Extradural Thecal Sac Indentation

Extradural thecal sac indentation, also known as thecal sac effacement or compression, is a radiological finding seen on MRI or CT scans when structures outside the dura mater press against and flatten the dural sac that encloses the spinal cord and cerebrospinal fluid. This indentation can be caused by many extradural processes—such as herniated discs, bony overgrowth (osteophytes), or epidural masses—that occupy space within the spinal canal and impinge on the thecal sac. Grading of indentation (mild, moderate, severe) depends on how much cerebrospinal fluid (CSF) around the spinal cord is obliterated:

• Mild: < 25 % CSF obliteration

• Moderate: 25 %–50 % CSF obliteration

• Severe: > 50 % CSF obliteration Spine InfoSpine Info

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Anatomy of the Thecal Sac

Structure and Location

The thecal sac is a single-layer dural membrane (meningeal layer of dura mater) forming a protective tubular sheath around the spinal cord and cauda equina. It begins at the foramen magnum at the skull base and extends downward to level S2 of the sacrum, where it tapers into the filum terminale. The space between the dura and vertebral canal walls—the epidural space—contains fat, blood vessels, and spinal nerve roots. PMC

Origin and Insertion

• Origin: Fusion of meningeal and periosteal dura at the foramen magnum

• Insertion: Ends at the second sacral vertebra (S2), blending into the filum terminale
  These anchoring points keep the spinal cord and CSF-filled sac aligned within the vertebral canal during movement. PMC

Blood Supply

The spinal dura mater (thecal sac) receives arterial blood primarily from anterior and posterior radicular arteries, which branch from segmental spinal arteries and anastomose around the dura. Venous drainage returns via the internal vertebral venous plexus into segmental veins. Radiopaedia

Nerve Supply

Sensory fibers from meningeal branches (sinuvertebral nerves) of each spinal nerve innervate the thecal sac. These recurrent nerves also supply the posterior longitudinal ligament and the walls of the epidural space, transmitting pain signals from dural irritation. Radiopaedia

Functions

1. Protection: Forms a tough barrier shielding the spinal cord from mechanical injury and pathogen invasion.

2. CSF Containment: Houses cerebrospinal fluid, providing buoyancy and cushioning against shocks.

3. Homeostasis: Maintains optimal chemical environment for nerve roots and spinal cord by circulating CSF.

4. Immune Barrier: Serves as an immunological interface, limiting spread of infection into the central nervous system.

5. Stabilization: Anchors and centers the spinal cord in the vertebral canal during flexion and extension.

6. Nutrient Exchange: Facilitates exchange of nutrients and waste between CSF and spinal cord vessels. Verywell Health

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Types of Extradural Thecal Sac Indentation

1. Focal Indentation: Localized flattening at a single spinal level, often from a focal disc protrusion.

2. Diffuse Indentation: Widespread circumferential effacement, typically from multilevel spondylotic changes.

3. Symmetric vs. Asymmetric: Symmetric when both sides of the sac are equally compressed; asymmetric when one side is more indented, causing lateral recess stenosis.

4. Graded Indentation: Classified as mild (< 25 %), moderate (25 %–50 %), or severe (> 50 %) based on CSF space obliteration.

5. By Etiology:

   • Degenerative: Osteophytes, facet hypertrophy, ligamentum flavum thickening

   • Disc‐Related: Bulge, protrusion, extrusion, sequestration PMCRadiopaedia

   • Epidural Fat: Lipomatosis causing global posterior indentation

   • Inflammatory/Infective: Abscess or granulomatous tissue

   • Neoplastic: Extradural tumors (metastases, meningioma extensions)

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Causes

1. Herniated intervertebral disc (protrusion, extrusion)

2. Osteophyte formation from spondylosis

3. Hypertrophy of ligamentum flavum

4. Facet joint arthrosis and cysts

5. Epidural lipomatosis (excess fat) RadiopaediaPMC

6. Vertebral fracture retropulsion

7. Synovial cysts in facet joints

8. Spinal epidural abscess

9. Spinal epidural hematoma

10. Extradural metastatic tumors

11. Primary bone tumors (e.g., chordoma)

12. Tuberculous spondylitis (Pott’s disease)

13. Epidural fibrosis (post-surgical scar)

14. Rheumatoid pannus at C1–C2

15. Spondylolisthesis with canal narrowing

16. Paget’s disease of bone

17. Desmoid tumors

18. Calcified epidural cysts

19. Anticoagulation-related bleeding

20. Idiopathic intracanal fat deposition

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Symptoms

1. Localized back or neck pain

2. Radicular pain (shooting down arms or legs)

3. Numbness or tingling in limbs

4. Muscle weakness in corresponding myotomes

5. Neurogenic claudication (leg pain on walking)

6. Reflex changes (hyperreflexia or hyporeflexia)

7. Gait disturbances or ataxia

8. Bowel or bladder dysfunction

9. Sexual dysfunction

10. Lhermitte’s sign (electric shock sensations)

11. Spasticity of lower limbs

12. Sensory level (dermatomal loss)

13. Neck stiffness

14. Upper motor neuron signs in cervical lesions

15. Cold intolerance or dysesthesia

16. Postural imbalance

17. Headache worsening with posture (cervical region)

18. Intracanal clonus

19. Myelopathic hand signs (Hoffmann’s sign)

20. In severe cases, partial paralysis PMC

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Diagnostic Tests

1. MRI (T1, T2, STIR): Gold standard for soft-tissue and CSF space visualization

2. CT Scan: Detects bony overgrowth and calcifications

3. CT Myelography: Alternative when MRI contraindicated

4. Plain Radiographs (X-ray): Show spondylosis, alignment, fractures

5. Dynamic (Flexion/Extension) X-rays: Assess instability

6. Bone Scan: Identifies infection or tumor activity

7. PET-CT: For metastatic disease evaluation

8. Discography: Pain mapping in discogenic pain

9. Electromyography (EMG): Evaluates nerve root function

10. Nerve Conduction Studies (NCS): Quantifies peripheral nerve involvement

11. Somatosensory Evoked Potentials (SSEP): Assesses dorsal column pathways

12. Motor Evoked Potentials (MEP): Evaluates corticospinal tracts

13. Ultrasound‐Guided Epidural Injection Test: Diagnostic and therapeutic

14. Cerebrospinal Fluid Analysis (Lumbar Puncture): In suspected infection

15. ESR/CRP: Inflammatory markers for infection/inflammation

16. Complete Blood Count: Infection screening

17. Serologic Tests: TB, rheumatoid factor

18. Biopsy (CT‐guided): For unknown epidural masses

19. Vascular Studies (Doppler): Exclude vascular etiologies

20. Neuropsychological Testing: For chronic pain assessment PMC

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Non-Pharmacological Treatments

1. Physical therapy with core stabilization

2. Stretching exercises (e.g., hamstring, hip flexor)

3. Aquatic therapy (water-based exercises)

4. Manual therapy (mobilization, massage)

5. Traction therapy (mechanical or manual)

6. Heat and cold application

7. Transcutaneous electrical nerve stimulation (TENS)

8. Spinal decompression therapy

9. Chiropractic spinal manipulation

10. Acupuncture and dry needling

11. Postural education and ergonomic training

12. Weight loss and nutritional counseling JPain

13. Yoga and Tai Chi

14. Pilates for spinal stability

15. Cognitive-behavioral therapy for pain

16. Biofeedback training

17. Gait training with assistive devices

18. Lumbosacral orthoses (back braces)

19. Activity modification and pacing

20. Self-management education

21. Kinesio taping

22. Neural mobilization techniques

23. Ergonomic workstation setup

24. Relaxation and breathing exercises

25. Sleep hygiene optimization

26. Smoking cessation support

27. Aquatic buoyancy-assisted stretches

28. Dry hydrotherapy (aqua-jets)

29. Vestibular therapy (for balance)

30. Mindfulness meditation

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Drugs

1. Acetaminophen (paracetamol)

2. Ibuprofen (NSAID)

3. Naproxen (NSAID)

4. Diclofenac (NSAID)

5. Meloxicam (NSAID)

6. Celecoxib (COX-2 inhibitor)

7. Tramadol (weak opioid)

8. Codeine (opioid)

9. Oxycodone (opioid)

10. Morphine (opioid)

11. Gabapentin (neuropathic pain)

12. Pregabalin (neuropathic pain)

13. Duloxetine (SNRI)

14. Amitriptyline (TCA)

15. Carbamazepine (anticonvulsant)

16. Baclofen (muscle relaxant)

17. Cyclobenzaprine (muscle relaxant)

18. Tizanidine (muscle relaxant)

19. Prednisone (oral corticosteroid)

20. Methylprednisolone (injectable corticosteroid) Verywell Health

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Surgeries

1. Decompressive laminectomy

2. Microdiscectomy

3. Laminotomy (unicompartmental decompression)

4. Posterior lumbar interbody fusion (PLIF)

5. Transforaminal lumbar interbody fusion (TLIF)

6. Anterior cervical discectomy and fusion (ACDF)

7. Foraminotomy

8. Endoscopic decompression

9. Kyphoplasty/vertebroplasty (for compression fractures)

10. Minimally invasive tubular decompression PMC

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Prevention Strategies

1. Maintain healthy body weight

2. Regular core and back strengthening exercises

3. Practice good posture (standing, sitting, lifting)

4. Ergonomic workstation setup

5. Avoid heavy lifting or twisting without support

6. Quit smoking to improve disc health

7. Balanced diet rich in calcium and vitamin D

8. Stay active with low-impact cardio (walking, swimming)

9. Use proper body mechanics in daily activities

10. Early treatment of minor back injuries Verywell Health

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When to See a Doctor

• Sudden or severe back/neck pain with weakness or numbness in legs or arms

• Loss of bowel or bladder control (cauda equina sign)

• Progressive neurological deficits (e.g., worsening gait disturbance)

• Unremitting pain unrelieved by rest or medications

• Fever, weight loss, or signs of infection with back pain

• History of cancer with new back pain

• Any sudden change in chronic spinal symptoms Spine Info

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Frequently Asked Questions

1. What exactly is extradural thecal sac indentation?
   It’s when something outside the dura mater presses inward on the dural sac, flattening its normally rounded shape and reducing the CSF space around the spinal cord.

2. Does thecal sac indentation always cause symptoms?
   No. Mild indentation may be an incidental finding on MRI and not produce any pain or neurological signs.

3. How is the degree of indentation measured?
   Radiologists grade indentation by the percentage of CSF space obliteration on axial MRI slices: mild (< 25 %), moderate (25 %–50 %), or severe (> 50 %).

4. Can extradural thecal sac indentation resolve on its own?
   Yes. If caused by a reversible process (e.g., mild disc bulge) and treated conservatively, indentation may improve over weeks to months.

5. What imaging test is best for diagnosing thecal sac compression?
   MRI is the gold standard because it clearly shows soft tissues, CSF, spinal cord, and indenting lesions.

6. Are there any non-surgical options to relieve indentation?
   Yes—physical therapy, exercise, weight loss, posture correction, and targeted manual therapies can reduce pressure on the thecal sac.

7. When is surgery necessary?
   Surgery is considered when severe indentation causes neurological deficits, intractable pain, or threatens permanent nerve damage.

8. What are the risks of surgery?
   Potential risks include infection, bleeding, nerve injury, instability requiring fusion, and scar tissue formation.

9. Can epidural steroid injections help?
   Yes. Injections of corticosteroids into the epidural space can reduce inflammation and relieve pain, but effects may be temporary.

10. How long is recovery after decompression surgery?
    Most patients recover mobility within 4–6 weeks, but full functional recovery can take 3–6 months with rehabilitation.

11. What lifestyle changes prevent recurrence?
    Maintaining a strong core, healthy weight, proper posture, and avoiding heavy lifting help prevent further spinal canal narrowing.

12. Is thecal sac indentation the same as spinal stenosis?
    Indentation is a radiological sign of compression, whereas stenosis refers to any narrowing of the spinal canal, which may or may not indent the thecal sac.

13. How does obesity contribute to indentation?
    Excess body fat, especially in the epidural space (lipomatosis), can push on the thecal sac and narrow the canal.

14. Can alternative therapies help?
    Techniques like acupuncture, yoga, Tai Chi, and mindfulness may complement medical treatments but should not replace conventional care for severe cases.

15. What is the long-term outlook?
    With appropriate management—conservative or surgical—most people experience significant symptom relief and improved function, although ongoing preventive care is important.

Disclaimer: Each person’s journey is unique, treatment plan, life style, food habit, hormonal condition, immune system, chronic disease condition, geological location, weather and previous medical  history is also unique. So always seek the best advice from a qualified medical professional or health care provider before trying any treatments to ensure to find out the best plan for you. This guide is for general information and educational purposes only. Regular check-ups and awareness can help to manage and prevent complications associated with these diseases conditions. If you or someone are suffering from this disease condition bookmark this website or share with someone who might find it useful! Boost your knowledge and stay ahead in your health journey. We always try to ensure that the content is regularly updated to reflect the latest medical research and treatment options. Thank you for giving your valuable time to read the article.

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

Last Updated: May 03, 2025.

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