Paracentral Thecal Sac Indentation

Paracentral thecal sac indentation is a focal deformation or inward pressure on the thecal sac— the dural sheath enclosing the spinal cord and cauda equina—caused by structures abutting its lateral aspects in the paracentral zone of the spinal canal. On axial MRI, the canal is divided into central (medial two quarters), paracentral (lateral two quarters), and foraminal/extraforaminal regions; herniated disc material extending into the lateral two quarters compresses the traversing nerve root and indents the thecal sac in that region PMCRadiology Key.

---

Anatomy of the Thecal Sac

1. Structure & Location

   • The thecal sac is formed by the meningeal layer of dura mater and surrounds the spinal cord, cauda equina, and cerebrospinal fluid (CSF) within the vertebral canal Wikipedia.

2. Origin & Insertion

   • Origin: Continuous with cranial dura mater at the foramen magnum.

   • Insertion: Terminates at the vertebral level of S2, anchored by the filum terminale .

3. Blood Supply

   • Receives branches from spinal (radicular) meningeal arteries; venous drainage via the internal vertebral (epidural) venous plexus Wikipedia.

4. Nerve Supply

   • Innervated by sinuvertebral (recurrent meningeal) nerves from spinal nerve roots and upper cervical nerves cranially; trigeminal branches supply cranial dura NCBI.

5. Functions

   1. Mechanical Protection: Shields neural elements from trauma Kenhub.

   2. CSF Containment: Maintains a closed CSF environment for nutrient delivery and waste removal Wikipedia.

   3. Pressure Dampening: Absorbs shock and distributes mechanical forces Kenhub.

   4. Neural Root Support: Guides and protects exiting nerve roots ScienceDirect.

   5. Barrier to Infection: Prevents epidural pathogens from entering the subarachnoid space ScienceDirect.

   6. Clinical Access: Serves as the target for lumbar puncture and epidural injections Medscape.

---

Types of Paracentral Thecal Sac Indentation

Indentation may arise from a variety of pathologies in the paracentral zone:

1. Paracentral Disc Bulge (diffuse annular protrusion >25% circumference) Radiopaedia

2. Paracentral Disc Protrusion (contained focal herniation <25% circumference) Radiology Assistant

3. Paracentral Disc Extrusion (non-contained herniation with larger base-to-apex ratio) Radiology Assistant

4. Sequestrated Disc Fragment (free fragment migrating in epidural space) Radiology Key

5. Facet Joint Arthrosis & Osteophyte Formation (bony overgrowth indenting lateral recess) Radiopaedia

6. Ligamentum Flavum Hypertrophy (thickened ligament compressing thecal sac) Radiopaedia

7. Synovial Cyst of Facet Joint (cystic fluid collection in lateral recess) Radiopaedia

8. Epidural Lipomatosis (excess epidural fat compressing thecal sac)

9. Dural-Based Tumors (e.g., meningioma) Radiopaedia

10. Schwannoma/Neurofibroma (nerve sheath tumors in lateral recess) Radiopaedia

11. Metastatic Epidural Disease (epidural metastases indenting thecal sac) Radiopaedia

12. Epidural Abscess (infectious collection compressing dura) Radiopaedia

13. Epidural Hematoma (blood collection in epidural space) Radiopaedia

14. Ossification of Posterior Longitudinal Ligament (OPLL) Radiopaedia

15. Spondylolisthesis (vertebral slippage narrowing canal) Radiopaedia

16. Paget’s Disease (bone remodeling causing canal narrowing) Radiopaedia

17. Spinal Tuberculosis (Pott’s Disease) (epidural granulation tissue) Radiopaedia

18. Synovial Hypertrophy in Rheumatoid Arthritis Radiopaedia

19. Vascular Malformations (e.g., hemangioma) Radiopaedia

20. Calcified Disc Herniation (disc ossification indenting dura) Radiopaedia

---

Causes

1. Degenerative Disc Disease leading to bulge/protrusion

2. Acute Trauma causing annular tear and extrusion

3. Repetitive Microtrauma (lifting, sports)

4. Age-Related Degeneration of annulus fibrosus

5. Obesity increasing axial load

6. Smoking impairing disc nutrition

7. Genetic Predisposition to disc degeneration PMC

8. Facet Arthropathy hypertrophy Radiopaedia

9. Ligamentum Flavum Hypertrophy Radiopaedia

10. OPLL (genetic/metabolic factors)

11. Synovial Cysts (facet joint degeneration) Radiopaedia

12. Epidural Lipomatosis (steroid use, obesity)

13. Tumors (primary or metastatic) Radiopaedia

14. Infection (abscess formation) Radiopaedia

15. Hematoma (anticoagulation, trauma) Radiopaedia

16. Post-Surgical Scar (epidural fibrosis)

17. Spondylolisthesis (instability) Radiopaedia

18. Rheumatoid Disease (synovial proliferation)

19. Paget’s Disease (bone overgrowth) Radiopaedia

20. Vascular Malformations (hemangiomas, AVMs) Radiopaedia

---

Symptoms

Patients with paracentral indentation frequently report:

• Low Back Pain PMC

• Unilateral Leg Pain (Sciatica) Orthobullets

• Numbness/Tingling in a dermatomal distribution Orthobullets

• Muscle Weakness in affected myotomes PMC

• Reduced Reflexes (e.g., diminished knee jerk) Orthobullets

• Gait Disturbance Orthobullets

• Positive Straight Leg Raise test Orthobullets

• Neurogenic Claudication (pain on walking) Radiopaedia

• Bladder/Bowel Dysfunction (cauda equina syndrome) PMC

• Saddle Anesthesia PMC

• Foot Drop Orthobullets

• Pain at Rest/Night PMC

• Hypoesthesia in lateral calf/foot Orthobullets

• Muscle Spasms AAFP

• Postural Stiffness ChoosePT

• Limited Lumbar Mobility ChoosePT

• Referred Buttock Pain Orthobullets

• Radicular Burning/Shooting Pain Orthobullets

• Sensory Loss in foot dorsum or sole Orthobullets

• Temperature Sensation Changes Orthobullets

---

Diagnostic Tests

1. MRI (gold standard for soft tissue and CSF-space imaging) Medscape

2. CT Scan (bony detail, calcified herniations) Medscape

3. Plain X-rays (degenerative changes, alignment) PMC

4. Myelography (contraindicated if standard MRI available) Medscape

5. CT Myelogram (for MRI-incompatible patients) Medscape

6. Electromyography (EMG) (denervation signs) PMC

7. Nerve Conduction Studies (radiculopathy assessment) PMC

8. Discography (controversial; pain reproduction) Medscape

9. Ultrasound (epidural lipomatosis detection)

10. Bone Scan (Paget’s disease, metastases) Radiopaedia

11. Blood Tests (infection markers, inflammatory) Radiopaedia

12. CSF Analysis (suspected epidural abscess) Radiopaedia

13. CT Angiography (vascular lesions) Radiopaedia

14. Gadolinium-Enhanced MRI (tumors, abscess) Medscape

15. Flexion-Extension X-rays (instability) PMC

16. Selective Nerve Root Block (diagnostic, therapeutic) Medscape

17. EMG with Paraspinal Sampling PMC

18. Somatosensory Evoked Potentials Radiopaedia

19. Visual Analog Scale (VAS) for pain quantification PMC

20. Oswestry Disability Index (functional assessment) PMC

---

Non-Pharmacological Treatments

1. Physical Therapy individualized programs ChoosePT

2. Core-Strengthening Exercises ChoosePT

3. Flexibility/Stretching (hamstrings, piriformis) Verywell Health

4. McKenzie (Directional Preference) Exercises Verywell Health

5. Aerobic Conditioning (walking, swimming) Verywell Health

6. Traction Therapy PMC

7. Transcutaneous Electrical Nerve Stimulation PMC

8. Thermal Therapy (heat/cold packs) ChoosePT

9. Aquatic Therapy ChoosePT

10. Yoga & Pilates Verywell Health

11. Tai Chi Verywell Health

12. Manual Therapy/Spinal Mobilization JOSPT

13. Massage Therapy Archives PMR

14. Ergonomic Adjustments at work/home ChoosePT

15. Postural Training Verywell Health

16. Bracing (temporary support) PMC

17. Weight Management Verywell Health

18. Lifestyle Modification (smoking cessation) PMC

19. Cognitive Behavioral Therapy for pain coping PMC

20. Acupuncture PMC

21. Dry Needling PMC

22. Ultrasound Therapy PMC

23. Electrical Stimulation PMC

24. Hydrotherapy ChoosePT

25. Biofeedback PMC

26. Relaxation Techniques PMC

27. Proprioceptive Training PMC

28. Functional Rehabilitation ChoosePT

29. Pilates-Based Core Control Verywell Health

30. Education on Back Care PMC

---

Drug Options

1. NSAIDs (ibuprofen, naproxen) PMC

2. Acetaminophen PMC

3. Oral Corticosteroids (prednisone burst) PMC

4. Muscle Relaxants (cyclobenzaprine) AAFP

5. Gabapentin PMC

6. Pregabalin PMC

7. Duloxetine PMC

8. Tramadol PMC

9. Opioids (short-term, monitored) PMC

10. Epidural Steroid Injection (ESI) Medscape

11. Transforaminal ESI Medscape

12. NSAID–Opioid Combination PMC

13. Topical NSAIDs PMC

14. Capsaicin Cream PMC

15. Lidocaine Patch PMC

16. Duloxetine PMC

17. Amitriptyline PMC

18. Venlafaxine PMC

19. Ketorolac (IM/IV) PMC

20. Calcitonin (rare) PMC

---

Surgical Procedures

1. Microdiscectomy (minimally invasive removal of herniated disc) JAMA Network

2. Open Discectomy JAMA Network

3. Laminectomy (removal of lamina to decompress) Orthobullets

4. Foraminotomy (widening neural foramen) Orthobullets

5. Laminotomy (partial lamina removal) Orthobullets

6. Endoscopic Discectomy Orthobullets

7. Transforaminal Endoscopic Surgery Medscape

8. Posterior Lumbar Interbody Fusion (PLIF) JAMA Network

9. Transforaminal Lumbar Interbody Fusion (TLIF) JAMA Network

10. Facet Joint Resection Orthobullets

---

Prevention Strategies

1. Proper Lifting Techniques Verywell Health

2. Core Strengthening Programs ChoosePT

3. Regular Aerobic Exercise Verywell Health

4. Ergonomic Workstation Setup ChoosePT

5. Weight Management Verywell Health

6. Smoking Cessation PMC

7. Flexibility & Stretching Routine Verywell Health

8. Posture Training Verywell Health

9. Avoid Prolonged Sitting/Standing ChoosePT

10. Periodic Back Care Education PMC

---

When to See a Doctor

Seek urgent evaluation if you experience:

• Severe or Progressive Weakness in legs PMC

• Loss of Bladder or Bowel Control PMC

• Saddle Anesthesia (numbness in groin) PMC

• Fever/Chills (possible infection) Radiopaedia

• Unremitting Night Pain PMC

• Trauma with Severe Pain Medscape
  Otherwise, consider consultation if pain persists beyond 6-12 weeks despite conservative therapy Lucia Zamorano.

---

Frequently Asked Questions

1. What is paracentral thecal sac indentation?
   It’s an inward pressure on the dural sac by adjacent structures (e.g., disc herniation) in the paracentral zone Radiology Key.

2. How is it diagnosed?
   Primarily by MRI, which shows thecal sac deformation in axial views Medscape.

3. What causes paracentral indentation?
   Degenerative disc herniations, facet arthrosis, ligament hypertrophy, tumors, abscesses, hematomas Radiopaedia.

4. Can it be treated without surgery?
   Yes—physical therapy, NSAIDs, epidural steroids, and lifestyle modifications often suffice Spine.org.

5. When is surgery indicated?
   Persistent pain despite 6–12 weeks of conservative care, progressive neurologic deficits, or cauda equina syndrome Lucia Zamorano.

6. What are the risks of microdiscectomy?
   Infection, dural tear, recurrent herniation, nerve injury JAMA Network.

7. How long is recovery after discectomy?
   Most return to light activities in 2–4 weeks; full recovery in 3–6 months JAMA Network.

8. Can herniated discs heal on their own?
   Yes—many regress or resorb over time with conservative care Guideline Central.

9. What exercises worsen indentation?
   Deep flexion, heavy lifting, twisting under load should be avoided initially Verywell Health.

10. Is MRI always necessary?
    Not if red flags are absent and symptoms respond to treatment, but MRI guides definitive care Spine.org.

11. What is the role of epidural steroid injections?
    Provide short-term pain relief in selected radiculopathy patients Medscape.

12. Are opioids recommended?
    Only for severe pain short-term, under careful supervision PMC.

13. How to prevent recurrence?
    Core stability, proper ergonomics, weight control, smoking cessation ChoosePT.

14. Do genetics play a role?
    Yes—family history influences disc degeneration and herniation risk PMC.

15. When should children be evaluated?
    Rare in children; any neurologic signs or severe pain warrant prompt imaging PMC.

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 02, 2025.

PDF Document For This Disease Conditions

References