CIM Case: Cauda Equina Syndrome

Clinical Scenario

Patient: 24-year-old male, 150kg security guard Presentation: 2-year history of low back pain with bilateral buttock pain, 2-day history of new right leg pain and weakness of right ankle, presented to ED with new urinary symptoms Relevant history: Long-standing LBP worsened 1 week ago after lifting at work, progressive bilateral leg symptoms over 48 hours, difficulty initiating urination since this morning, no bowel symptoms, no trauma, no previous spinal surgery Examination findings:

Difficulty walking, requires support
Forward flexed posture (antalgic)
Reduced perianal sensation bilaterally (S2-S4 dermatomes)
Reduced anal tone on PR examination
Bulbocavernosus reflex absent
Right ankle dorsiflexion 2/5 (L5), plantar flexion 4/5 (S1)
Left ankle dorsiflexion 4/5, plantar flexion 5/5
Knee extension 5/5 bilaterally
Hip flexion 5/5 bilaterally
Right-sided positive straight leg raise at 30°
Crossed straight leg raise positive
Reduced sensation right L5 and S1 dermatomes
Bilateral reduced ankle reflexes
Post-void bladder scan shows 450mL residual urine

Investigations Provided

Laboratory Results

Test	Result	Normal Range	Interpretation
Hb	152 g/L	130-180 g/L	Normal
WCC	7.8 ×10⁹/L	4-11 ×10⁹/L	Normal
Platelets	289 ×10⁹/L	150-400 ×10⁹/L	Normal
ESR	6 mm/hr	<15 mm/hr	Normal (no infective/inflammatory cause)
CRP	2 mg/L	<5 mg/L	Normal
Creatinine	92 μmol/L	60-110 μmol/L	Normal
Coagulation	Normal	-	Safe for surgery

Imaging

Image 1: MRI Lumbar Spine (performed urgently at 1am)

MRI findings:

Large central and right paracentral disc herniation at L4-L5
Disc fragment measures approximately 15mm × 12mm
Severe compression of the cauda equina
Complete effacement of thecal sac at L4-L5 level
Nerve roots displaced and compressed
Moderate L5-S1 disc degeneration with annular bulge (no prolapse)
No epidural collection or haematoma
No tumour or fracture

Sequences:

T1-weighted: Demonstrates disc material isointense to native disc
T2-weighted: Compressed CSF signal, loss of normal "horse tail" appearance
STIR: No cord oedema (conus at L1 - normal)
Axial images: Confirm central and right-sided compression

Questions & Model Answers

What is cauda equina syndrome and what are the key clinical features to elicit?

What is the classification of cauda equina syndrome and why does it matter?

What are the causes of CES and how do you interpret the MRI findings?

What is your management plan for this patient?

During surgery you encounter a sudden rush of clear fluid. What has happened and how do you manage it?

What is the prognosis for this patient and how do you counsel him?

Key Teaching Points

Pattern Recognition

This pattern suggests Cauda Equina Syndrome:

Low back pain with bilateral leg symptoms
Urinary retention or incontinence
Saddle anaesthesia (perineal numbness)
Reduced anal tone
Absent bulbocavernosus reflex
Large central disc herniation on MRI

Red Flags for CES (MUST Ask/Examine):

Feature	How to Assess
Bladder function	"Any trouble passing urine?"
Bowel function	"Any accidents with your bowels?"
Saddle anaesthesia	Test S2-S4 dermatomes
Anal tone	Digital rectal examination
Sexual function	"Any problems with erections?"

Critical Management Points

CES is a surgical EMERGENCY - operate within 24-48 hours, ideally immediately
CES-I vs CES-R determines prognosis - retention has worse outcomes
Time is critical - document symptom onset precisely
Large central disc is most common cause - confirm on MRI
Dural tear is manageable - don't panic, repair primarily if possible
Prognosis is guarded - counsel honestly about uncertain outcomes

Common Examiner Follow-ups

Q: "What is the evidence for timing of surgery in CES?"

Evidence for early surgery:

Ahn et al. (2000): Better outcomes with surgery <24 hours
Kohles et al. (2004): Meta-analysis showed <48 hours better than later
Todd (2005): CES-I to CES-R transition is critical event
British Association of Spine Surgeons (BASS) guidelines: Surgery as soon as reasonably practicable, ideally within 48 hours of onset

Current consensus:

CES-I: Operate within 24-48 hours (urgent)
CES-R: Operate immediately (emergency)
Transition from CES-I to CES-R can occur at any time

Q: "What if surgery is delayed due to theatre availability?"

If surgery cannot be performed immediately:

Document reason for delay (e.g., theatre in use, surgeon travel time)
Monitor neurology closely - any deterioration escalates urgency
Keep NBM and ready for theatre
Inform patient of situation and reason for delay
Escalate to hospital management if needed to access theatre

Medico-legal considerations:

Delays in CES surgery are a leading cause of spinal litigation
Every hour of delay should be justified and documented
"Waiting for morning theatre" is not acceptable for CES-R

Q: "How do you differentiate CES from conus medullaris syndrome?"

Feature	CES	Conus
Level	Below L1-L2	At L1-L2
Presentation	Often asymmetric	Symmetric, perianal predominant
Motor findings	LMN only (flaccid)	Mixed UMN/LMN
Reflexes	Absent	Variable, may have Babinski
Bladder	Atonic, painless retention	Spastic, may have urgency
Pain	Severe radicular	Less severe
Onset	May be gradual	Often sudden

Pure conus syndrome is rare - most lesions at thoracolumbar junction cause mixed picture.

Q: "What is your follow-up plan after surgery?"

Follow-up protocol:

24-48 hours: Trial of void, remove catheter if able
1-2 weeks: Wound check, remove sutures
6 weeks: Neurology assessment, return to light activity
3 months: Full assessment, physiotherapy review
6-12 months: Final outcome assessment

If bladder doesn't recover:

Urology referral for long-term management
Intermittent self-catheterisation training
Consider urodynamic studies

If motor function doesn't recover:

Physiotherapy for gait training
Consider AFO if foot drop persists
Vocational rehabilitation

Lumbar Disc Herniation
Spinal Stenosis
Spinal Cord Injury
Lumbar Discectomy
Dural Tear Management
Neurogenic Bladder

Cauda Equina Syndrome