Posterolateral Thecal Sac Indentation

Anatomy?

Structure and Location

The thecal sac is a tubular sheath of dura mater that begins at the foramen magnum (the large opening at the base of the skull?) and extends down the spinal canal to the second sacral vertebra? (S2), where it narrows into the filum terminale WikipediaRadiopaedia. Within the vertebral canal, it sits just inside the epidural space, surrounded by fatty tissue and the bony walls of vertebrae?.

Origin and Insertion

• Origin: The dura mater of the thecal sac is continuous with the cranial dura at the foramen magnum and attaches anteriorly to the posterior longitudinal ligament via fibrous Hofmann ligaments?.

• Insertion: It terminates at S2, anchoring to the coccyx? through the filum terminale, and sends out dural sleeves along each exiting nerve root PMC.

Blood Supply

The spinal dura receives arterial blood mainly from anterior and posterior radicular arteries?—branches of the segmental spinal arteries (vertebral in the neck, intercostal in the thorax, lumbar? and lateral sacral in the lower spine). These small vessels anastomose along the dural sac. Venous drainage empties into the internal vertebral venous plexus within the epidural space Radiopaedia.

Nerve Supply

Sensory fibers in the dura and thecal sac arise from recurrent? meningeal (sinuvertebral) nerves, which branch off the ventral primary rami of each spinal nerve and re-enter the canal to supply the dura. These nerves carry pain? and proprioceptive signals from the dura to the central nervous system Wikipedia.

Functions

1. Protection: Shields the spinal cord and cauda equina against external injury.

2. Containment of CSF: Encloses cerebrospinal fluid, which cushions and nourishes neural tissue.

3. Buoyancy: Provides even fluid pressure to reduce mechanical stress on the cord Wikipedia.

4. Stabilization: Suspends the spinal cord via denticulate ligaments and the filum terminale.

5. Shock? Absorption: Works with epidural fat to buffer shocks and vibrations.

6. Pathway for Nerve Roots: Forms protective dural sleeves as nerve roots exit the canal.

Types of Indentation

1. Central Indentation: Compression of the middle (ventral) surface of the thecal sac.

2. Posterolateral Indentation: Focal impressing of the back‐and‐side margins (the lateral recess) Radiopaedia.

3. Foraminal Indentation: Narrowing at the neural foramen where nerve roots exit.

4. Extraforaminal (Far‐Lateral) Indentation: Compression outside the foramen by migrated disc fragments or soft tissue masses.

Potential Causes

Most causes reflect anything that narrows the spinal canal or lateral recess SpineInfoPMC:

1. Herniated (protruded) disc

2. Disc bulge with annular tear

3. Ligamentum flavum hypertrophy?

4. Osteophyte? (bone spur) formation

5. Facet joint hypertrophy

6. Spondylolisthesis? (vertebral slippage)

7. Epidural lipomatosis (fat overgrowth)

8. Synovial cyst from facet joints

9. Spinal canal tumors (meningioma, schwannoma)

10. Epidural abscess?

11. Epidural hematoma

12. Paget’s disease of bone

13. Rheumatoid pannus formation

14. Congenital? canal narrowing (achondroplasia)

15. Spinal stenosis? (degenerative)

16. Traumatic fractures or bone fragments

17. Post‐surgical scar tissue (arachnoiditis)

18. Dural ectasia (ballooning)

19. Inflammatory arthritis? (ankylosing spondylitis?)

20. Metastatic lesions to vertebrae

Common Symptoms

Compression severity and location dictate symptoms, which may include:

1. Local back or neck pain

2. Radicular (nerve root) pain down an arm or leg

3. Paresthesia? (tingling?)

4. Numbness? or sensory loss

5. Muscle weakness

6. Reflex changes (diminished or hyperactive)

7. Gait disturbance

8. Neurogenic claudication (leg cramping when walking)

9. Bowel or bladder dysfunction

10. Sexual dysfunction

11. Saddle anesthesia

12. Hyperalgesia (increased pain sensitivity)

13. Muscle spasm

14. Stiffness

15. Balance issues

16. Fatigue from chronic pain

17. Pain at rest or nighttime pain

18. Loss of fine motor control (in the hands)

19. Postural intolerance

20. Cauda equina syndrome signs (emergency)

Diagnostic Tests

A thorough workup may involve:

1. Physical exam (strength, reflexes, sensation)

2. Straight‐leg raise test

3. Neurological exam (gait, coordination)

4. X-ray (alignment, bone spurs) Hospital for Special Surgery

5. MRI (soft tissue detail, disc, cord) Hospital for Special Surgery

6. CT scan (bone detail, canal dimensions)

7. CT-myelogram (contrast in thecal sac)

8. Discography (provocative disc injection)

9. Electromyography (EMG)

10. Nerve conduction studies (NCS)

11. Myelography

12. Bone scan (tumor/infection)

13. Blood tests (ESR, CRP, infection markers)

14. Lumbar puncture (CSF analysis)

15. Dynamic X-rays (flexion/extension views)

16. Ultrasound (guided injections)

17. DEXA scan (osteoporosis assessment)

18. PET-CT (metastatic evaluation)

19. Gait analysis

20. CT‐guided biopsy (for tumors/abscess)

Non-Pharmacological Treatments

Conservative care often begins before drugs or surgery:

1. Physical therapy (flexibility, core strength)

2. McKenzie exercises

3. Aquatic therapy

4. Yoga

5. Pilates

6. Tai Chi

7. Traction therapy

8. Inversion table therapy

9. Spinal decompression table

10. TENS (electrical nerve stimulation)

11. Ultrasound therapy

12. Heat therapy

13. Cold therapy

14. Massage therapy

15. Chiropractic manipulation

16. Acupuncture

17. Dry needling

18. Ergonomic assessment

19. Postural training

20. Workstation modification

21. Activity modification

22. Weight management

23. Smoking cessation

24. Core-stabilization exercises

25. Education on proper lifting

26. Bracing (lumbar corset)

27. Orthotics (foot support)

28. Cognitive behavioral therapy

29. Relaxation techniques

30. Aquatic pool walking

Medications

When needed, pharmacological agents may include:

1. Ibuprofen (NSAID)

2. Naproxen (NSAID)

3. Diclofenac (NSAID)

4. Celecoxib (COX-2 inhibitor)

5. Acetaminophen

6. Tramadol

7. Hydrocodone

8. Morphine

9. Cyclobenzaprine (muscle relaxant)

10. Baclofen (muscle relaxant)

11. Tizanidine (muscle relaxant)

12. Gabapentin (neuropathic pain)

13. Pregabalin (neuropathic pain)

14. Duloxetine (SNRI)

15. Amitriptyline (TCA)

16. Prednisone (oral steroid)

17. Methylprednisolone (burst pack)

18. Epidural steroid injection

19. Lidocaine patch

20. Capsaicin cream

Surgical Options

Reserved for severe or refractory cases:

1. Microdiscectomy

2. Laminectomy (open decompression)

3. Laminotomy (partial bone removal)

4. Foraminotomy (nerve outlet widening)

5. Facetectomy (facet joint removal)

6. Posterior lumbar interbody fusion (PLIF)

7. Transforaminal lumbar interbody fusion (TLIF)

8. Extreme lateral interbody fusion (XLIF)

9. Endoscopic discectomy

10. Artificial disc replacement

Prevention Strategies

To reduce risk of posterolateral thecal sac indentation:

1. Maintain a healthy weight

2. Practice proper lifting technique

3. Strengthen core muscles regularly

4. Use ergonomic workstations

5. Take frequent breaks when seated

6. Avoid prolonged bending or twisting

7. Wear supportive footwear

8. Stay active with low-impact exercise

9. Quit smoking

10. Get regular check-ups if you have arthritis

When to See a Doctor

Seek prompt medical attention if you experience:

• Sudden weakness or numbness in legs or arms

• New bowel or bladder incontinence

• Saddle anesthesia (numbness around groin)

• Unrelenting night pain

• Fever with back pain (possible infection)

• Recent severe trauma

• Progressive neurological deficits

• Difficulty walking or balance loss

• Pain that fails to improve after 6 weeks of conservative care

Frequently Asked Questions

1. What exactly is posterolateral thecal sac indentation?
   It’s when a structure at the back and side of the spine presses into the dural sac, compressing the space around the spinal cord.

2. How is it diagnosed?
   MRI is the gold standard; CT and myelography can help with bone detail and operative planning.

3. Can mild indentation resolve on its own?
   Yes—if the source is a minor disc bulge or reversible inflammation, physical therapy and rest often suffice.

4. When is surgery necessary?
   Surgery is considered when neurological deficits worsen or conservative care fails after 6–12 weeks.

5. What are non-surgical treatment goals?
   To relieve pain, improve function, and strengthen the spine to prevent recurrence.

6. Are injections helpful?
   Yes—epidural steroid injections can reduce inflammation around compressed nerve roots.

7. Can medications alone fix it?
   Medications control symptoms but do not reverse structural indentation.

8. Is physical therapy safe?
   When guided by a trained therapist, it’s highly effective and low risk.

9. Will this condition cause paralysis?
   Rarely—only severe compression of the spinal cord or cauda equina can lead to paralysis if untreated.

10. How long is recovery after surgery?
    Most patients return to normal activities within 6–12 weeks, depending on procedure and overall health.

11. Can lifestyle changes prevent recurrence?
    Yes—weight management, posture correction, and core strengthening are key.

12. Is imaging always needed?
    Not for mild, typical back pain. Imaging is indicated if red-flag signs appear or pain persists.

13. What is the role of braces?
    Braces can offload stress from the spine temporarily, aiding pain control during flare-ups.

14. Does age matter?
    Degenerative causes increase with age, but even younger individuals can develop it from trauma or congenital narrowing.

15. Where can I learn more?
    Reliable sources include peer-reviewed journals (e.g., JAMA, StatPearls) and trusted medical sites (Radiopaedia, SpineInfo).

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

Last Updated: May 03, 2025.