the L4 level with a posterior approach. After the removal of the ligamentum flavum, a big disc herniation migrates in the dorsal epidural space was found. We proceeded with the herniotomy. At the end of the procedure, the dural sac appeared loose of compressions. The day after surgery, we found good pain relief (VAS leg 2). The patient was discharged 2 days after the operation. At 1-month follow-up evaluation, no hypoesthesia was found and the patient had no pain.

Case 4

A 52-year-old man was admitted to our emergency room for low back pain and sciatica for 8 days and urinary retention. A neurological examination revealed saddle sensory loss, no loss in leg strength, plantar and Achilles reflexes were decreased in both legs, and cremasteric reflex was absent on the left side. Computed tomography (CT) scan and MRI were performed and showed at L4–L5 level a rent in the posterior annulus through which a coarse disc fragment found a path to the dorsal aspect of the dural sac.

A right laminectomy L4–L5 was performed, after which the dural sac was no longer compressed.

A week after surgery, he experienced an improvement in all neurological deficits, and after three weeks, he had a full recovery.

Case 5

A 47-year-old man presented to the emergency department with acute low back pain and urinary retention. Neurological examination revealed motor and sensory deficits in the lower limbs, prompting an MRI, which showed posterior compression suggestive of an epidural abscess. The patient underwent urgent laminectomy, during which a posteriorly migrated disc fragment was discovered posterior to the dural sac and subsequently removed. He was then transferred to neurological rehabilitation, where he demonstrated a full recovery, confirmed at the 3-month follow-up.

Epidemiology of dorsal disc migration

Although sequestered disc fragments account for 28.6% of all disc herniations,^[58] migration to the posterior epidural space or into the dural sac is rare, with an incidence rate of about 0.27–1.04%.

We identified 108 patients, including our report, with posterior epidural migration of herniated disc, of mean age 53,58 (Standard deviation = 11,18201527). Most patients (n = 52; 50%) were aged 40–59. In addition, of the identified patients, 86 (82.5%) were male, which suggests that posterior epidural lumbar disc fragment occurs mainly in middle-aged men, and these results agreed with previous research.^[40]

The most frequently involved levels are L3–L4 (32%) and L4–L5 (35%), followed by L2–L3 (15%), L5–S1 (9%), 5 cases L1–L2, 3 cases thoracic spine, 1 case cervical spine.

In 25% of the cases, patients had a history of spine disorders (chronic low back pain, spondylolisthesis, infective spondylitis, previous surgery, and trauma).

Mechanism of dorsal migration: Why not L5–S1 in young patients?

Posterior epidural migration of extruded disc fragments is a rare condition due to the presence of PLL with Trolard’s ligament, peridural or lateral membrane, epidural fat, dural venous plexus, and the nerve root itself.^[24] The sagittal midline septum of the PLL joins the space between the vertebral body and PLL. Another membrane, the peridural or lateral membrane, extends from the PLL to the wall of the spinal canal, preventing posterolateral migration. Any failure of these tissues may facilitate the posterior epidural migration of an extruded disc fragment.^[15]

When the sequestrated disc fragment is located proximal or distal to the intervertebral foramen, the nerve root is no longer in its position as an anatomical barrier, allowing the free fragments to migrate more easily posteriorly.^[39]

This pattern may result from a combination of:

• Age-related degeneration: Patients with herniation at L3–L4 and L4–L5 levels are significantly older than patients with L5–S1 herniation; and disc degeneration in elders may be associated with impaired ligaments;

• Anatomical factors: The L3–L4 disc is horizontal and the spinal canal is larger, which appears to weaken the nerve root’s protective function at the L3–L4 level;^[51]

• Load: Biomechanical models have shown that the load on the L3 and L4 vertebrae in both sitting and standing positions with flexion is two and a half times the total body weight.^[58]

Previous studies demonstrated a relationship between heavy physical jobs and disc degeneration.

There is an evaluation bias with these patients: The cases that come to medical attention are often those with significant deficits, where MRI and surgery are performed in an emergency setting. As a result, it is often challenging to document natural history.

Radiological features and differential diagnosis

MRI is the diagnostic gold standard, with or without contrast. It was the diagnostic imaging choice in 78% of cases. The herniated disc usually appears similar to the cerebral spinal fluid signal intensity and exhibits ring enhancement on the post-contrast sequences.^[26]

The MRI findings of posterior epidural lumbar disc fragments include: on T1-weighted images, a concave indentation of the posterior thecal sac due to a mass surrounded by hyperintense fat tissue; and rim enhancement on gadolinium-enhanced MRI. The first finding is a particularly decisive clue that the lesion is located in the epidural space.^[39]

CT scan was the radiological exam in 14% of cases, more accessible in the emergency room. CT scans usually demonstrate a soft tissue nodule indenting and displacing the dural sac anteriorly. In 5 cases CT scan studies required the integration with MRI. Other radiologic imaging used was myelography (4%), a more invasive procedure. In a few cases, further tests were performed such as muscle or sensory– evoked potential. There are several differential diagnoses including abscess,^[59] meningioma, tumors, lymphoma, hemangioma, and synovial cyst,^[11] especially in Baastrup’s disease because cysts are located between spinous processes and may extend in the epidural space,^[60,61] infection and epidural hematoma. Other rarer differential diagnoses are benign tumors: lipomas that are usually asymptomatic,^[62] but can become, much more rarely, the cause of neurologic impairment syndrome due to the compression of the neural elements inside the spinal canal, hemangioma, usually symptomless and discovered incidentally, but condition, such as pregnancy, can lead to rapid onset of neurologic symptoms.^[63]

Meningiomas, metastasis, tumors, and hemangiomas usually reveal a ring–like peripheral enhancement, which is not specific. In cases of metastases and lymphomas the patients usually present with multisystem involvement and marrow abnormalities. Abscesses are associated with an infectious illness and hematomas with rheumatologic diseases [ankylosing spondylitis and diffuse idiopathic skeletal hyperostosis (DISH)] or trauma in patients with elevated INR.^[55]

The differential diagnosis between posterior epidural herniation of a lumbar disc fragment and epidural hematoma can be quite challenging. Disc herniation with migration often maintains contact with the disk space from which the fragment originated, while hematomas typically have less direct contact with the disk space.^[37]

Clinical manifestation

Clinical manifestations of posterior epidural migration of herniated disc range from low back pain without neurological deficit to CES. Among the 108 patients included in this review, in 63% of cases, motor function was involved, in 56% there was a sensory loss, in 36% hyporeflexia and in 37% sphincter disorders. Akhaddar et al. reported no correlation between the size of the migrating disk hernia and the degree of neurological deficits.^[24]

We found no statistically significant correlations between the level of the herniated disc and the gravity of the clinical manifestations. Obviously, neurological deficits guide surgery timing.

Treatment

Surgery is the most common treatment choice (97% of cases), including hemilaminectomy or laminectomy, facetectomy, and discectomy (24%). One case was treated using an endoscopic approach.^[47]

Tarukado et al. reported 3 cases treated with spontaneous regression of posterior epidural herniated disc: Two over 3 cases showed hypoesthesia, 1 over 3 showed a mild reduced strength of one leg, and none of them showed hyporeflexia or sphincter involvement.^[30]

Open surgery is considered the best choice because surgeons are often unable to make a definitive diagnosis using radiological findings. Moreover, pathologic confirmation can be performed, and in case of the presence of signs of infection surgeons using a minimally invasive approach can decompress the spinal cord, isolate the pathogen, and evacuate the abscess.^[64]

Early surgery should be performed to prevent severe neurological deficits. Previous studies indicate that prognosis is better for patients who receive surgical treatment promptly.^[39]

Outcomes

There were 14% incomplete recovery with sequelae, usually with complications related to the urinary system (5 cases). A full recovery was reported in 55% of cases, while 31% experienced improvement without significant deficits. Delayed diagnosis often results in late surgical decompression, increasing the likelihood of sequelae.^[39]

Limitations

The rarity of this condition makes it difficult to perform prospective studies which would be helpful to decide the diagnostic algorithm and surgery timing.