Workup of Malfunctioning VP Shunt
In hemodynamically stable patients with suspected VP shunt malfunction, obtain a non-contrast head CT comparing ventricular size to prior imaging, followed by lumbar puncture to assess opening pressure and CSF analysis for infection, with neurosurgical consultation for consideration of shunt tap or radionuclide shuntogram if diagnosis remains unclear.
Clinical Presentation
Look specifically for:
- Acute malfunction: Nausea, vomiting, irritability, seizures, headache, lethargy, altered mental status, gait abnormality
- Chronic malfunction: Neuropsychological changes, feeding pattern changes, developmental delay, decline in school performance, progressive headaches, increased head size in children 1
Imaging Algorithm
Step 1: Non-Contrast Head CT
- Compare to prior imaging - this is critical. Ventricular enlargement over time confirms malfunction 1
- Look for ventriculomegaly and transependymal edema 2
- If no prior imaging exists, proceed to functional testing
- Important caveat: Normal or small ventricles do NOT exclude shunt malfunction - consider "slit ventricle syndrome" 1
Step 2: Plain Radiography (Shunt Series)
- Obtain skull, neck, chest, and abdominal films
- Evaluate for disconnections, breaks, or catheter migration 3
- Barium-impregnated tubing makes this more reliable 3
Functional Assessment
Lumbar Puncture
- Measure opening pressure to indirectly assess shunt function 2
- Send CSF for cell count, glucose, protein, Gram stain, and culture to evaluate for infection 2
- Critical point: This should be done even with hydrocephalus present - the risk is low 2
Shunt Tap (if diagnosis unclear)
- Sample CSF directly from reservoir for infection workup
- Assess patency and function of shunt apparatus
- Weigh risks: May introduce infection or cause malfunction 2
- If no CSF obtained on reservoir puncture, ventricular catheter replacement is indicated 4
Advanced Functional Testing (when needed)
Radionuclide shuntogram is the preferred functional study:
- Inject Tc-99m DTPA into shunt reservoir 5
- Visualizes CSF flow through entire system
- Non-invasive and identifies exact location of obstruction 5
Fluoroscopic contrast injection (alternative):
- Inject iodinated contrast into reservoir under fluoroscopy
- Allows selective exclusion of proximal vs. distal catheters
- Identifies exact level of failure 4, 3
Infection Workup
When infection is suspected:
- CSF analysis from lumbar puncture or shunt tap
- Blood cultures if systemically ill
- Management differs by organism 2:
- Bacterial infection: Remove shunt, place external ventricular drain (EVD), treat until CSF sterilized, then replace as second procedure
- Low pathogenicity organisms: Consider single-stage replacement
- Fungal (Coccidioides): May consider single-stage approach
Pediatric Considerations
For children, rapid MRI should be considered over CT when available to reduce lifetime radiation exposure 6. Ultra-low-dose CT protocols specific to shunt evaluation are acceptable alternatives if MRI unavailable or programmable shunt needs assessment 6.
Common Pitfalls
- Don't rely solely on ventricular size - slit ventricle syndrome can present with normal or small ventricles despite malfunction 1
- Don't skip comparison imaging - acute changes are more diagnostic than absolute size 6, 1
- Don't assume infection without CSF analysis - mechanical failure is more common 7
- Don't delay neurosurgical consultation - early involvement improves outcomes 2
Neurosurgical Consultation Timing
Obtain early neurosurgical consultation in all cases of suspected malfunction 2. If strong clinical suspicion exists without baseline imaging available, imaging may be deferred and performed where definitive treatment can be delivered 6.