Clinical use
Investigation of CSF shunts, associated devices and CSF
Background
CSF shunts are used in the setting of hydrocephalus to divert CSF to an alternative part of the body for absorption. Hydrocephalus is a condition characterised by the accumulation of excess CSF within the cerebral ventricular system. If untreated, the prognosis is poor. It may be classified as communicating where there is no block between the bentribles and subarachnoid space; non-communicating where there is a block present or an obstruction to the flow of CSF or failure to absorb. This can be attributed to developmental abnormalities, meningitis, tumors, or trauma.
Proximal ends of the shunt catheter are commonly placed in one of the cerebral ventricles with the distal portion internalised or externalised. Internalised shunts most commonly drain into the peritoneum (ventriculoperitoneal shunt [VP]), with less common variants including ventriculoatrial or ventriculopleural shunts. Externalised devices (external ventricular drains [EVD]) are temporary devices placed in the setting of acute hydrocephalus for the therapeutic diversion of CSF and intracranial pressure monitoring. These systems also allow for the instillation of intrathecal antibiotics to treat ventriculitis before implantation of a new shunt.
Shunt infections typically occur in the first few months of insertion, developing most commonly from colonisation of the shunt with skin organisms. This is shown by approximately half of all shunt infections being related to coagulase-negative Staphylococci and a further third being S. aureus. Some of the organisms associated with shunt infection can be difficult to culture and may require extended incubation, this may affect the turnaround time of the test. Infections can also occur via direct contamination of the distal end occurring in the setting of bowel perforation or peritonitis, leading to infection of the shunt via retrograde spread. Alternatively, infection can be attributed to haematogenous spread.
Clinical manifestations
Shunt infections can present with few or no symptoms and may only develop when the shunt has become obstructed due to infection. This is then associated with clinical signs of increased intracranial pressure. Meningeal symptoms may not be observed, given the lack of communication between the infected ventricles and the meninges. Infection indicators may also differ according to the type of shut and therefore location of the distal portion. For example, VP shunt infections may manifest with symptoms of peritonitis.
Diagnosis
If there is clinical suspicion of shunt infection diagnostic evaluation should be initated with blood cultures, imaging and CSF analysis. CSF aspiration via the shunt is preferred over lubar puncture where possible. The laboratory examination of CSF includes:
- White Blood Cell (WBC) and Red Blood Cell (RBC) counts
- WBC differential (lymphocytes vs. polymorphs)
- Examination of Gram-stained smear
- Culture
- Determination of glucose and protein concentrations (performed by clinical biochemistry departments)
- Polymerase chain reaction (on request from a Consultant Microbiologist with consideration of the clinical findings).
- The reference ranges are listed below.
In cases where the shunt is removed for suspected infection, the shunt components should be sent for culture. This will include the proximal catheter, a valve or reservoir, and a distal catheter. These components must only be sent if there is an indication of infection.
Reference ranges
CSF Microscopy:
Leucocytes
| Age range | Age | Range |
|---|---|---|
| Neonates | less than 28 days | 0-30 cells x 106/L |
| Infants | 1 to 12 months | 0-15 cells x 106/L |
| Children/Adults | 1 year + | 0-5 cells x 106/L |
Erythrocytes
No RBCs should be present in normal CSF
Glucose
| Age range | Age | Range |
|---|---|---|
| Neonates | less than 28 days | 1.94-5.55 mmol/L |
| Infants | 29 to 58 days 2 to 12 months | 1.55-5.55 mmol/L 1.94-5.0 mmol/L |
| Children/Adults | 1 year + | 2.22-4.44 mmol/L |
Proteins
| Age range | Age | Range |
|---|---|---|
| Neonates | less than 28 days | 0.65-1.5 g/L |
| Infants | 29 to 56 days | 0.5-0.9 g/L |
| Children | 2 months to 18 years | 0.05-0.6 g/L |
| Adults | 18 to 60 over 60 | 0.15-0.6 g/L 0.15-0.45 g/L |
Patient preparation
Collect samples before antibiotic administration where possible. CSF should be collected sequentially into 3 or more separate containers together with a fluoride sample for glucose estimation. Each container must be numbered, indicating the order of collection.
The first and the third specimens are used for microbiological examination and the second specimen for biochemical analysis. An aseptic technique should be employed.
Specimen requirements
CSF:
- Yellow top sterile universal
- Specimens 1 and 3 should be sent urgently to microbiology within two hours of the sample being collected.
- Do not refrigerate the sample before sending it to the laboratory
When a shunt is removed, all three portions should be sent in separate microbiologically approved sterile containers of the appropriate size.
Minimum volume
1-2ml
Limitations and restrictions
The cell counts for CSF samples may be inaccurate if there is a delay in sending samples; this is because cells will disintegrate in the sample over time. Microscopy should be performed within 2 hours of the sample collection time to ensure the accuracy of the result.
Samples containing blood clots will not have a cell count performed or reported. Clotted samples will only be investigated with a Gram’s stain and culture.
Turnaround time
- Microscopy: 2 hours
- Culture: 4 days
Analysing laboratory
Microbiology Lab, James Cook University Hospital, Marton Road, TS4 3BW
Additional information
TThe microbiology laboratory must be contacted by telephone to inform them of the subsequent arrival of a CSF sample. The requested should provide the laboratory with:
- Patient name
- Hospital number
- Date of birth
- Tests required
- Requestors name and role
- Contact number for the microscopy result to be telephoned back to
CSF samples are not routinely tested for fungal pathogens. If a fungal investigation is required, please contact the Consultant Microbiologist to discuss this before sending samples to the lab.
Additional tests may be requested for Mycobacterium sp. , bacterial PCR, and other pathogens depending on the clinical risk factors of the case (travel, immunosuppression, occupational exposure), please discuss with the Consultant Microbiologist if required. These tests should be requested on a separate request form and a separate sample provided where possible.