Neurosurgery notes/Procedures/Cranial procedures/CSF procedures/Shunts/Shunt complications

Shunt complications

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Shunts

Shunt complication

  • Studies show remarkably similar stories of failure across different units and different patients
  • Failure rate at I year
    • 30-40%
    • No difference between elective vs emergency failure rates
    • No difference between senior surgeons and trainees
    • Higher chance of failure if
      • More likely to fail if patients presents in coma
      • Children younger than 2 have significantly higher failure rates

Types of failure

Obstruction
  • Most common cause of mechanical shunt failure (>60%)
  • Usually occurs in the ventricular catheter
  • Distal obstruction tends to occur later
  • Valve obstruction is thought to be rare
  • Mechanism probably quite complicated
Disconnection / fracture / migration
  • Disconnection and migration are rare,
    • Tend to occur early after shunt insertion
  • Fracture
    • A late complication, following calcification then cracking of the tubing
    • CSF flow continues for a time through the fibrous sheath
    • In this case shunt dysfunction may present subacutely
    • Usually occurs in the neck
Over drainage
  • Features
    • Postural headaches (with or without nausea or other ill feelings) or imaging evidence of pathological subdural fluid collections.
  • Some degree of intracranial hypotension is the norm in shunted patients (data exist primarily for differential pressure valve shunts), but only a small percentage complain of postural headache.
  • Risk factors
    • When the baseline pressure measured in the horizontal body position is low (usually negative), over drainage is possible.
    • A change in posture to sitting generally produces a further decrease in pressure.
      • If the pressure decreases to a value lower than −10 mmHg (the 95% confidence limit for ICP in the upright position in nonshunted patients is around − 8 mmHg), over drainage is likely.
  • Management
    • If postural headaches are mild
      • Conservative measures such as hydration can often bide the patient over until the body re-equilibrates and the symptoms abate spontaneously.
    • If postural headache are severe and has radiological features of subdural
      • Increasing the valve opening pressure (by at least 30 mm H₂O) usually alleviates postural headache symptoms within 1 h of the intervention.
      • Surgery to swap to a programmable valve → dial up pressure setting to high → If patient is already at the maximum valve opening pressure of an adjustable valve → add an antiphon device or gravitational device
  • A patient who has been doing fine for months will not spontaneously present with over drainage symptoms.
    • Exceptions to this rule
      • New subdural fluid collection
      • Inadvertent shunt adjustment (such as with an MRI).
  • Small subdural hygromas (< 5 mm) are usually asymptomatic and are often associated with improvement in NPH symptoms because they occur only in conjunction with reduction of the ventricular system.
    • As a result, the presence of a subdural hygroma is not by itself diagnostic of shunt over drainage.
    • Expanding or large subdural hygromas are more worrisome and, many would agree, are risk factors for the development of acute hemorrhage (subdural hematoma).
    • A nontrauma-related subdural hematoma in a shunted patient is obviously an overdrainage presentation
Extra-axial fluid collections
  • Collapse of the ventricular system can cause accumulation of extra-axial fluid or blood
  • This tends to be an early complication, often when large ventricles have been shunted
  • Treatment
    • Increasing resistance to CSF outflow and possibly draining the collections via burr holes
Loculation
  • Occasionally a shunt will drain only a portion of the ventricular system with enlargement of another area
  • Usually seen in post-infectious patients
  • Also described as a functional obstruction of Munro due to overdrainage of a single lateral ventricle
  • Isolated or "trapped" fourth ventricles should be viewed very suspiciously and treated
  • Management
    • Endoscopic / frameless stereotactic techniques
Infection
  • Number
    • New shunt infection rate of 8.1% over the follow-up period of 1-3 years
    • Cumulative likelihood of shunt infection related to multiple shunt procedures ranges from 19% to 38%.
  • Usually occurs early due to
    • Inoculation at the time of surgery
    • Prior to wound integrity being established
  • Microbiology
    • Vast majority are staphylococcal;
    • However late infections are usually Gram negative
    • Coagulase-negative S. epidermidis
      • Typical skin flora
      • S epi: S aureus 2:1 ratio
      • Secretes a mucoid material that enhances its ability to adhere to foreign bodies such as shunt material.
    • S. aureus
    • Enteric organisms
      • Gram-negative bacteria such as E. coli, Proteus, and Klebsiella
    • Delayed infections with anaerobic diphtheroids such as Propionobacterium are particularly difficult to assess and treat because cultures may remain negative for more than week.
      • In the setting of repeated shunt failure, an indolent infection with Propionobacterium acnes should be considered, and CSF cultures should be followed for at least 1 week.
  • Time line
    • Median time to infection is 3 weeks,
    • 70% present within 2 months
  • CSF ventricular shunt catheter infections occur via three routes:
    • Contamination of the shunt material with skin organisms at the time of surgery,
    • Contamination from the bloodstream,
    • Contamination along the shunt tubing from an abdominal source (e.g. inflammatory bowel disease, bowel perforation).
  • Risk factors
    • Young age
    • IVH of prematurity
    • Previous shunt surgery
    • CSF leak and wound infection and inexperienced shunt surgeons
  • BASICS trial infection definition
        • Category
        Culture
        Signs of Infection
        CSF Pleocytosis
        Organisms on Gram Stain
        Growth of Organisms from CSF
        Management
        Definite
        Positive
        With or without
        Not specified
        Not specified
        On primary culture or repeated subculture
        Shunt removal and antibiotic treatment
        Probable
        Uncertain
        With or without
        Yes
        Yes or No
        On one subculture only
        Shunt removal and antibiotic treatment
        Probable
        Negative
        Irrespective
        Yes
        Yes or No
        No organisms grown
        Shunt removal and antibiotic treatment
        Possible
        Uncertain
        No
        No
        No
        Growth after enrichment in one CSF sample only
        Shunt removal and antibiotic treatment
  • How to reduce infection
    • BASICS trial: use antibiotic impregnated catheters
    • Shunt deep incision infection—infection of the deep surgical wound and subcutaneous shunt without any evidence of CSF infection, and managed by shunt removal and antibiotic treatment
True shunt allergies
  • Are rare.
  • Due to
    • Unpolymerized silicone in the literature.
  • Presentation
    • CSF often demonstrates persistent eosinophilia (3-36%),
    • Negative cultures.
    • Recurrent shunt failure is a common presentation.
    • Pathologic examination of the ventricular catheter often demonstrates mechanical obstruction by inflammatory debris consisting of eosinophils and multinucleated giant cells.
  • Management
    • ETV
    • Remove the offending shunt
    • Use a shunt system devoid of silicone
      • Such as a polyurethane shunt system or hyperextruded silicone components.

Shunt infection

  • Removal of shunt
  • Place EVD
  • Start antibiotics
    • IT antibiotics
      • Pros
        • Get antibiotics to source to treat infection
      • Cons
        • Potential adverse effects of intrathecal therapy, including neurotoxicity.
      • IT antibiotic indication not well established can be used for the following reasons
        • Any shunt infection
        • Use in only those infections in which the CSF cannot be sterilized by systemic antibiotics alone (for example, persistent positive cultures),
        • Use in those ventricular shunt infections caused by specific organisms (for example, gram-negative infections).
  • When CSF clear reimplant shunt

Multilocuated HCP (post infection or post haemorrhagic)

  • Management options
      • Endoscopic fenestration of loculation and single shunt
      • Pros
        • Does not have multiple catheter complicating surgery and future revision.
        • Able to recommunicate all loculations
      Multiple shunts or multiperforated catheters
      • Cons
        • Multiple shunts have increased the risks of
          • Infection
          • Mechanical obstruction
        • Removal has been problematic
          • Associated risk of intraventricular haemorrhage.
      Stereotactic fenestration in uniloculated hydrocephalus
      • Cons
        • Associated with a high recurrence rate (up to 80%) because the cyst wall could not be widely fenestrated,
        • Unsuitable in cases of multiloculated hydrocephalus.
      Transcallosal fenestration via craniotomy
      • Pros
        • Reduce shunt revision rates or achieve shunt independence in both multiloculated hydrocephalus and uniloculated hydrocephalus,
      • Cons
        • Risk associated with craniotomy

Reference