A free fragment thecal sac indentation refers to a condition where a sequestered disc fragment—a piece of intervertebral disc material that has broken away completely—migrates into the spinal canal and presses on the thecal sac, the protective dura mater sheath containing the spinal cord and cerebrospinal fluid (CSF). This indentation can be seen on MRI as a focal “dent” on the anterior (ventral) surface of the thecal sac, often causing pain, nerve irritation, or neurological symptoms when the fragment impinges on adjacent nerve roots or the cord itself Radiology Key.
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.
It extends from the foramen magnum at the skull base to around the second sacral vertebra (S2), tapering over the filum terminale Wikipedia.
Origin & Insertion
The dura mater adheres to bone at the foramen magnum and loosely attaches along each vertebral foramen via dura-ligamentous connections.
It ends as the filum terminale, which anchors it to the coccyx.
Blood Supply
Posterior meningeal arteries (branches of segmental arteries) supply the dorsal aspect of the thecal sac.
Anterior meningeal arteries (from the vertebral and radicular arteries) supply the ventral dura.
Nerve Supply
Innervated by recurrent meningeal nerves (sinuvertebral nerves), which carry pain signals from the dura and epidural structures.
Key Functions
Protection: Shields the spinal cord and nerve roots from mechanical injury.
CSF Containment: Maintains a sealed space for cerebrospinal fluid, which cushions neural structures.
Nutrient Transport: Allows diffusion of nutrients and removal of waste in CSF.
Shock Absorption: Dura’s toughness absorbs minor impacts and pressure changes.
Nerve Exit Conduits: Forms sleeves around exiting nerve roots, guiding them through the intervertebral foramina.
Pressure Regulation: Maintains stable intracanal pressure, important for spinal cord perfusion.
Types of Free Fragment Thecal Sac Indentation
Sequestered Disc Fragment: Fully detached disc material migrating in the canal.
Extruded Fragment with Narrow Neck: Disc material still linked by a thin “neck” but indenting the dura Radiology Key.
Migrated Fragment: Sequestered piece that travels superiorly, inferiorly, or laterally within the canal.
Calcified Fragment: Disc material with bone spur formation causing rigid compression.
Infected/Abscess Fragment: Rarely, infected disc material forms an abscess pressing on the sac.
Causes
Degenerative Disc Disease (age-related wear) Spine Info
Intervertebral Disc Herniation (protrusion → extrusion → sequestered)
Trauma (e.g., falls, accidents) leading to acute disc rupture
Repetitive Strain (heavy lifting, poor ergonomics)
Obesity (increased axial load)
Ligamentum Flavum Hypertrophy (thickening of posterior ligaments) Spine Info
Osteophyte Formation (bone spurs) Spine Info
Spondylolisthesis (vertebral slippage)
Spinal Stenosis (canal narrowing)
Tumors (benign or malignant growths)
Epidural Hematoma (bleeding in the canal)
Infections (e.g., spinal epidural abscess)
Inflammatory Arthritis (e.g., ankylosing spondylitis)
Paget’s Disease of Bone (abnormal bone remodeling)
Congenital Spinal Canal Narrowing
Scheuermann’s Disease (juvenile kyphosis)
Smoking (disc degeneration accelerator)
Poor Posture (chronic axial stress)
Genetic Predisposition (familial disc disorders)
Metabolic Disorders (e.g., diabetes affecting disc health)
Symptoms
Localized Back Pain (thoracic or lumbar)
Radiating (Radicular) Pain (sciatica or cervicobrachialgia)
Numbness/Tingling in extremities
Muscle Weakness (foot drop, grip weakness)
Reflex Changes (hypo- or hyperreflexia)
Gait Disturbance
Muscle Spasm
Claudication (leg pain on walking)
Bladder Dysfunction (urgency, retention)
Bowel Dysfunction (incontinence)
Saddle Anesthesia (perineal numbness)
Sexual Dysfunction
Allodynia/Hyperesthesia (pain from light touch)
Postural Pain (worse with standing or sitting)
Night Pain (disturbs sleep)
Lhermitte’s Sign (electric shock on neck flexion)
Spasticity (if spinal cord involved)
Balance Problems
Weight Loss (if tumor/infection)
Fever/Chills (suggests infection)
Diagnostic Tests
Magnetic Resonance Imaging (MRI) – gold standard to visualize thecal sac indentation and disc fragments.
Computed Tomography (CT) – detects bone spurs and calcified fragments.
CT Myelogram – contrast-enhanced CT to outline dural sac.
X-ray – rules out fractures, alignment issues.
Discography – provokes pain via disc injection.
Electromyography (EMG) – assesses nerve root irritation.
Nerve Conduction Studies (NCS) – measures nerve signal velocity.
Ultrasound – guides injections, less common for sac evaluation.
Straight Leg Raise Test – provokes sciatica.
Slump Test – assesses neural tension.
Neurological Exam – motor, sensory, reflex testing.
Gait Analysis – identifies balance/coordination deficits.
Urodynamic Studies – evaluates bladder function if suspect cauda equina.
Blood Tests:
ESR/CRP (inflammation/infection)
CBC (infection signs)
Blood cultures (if abscess suspected)
Bone Scan – detects osteomyelitis or tumor.
PET-CT – for metastatic disease.
Myelography – contrast X-ray of spinal canal.
Somatosensory Evoked Potentials (SSEPs) – cord pathway integrity.
Flexion/Extension X-rays – dynamic instability.
Provocative Discogram – confirms symptomatic disc.
Non-Pharmacological Treatments
Physical Therapy (PT) with targeted exercises
Core Strengthening (abdominals, paraspinals)
Stretching Regimen (hamstrings, hip flexors)
Posture Correction (ergonomic training)
Weight Management
Heat Therapy (warm packs)
Cold Therapy (ice packs)
Traction Therapy (mechanical or manual)
Transcutaneous Electrical Nerve Stimulation (TENS)
Acupuncture
Chiropractic Manipulation
Massage Therapy
Yoga (spinal mobilization)
Pilates (core control)
Tai Chi (balance training)
Aquatic Therapy (low-impact exercise)
Ultrasound Therapy (deep heating)
Laser Therapy
Shockwave Therapy
Spinal Decompression Tables
Bracing (lumbar corset)
Ergonomic Adjustments (workstation)
Education Programs (back care)
Cognitive Behavioral Therapy (CBT)
Biofeedback
Mindfulness & Relaxation
Activity Modification (avoid triggers)
Smoking Cessation Programs
Nutritional Guidance (anti-inflammatory diet)
Breathing Exercises (diaphragmatic breathing)
Pharmacological Treatments
NSAIDs (ibuprofen, naproxen)
Acetaminophen
Oral Corticosteroids (prednisone taper)
Epidural Steroid Injections (methylprednisolone)
Muscle Relaxants (cyclobenzaprine, tizanidine)
Opioids (tramadol, oxycodone) – short-term only
Gabapentin
Pregabalin
Duloxetine (SNRI)
Amitriptyline (TCA)
Carbamazepine
Baclofen
Lidocaine Patches
Topical NSAIDs (diclofenac gel)
Capsaicin Cream
Calcitonin (for bone-related pain)
Bisphosphonates (if osteoporosis component)
Vitamin D & Calcium (adjunct)
Biologic Agents (for inflammatory arthritis)
Antibiotics (if infectious cause)
Surgical Options
Microdiscectomy – minimally invasive removal of fragment.
Open Discectomy – traditional removal of herniated disc.
Laminectomy – decompresses canal by removing lamina.
Hemilaminectomy – partial lamina removal.
Foraminotomy – widens nerve exit foramen.
Endoscopic Discectomy – camera-guided fragment removal.
Spinal Fusion – stabilizes unstable segments.
Artificial Disc Replacement – preserves motion.
Laminoplasty – reconstruction of lamina to enlarge canal.
Chemonucleolysis – enzymatic disc dissolution (rare).
Prevention Strategies
Maintain Healthy Weight
Regular Exercise (strength & flexibility)
Proper Lifting Techniques
Ergonomic Workstation Setup
Good Posture (sitting/standing)
Core Conditioning
Avoid Prolonged Sitting/Standing
Use Supportive Footwear
Quit Smoking
Balanced Diet & Hydration
When to See a Doctor
Severe or worsening neurological signs (weakness, numbness)
Bladder/bowel dysfunction or saddle anesthesia (cauda equina concern)
Unrelenting night pain that disturbs sleep
Fever, chills, unexplained weight loss (infection or tumor)
Traumatic onset with vertebral fracture suspicion
Frequently Asked Questions
What exactly is a free fragment?
A free fragment is a piece of disc nucleus that has completely separated from the main disc and moves freely in the spinal canal.How does it indent the thecal sac?
The fragment presses against the dura mater tube, creating a visible dent on MRI.Is this condition always painful?
Not always—some indentations are asymptomatic if they don’t compress nerves.Can it heal on its own?
Small fragments may be resorbed by the body over months.How long until symptoms improve?
With conservative care, many improve in 6–12 weeks.Will I need surgery?
Surgery is considered if severe pain or neurological deficits persist after 6–12 weeks of treatment.Are imaging tests safe?
MRI uses no radiation; CT and X-rays use low-dose radiation.Can I work with this condition?
Many continue light duties; heavy lifting may need restriction.What activities should I avoid?
Avoid bending, twisting, and heavy lifting until stable.Is exercise beneficial?
Yes—guided physical therapy helps strengthen and stabilize.Do injections really help?
Epidural steroids can reduce inflammation and pain temporarily.Are opioids necessary?
Only for short-term severe pain; not recommended long-term.What’s the recovery time after surgery?
Microdiscectomy: 4–6 weeks; fusion: 3–6 months.Can the fragment come back?
Recurrence risk is 5–10% after discectomy.How can I prevent future herniations?
Maintain core strength, good posture, and ergonomic habits.
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.
