Cauda Equina Syndrome
High Yield Overview
CAUDA EQUINA SYNDROME
Emergency Diagnosis | CES-I vs CES-R | Urgent Decompression
0.04%Of LBP presentations
L4/5Most common level
48hSurgery window
S2-S4Bladder innervation
Critical Must-Knows
- CES-I (Incomplete) = altered bladder sensation but control preserved - URGENT surgery to prevent progression
- CES-R (Retention) = painless urinary retention with overflow - poorer prognosis regardless of timing
- MRI is mandatory emergency - do not wait until morning if red flags present
- Post-void residual greater than 500ml is significantly predictive of CES
- Bilateral sciatica + saddle anaesthesia + bladder dysfunction = assume CES until proven otherwise
Examiner's Pearls
- "Know Gleave & Macfarlane classification: CES-I vs CES-R distinction is prognostically critical
- "Timing debate: state of patient (CES-I vs R) matters more than exact surgical timing
- "Medico-legal hot topic: 'Better to scan 100 negatives than miss 1 positive'
- "Digital rectal exam is mandatory: assess anal tone AND sensation
Clinical Imaging
Imaging Gallery
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Exam Warning - Major Medico-Legal Pitfall
CES-I vs CES-R
CES-I (Incomplete): Altered sensation but voluntary control preserved. URGENT surgery often prevents progression. CES-R (Retention): Painless retention with overflow. Poorer prognosis regardless of timing.
Medico-Legal Trap
"Better to scan 100 negatives than miss 1 positive." Low threshold for MRI. This is the most litigated condition in spinal surgery.
Timing Matters
Decompression in CES-I is time-critical. Once CES-R occurs, recovery is unpredictable. Do not wait for morning if red flags are present.
Exam Strategy
Always define the difference between I and R. Examiners look for this distinction immediately.
Key Mnemonics
Mnemonic
BB-SADDLERed Flags for CES
B
Bilateral sciatica
Pain radiating down both legs (though can be unilateral)
B
Bladder dysfunction
Retention, hesitancy, or incontinence - the critical symptom
S
Saddle anaesthesia
Perineal numbness - ask about wiping sensation
A
Anal tone loss
Reduced voluntary squeeze on DRE - mandatory examination
D
Deficit in legs
Motor weakness or sensory changes L2-S1 distribution
D
Disturbance of bowels
Faecal incontinence or loss of awareness
L
Lower back pain
Severe LBP often present (but not always)
E
Erectile/Sexual dysfunction
Loss of sensation or function
Memory Hook:Sitting on a numbness SADDLE - think CES when patients describe perineal symptoms!
Mnemonic
WIPECES Clinical Questions
W
Wetting accidents?
Ask about urinary incontinence or overflow
I
Inability to void?
Painless retention is ominous - indicates CES-R
P
Paper sensation?
Can you feel the toilet paper when wiping? Tests S2-S4
E
Erection/Sexual function?
Changes in sensation or function
Memory Hook:WIPE - the key questions to ask every patient with red flag back pain!
Mnemonic
S2-3-4Bladder Innervation
S2
Sensory afferents
Bladder fullness sensation travels via S2-S4
S3
Sphincter control
External urethral sphincter innervation
S4
Somatic pudendal
Voluntary control of micturition reflex
Memory Hook:S2, 3, 4 keeps the wee off the floor - and the poo out of the shoe!
Clinical Significance
Definition
Cauda equina syndrome (CES) is compression of the cauda equina nerve roots (L2-S5) below the conus medullaris, causing a constellation of lower back pain, unilateral or bilateral sciatica, saddle anaesthesia, and motor/sphincter dysfunction. It represents a surgical emergency requiring urgent decompression.
Demographics and Incidence
- Incidence: 0.04% of all lower back pain presentations
- Rarity: 1-2 per 100,000 population annually
- Age: Any age, peak 40-60 years
- Gender: Equal distribution
- Most common cause: Large central lumbar disc herniation (L4/5 or L5/S1)
- Other causes: Tumour, infection (epidural abscess), haematoma, trauma
Despite rarity, high index of suspicion is essential due to catastrophic consequences of missed diagnosis.
Clinical Impact
- Permanent bladder dysfunction: Up to 50% in CES-R
- Permanent bowel dysfunction: 30-40%
- Sexual dysfunction: Up to 50%
- Chronic pain: Very common
- Litigation: Extremely common for delayed diagnosis
- Quality of life: Severely impacted
Economic and personal burden is substantial. Delayed diagnosis is the leading cause of spine-related litigation.
Anatomy of the Cauda Equina
Cauda Equina ("Horse's Tail"):
- Collection of nerve roots distal to conus medullaris (which ends at L1/L2 in adults)
- Contains nerve roots L2 to S5
- Provides motor and sensory innervation to legs, perineum, and sphincters
- Contains parasympathetic bladder supply (S2-S4 - "S2, 3, 4 keeps the wee off the floor")
Pathophysiology of Compression:
- Nerve roots are tethered within the spinal canal and have less protective connective tissue than peripheral nerves
- Compression compromises intraneural blood flow (venous congestion leading to arterial ischaemia)
- Autonomic fibres to bladder (S2-S4) are most vulnerable due to small diameter and peripheral location
- Sensory fibres affected before motor fibres in early stages
CES Staging - Critical for Prognosis
CES-I vs CES-R Classification
The Critical Distinction
CES-I patients have altered bladder sensation but can still voluntarily void. They often describe needing to strain to urinate, incomplete emptying, or loss of normal desire to void. However, they retain control.
CES-R patients have a paralysed bladder. They develop painless urinary retention (bladder fills without sensation) and overflow incontinence (dribbling when bladder is overfull). This represents established neurological damage.
The transition from CES-I to CES-R is often irreversible - hence the urgency to operate while still CES-I.
History
Key Questions:
- Onset: Acute vs gradual deterioration
- Back pain: Severity, radiation pattern
- Leg symptoms: Unilateral vs bilateral, dermatomal distribution
Bladder Questions (CRITICAL):
- "Can you feel when your bladder is full?"
- "Can you start and stop urinating normally?"
- "Have you had any wetting accidents?"
- "Have you noticed you're not passing urine as often?"
Bowel Questions:
- "Can you feel the paper when wiping?" (S2-S4 sensation)
- "Any change in bowel control?"
- "Can you feel when you need to pass a motion?"
Sexual Function:
- Sensation changes
- Erectile dysfunction (males)
- Loss of genital sensation (both sexes)
Examination
Neurological Examination:
- Full lower limb motor exam (L2-S1 myotomes)
- Full lower limb sensory exam (L2-S1 dermatomes)
- Reflexes: knee (L3/4), ankle (S1), Babinski
Perineal Examination (MANDATORY):
- Light touch sensation in saddle area (S2-S5)
- Pin-prick sensation perineum
- Compare both sides for asymmetry
Digital Rectal Examination (MANDATORY):
- Resting anal tone: Assess baseline sphincter tone
- Voluntary squeeze: Ask patient to squeeze examiner's finger
- Perianal sensation: Light touch around anus
- Document findings: Essential for medico-legal purposes
Bladder Assessment:
- Palpate suprapubically for distended bladder
- Bladder scan: PVR greater than 200ml suspicious, greater than 500ml highly predictive
Bladder Sensation Warning Sign
Loss of bladder sensation (desire to void) is often the earliest sign of autonomic dysfunction in CES-I, occurring before painless retention. Ask specifically about alteration in sensation, not just ability to urinate.
Clinical Pearl: Subjective change in urinary function is a RED FLAG - do not dismiss.
Emergency Imaging
MRI Lumbar Spine:
- Gold Standard investigation for suspected CES
- Must be performed urgently (day or night) if red flags present
- Whole lumbar spine with sagittal and axial T2-weighted sequences
- Look for: Canal occlusion (usually greater than 50-75%), disc herniation level, nerve root compression, other pathology (tumour, abscess)
CT Myelogram:
- If MRI contraindicated (pacemaker, severe claustrophobia)
- Requires lumbar puncture and intrathecal contrast
- Second-line but still diagnostic
Bladder Ultrasound:
- Post-void residual (PVR) measurement
- PVR greater than 200ml: suspicious
- PVR greater than 500ml: highly predictive of CES
- Quick, non-invasive, can be performed at bedside
MRI Imaging Gallery
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📊 Management Algorithm
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Management Algorithm
On Presentation:
- Full history and examination (including DRE)
- Bladder scan for PVR
- Catheterise if retention confirmed (document volume - medico-legal)
- Keep nil by mouth in anticipation of surgery
- Analgesia (avoid masking neurological progression)
- Request EMERGENCY MRI - do not wait until morning
MRI Confirms CES:
- Contact on-call spine surgeon immediately
- Book emergency theatre
- Consent for surgery (high risk of permanent dysfunction despite surgery)
- Thromboprophylaxis
Evidence Base
Timing of Surgery - Ahuja Meta-analysis
Ahuja S, et al. • Spine J (2010)
Key Findings:
- Meta-analysis of 322 patients with CES
- No statistical difference in outcome between surgery within 24h vs after 24h (up to 48h)
- However, CES-I patients had significantly better outcomes than CES-R regardless of timing
- Conclusion: Surgery should be expedited, but the '4-6 hour' rule is not evidence-based
Clinical Implication: The state of the patient (CES-I vs CES-R) is more predictive of outcome than the exact hour of surgery. The goal is to operate ASAP to prevent CES-I progressing to CES-R.
CES Classification and Prognosis
Gleave JR, Macfarlane R • Br J Neurosurg (2002)
Key Findings:
- Defined CES-I (Incomplete) and CES-R (Retention) classification
- CES-I: subjective bladder symptoms, volitional control preserved
- CES-R: painless urinary retention, paralysed bladder
- CES-I has significantly better prognosis than CES-R with urgent surgery
Clinical Implication: This classification is essential for prognosis and counselling. The window to prevent CES-R is narrow - urgent surgery in CES-I can prevent permanent bladder dysfunction.
BASS Guidelines for CES Management
British Association of Spine Surgeons • BASS Guidelines (2018)
Key Findings:
- Emergency MRI mandatory for suspected CES (day or night)
- Surgery should be performed as soon as safely possible
- No arbitrary time limit - operate when safe to do so
- Document all findings meticulously for medico-legal purposes
Clinical Implication: UK national guidelines emphasise urgency of diagnosis and treatment. Documentation is critical given high litigation rates for delayed diagnosis.
Long-term Outcomes Following CES
Korse NS, et al. • Spine (2017)
Key Findings:
- Systematic review of 3,260 patients
- Bladder function recovery: 47-87% depending on CES type
- Bowel function recovery: 56-73%
- Sexual dysfunction persists in approximately 50%
- Chronic pain common regardless of surgical timing
Clinical Implication: Patients need realistic counselling about outcomes. Even with prompt surgery, many patients have long-term sequelae, particularly those presenting with CES-R.
Long-term Outcomes and Complications
Long-term Outcomes by CES Type
Surgical Complications:
- Wound infection (1-2%)
- CSF leak/dural tear (2-5%)
- Haematoma requiring return to theatre (rare)
- Recurrent disc herniation (5-10%)
- Wrong level surgery (rare but documented)
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOAdvanced
Classic CES Presentation
EXAMINER
"A 45-year-old man presents to ED at 2am with severe back pain and bilateral sciatica. He mentions he hasn't passed urine since the morning (16 hours ago) but 'doesn't feel the need to go'. DRE reveals reduced anal tone. What do you do?"
EXCEPTIONAL ANSWER
This is a classic presentation of **Cauda Equina Syndrome**.
**Immediate Actions:**
1. **Clinical Assessment:** Determine if retention is present - palpate bladder, perform bladder scan. He has painless retention and lost sensation, indicating **CES-R (Retention)**.
2. **MRI:** Request **Emergency MRI Lumbar Spine** immediately. Do not wait for the morning - this is a surgical emergency (hospital protocol dependent, but clinically this requires urgent imaging).
3. **Preparation:** Keep nil by mouth, provide analgesia, catheterise if retention confirmed (document volume for medico-legal purposes).
**MRI confirms large central disc at L4/5.**
**Management:**
- **Consent:** High risk of permanent bladder/bowel/sexual dysfunction despite surgery. Surgery attempts to halt progression and aid recovery.
- **Surgery:** **Emergency Decompressive Laminectomy and Discectomy**.
- **Timing:** "As soon as safe". If team and theatre available at night, proceed. If not, first on morning list (within hours).
- **Post-op:** Monitor voiding trials (TWOC). Repeat MRI if new symptoms develop.
**Prognosis Discussion:**
- Since he is already CES-R (painless retention), his prognosis for full bladder recovery is guarded (approximately 50-60% have permanent issues).
- If he was CES-I, I would emphasise even greater urgency to prevent progression to CES-R.
KEY POINTS TO SCORE
Painless retention = CES-R (poor prognostic sign)
Reduced anal tone = S2-S4 compromise
MRI is mandatory emergency investigation
Decompress ASAP (aim within 24-48h of symptom onset)
COMMON TRAPS
✗Sending home for outpatient MRI in morning (potential negligence)
✗Failing to check anal tone and sensation
✗Not documenting bladder volume pre-catheterisation
✗Promising full recovery - outcomes are guarded in CES-R
LIKELY FOLLOW-UPS
"What defines the difference between CES-I and CES-R?"
"Describe the micturition reflex and which spinal levels control it"
"Which disc levels are most commonly affected and why?"
VIVA SCENARIOChallenging
Early CES-I Recognition
EXAMINER
"A 38-year-old woman presents with 3 days of worsening back pain radiating to both legs. She mentions her bladder 'feels strange' - she has to strain to start urinating and doesn't feel like she empties fully. On examination, she has reduced perineal sensation but intact anal tone. What are your concerns?"
EXCEPTIONAL ANSWER
This presentation is concerning for **CES-I (Incomplete)** - which represents a critical window for intervention.
**Key Features Suggesting CES-I:**
- Bilateral sciatica (red flag)
- Subjective bladder symptoms (altered sensation, straining, incomplete emptying)
- Reduced perineal sensation
- **Crucially:** She retains volitional control - no overflow, can still initiate voiding
**Why This is Critical:**
CES-I represents the **window of opportunity**. She still has bladder control but has early autonomic dysfunction. Urgent decompression can prevent progression to CES-R (retention) with its much poorer prognosis.
**Management:**
1. **Complete examination:** Full neuro exam, DRE (her anal tone is preserved - good sign)
2. **Bladder scan:** Check PVR - if elevated (greater than 200ml), adds urgency
3. **Emergency MRI:** Today, not tomorrow
4. **Surgical planning:** If MRI confirms compression, book emergency theatre
**Counselling:**
- Emphasise urgency - we want to operate before she develops retention
- Good prognosis if decompressed while still CES-I
- Without intervention, high risk of progression to CES-R
**Key message:** Altered bladder sensation with preserved control is CES-I - the time to act is NOW.
KEY POINTS TO SCORE
Straining to void + incomplete emptying = early autonomic dysfunction
Preserved volitional control = CES-I (not yet CES-R)
This is the critical window - surgery can prevent CES-R
Reduced perineal sensation confirms S2-S4 involvement
COMMON TRAPS
✗Dismissing symptoms as 'just back pain' without full assessment
✗Waiting for retention to develop before acting
✗Not recognising that subtle bladder symptoms precede retention
✗Failing to perform DRE because patient is young female
LIKELY FOLLOW-UPS
"What is the prognosis for bladder function in CES-I vs CES-R?"
"What surgical approach would you use?"
"How would you counsel this patient pre-operatively?"
Cauda Equina Quick Reference
High-Yield Exam Summary
Red Flags (BB-SADDLE)
- •Bilateral sciatica (though can be unilateral)
- •Bladder dysfunction - THE critical symptom
- •Saddle anaesthesia (perineal numbness)
- •Anal tone loss on DRE
- •Deficit in legs (motor/sensory)
- •Disturbance of bowels
- •Lower back pain (severe)
- •Erectile/Sexual dysfunction
Classification (Gleave & Macfarlane)
- •CES-I (Incomplete): Altered bladder sensation, volitional control PRESERVED - URGENT
- •CES-R (Retention): Painless retention, overflow incontinence - POORER PROGNOSIS
Investigation
- •Gold Standard: Emergency MRI Lumbar Spine
- •Bladder scan: PVR greater than 500ml highly predictive
- •CT Myelogram if MRI contraindicated
Management
- •Emergency surgical decompression
- •Laminectomy +/- discectomy
- •Timing: As soon as safely possible (within 24-48h)
- •Goal: Operate while CES-I to prevent CES-R
References
- Gleave JR, Macfarlane R. Cauda equina syndrome: what is the relationship between timing of surgery and outcome? Br J Neurosurg. 2002;16(4):325-328.
- Ahuja S, et al. Cauda equina syndrome and timing of surgery: a systematic review. Spine J. 2010;10(6):471-479.
- Korse NS, et al. Cauda Equina Syndrome: presentation, outcome, and predictors with focus on micturition, defecation, and sexual dysfunction. Eur Spine J. 2017;26(3):894-904.
- British Association of Spine Surgeons. Guidelines for the management of suspected cauda equina syndrome. 2018.
- Todd NV. Guidelines for cauda equina syndrome: red flags and white flags. Br J Neurosurg. 2017;31(6):685-690.