headache

Case: John is a 6-year-old boy with a history of congenital hydrocephalus, status post ventriculo-peritoneal (VP) shunt, who presents with acute onset of headache, which is associated with nausea and vomiting. His mother is worried about a problem with the shunt. Should you be?

 

 

Answer: YES! The remainder of the post is dedicated to the ins and outs of shunts, but we cannot overstate the importance of parental insight. In one study, parental concern had a similar sensitivity and specificity as a CT scan (Kim et al, 2007)

 

A CT scan was completed on this patient (shown below), demonstrating a marked interval increase in ventricle  size, consistent with shunt failure. John was subsequently admitted to the neurosurgery service for operative revision of the shunt.

 

vp-shunt-fail

Non contrast Head CT: Axial Reformat

vp-shunt-fail-coronalNon-contrast Head CT: coronal imaging

What is a VP Shunt?

  • A VP shunts is a plastic catheter that diverts cerebrospinal fluid (CSF) from the lateral ventricles to the peritoneal cavity
    • While VP shunts are the most common, CSF can be diverted from the ventricles to the pleural cavity and the atria of the heart (VA shunt).

Why are they placed?

  • VP shunts are intended to palliate hydrocephalus, and are one of the most commonly performed neurosurgical procedures (Pietetti et al, 2007)
  • Epidemiological studies indicate the prevalence of VP shunts is 8.2/10,000 (Piatt et al, 2008). 
  • Unfortunately, VP shunts do not correct the underlying etiology of the hydrocephalus and are therefore not curative

What can go wrong with a shunt?

  • A variety of complications can occur with a VP shunt including: mechanical obstruction or over-drainage, infection, fracture, and/or migration (Piatt et al, 2008).
  • In the first year of placement, almost 40% of shunts fail (Kestle et al, 2000; Piatt et al, 2008)
    • The rates of infection (common cause of shunt failure) tend to be highest in the first 6 months of placement.

What symptoms should be concerning?

  • The most common symptoms include: nausea, vomiting, irritability, fever, or altered level of consciousness (Browd et al, 2006)
    • Specific findings and their Likelihood Ratio (Piatt et al, 2008)
      • Bulging Fontanel: 46.1
      • Decreased level of Consciousness: 26.2
      • Irritability: 13.7
  • Less common findings include: weakness, diplopia, cranial nerve palsies (CN VI especially), ataxia
  • Examination of the tract itself is very important (ventricular insertion site in skull generally traverses posterior to ear along neck). Some findings that could indicate problems:
    • Palpation of fracture
    • Erythema of tract may herald infection
    • Evidence of fluid collection over ventricular insertion site
  • Very Important to perform abdominal exam (Browd et al, 2006)
    • Abdominal Pain carries a likelihood ratio of 12.8 for failure
    • Other signs: ascites or intra-abdominal mass (pseuodocyst)

How can I evaluate a shunt?

  • Shunt Series:
    • What It Is: An anterior-posterior and lateral x-ray detailing the entire length of the catheter
    • Given poor sensitivity for shunt malfunction, authors do not recommend as first line (Boyle et al, 2015)
  • Head CT
    • Historically, the diagnostic standard for shunt malfunction
    • If enlarged ventricles are demonstrated on exam, this is consistent with shunt malfunction (Boyle et al, 2015)
    • Pros: Fast, sensitive; Con: large dose of radiation
  • FAST MRI (also known as: half-fournier acquisition single shit turbo-spin echo sequences)
    • Use single-section T2-weighted images, acquiring images in 1-4 minutes (Boyle et al, 2015)
    • Non-inferior to head CT* (Boyle et al, 2014)- Note: study not powered to compare sensitivities
    • Pro: No radiation; Con: variable access to MRI, cost (though notably less expensive than conventional MRI)

Diagnosing Shunt Malfunction

 Modality Reported Sensitivity Reported Specificity
Shunt Series 4- 26% 92-98%
Head CT 53-92% 76-93%
FAST MRI 51-59% 89- 93%
Experienced Parents 88.90% 62.20%

Adapted from Kim et al, 2007

Conclusions

  • VP shunts offer a mechanical “solution” (not cure), to patients who are otherwise unable to adequately drain CSF
  • Shunt malfunction and/or failure is common (40% fail in the first year of placement)
  • Failures can be mechanical (fracture, obstruction, dislodged) or related to infection
  • Symptoms of shunt failure are diverse and often non-specific
  • ALWAYS take parental concerns seriously!
Reviewer: Yunika Presson, CPNP (Department of Neurosurgery)

References

Blumstein H et al. “Utility of Radiography in Suspected Ventricular Shunt Malfunction.” The Journal of Emergency Medicine. 2009;36(1)50-54

Boyle TP et al. “Radiolgraphic Evaluation of Pediatric Cerebrospinal Fluid Shunt Malfunction in the Emergency Setting.” Pediatric Emergency Care. 2015;31(6)435-440

Boyle TPet al. Comparison of rapid cranial MRI to CT for ventricular shunt malfunction.”
Pediatrics. 2014;134(1)e47-e54

Browd SR et al. “Failure of Cerebrospinal Fluid Shunts: Part I: Obstruction and Mechanical Failure.” Pediatric Neurology. 2006;34(2)83-92

Kestle J et al. “Long-term Follow-up Data from the Shunt Design Trial.” Pediatric Neurosurgery. 2000;33(5)230-236

Kim TY et al. “Test Characteristics of Parent’s Visual Analog Scale Score in Predicting Ventriculoperitoneal Shunt Malfunction in the Pediatric Emergency Department.” Pediatric Emergency Care. 2007;23(8)549-552.

Piatt JH et al. “Clinical Diagnosis of Ventriculoperitoneal Shunt Failure Among Children with Hydrocephalus.” Pediatric Emergency Care. 2008;24(4)201- 210

Pitetti R. “Emergency Department Evaluation of Ventricular Shunt Malfunction: Is a shunt series really necessary?” Pediatric Emergency Care. 2007;23(3)137-141