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
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
Protection: Forms a tough barrier shielding the spinal cord from mechanical injury and pathogen invasion.
CSF Containment: Houses cerebrospinal fluid, providing buoyancy and cushioning against shocks.
Homeostasis: Maintains optimal chemical environment for nerve roots and spinal cord by circulating CSF.
Immune Barrier: Serves as an immunological interface, limiting spread of infection into the central nervous system.
Stabilization: Anchors and centers the spinal cord in the vertebral canal during flexion and extension.
Nutrient Exchange: Facilitates exchange of nutrients and waste between CSF and spinal cord vessels. Verywell Health
Types of Extradural Thecal Sac Indentation
Focal Indentation: Localized flattening at a single spinal level, often from a focal disc protrusion.
Diffuse Indentation: Widespread circumferential effacement, typically from multilevel spondylotic changes.
Symmetric vs. Asymmetric: Symmetric when both sides of the sac are equally compressed; asymmetric when one side is more indented, causing lateral recess stenosis.
Graded Indentation: Classified as mild (< 25 %), moderate (25 %–50 %), or severe (> 50 %) based on CSF space obliteration.
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)
Causes
Herniated intervertebral disc (protrusion, extrusion)
Osteophyte formation from spondylosis
Hypertrophy of ligamentum flavum
Facet joint arthrosis and cysts
Epidural lipomatosis (excess fat) RadiopaediaPMC
Vertebral fracture retropulsion
Synovial cysts in facet joints
Spinal epidural abscess
Spinal epidural hematoma
Extradural metastatic tumors
Primary bone tumors (e.g., chordoma)
Tuberculous spondylitis (Pott’s disease)
Epidural fibrosis (post-surgical scar)
Rheumatoid pannus at C1–C2
Spondylolisthesis with canal narrowing
Paget’s disease of bone
Desmoid tumors
Calcified epidural cysts
Anticoagulation-related bleeding
Idiopathic intracanal fat deposition
Symptoms
Localized back or neck pain
Radicular pain (shooting down arms or legs)
Numbness or tingling in limbs
Muscle weakness in corresponding myotomes
Neurogenic claudication (leg pain on walking)
Reflex changes (hyperreflexia or hyporeflexia)
Gait disturbances or ataxia
Bowel or bladder dysfunction
Sexual dysfunction
Lhermitte’s sign (electric shock sensations)
Spasticity of lower limbs
Sensory level (dermatomal loss)
Neck stiffness
Upper motor neuron signs in cervical lesions
Cold intolerance or dysesthesia
Postural imbalance
Headache worsening with posture (cervical region)
Intracanal clonus
Myelopathic hand signs (Hoffmann’s sign)
In severe cases, partial paralysis PMC
Diagnostic Tests
MRI (T1, T2, STIR): Gold standard for soft-tissue and CSF space visualization
CT Scan: Detects bony overgrowth and calcifications
CT Myelography: Alternative when MRI contraindicated
Plain Radiographs (X-ray): Show spondylosis, alignment, fractures
Dynamic (Flexion/Extension) X-rays: Assess instability
Bone Scan: Identifies infection or tumor activity
PET-CT: For metastatic disease evaluation
Discography: Pain mapping in discogenic pain
Electromyography (EMG): Evaluates nerve root function
Nerve Conduction Studies (NCS): Quantifies peripheral nerve involvement
Somatosensory Evoked Potentials (SSEP): Assesses dorsal column pathways
Motor Evoked Potentials (MEP): Evaluates corticospinal tracts
Ultrasound‐Guided Epidural Injection Test: Diagnostic and therapeutic
Cerebrospinal Fluid Analysis (Lumbar Puncture): In suspected infection
ESR/CRP: Inflammatory markers for infection/inflammation
Complete Blood Count: Infection screening
Serologic Tests: TB, rheumatoid factor
Biopsy (CT‐guided): For unknown epidural masses
Vascular Studies (Doppler): Exclude vascular etiologies
Neuropsychological Testing: For chronic pain assessment PMC
Non-Pharmacological Treatments
Physical therapy with core stabilization
Stretching exercises (e.g., hamstring, hip flexor)
Aquatic therapy (water-based exercises)
Manual therapy (mobilization, massage)
Traction therapy (mechanical or manual)
Heat and cold application
Transcutaneous electrical nerve stimulation (TENS)
Spinal decompression therapy
Chiropractic spinal manipulation
Acupuncture and dry needling
Postural education and ergonomic training
Weight loss and nutritional counseling JPain
Yoga and Tai Chi
Pilates for spinal stability
Cognitive-behavioral therapy for pain
Biofeedback training
Gait training with assistive devices
Lumbosacral orthoses (back braces)
Activity modification and pacing
Self-management education
Kinesio taping
Neural mobilization techniques
Ergonomic workstation setup
Relaxation and breathing exercises
Sleep hygiene optimization
Smoking cessation support
Aquatic buoyancy-assisted stretches
Dry hydrotherapy (aqua-jets)
Vestibular therapy (for balance)
Mindfulness meditation
Drugs
Acetaminophen (paracetamol)
Ibuprofen (NSAID)
Naproxen (NSAID)
Diclofenac (NSAID)
Meloxicam (NSAID)
Celecoxib (COX-2 inhibitor)
Tramadol (weak opioid)
Codeine (opioid)
Oxycodone (opioid)
Morphine (opioid)
Gabapentin (neuropathic pain)
Pregabalin (neuropathic pain)
Duloxetine (SNRI)
Amitriptyline (TCA)
Carbamazepine (anticonvulsant)
Baclofen (muscle relaxant)
Cyclobenzaprine (muscle relaxant)
Tizanidine (muscle relaxant)
Prednisone (oral corticosteroid)
Methylprednisolone (injectable corticosteroid) Verywell Health
Surgeries
Decompressive laminectomy
Microdiscectomy
Laminotomy (unicompartmental decompression)
Posterior lumbar interbody fusion (PLIF)
Transforaminal lumbar interbody fusion (TLIF)
Anterior cervical discectomy and fusion (ACDF)
Foraminotomy
Endoscopic decompression
Kyphoplasty/vertebroplasty (for compression fractures)
Minimally invasive tubular decompression PMC
Prevention Strategies
Maintain healthy body weight
Regular core and back strengthening exercises
Practice good posture (standing, sitting, lifting)
Ergonomic workstation setup
Avoid heavy lifting or twisting without support
Quit smoking to improve disc health
Balanced diet rich in calcium and vitamin D
Stay active with low-impact cardio (walking, swimming)
Use proper body mechanics in daily activities
Early treatment of minor back injuries Verywell Health
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
Frequently Asked Questions
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.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.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 %).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.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.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.When is surgery necessary?
Surgery is considered when severe indentation causes neurological deficits, intractable pain, or threatens permanent nerve damage.What are the risks of surgery?
Potential risks include infection, bleeding, nerve injury, instability requiring fusion, and scar tissue formation.Can epidural steroid injections help?
Yes. Injections of corticosteroids into the epidural space can reduce inflammation and relieve pain, but effects may be temporary.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.What lifestyle changes prevent recurrence?
Maintaining a strong core, healthy weight, proper posture, and avoiding heavy lifting help prevent further spinal canal narrowing.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.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.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.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.
