Subarticular Thecal Sac Indentation

Subarticular thecal sac indentation is a radiologic finding on spinal imaging (MRI, CT) characterized by focal inward deformation of the thecal (dural) sac at the subarticular (lateral recess) zone. It occurs when structures—such as herniated disc material, hypertrophied facet joints, thickened ligamentum flavum, osteophytes, or other soft tissue masses—encroach upon the dural sac, causing effacement of cerebrospinal fluid in that region on axial images .

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Anatomy of the Thecal Sac

Structure & Location:
The thecal sac (or dural sac) is a tubular sheath of dura mater that encloses the spinal cord and cauda equina within the vertebral canal, extending from the foramen magnum to the level of the second sacral vertebra (S2) .

Origin & Termination:
It arises as dura mater exits the skull at the foramen magnum, surrounding the spinal cord. Inferiorly, it tapers at S2, where it anchors to the coccyx via the filum terminale externum .

Blood Supply:
The spinal dura receives arterial blood primarily from the anterior and posterior radicular arteries—branches of segmental spinal arteries—that anastomose around the nerve roots and dura .

Nerve Supply:
A dense ventral dural plexus, formed by the sinuvertebral nerves (recurrent meningeal nerves), the posterior longitudinal ligament plexus, and radicular branches of segmental arteries, innervates the anterior and lateral spinal dura; the dorsal dura has fewer, smaller nerves derived from this plexus .

Functions:

1. Support Spinal Vasculature: Provides a scaffold for spinal blood vessels.

2. Mechanical Cushioning: Works with CSF to absorb shocks and prevent tissue injury.

3. CSF Containment: Forms a continuous cavity through which CSF circulates.

4. Nutrient/Waste Transport: Maintains CSF volume for nutrient delivery and waste removal.

5. Barrier Function: Protects against infection and hemorrhage.

6. Dural Root Sheaths: Extends along spinal nerves forming dural root sleeves as they exit the canal.

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Types of Subarticular Thecal Sac Indentation

1. Subarticular Disc Bulge: Broad-based protrusion indenting the thecal sac ventrally.

2. Subarticular Disc Protrusion: Focal herniation pressing into the lateral recess.

3. Subarticular Disc Extrusion: Extruded nucleus pulposus penetrating the thecal sac.

4. Facet Joint Hypertrophy: Overgrowth of facet joints compressing the lateral recess.

5. Ligamentum Flavum Thickening: Hypertrophied ligament encroaching on the dural sac.

6. Synovial Cyst: Fluid‐filled cyst from the facet joint indenting thecal sac.

7. Osteophyte Formation: Bony spurs from vertebral endplates narrowing the recess.

8. Postoperative Epidural Fibrosis: Scar tissue after surgery causing indentation.

9. Epidural Hematoma: Blood collection compresses the thecal sac acutely.

10. Epidural Abscess: Infected material indenting the sac.

11. Metastatic Epidural Tumor: Neoplastic tissue in the epidural space.

12. Paget’s Disease of Bone: Bone remodeling leading to canal narrowing.

13. Coagulopathy‐Related Bleeds: Spontaneous hematoma from blood disorders.

14. Vascular Anomalies: Arteriovenous malformation masses compressing dura.

15. Traumatic Bony Fragments: Fracture pieces indenting thecal sac.

16. Developmental Subarticular Stenosis: Congenital short pedicles narrow recess.

17. Achondroplasia: Genetic bone growth disorder causing canal narrowing.

18. Epidural Lipomatosis: Excess fat deposition compresses thecal sac.

19. Degenerative Spondylotic Ridges: Hypertrophic bony ridges from spondylosis.

20. Tarlov Cysts: Perineural cysts may indent the lateral aspect of the sac.

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Causes

1. Herniated Disc (bulge, protrusion, extrusion, sequestration)

2. Degenerative Spinal Stenosis (central/subarticular)

3. Facet Arthrosis & Hypertrophy

4. Ligamentum Flavum Thickening

5. Synovial Cyst Formation

6. Osteophyte Spurs

7. Disc Extrusion into Recess

8. Disc Sequestration

9. Spinal Epidural Hematoma

10. Epidural Abscess/Infection

11. Epidural Neoplasms/Metastases

12. Paget’s Disease of Bone

13. Coagulopathy / Anticoagulation Therapy

14. Vascular Anomalies

15. Minor Vertebral Trauma/Fracture Fragments

16. Congenital Pedicle Shortening

17. Achondroplasia

18. Epidural Lipomatosis

19. Degenerative Spondylotic Ridges

20. Tarlov (Perineural) Cysts

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Symptoms

1. Localized back pain

2. Radicular pain radiating into arms/legs

3. Numbness or tingling in limbs

4. Muscle weakness

5. Neurogenic claudication (leg cramping when walking)

6. Burning pain in buttocks/legs

7. Leg/foot numbness

8. Pins-and-needles sensation

9. Leg/foot weakness

10. Reduced deep tendon reflexes

11. Bowel/bladder dysfunction (incontinence)

12. Saddle anesthesia

13. Sexual dysfunction

14. Symptoms improve when bending forward

15. Paraspinal muscle spasm

16. Gait disturbance/unsteady walking

17. Clonus or hyperreflexia (in cord compression)

18. Muscle atrophy (chronic cases)

19. Neck pain/stiffness (cervical level)

20. Dysphagia or swallowing difficulty (high cervical compression)

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Diagnostic Tests

1. X-rays (plain radiography to assess bony anatomy)

2. Magnetic Resonance Imaging (MRI) for detailed soft-tissue evaluation

3. Computed Tomography (CT) scan for bone detail

4. CT Myelography (contrast-enhanced CT)

5. Myelogram with fluoroscopic contrast

6. Electromyography (EMG) for nerve function assessment

7. Nerve Conduction Studies (NCS)

8. Somatosensory Evoked Potentials (SSEP)

9. Neurological Examination (motor strength, sensation, reflexes)

10. Medical History & Symptom Review

11. Laboratory Tests (CBC, ESR, CRP) to rule out infection/inflammation

12. Bone Scan (nuclear imaging) for metastases or bone disease

13. Provocative Discography to localize symptomatic discs

14. Dynamic (Flexion-Extension) X-rays for instability

15. CT–Myelogram for detailed root sleeve visualization

16. Quantitative MRI Measurements (canal diameter, cross-sectional area)

17. Selective Nerve Root Block (diagnostic injection)

18. Urodynamic Studies for bladder dysfunction

19. Physical Performance Tests (treadmill, walking distance)

20. Psychological Assessment (Waddell’s signs, CBT evaluation)

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Non-Pharmacological Treatments

1. Tailored Physical Therapy programs of stretching & strengthening

2. Soft Tissue Massage to reduce muscle tension

3. Joint Mobilization techniques for spine segments

4. Spinal Traction Therapy (mechanical/manual)

5. Core Stabilization Exercises (e.g., bird-dog, bridges)

6. Knee-to-Chest Stretch for neural relief

7. Posterior Pelvic Tilt (Bridge)

8. Neural Tension Exercises (leg neural stretch)

9. Hip-Flexor Stretch

10. Lower Trunk Rotation

11. Aquatic Therapy for reduced axial load

12. Low-Impact Aerobic Exercise (walking, cycling, swimming)

13. Supervised Weight-Loss Programs

14. Lumbosacral Bracing/Corsets

15. Gait Aids (cane, walker)

16. Ergonomic & Postural Education

17. Chiropractic Manipulation

18. Acupuncture

19. TENS (Transcutaneous Electrical Nerve Stimulation)

20. Heat Therapy (moist heat packs)

21. Cold Therapy (ice packs)

22. Ultrasound Therapy

23. NMES (Neuromuscular Electrical Stimulation)

24. Myofascial Release manual technique

25. Yoga for flexibility & core strength

26. Pilates for posture & core control

27. Tai Chi for balance & coordination

28. Massage Therapy

29. Activity Modification to avoid aggravating positions

30. Self-Management Education strategies

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Drugs

1. Ibuprofen (NSAID)

2. Naproxen (NSAID)

3. Diclofenac (NSAID)

4. Aspirin

5. Acetaminophen

6. Celecoxib (COX-2 inhibitor)

7. Cyclobenzaprine (muscle relaxant)

8. Baclofen

9. Tizanidine

10. Gabapentin

11. Pregabalin

12. Duloxetine (SNRI)

13. Nortriptyline (TCA)

14. Prostaglandin-based agents

15. Methylcobalamin

16. Epidural methylprednisolone (steroid injection)

17. Epidural dexamethasone

18. Carbamazepine

19. Oxcarbazepine

20. Lidocaine patch (topical)

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Surgeries

1. Open Laminectomy (decompressive laminectomy)

2. Minimally Invasive Laminectomy

3. Laminotomy (partial lamina removal)

4. Foraminotomy

5. Discectomy (microdiscectomy)

6. Spinal Fusion (instrumented)

7. Ligamentum Flavum Resection

8. Endoscopic Decompression

9. Microsurgical Laminoplasty Wikipedia

10. Cervical Laminoplasty Cleveland Clinic

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 Preventions

1. Maintain a healthy weight to reduce spinal load.

2. Regular low-impact exercise (walking, swimming).

3. Good posture when sitting/standing.

4. Ergonomic workstation setup.

5. Core strengthening (e.g., Pilates).

6. Proper lifting techniques—bend knees, keep back straight.

7. Regular stretching to maintain flexibility.

8. Take breaks to avoid prolonged sitting or standing.

9. Use lumbar support cushions when sitting.

10. Follow ergonomic guidelines for driving and computer use.

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When to See a Doctor

See a healthcare provider promptly if you experience:

• Sudden weakness in legs or arms

• Loss of bladder or bowel control

• Saddle anesthesia (numbness in groin)

• Severe, unrelenting pain at rest or at night

• Fever or signs of infection

• History of cancer with new back pain

• Progressive neurological deficits (e.g., increasing weakness, reflex changes)

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Frequently Asked Questions

1. What exactly is subarticular thecal sac indentation?
   It’s when nearby structures push into the lateral part of your spinal canal, indenting the dural sac that contains your spinal cord or nerves.

2. How is it diagnosed?
   Primarily by MRI or CT myelography, which show detailed images of the spinal canal and any indentations.

3. Can mild indentations cause symptoms?
   Mild cases often are painless and found incidentally. Symptoms depend on severity and nerve involvement.

4. What symptoms should alert me?
   Look for radicular pain, numbness, muscle weakness, and neurogenic claudication (leg cramps with walking).

5. Is it the same as spinal stenosis?
   It’s a form of lateral recess stenosis—spinal stenosis normally refers to central canal narrowing, while subarticular indentations affect the lateral recess.

6. What non-surgical treatments help most?
   Physical therapy, core-strengthening exercises, posture correction, and low-impact aerobic activity are first-line.

7. When are injections used?
   Epidural steroid injections can ease inflammation and pain for weeks to months but don’t fix the underlying indentation.

8. Are opioids ever prescribed?
   They may be used short-term for severe pain but carry risks of dependence and side effects.

9. When is surgery recommended?
   If there’s progressive neurological deficit, intractable pain unresponsive to conservative care, or cauda equina syndrome signs.

10. What surgical options exist?
    Decompressive laminectomy, laminotomy, discectomy, endoscopic decompression, and sometimes fusion if instability is present.

11. What are the risks of surgery?
    Infection, bleeding, nerve injury, CSF leak, instability requiring fusion, and anesthesia risks.

12. Can indentations recur after surgery?
    Yes—scar tissue (epidural fibrosis) or further degeneration can cause recurrent symptoms.

13. How can I prevent subarticular stenosis?
    Maintain healthy weight, exercise regularly, practice good posture, and avoid heavy spinal loads.

14. Is physical therapy enough?
    Many patients gain substantial relief; severe cases sometimes still require surgery.

15. What’s the long-term outlook?
    With appropriate management, most achieve stable symptom control. Ongoing exercise and weight management help maintain improvements.

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.