Annular Thecal Sac Indentation

Annular thecal sac indentation occurs when the outer ring of an intervertebral disc (the annulus fibrosus) bulges or protrudes into the spinal canal, pressing against and deforming the thecal sac—the protective membrane that surrounds the spinal cord and cerebrospinal fluid. On MRI, it appears as a focal or broad-based “flattening” or inward bowing of the dural sac where the disc abuts it. Although mild indentation may be asymptomatic, significant pressure can lead to nerve compression and neurological symptoms Spine Info.

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Anatomy of the Annulus Fibrosus

1. Structure & Composition
   The annulus fibrosus is made of 15–25 concentric layers (lamellae) of fibrocartilage, primarily type I collagen at the periphery and type II collagen centrally. These lamellae are oriented at alternating angles (~ 30° to the vertical), giving the ring its strength and flexibility Wikipedia.

2. Location
   It forms the outer ring of each intervertebral disc, sandwiched between the cartilaginous endplates of adjacent vertebral bodies from C2–C3 down to L5–S1 Wikipedia.

3. Attachments (Origin & Insertion)

   • Peripheral fibers (Sharpey’s fibers) anchor into the bony ring apophyses of vertebral bodies.

   • Inner fibers attach to the hyaline cartilage endplates that cap each vertebra Kenhub.

4. Blood Supply
   In early life, vessels penetrate the endplates and outer annulus. In adults, only the outer third remains vascularized via capillaries from segmental arteries and cartilaginous endplate branches. Nutrients diffuse inward from these peripheral vessels Wheeless’ Textbook of Orthopaedics.

5. Nerve Supply
   The outer one-third is innervated by the sinuvertebral nerves (recurrent meningeal branches) and gray rami communicantes, which convey pain when the ring is torn or stretched NCBI.

6. Functions

   1. Containment: Holds the gel-like nucleus pulposus in place.

   2. Load Distribution: Spreads compressive forces evenly across vertebral bodies.

   3. Tensile Strength: Resists ring expansion under pressure.

   4. Flexibility: Permits motion in flexion, extension, rotation, and lateral bending.

   5. Shock Absorption: Dampens impact during movement.

   6. Stability: Maintains intervertebral height and alignment RadiopaediaKenhub.

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Types of Indentation

Indentation of the thecal sac by disc tissue may present in various forms of disc pathology:

• Concentric bulge: Broad-based ballooning of the annulus fibers Radiopaedia

• Focal protrusion: Localized annular tear with narrowed base Radiopaedia

• Extrusion: Disc material extends beyond the annulus with a narrow connection Radiopaedia

• Sequestration: Free fragment separates completely and may migrate Radiopaedia

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Causes of Annular Thecal Sac Indentation

1. Herniated (ruptured) disc Spine Info

2. Concentric disc bulge Radiopaedia

3. Degenerative disc disease (disc dehydration & collapse) PMC

4. Ligamentum flavum hypertrophy Spine Info

5. Osteophyte (bone spur) formation Spine Info

6. Facet joint hypertrophy Radiology Assistant

7. Spondylolisthesis (vertebral slippage) Spine Info

8. Compression fracture (vertebral collapse fragment) Radiopaedia

9. Spinal tumors (metastatic or primary) Spine Info

10. Epidural lipomatosis (excess fat in canal) Radiopaedia

11. Spinal arachnoid cysts Optimal Wellness Health Center (UT)

12. Spinal cord herniation through dura defect Optimal Wellness Health Center (UT)

13. Tarlov (perineural) cysts Deuk Spine

14. Synovial cysts of facet joints Radiology Assistant

15. Angiolipoma in epidural space PMC

16. Discitis & spondylodiscitis (disc infection) Radiopaedia

17. Spinal epidural abscess NCBI

18. Spinal epidural hematoma Radiopaedia

19. Vertebral hemangioma expansion Radiopaedia

20. Multiple myeloma infiltration Radiopaedia

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Symptoms

Patients with annular thecal sac indentation may experience:

1. Localized back/neck pain

2. Radicular pain (sciatica or arm pain)

3. Numbness or tingling in limbs

4. Muscle weakness in affected myotomes

5. Reflex changes (diminished or absent)

6. Gait instability

7. Claudication (leg pain on walking)

8. Bowel/bladder dysfunction (cauda equina sign)

9. Sexual dysfunction

10. Stiffness of spine

11. Postural changes

12. Muscle spasms

13. Sensory loss to light touch

14. Hyperalgesia or allodynia

15. Lhermitte’s sign (electric shock sensation)

16. Balance issues

17. Muscle atrophy in chronic cases

18. Visual analogue scale pain > 7/10

19. Night pain disturbing sleep

20. Activity limitation in daily tasks

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Diagnostic Tests

1. MRI (gold standard for soft tissue)

2. CT scan (bony detail)

3. X-ray (alignment, spondylolisthesis)

4. Myelography (contrast flow)

5. CT myelogram

6. Electromyography (EMG)

7. Nerve conduction study (NCS)

8. Discography

9. Ultrasound (guided injections)

10. Bone scan (tumor/infection)

11. Blood tests (CBC, ESR, CRP)

12. Biopsy (tumor/infection)

13. CSF analysis (if myelographic)

14. Dynamic flexion/extension X-rays

15. Dual-energy CT (gout, calcium)

16. PET-CT (metastases)

17. Ultrafine CT (nerve root sleeve)

18. Somatosensory evoked potentials

19. Visual analogue scale (VAS)

20. Oswestry Disability Index

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Non-Pharmacological Treatments

1. Physical therapy (strengthening & stretching)

2. Core stabilization exercises

3. McKenzie extension protocol

4. Williams flexion exercises

5. Chiropractic manipulation

6. Acupuncture

7. Yoga & Pilates

8. McKenzie mechanical traction

9. Spinal decompression therapy

10. Massage therapy

11. TENS (transcutaneous electrical stimulation)

12. Heat therapy

13. Cold therapy

14. Ultrasound therapy

15. Hydrotherapy (aquatic therapy)

16. Ergonomic workplace adjustments

17. Postural training

18. Bracing (lumbar or cervical)

19. Weight management & nutrition

20. Mindfulness & meditation

21. Cognitive behavioral therapy

22. Biofeedback

23. Relaxation techniques

24. Tai Chi

25. Proprioceptive training

26. Postural taping

27. Education on body mechanics

28. Smoking cessation

29. Sleep hygiene & supportive mattress

30. Low-impact aerobic conditioning Spine Info

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 Drugs

1. Ibuprofen (NSAID)

2. Naproxen (NSAID)

3. Celecoxib (COX-2 inhibitor)

4. Acetaminophen (analgesic)

5. Aspirin (salicylate)

6. Diclofenac (NSAID)

7. Gabapentin (anticonvulsant)

8. Pregabalin (anticonvulsant)

9. Amitriptyline (TCA)

10. Duloxetine (SNRI)

11. Baclofen (muscle relaxant)

12. Cyclobenzaprine (muscle relaxant)

13. Tizanidine (muscle relaxant)

14. Tramadol (opioid-like)

15. Oxycodone (opioid)

16. Morphine (opioid)

17. Lidocaine patch (topical local anesthetic)

18. Capsaicin cream (topical analgesic)

19. Methylprednisolone (systemic steroid)

20. Epidural dexamethasone (injection) Spine Info

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Surgeries

1. Microdiscectomy

2. Open discectomy

3. Laminectomy

4. Laminotomy/hemilaminectomy

5. Posterior lumbar interbody fusion (PLIF)

6. Transforaminal lumbar interbody fusion (TLIF)

7. Anterior cervical discectomy & fusion (ACDF)

8. Kyphoplasty/vertebroplasty

9. Spinal fusion (instrumented)

10. Endoscopic spine surgery Spine Info

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Prevention Strategies

1. Maintain healthy weight

2. Regular core strengthening

3. Proper lifting techniques

4. Ergonomic workstation setup

5. Good posture when sitting/standing

6. Avoid prolonged sitting—take breaks

7. Quit smoking

8. Stay active with low-impact exercise

9. Use back-supportive chairs & mattress

10. Balanced nutrition (vitamin D & calcium) Spine Info

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When to See a Doctor

• New or worsening weakness in legs or arms

• Loss of bladder or bowel control (emergency)

• Severe pain unrelieved by rest or medications

• Progressive numbness or tingling

• Fever with back pain (infection risk)

• Unexplained weight loss with pain (tumor risk)

• Vertigo or gait instability

• Night pain that wakes you

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Frequently Asked Questions

1. What exactly is annular thecal sac indentation?
   It’s when a weakened disc ring bulges inward, pressing on the protective membrane around your spinal cord.

2. Is it the same as a herniated disc?
   Not quite—herniation means the inner gel leaks out; indentation simply presses the dural sac without necessarily rupturing it.

3. Can mild indentation heal on its own?
   Often yes—mild bulges can shrink with rest, exercise, and physical therapy over weeks to months.

4. What imaging test shows it best?
   MRI is the gold standard because it visualizes soft tissues and nerve compression clearly.

5. Will I always need surgery?
   No—over 80% improve with non-surgical treatments like physiotherapy, pain medicines, and lifestyle changes.

6. Can I exercise with this condition?
   Yes—guided core and flexibility exercises help stabilize the spine and relieve pressure.

7. What medications work best?
   NSAIDs (e.g., ibuprofen), muscle relaxants, and neuropathic agents (e.g., gabapentin) are first line.

8. Are steroid injections safe?
   When done by specialists, epidural steroids can reduce inflammation; risks are low if guidelines are followed.

9. How soon after surgery can I walk?
   Most patients walk the same day or next morning after microdiscectomy or laminectomy.

10. Does posture affect indentation?
    Yes—slouching increases disc pressure; good posture lessens stress on weakened discs.

11. Will it lead to permanent nerve damage?
    Severe, untreated compression (especially cauda equina syndrome) can; early care prevents this.

12. Can weight loss help?
    Losing excess weight decreases spinal load and may reduce bulge severity.

13. Is it inherited?
    Family history of degenerative disc disease increases risk, but lifestyle plays a bigger role.

14. Can I drive with this condition?
    Generally yes, if pain is controlled and you can move safely; discuss with your doctor.

15. What’s the long-term outlook?
    With appropriate management, most people return to normal activities; some may have mild chronic symptoms.

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.