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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.
  • ETIOLOGY
    • 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
  • DIAGNOSIS
    • 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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