CNS Procedures and Devices

Lumbar puncture

• Transverse line at iliac crests is L4
• 22G needle in adults
• >20G doubles risk of post-LP heaache
• Atraumatic/pencil-point needle (Whitacre or Sprotte) reduces post-LP headache
• Smaller needle size using stylet reduces post-LP headache
• Whitacre and Sprotte (side eye) reduce epidural sterile abscess formation (if stylet used with it)
• Bevel (Quincke) or notch (Whitacre) facing ceiling (if on side) or side (if sitting up)
• Collect at least 1mL in each of four tubes
• If unable to penetrate subarachnoid space, come out and start again (US guidance may be helpful)
  • Reduces number of failed attempts to identify spinous processes and marking midline
• Measuring pressure is only valid if lying down and legs extended

• Chiari malformation
  • CM-I: Abnormally shaped cerebellar tonsils displaced below level of foramen magnum
    • Tonsils >5mm below foramen magnum in adults
    • Mean age of presentation is 18yo
  • CM-II (Arnold-Chiari): Downward displacement of cerebellar vermis and tonsils, beaked midbrain on imaging and spinal myelomeningocoele
    • Leads to hydrocephalus due to obstruction of CSF flow
  • CM-III: Small posterior fossa with high cervical or occipital encephalocoele
  • Incidence
    • CM-I incidence up to 0.5% and is a contraindication to LP given propensity for coning

• Complications
  • Local discomfort
  • Radicular pain indicates too lateral so need to reposition (helpful for guiding needle if ask ‘which side’)
  • Spinal haematoma is ominous
    • Severe or persistent back pain, radicular pain, new neurological symptoms or sphincter disturbance
    • Usually in patients with coagulopathy, anticoagulation or antiplatelets
    • Source of bleeding usually venous and slowly progressive
    • Most occur in first 6 hours and need urgent MRI and neurosurgical consult
    • Laminectomy and haematoma evacuation is indicated in progressive neurological deficit
    • If no or minor neurology, can often be managed conservatively
  • Post-LP headache
    • Most common complication
    • Usually begins 24-48 hours after procedure in frontal/occipital areas
    • Intensified by standing or sitting upright or Valsalva
    • Improves with supination
    • Nausea, vomiting, vertigo and tinnitus can all occur
    • Risk factors include needle >22G, Quincke cutting needle, multiple attempts, failure to insert stylet before withdrawal
    • Not related to opening pressure, volume of CSF removed or bed rest post-procedure
    • Treatment
      • Supination, IV hydration, antiemetics and analgesics
      • IV caffeine 500mg not proven
      • >24 hour or debilitating headache warrants epidural blood patch (20-30mL of aspirated blood injected into epidural space)

CSF shunts

• Silastic tube to valve chamber (established pressure gradient to ensure drainage of fluid away from ventricle) then distal tubing to drainage point (peritoneal cavity, right atrium, pleural cavity, gallbladder or ureter)
• May have reservoir at valve chamber for patency testing, pressure measurement, CSF sampling, medication delivery or contrast administration
• Malfunction
  • Obstruction
    • Most common malfunction and usually proximal tubing that obstructs, then distal tubing, then valve chamber
    • Proximal obstructions usually occur within first years after insertion
    • Causes
      • Proximal obstruction – Tissue debris, choroid plexus, clot, infection, catheter tip migration or local immune response
      • Distal obstruction – Kinking, disconnection, pseudocyst or infection

CSF shunts

• Obstruction continued…
  • Distal obstruction most common complication if in place >2 years
  • Presentation – Headache, vomiting, irritability, bulging fontanelle (infants), lethargy, ataxia or CN palsies
• Mechanical failure
  • Fracture
    • Fractures seen in distal tubing many years after placement due to degrading and stress from patient growth
    • Most commonly fractures at clavicle or lower ribs
    • Present with mild symptoms of raised ICP +- local pain, erythema or oedema
  • Disconnection
    • Often shortly after insertion with raised ICP and fluid at skin site
  • Migration
    • Migration of properly placed tube with subsequent impairment of drainage
    • Catheter may move into brain parenchyma, choroid plexus or temporal horns manifesting as evidence of failure

CSF shunts

• Overdrainage
  • Slit ventricle syndrome seen in 5% of patients
  • Overdrainge leads to shrinkage around tubing and tissues occlude the orifices of proximal shunt apparatus
  • As ICP rises, same occluding tissue is disengaged and drainage can continue
  • Leads to cyclical, episodic headache, focal neurology, ataxia, lethargy
• Loculation
  • Separate non-communicating CSF accumulations can form within a ventricle leading to failure of drainage system
  • Trapped fourth ventricle syndrome occurs when fourth ventricle becomes loculated from closure of Sylvian aqueduct presenting with raised ICP, brainstem compression, poor feeding, disconjugate gaze and difficult swallowing
• Abdominal complications
  • Malfunction due to pseudocyst formation
  • Infection is the major cause with infection rate of 40%
  • Often asymptomatic until large enough to cause abdominal pain

Csf shunts

• Clinical presentation
  • Typically develop over days but can be rapid
  • Mental status change, ataxia, headache, nausea, vomiting, abdo pain, lethargy, coma and autonomic instability are typical
  • Decrease in LOC has highest correlation with shunt malfunction
  • As ICP rises, paralysis of upward gaze, dilated pupils and papilloedema may develop
  • Paralysis of upward gaze is due to third ventricle engorgement with impingement of brainstem
  • Slit ventricle syndrome worsens with standing up or exercising and relieved by lying down or Trendelenberg

Csf shunts

• Shunt evaluation
  • Palpation allows location of valve chamber
  • Gently compress chamber and see that it refills
  • Difficulty compressing the chamber = distal obstruction
  • Slow refill = Proximal obstruction (>3 seconds)
  • 40% of obstructed shunts show normal refill during manual palpation
• Shunt series of plain radiographs
  • AP and lateral skull radiographs and AP view of chest and abdomen
  • Identifies kinking, migration or disconnection
  • CT is required to evaluate ventricular size
    • Compare to previous as often abnormal at baseline
    • One series showed sensitivity 83% and NPV 95%
    • If clinical suspicion exists, normal CT cannot rule out obstruction so get neurosurgical consultation

Csf shunts

• Shunt tap
  • Makes diagnosis of shunt malfunction, infection  and can alleviate raised ICP
  • ED may have to do this if neurosurgery not available or needed to control life-threatening raised ICP
  • Locate and prepare site over valve or reservoir of shaved scalp
  • 23G needle or butterfly attached to manometer
  • If no fluid obtained or flow ceases, proximal obstruction likely
  • Opening pressure >20cmH20 indicates distal obstruction
  • Low pressure indicates proximal obstruction

Csf shunts

• Treatment of shunt malfunction
  • Surgical intervention usually required
  • Can lower ICP with standard means if required
  • Can aspirate from valve if emergency
    • Remove slowly to prevent choroid plexus bleeding and stop at 10-20cmH20 pressure

Csf shunts

• Shunt infection
  • 0.6-21% rate per procedure
  • Highest infection rates in very young and old
  • 26% recurrence rate of infection
  • 50% occur in first 2 weeks, 70% within 2 months and 80% within 6 months and 10% after 1 year
  • External infections: Subcutaneous tract around shunt – tender, fluid collection
  • Internal infection: Shunt and CSF within shunt
  • Have higher risk of typical meningitis
  • If ventriculitis is allowed to develop, mortality is 30-40%

Csf shunts

• Shunt infection
  • Typically low virulence organisms such as S. epidermidis (50%), S. aureus or P. acnes
  • Gram-negative have highest mortality
  • Candida is rare but seen in premature newborns, immunocompromised and those on long-term broad-spectrum antibiotics. 5.8% mortality rate
  • Clinical features
    • Obstructive/meningitis symptoms, fever (variable)
    • Meningismus may be seen in only 1/3 of cases
    • Abdominal pain may predominate if VP shunt
    • Swelling, erythema and fluctuance around shunt is common in external shunt infection
    • Chronic bacteraemia from S. epidermidis can lead to shunt nephritis with fever and urinary sediment
      • Treatment of underlying infection leads to resolution of nephritis

Csf shunts

• Shunt infection
  • Diagnosis
    • Shunt tap crucial to make diagnosis – 1/5^th of cases have positive culture despite normal cell analysis
    • LP often misses shunt infection and has no meaningful role when shunt infection suspected
    • BC of limited value as rarely haematogenously spread
  • Treatment
    • Cef + Vanc until organism identified
    • Neurosurgical consult and admission
    • Early removal of colonised device

Halo devices

• Complications
  • Pin loosening
    • Obtain neurosurgical consult and exclude infection at pin site
    • If movement of halo device has occurred, assume unstable cervical spine and immobilise using alternative technique and obtain radiographs to assess proper alignment
    • Tangential plain X-ray, CT or MRI can all exclude penetrating of pain through inner table of skull
  • Pin-site infection
    • Seen in 10-20% of halo devices
    • 50% occur in first 4 weeks and 60% involve anterior pins
    • <1% have more severe cellulitis, osteomyelitis or abscess formation vs. localised pin-site infection
      • More serious infections associated with persistent pain, continued drainage despite antibiotics, clear drainage of history of a fall
      • Cellulitis often has fever and systemic signs/symptoms of infection
      • Osteomyelitis usually has pin loosening, prolonged infection and radiographic changes
      • Abscess often have neurological changes and evidence of inner table penetration e.g. CSF leak or trauma

Halo devices

• Local pinsite infection
  • Treated with local wound care, pull away skin from pin to clean beneath it and the pin-skin interface with soap and water four times a day
  • Obtain culture specimens and administer antibiotics for skin pathogens e.g. Staph and strep
  • Obtain Neurosurgical admission if suspicion of more serious infection
• Pin-site discomfort
  • 20% of patients usually due to local inflammation
  • Always consider infection
  • Sensory or motor deficits indicate nerve damage and painful mastication indicates temporalis muscle inflammation (? Too lateral placement)
  • Neurosurgical consult if pain persists despite simple analgesia or complication is suspected
• Ring migration or loss of immobilisation
  • 10-13% of halos
  • Suspect if neck pain, change in fit of ring or vest
  • Immobilise C-spine and image with neurosurgical consult for re-fitting

Halo devices

• Skin breakdown
  • 11-30% of cases
  • Inspect vest for padding and strap position
  • Urgent consult to Neurosurg for refitting
• Dysphagia
  • 1-2% of patients usually due to hyperextension of neck immobilisation
  • Halo adjustment all that is usually required
• Dural puncture
  • 1-2% of patients due to halo system trauma
• If CPR is required
  • Remove anterior portion of vest and intubation performed with halo in place
• Halo devices in the elderly
  • Mortality of 21% if >79 years old
  • Serious complications such as respiratory failure (8% of cases) and dysphagia (11%) are much more common

Intrathecal baclofen pumps

• Impedes release of glutamate in spinal cord itself to decrease spasticity
• Complications
  • Medication-related: Hypotension, bradycardia, apnoea, oversedation, respiratory depression
  • Mechanical: Pump pocket effusions, Pump failure, Catheter extrusion, Catheter dislodgement
  • Infection: Local infection, Meningitis, CSF fistula formation
• If delivery of drug impeded, withdrawal symptoms can be life-threatening including extreme hypertonicity and spasms with rhabdomyolysis
• Oral baclofen, dantrolene and oral/parenteral benzodiazepines are all effective
• Infection rate is 10%, with most in first month
  • Mostly S. aureus and most need Neurosurgical admission and IV antibiotics

Implantable CNS stimulators

• Infection rate 3-10%
• May present with temporary or permanent paraesthesias, dysarthria, dysequilibrium or failure to suppress tremors
• Neurosurgical consult for all cases

Spinal cord stimulation

• Used for chronic back pain, MS, complex regional pain syndromes, phantom limb pain, diabetic neuropathy, herpetic neuralgia, angina pectoris, malignancy pain and vascular pain
• Complications include dural puncture, spinal cord compression, CSF leak, haemorrhage, infection, abscess, epidural fibrosis, migration, interrption of wires and battery failure

Peripheral nerve stimulators

• Used for intractable neuropathic pain
• Electrode placed in subcut tissue overlying peripheral nerves
• Can cause pauses in cardiac pacemakers so always consider this if new conduction abnormality

Last Updated on August 29, 2023 by Andrew Crofton