Transligamentous Thecal Sac Indentation

Transligamentous thecal sac indentation is a radiologic finding where a fragment of intervertebral disc material protrudes through the posterior longitudinal ligament and creates a focal indentation on the front (ventral) surface of the dural sac (thecal sac) that surrounds the spinal cord and nerve roots. On CT imaging, these herniated fragments appear as a soft-tissue mass effacing the epidural fat and displacing the thecal sac; when the fragment punctures the ligament but remains attached to the disc margin, it often appears as an irregular, lobulated outgrowth indenting the dural sac Medscape. On myelography or MRI, one may observe a sharp, angular indentation on the lateral aspect of the thecal sac corresponding to the herniation site ScienceDirect.

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Anatomy of the Thecal Sac

Structure

The thecal sac (dural sac) is a tubular sheath composed of the meningeal layer of dura mater. It encases the spinal cord in the cervical and thoracic regions and the cauda equina (nerve roots) in the lumbar and sacral regions, providing a tough protective covering around neural tissue Wikipedia.

Location

This dural tube begins at the foramen magnum (where it is continuous with the cranial dura) and extends down the vertebral canal to the level of the second sacral vertebra (S2), where it tapers and transitions into the filum terminale Wikipedia.

Origin and Termination

• Origin: Continuation of intracranial dura mater at the foramen magnum.

• Termination: Tapers at S2 to envelop the filum terminale, anchoring the spinal cord within the canal Wikipedia.

Blood Supply

The spinal dura mater and thecal sac receive arterial blood from the radicular arteries, which branch off segmental spinal arteries (e.g., vertebral, intercostal, lumbar, and sacral arteries). These radicular arteries enter through the intervertebral foramina, branch along nerve roots, and feed small epidural and dural vessels, supporting the dural sac’s metabolic needs Kenhub.

Nerve Supply

Sensory innervation of the spinal dura and thecal sac is provided by recurrent meningeal (sinuvertebral) branches of each spinal nerve. These nerve fibers convey pain and proprioceptive signals from the dura Radiopaedia.

Functions

1. Protection: Acts as a tough barrier against mechanical injury to the spinal cord and nerve roots.

2. CSF Containment: Holds cerebrospinal fluid (CSF), which cushions neural tissue and delivers nutrients.

3. Pressure Maintenance: Maintains stable CSF pressure around the cord for optimal neural function.

4. Nerve Root Passage: Sends dural root sleeves alongside each nerve root as they exit the spinal canal.

5. Immune Barrier: Serves as a barrier to infections spreading into the subarachnoid space.

6. Anchoring: Anchors the lower spinal cord via the filum terminale, preventing excessive movement Wikipedia.

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Types of Disc Herniation Causing Thecal Sac Indentation

Disc herniations are classified by their relationship to the posterior longitudinal ligament (PLL) and degree of fragment separation:

• Subligamentous Herniation: The nucleous pulposus protrudes beneath the intact PLL, causing smooth dural indentation without breaching the ligament. Medscape

• Transligamentous Herniation: Disc material tears through the PLL but remains connected to the parent disc, producing an irregular, lobulated projection that indents the thecal sac Medscape.

• Extraligamentous Herniation: The disc fragment passes completely beyond the PLL and neural foramen, often causing severe canal compromise; MRI criteria include loss of the continuous low-signal PLL line and an internal dark line within the herniated material PMC.

• Sequestration: A free fragment separates entirely from the disc, migrating within the epidural space and often lodging adjacent to nerve roots, producing focal thecal sac or nerve root indentation.

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Causes

Transligamentous thecal sac indentation most commonly results from intervertebral disc herniations, with contributing factors including:

1. Age-related degenerative disc disease

2. Acute trauma (e.g., fall, motor vehicle collision)

3. Repetitive strain and overuse (e.g., poor lifting technique)

4. Obesity and excess body weight

5. Smoking (promotes disc degeneration)

6. Genetic predisposition (collagen gene variants)

7. Poor posture (prolonged forward flexion)

8. Occupational hazards (heavy manual labor)

9. Sedentary lifestyle and deconditioning

10. Sports injuries (contact sports, weightlifting)

11. Hyperflexion/hyperextension movements

12. Microtrauma over time (vibration, cycling)

13. Osteophyte formation and spondylosis

14. Facet joint arthropathy

15. Spondylolisthesis

16. Spinal tumors (erosion through PLL)

17. Disc infection (discitis)

18. Epidural lipomatosis (fat hypertrophy compressing ligament)

19. Calcium pyrophosphate deposition (CPPD) disease

20. Tethered cord or congenital dural anomalies Mayo ClinicMedscapeWikipedia

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Symptoms

Symptoms vary by level and severity of indentation:

1. Localized back or neck pain

2. Radicular pain (shooting pain down arm or leg)

3. Numbness or tingling (paresthesia)

4. Muscle weakness in affected myotomes

5. Decreased reflexes (hyporeflexia)

6. Absent or diminished Achilles reflex

7. Sciatica (lumbar) or brachialgia (cervical)

8. Gait disturbances or foot drop

9. Sensory loss (hypoesthesia)

10. Cauda equina syndrome (saddle anesthesia)

11. Bladder or bowel dysfunction

12. Sexual dysfunction (erectile issues)

13. Muscle spasms or cramps

14. Hyperalgesia (increased pain sensitivity)

15. Lhermitte’s sign (electric shock radiating down spine)

16. Ataxia or coordination problems

17. Postural imbalance

18. Fatigue due to chronic pain

19. Radiating chest or abdominal pain (thoracic level)

20. Sleep disturbance from pain Mayo ClinicWikipedia

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Diagnostic Tests

1. Physical Examination (inspection, palpation)

2. Neurological Exam (reflexes, strength, sensation)

3. Straight Leg Raise Test (lumbar)

4. Spurling’s Test (cervical radiculopathy)

5. MRI – gold standard for disc and ligament evaluation Wikipedia

6. CT Scan (best for bony detail and acute herniation) Medscape

7. X-ray (rule out fracture, alignment)

8. Myelography (contrast under fluoroscopy)

9. CT Myelogram (dural sac outline)

10. Electromyography (EMG)

11. Nerve Conduction Study (NCS)

12. Discography

13. Bone Scan (tumor, infection)

14. Ultrasound (guided injections)

15. Fluoroscopy-guided injections

16. MRI with contrast

17. Dynamic (flexion/extension) X-rays

18. Blood tests (infection markers)

19. CSF analysis (rare, for meningitis)

20. Gait and posture analysis Wikipedia

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Non-Pharmacological Treatments

1. Patient education on body mechanics

2. Activity modification

3. Physical therapy (core stabilization) Mayo Clinic News Network

4. McKenzie exercises

5. Yoga and Pilates

6. Aquatic therapy

7. Spinal manipulation (chiropractic)

8. Massage therapy

9. Acupuncture

10. Ergonomic workstation adjustments

11. Heat and cold therapy

12. Electrical stimulation (TENS)

13. Traction therapy

14. Posture correction

15. Weight loss programs

16. Smoking cessation

17. Cognitive behavioral therapy (pain coping)

18. Relaxation and breathing techniques

19. Trigger point release

20. Hydrotherapy

21. Ultrasound therapy

22. Kinesio taping

23. Bracing or corset support

24. Orthotic insoles

25. Limited bed rest (48–72 h)

26. Progressive mobilization

27. Educational literature and videos

28. Breathing and core activation drills

29. Anti-inflammatory diet

30. Ergonomic lifting techniques Medscape

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Pharmacological Treatments (Drugs)

1. Ibuprofen (NSAID)

2. Naproxen (NSAID)

3. Diclofenac (NSAID)

4. Aspirin

5. Acetaminophen (paracetamol)

6. Cyclobenzaprine (muscle relaxant)

7. Baclofen (muscle relaxant)

8. Prednisone (oral corticosteroid)

9. Methylprednisolone (oral corticosteroid)

10. Celecoxib (COX-2 inhibitor)

11. Tramadol (opioid analgesic)

12. Oxycodone (opioid analgesic)

13. Amitriptyline (TCA for neuropathic pain)

14. Duloxetine (SNRI)

15. Gabapentin (anticonvulsant)

16. Pregabalin (anticonvulsant)

17. Lidocaine patch (topical analgesic)

18. Capsaicin cream (topical)

19. Epidural methylprednisolone injection

20. Dexamethasone injection MedscapeMedscapeMedscapeMedscape

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Surgical Treatments

1. Open Discectomy – removal of herniated disc material MedscapeMedscape

2. Microdiscectomy – minimally invasive variant

3. Endoscopic Discectomy – through small portals

4. Chemonucleolysis – enzyme dissolution of nucleus

5. Laminectomy – removal of posterior arch

6. Laminotomy – partial removal to decompress nerve

7. Spinal Fusion – stabilize adjacent vertebrae

8. Artificial Disc Replacement

9. Percutaneous Diskectomy – percutaneous removal

10. Spinal Cord Stimulation – neuromodulation for persistent pain MedscapeMedscape

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Prevention Strategies

1. Learn and practice proper lifting techniques

2. Maintain strong core and back muscles

3. Keep a healthy body weight

4. Avoid prolonged sitting; take frequent breaks

5. Use ergonomic workstations

6. Practice good posture when standing and sitting

7. Perform regular low-impact exercise (walking, swimming)

8. Quit smoking to preserve disc health

9. Wear supportive footwear

10. Educate on body mechanics and safe sports techniques Wikipedia

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When to See a Doctor

Seek medical attention if you experience:

• Persistent pain beyond six to eight weeks despite self-care

• Progressive leg or arm weakness or numbness

• Significant bowel or bladder changes (incontinence or retention)

• Numbness in the saddle area (around groin/genitals)

• Fever, chills, or signs of infection with back pain

• Unexplained weight loss accompanying pain

• Severe, unremitting pain that limits daily activities
  Early evaluation often involves MRI and possibly EMG to guide treatment Mayo Clinic News Network.

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Frequently Asked Questions

1. What exactly is transligamentous thecal sac indentation?
   It’s when disc material pushes through the posterior ligament into the spinal canal, creating a visible dent on the front of the dural sac that encases the spinal cord MedscapeScienceDirect.

2. How is it diagnosed?
   MRI is the gold standard because it shows soft tissue and ligament tears; CT myelography can also outline the indentation by highlighting contrast around the thecal sac WikipediaMedscape.

3. What symptoms should raise concern?
   Sharp radiating pain, numbness or weakness in limbs, and any signs of bowel or bladder dysfunction require prompt evaluation Mayo Clinic News Network.

4. Can it heal on its own?
   Many herniations improve with conservative measures over weeks to months; spontaneous resorption of extruded material occurs in a subset of patients Wikipedia.

5. When is surgery necessary?
   Surgery is considered for severe or worsening neurological deficits, cauda equina syndrome, or intractable pain unresponsive to non-surgical treatments Mayo Clinic News Network.

6. What non-drug options help most?
   Physical therapy focusing on core strengthening and posture retraining, along with gentle exercises like yoga or aquatic therapy, often yield good results Mayo Clinic News Network.

7. Are epidural steroid injections safe?
   They provide short-term relief for radicular pain but carry rare risks (e.g., nerve damage); benefits and risks should be discussed with your physician MedscapeMedscape.

8. Which medications are first-line?
   NSAIDs (ibuprofen, naproxen) and acetaminophen are typically tried first, sometimes combined with a short course of muscle relaxants or oral steroids MedscapeMedscape.

9. How long does recovery take?
   With conservative care, most people see significant improvement in 4–6 weeks; complete recovery may take 3–6 months depending on severity Wikipedia.

10. Can exercise make it worse?
    High-impact or improper exercises can aggravate symptoms; a tailored program supervised by a therapist is safest Mayo Clinic News Network.

11. Is recurrence common?
    Reherniation occurs in roughly 5–15% of patients after discectomy; prevention focuses on strengthening and proper mechanics Mayo Clinic News Network.

12. What is cauda equina syndrome?
    It’s a medical emergency marked by compression of multiple lumbar nerve roots, causing saddle anesthesia, severe weakness, and bladder or bowel loss Wikipedia.

13. Is walking good or bad?
    Gentle walking promotes circulation and muscle endurance without stressing the spine, aiding overall recovery Mayo Clinic News Network.

14. Can I fly after surgery?
    Most surgeons allow air travel after incisional healing (around 2–3 weeks), but always follow specific postoperative instructions Mayo Clinic.

15. How do I prevent it from happening again?
    Maintain strong core muscles, use ergonomic lifting and sitting practices, avoid smoking, and stay active to reduce future risk Wikipedia.

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The article is written by Team Rxharun and reviewed by the Rx Editorial Board Members

Last Updated: May 03, 2025.

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