Updated: 7/30/2021

Cauda Equina Syndrome

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  • Summary
    • Cauda Equina Syndrome is caused by severe compression of the nerve roots in the thecal sac of the lumbar spine, most commonly due to an acute lumbar disc herniation.
    • Early diagnosis is critical and is made clinically by characteristic symptoms of saddle-like paresthesias combined with acute back and leg pain. Urgent MRI is performed to confirm the cause. 
    • Treatment is prompt surgical decompression that should preferably be performed within 24 hours, absolutely within 48 hours.
    • Epidemiology
      • incidence
        • rare (annual incidence between 1.5 to 3.4 cases per million)
          • estimated prevalence of ~ 1 in 65,000
          • about 1000 new cases per year in US
        • occurs with ~3% of all lumbar disc herniations
      • demographics
        • more common in males
        • 4th decade (30s) of life is most common age group
      • location
        • most commonly occurs at the L4-5 level
    • Pathophysiology
      • pathoanatomy
        • massive space-occupying lesion within lumbosacral canal
          • disc herniation (most common)
          • spinal epidural hematoma
            • may be spontaneous with aggressive DVT prophylaxis 
            • can occur after neuraxial anesthesia (epidural) 
            • can occur in postoperative period with early DVT prophylaxis
          • spinal cord tumors
            • myxopapillary ependymoma
            • schwannoma
            • spinal meningioma
          • synovial facet cyst
          • spinal epidural abscess
          • trauma (retropulsion of fracture fragment, dislocation or collapse)
            • lumbar burst fractures
          • developmental spondylolisthesis
      • pathobiology
        • mechanical compression decreases nutrient delivery to the nerve root
          • decreased blood flow
          • decreased CSF diffusion
        • intraneural compartment syndrome
          • venous congestion and intraneural edema from hypoperfusion injury further decreases arterial perfusion pressures
          • nerve root ischemia follows
    • Associated conditions
      • orthopedic conditions
        • conus medullaris syndrome
        • lumbar disc herniation 
        • spinal cord tumors 
        • spondylolisthesis
        • lumbar burst fractures
        • sacral fractures
        • epidural hematoma
      • medical conditions
        • deep vein thrombosis (DVT)
          • is a well known complication after spinal trauma or spine surgery
            • often DVT prophylaxis is held out of concern for epidural hematoma
              • antiplatelet medications can be safely resumed approximately 48-72 hours post-op from spinal procedures
    • Prognosis
      • natural history
        • delays in diagnosis and management can lead to devastating life-long impairment.
          • progressive weakness of the lower extremities without surgery
          • progressive loss of bowel and bladder function without surgery
        • even with early surgery neurologic recovery is variable
        • long term urinary dysfunction is common 
      • prognostic variables
        • presence of saddle anesthesia or bladder dysfunction is associated with worse outcomes 
        • surgical decompression after 48 hours is associated with worse outcomes
  • Anatomy
    • Spinal cord
      • conus medullaris
        • tapered, terminal end of the spinal cord
        • terminates at T12 or L1 vertebral body
      • filum terminale
        • non-neural, fibrous extension of the conus medullaris that attaches to the coccyx
      • cauda equina (horse's tail)
        • collection of L1-S5 peripheral nerves within the lumbar canal
        • compression considered to cause lower motor neuron lesions
          • roots only covered with endoneurium and therefore are sensitive to compression
    • Bladder
      • receives innervation from
        • parasympathetic nervous system (pelvic splanchnic nerves and the inferior hypogastric plexus)
          • promotes urination
            • contraction of the detrusor urinae muscles
            • relaxation of the internal sphincter
        • sympathetic plexus (hypogastric plexus)
          • promotes urinary retention
            • relaxation of the detrusor urinae muscles
            • contraction of the internal sphincter
      • external sphincter of the bladder is controlled by the pudendal nerve
        • voluntary control
      • lower motor neuron lesions of cauda equina will interrupt the nerves forming the bladder reflex arcs
        • unable to sense bladder filling
        • unable to initiate appropriate muscle contraction and relaxation
  • Classification 
    • Bladder Function Classification
      • incomplete
        • loss of urgency or decreased urinary sensation but no incontinence or retention
      • complete
        • clear urinary and/or bowel retention or incontinence
  • Presentation
    • History
      • might have history of lifting heavy object with lumbar spine in flexed position
      • ask about use of anticoagulation (hematoma) and invasive procedure and IV drug use (infection)
    • Symptoms
      • common
        • back pain (most common)
          • may be initial presenting symptom alone
        • unilateral or bilateral leg pain (2nd most common)
        • saddle anesthesia
          • while less common, more specific for CES, and if present should initiate surgery emergency protocol.
        • bladder dysfunction
          • disruption of bladder contraction and sensation leads to urinary retention and eventually to overflow incontinence
          • important to document presence of bladder dysfunction prior to surgery
        • unilateral or bilateral sensory changes in legs
        • unilateral or bilateral motor weakness in legs
      • rare
        • sexual dysfunction (impotence in men)
        • bowel dysfunction
    • Physical exam
      • inspection
        • patient in distress due to low back pain, leg pain, and weakness
      • palpation
        • lower back pain/tenderness is not a distinguishing feature
        • palpation of the bladder for urinary retention
      • neurologic
        • motor
          • bilateral or unilateral lower extremity weakness
          • decreased rectal tone on voluntary contracture
        • sensory
          • reduced or absent sensation to pinprick in the perianal region (S2-S4 dermatomes), perineum, and posterior thigh
            • must distinguish between pinprick and light touch sensation
          • bilateral or unilateral lower extremity sensory disturbances
        • reflex
          • decreased or absent lower extremity reflexes
      • provocative tests
        • diminished or absent bulbocavernosus reflex
        • diminished or absent anal wink test
          • reflex contraction of the external anal sphincter upon pinprick stimulation of skin around the anus
  • Imaging
    • Radiographs
      • indications
        • if high suspicion of CES study of choice is MRI
        • can obtain radiographs but initiate process of obtaining MRI immediately
      • recommended views
        • AP, lateral
      • findings
        • usually normal with most common cause of lumbar disc herniation
        • may see other cause of spinal canal stenosis
          • burst fractures
          • high-grade developmental spondylolisthesis (intact-lamina)
    • MRI
      • indications
        • study of choice to evaluate neurologic compression
          • must be performed emergently if cauda equina syndrome is suspected
        • ideally obtained within 1-2 hours of presentation to ER
      • findings
        • often reveals large central disc herniation with complete spinal canal obliteration
        • presence of spinal stenosis
        • epidural hematoma
        • epidural abscess
    • CT myelography
      • indications
        • study of choice if patient unable to undergo MRI
          • e.g. pacemaker, MRI-incompatible implants
      • findings
        • sagittal and axial reconstructions can reveal space-occupying lesion
        • partial or complete blockage of contrast
  • Studies
    • Laboratory
      • CBC, ESR, CRP
        • concern for infectious etiology (i.e. epidural abscess)
    • Urodynamic studies
      • preoperative postvoid residual volumes (PVR)
        • recommended to be obtained prior to decompression but not at delay of decompression
        • normal post-void residual volume is less than 50 to 100 mL
          • PVR values < 200 ml with a 97% negative predictive value for cauda equina syndrome
      • postoperative postvoid residual volume
        • assessment for return of bladder function
    • Key differential
      • conus medullaris syndrome
      • spinal cord infarct
      • myelopathy
    • Diagnosis
      • diagnosis of cauda equina syndrome is made by history, symptoms, and physical exam
      • MRI imaging confirms the cause of the CES and is critical for surgical planning
  • Treatment
    • Operative
      • emergent surgical decompression 
        • indications
          • clinical symptoms of CES with imaging to support diagnosis
        • timing
          • as soon as safety possible
            • within 24 hours preferable.
            • within 48 hours considered acceptable standard of care. 
        • techniques
          • microdiskectomy (unilateral laminotomy, medial facetectomy, diskectomy)
          • laminectomy (bilateral laminectomy and medial facetectomy)
          • laminectomy with fusion (rarely indicated)
        • outcomes
          • studies have shown improved outcomes in bowel and bladder function and resolution of motor and sensory deficits when decompression performed within 48 hours of the onset of symptoms
            • residual bladder deficits may persist despite successful decompression
          • motor recovery may continue up to 1 year post-op
          • bladder function may continue to improve up to 16 months post-op
          • no comparison studies between microdiskectomy alone and wide decompression combined with microdiskectomy
  • Techniques
    • Microdiskectomy (unilateral laminotomy, medial facetectomy, diskectomy)
      • indications
        • massive soft disc herniation in younger patient with minimal degenerative changes
      • approach
        • 2 cm midline (or slightly paramedian) incision made on one side of pathology
        • expose lamina from spinous process to facet joint
      • laminotomy
        • 5-10mm laminotomy made over area of disc herniation
      • medial facetectomy
        • minimal facetectomy made with kerrison
      • ligamenum flavum window
        • cleft in ligametum flavum made and lateral section removed
      • anulotomy
        • dural retraction
        • removal of offending disc material
          • micropituitary rongeur
          • irrigation through a metal cannula
          • ensure disc material is thoroughly removed
    • Laminectomy (bilateral laminectomy and medial facetectomy)
      • indications
        • older patient with degenerative changes included hypertrophic ligamentum flavum, lateral recesss stenosis
      • approach
        • preservation of spinous process and PLC
          • can be performed with PLC preserving undercutting approach or spinous process resection
          • comes with risk of incomplete decompression
        • spinous process (and PLC) resection 
          • tradition method of resection of spinous process with complete laminectomy may be preferred to ensure complete decompression
        • technique
          • bilateral laminectomy
          • bilateral ligamentum flavum resection
          • bilateral medial facetectomyunilateral diskectomy
        • advantages
          • wide laminectomy performed
            • decreases the amount of dural retraction
            • greater degree of decompression
            • better visualization of the dura
          • removal of offending disc fragment
    • Laminectomy and Fusion
      • indications
        • high-grade spondylolisthesis
        • insidious-type cauda equina syndrome in the context of degenerative spondylolisthesis
  • Complications
    • Nonoperative
      • sexual dysfunction
        • risk factors
          • delay in surgical decompression
        • prognosis
          • recovery may be prolonged over several years
          • worse prognosis for recovery in older patients
      • urinary dysfunction
        • risk factors
          • delay in surgical decompression
        • treatment
          • may require permanent catheterization
      • chronic pain
      • persistent leg weaknes
    • Operative
      • dural tear
        • incidence
          • occurs in 1-4% of cases
        • treatment
          • treatment involves primary repair of the dura with or without dural graft of fat grafting
            • prevents pseudomeningocele and durocutaneous fistula sequalae
          • postoperative bed rest for 4-7 days
          • may require a lumbar drain
          • no difference in outcomes if adequately treated
      • iatrogenic segmental instability
        • occurs with overlying aggressive medial facetectomy
      • epidural fibrosis (scarring)
        • cause of postoperative back and leg pain
          • presents about 3 months post-op
        • treatment
          • responds poorly to re-exploration
          • evaluates with gadolinium-enhanced MRI
            • differentiates from recurrent HNP
      • wound infection
        • incidence
          • approximately 1% of cases
        • risk factors
          • increased risk with diabetics
      • vascular injury
        • incidence
          • rare complication
        • risk factors
          • perforation of the ALL with curettes during disc removal
        • treatment
          • requires immediate resuscitation and intraoperative vascular consultation
          • mortality up to 50%
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Questions (10)
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(SBQ12SP.72) A 32-year-old male presents with back pain and saddle anesthesia after lifting a heavy object. Figures A and B show T-2 MRI sagittal and axial images, respectively. Which of the following most accurately lists the additional symptoms or physical exam findings this patient may have from most common to least common?

QID: 3770

Leg pain > urinary retention > urinary incontinence



Urinary retention > leg pain > absent ankle jerk



Urinary retention > leg pain > urinary incontinence



Leg pain > urinary incontinence > urinary retention



Reduced rectal tone > urinary retention > leg pain



L 4 B

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(SBQ12SP.38) A 32-year-old woman presents to the emergency department with two days of worsening back and leg pain after feeling a sharp pop in her low back after an episode of coughing. She complains of numbness in her perianal region and bilateral buttocks that she notices when wiping herself with toilet paper after urinating. She also reports she is having difficulty urinating and had some episodes of incontinence. She complains of bilateral leg pain that is worse on the left in the region of the anterolateral calf. On physical exam she has weakness to big toe extension of 3/5 and is unable to walk on her heels with the toes elevated. MRI of her spine is shown in figures A through C. After surgical intervention, which of her symptoms is least likely to improve?

QID: 3736

Big toe extension weakness



Bladder dysfuction



Loss of perianal sensation



Numbness in the left foot



Burning pain in left leg



L 4 B

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(SAE09SN.15) A 56-year-old man with a history of chronic lower back pain from lumbar spondylosis reports a 2-day history of acute incapacitating back pain. He denies any history of acute trauma, although he reports the pain starting after a coughing spell. He also reports difficulty urinating and some fecal incontinence. Examination reveals generalized lower extremity weakness, saddle paresthesia, hyporeflexia in the lower extremities, and loss of rectal tone. What is the most appropriate management at this time?

QID: 6803

Immediate MRI of the lumbar spine



General reassurance, anti-inflammatory drugs, and an early home exercise program



Immediate radiographs of the lumbar spine and pain medications with 2 days of bed rest if the radiographs are normal



Office caudal epidural steroid injection with follow-up in 1 week



Outpatient MRI of the lumbar spine with follow-up in 1 week for test results



L 1 E

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(OBQ04.101) A 49-year-old male presents with saddle anesthesia, lower extremity weakness, and urinary retention. When must surgical decompression be done to improve bladder and motor recovery?

QID: 1206

less than 24 hours after symptom onset



less than 48 hours after symptom onset



less than 60 hours after symptom onset



less than one week after symptom onset



less than two weeks after symptom onset



L 3 C

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Evidence (21)
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