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Posterior epidural disc migration – Unraveling the practical challenges
, J. Balaji2, Sibi Krishna Thiyagarajan1, T. Balamurugan2, Somesh Vanchilingam2
*Corresponding author: Shyam Sundar Krishnan, Department of Neurosurgery, Kauvery Hospital, Alwarpet, Chennai, Tamil Nadu, India. shyamsundarkrishnan76@gmail.com
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Received: ,
Accepted: ,
How to cite this article: Krishnan SS, Balaji J, Thiyagarajan S, Balamurugan T, Vanchilingam S. Posterior epidural disc migration – Unraveling the practical challenges. J Neurosci Rural Pract. 2025:16:318-22. doi: 10.25259/JNRP_429_2024
Abstract
Posterior epidural migration of a sequestered disc at the lumbar level is a rare entity that warrants early surgical intervention due to the neurological sequelae of cauda-equina syndrome. It is often misdiagnosed on imaging and needs intraoperative and histopathological confirmation. We present two patients with similar complaints, the diagnostic difficulties, and anatomic-pathological correlation for posterior disc migration at the lumbar level. In both patients, contrast-enhanced magnetic resonance imaging lumbar spine revealed an extradural lesion compressing and displacing the cauda, which was T1 isointense with an enhancing peripheral rim. With a sequestered disc being one of the differential diagnoses, both underwent microdiscectomy, and the biopsy confirmed the same. Both patients had significant clinical improvement noted during regular follow-up. We conclude that swift clinical assessment and early surgical intervention can prevent morbidity and improve the quality of life in patients with posterior epidural migration of disc at the lumbar level presenting as cauda equina syndrome.
Keywords
Cauda equina syndrome
Herniated disc
Lower backache
Lumbar spine
MISS
Posterior epidural disc
Sequestrated disc
INTRODUCTION
Posterior epidural migration of a sequestrated disc fragment is a very rare clinical entity with only 120–150 case reports published so far since it was first reported in 1973 by Lombardi.[1] Although it is uncommon, it can cause severe neurological deficits, especially at the mid-lumbar level. It requires swift clinical assessment and early surgery to prevent morbidity and improve the quality of life. One of the intriguing aspects of a sequestrated disc is the difficulty in diagnosing with the help of imaging. Disc sequestration at the lumbar level is more challenging for a surgeon due to its anatomical complexities.
In this article, we present two patients with different presentations and different pre-operative diagnoses. Sequestrated disc was the pre-operative diagnosis.
CASE REPORT
Case 1
A 52-year-old female patient presented to the outpatient department (OPD) on a wheelchair with the complaint of pain over the anterior aspect of the left thigh for a few months, which increased in severity over 15 days. She was nil comorbid with no history of fall or bladder/bowel incontinence or prior surgeries. Clinical examination and blood parameters were unremarkable. Contrast-enhanced magnetic resonance imaging (CE-MRI) Dorso-lumbar spine revealed a T2 hypo T1 isointense lesion at L2–L3 measuring 16 mm × 8 mm in size, extra-dural in location, compressing and displacing the cauda anteriorly, closely abutting the exiting nerve root and to the right, as shown in Figures 1 and 2. There was minimal peripheral enhancement with a central non-enhancing foci. The lesion measured about 8 mm anteroposteriorly, 6 mm transversely, and 17 mm craniocaudally. The provisional diagnosis was a schwannoma.
- Sagittal view of the lumbar disc extrusion noted at L2–L3 level.
- Axial view of the lumbar disc extrusion noted at L2–L3 level.
Case 2
A 38-year-old gentleman presented to the OPD with B/L foot drop and right leg pain for 10 days. He had a history of lower back pain for 1 year, which has progressed in severity over the past 10 days. He was wheelchair-bound, and a general physical examination was unremarkable. Central nervous system examination revealed a decreased and absent ankle reflex on the right and left sides, respectively. Extensor hallucis longus (EHL) power was zero with reduced plantar on both sides. There was no bowel/bladder incontinence or any sensory deficit. He was nil comorbid with no history of previous surgeries/illnesses. Routine blood investigations were within normal limits.
A CE-MRI of the lumbar spine with whole-spine screening revealed a disc extrusion with complete sequestration of the disc material into the spinal canal, causing severe compression of cauda equina nerve roots at L3–L4 with peripheral rim enhancement. Severe bilateral foraminal narrowing with impingement of the exiting L3 nerve root on the right was noted, as shown in Figures 3 and 4.
- Post contrast sagittal view of the lumbar disc extrusion noted at L3–L4 level.
- Post contrast axial view of the lumbar disc extrusion noted at L3–L4 level.
Surgical management
In both the patients, a needle was used as a landmark to confirm the location of pathology using a C-arm [Figure 5]. A paramedian incision was made 3 cm from the midline over the L2-L3 and L3–L4 region, respectively, and the location of the pathology was confirmed by C-arm. On confirmation, discectomy using a minimally invasive tubular approach was performed, and the specimen, as shown in Figure 6, was sent for histopathological examination in both patients.
- C-arm marking of the protruded disc.
- Post-discectomy specimen.
Post-operative management
Both patients were under strict neuro-monitoring in the intensive care unit immediately post-operatively, following which they were shifted to the ward for further care. Both of them showed improvement in the power of lower limb muscles from post-operative day (POD)-2. Aggressive limb physiotherapy and out-of-bed mobilization with support were done from POD-3. Regular sterile dressing of the surgical site was done, and there was no cerebrospinal fluid leak leak/abscess formation. They were engaged in muscle-strengthening exercises and, on POD-5, both of them were discharged. Both patients went back home walking with support in comparison to their wheelchair-bound presentation.
Follow-up
Staplers were removed after 1 week, and follow-up appointments were scheduled at 2 weeks, 1 month, and 2 months post-operative. The surgical site was healthy. Foot drop (in the 2nd patient) improved significantly that he was able to walk without support. There was a marked reduction in lower back pain in both patients. Limb physiotherapy was continued, and patients were advised to refrain from heavyweight lifting.
DISCUSSION
Disc extrusions occur when there is a defect in the annulus fibrosus, allowing the nucleus pulposus to herniate out of the disc. In cases of sequestration, disc material separates completely from the remaining portion of the herniated disc. Although sequestrated disc material is typically found paracentral or lateral to the anterior epidural space, posterior sequestration is less common but still significant.[2] When present, posterior sequestration can pose unique challenges for diagnosis and treatment due to its less frequent occurrence and potential implications.
Posterior migration of disc fragments is uncommon due to several anatomical structures within the anterior epidural space[3,4] [Figures 7 and 8].
- Transverse section of lumbar vertebra showing various anatomical structures in the anterior epidural space.
- Coronal section of lumbar vertebra showing important structures preventing posterior disc migration.
Posterior longitudinal ligament (PLL)
Septum posticum: Also known as the sagittal midline septum, this structure divides the anterior epidural space into two distinct compartments
Lateral or peridural membrane: This membrane attaches medially to the PLL
Hoffmann’s ligaments: These ligaments connect the anterior dural surface to the PLL.
Even when PLL is breached, the disc material is contained from becoming a free fragment due to the presence of the epidural venous plexus, epidural fat, and the traversing nerve root itself.[5] During imaging, the disc appears convex due to the smooth surface maintained by the containment[6] [Figure 9]. Once the disc becomes a free fragment, it adopts an irregular shape[6] [Figure 10]. Despite numerous anatomical barriers, posterior disc migration could still occur due to the severity/violence of the injury in certain postures that exert significant pressure on the lumbar disc.[7]
- Transverse section of lumbar vertebra showing smooth contour of the extruding disc – sequestration of the disc is prevented by the posterior longitudinal ligament.
- Transverse section of lumbar vertebra showing irregular shape of the sequestered disc.
Although disc herniations are frequently observed at the L4–L5 and L5–S1 levels, the L3–L4 level is considered as an inflection point where posterior migration is more likely to occur, due to its unique characteristics such as reduced anterior space due to narrow spinal canal[8] and horizontally oriented disc; low lying transverse nerve root; and disc-nerve root angle (DRA) variations resulting in narrower DRA at the lower lumbar levels [Figure 11].[9] Understanding these characteristics is crucial in managing mid-lumbar disc pathologies.
- Sagittal section of lumbar vertebra showing the disc-root angle and the exiting nerve root from L1 to L5.
Enhanced imaging for detailed assessment
CE-MRI with gadolinium is the preferred investigation following initial clinical and laboratory work-ups.[10]
The high T2 signal intensity observed in a ruptured or herniated disc is often attributed to the increased water content in the disc due to the reparative process.[11]
Peripheral rim enhancement of a sequestered disc on CE-MRI is a distinctive feature. This enhancement is indicative of an inflammatory response surrounding the disc.[12] It is caused by increased vascularity and granulation tissue production. It is often mistaken for a tumor, an abscess, or synovial cysts.[13]
CONCLUSION
Thus, we postulate the following vignettes for a better understanding of posterior disc migration at the L3–L4 level based on our clinical experience.
Violent physical activities such as high-velocity injuries or improper weight lifting techniques, particularly those involving specific postures that stress the lumbar spine, can lead to posterior disc migration. Posterior disc migration is more common at the L3–L4 level due to a low-lying traversing nerve root at this level. The anatomical configuration at this level can create a tight working environment for surgical instruments, making it challenging to manage the operative field. The L3–L4 level is in close proximity to the cauda equina, and extensive disc migration can impinge on multiple nerve roots, leading to symptoms consistent with cauda equina syndrome in most of the patients. At the L3–L4 level, severe impingement of the exiting nerve root also occurs due to the disc occupying much of the spinal canal.
Ethical approval:
Institutional Review Board approval is not required.
Declaration of patient consent:
The authors certify that they have obtained all appropriate patient consent.
Conflicts of interest:
There are no conflicts of interest.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation:
The authors confirm that there was no use of AI-assisted technology in the writing or editing of the manuscript, and no images were manipulated using AI.
Financial support and sponsorship: Nil.
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