Clinical use
Investigation of CSF shunts, associated devices and CSF
Background
Hydrocephalus is a condition caused by the accumulation of excess cerebrospinal fluid (CSF) within the cerebral ventricular system. It occurs in both adults and children. If untreated, the prognosis is poor. It may be classified as:
- Communicating (no block between the ventricles and subarachnoid space)
- Non-communicating (a block is present between the ventricles and subarachnoid space)
- The common causes of hydrocephalus are an obstruction of the flow of CSF or a failure to absorb it, resulting from:
- Major developmental abnormalities
- Meningitis
- Overproduction of CSF
- Perinatal haemorrhage
- Trauma
- Tumours, especially in the posterior fossa
Treatment for hydrocephalus involves diverting CSF from the ventricular system to another compartment where it can be absorbed directly or indirectly into the bloodstream. This is done by means of a shunt. There is a risk of infection at the initial shunt insertion and at each subsequent insertion, and shunts may also be infected at other times.
Shunts consist of drainage tubes incorporating one or more valves to control the direction and rate of CSF flow. The devices may also incorporate a reservoir. There are two main types of shunts:
- Ventriculo-atrial (VA) shunts are used to drain CSF from the ventricle to the right atrium.
- Ventriculo-peritoneal (VP) shunts are more commonly used in contemporary neurosurgical practice. In these, the route of drainage is from the ventricle to the peritoneal cavity.
Shunt replacement is necessary from time to time due to growth of the recipient or to mechanical obstruction or infection of the device. If a shunt must be removed because of infection, CSF drainage has to be maintained. This can be achieved by means of an implanted reservoir (which can be tapped as required) or by an external ventricular drain (EVD). These systems allow instillation of intrathecal antibiotics to treat ventriculitis before implantation of a new shunt. They may themselves become secondarily infected. These systems are also used to relieve hydrocephalus in the short term in patients who may not require a permanent shunt. CSF shunts become infected by the following routes, in order of significance:
- organisms directly colonise the shunt, usually at the time of surgery
- organisms travel along the shunt by retrograde spread
- organisms reach the CSF and the shunt via haematogenous spread
Indicators of infection differ according to the type of shunt. For instance:
- signs of VA and VP shunt malfunction (and/or meningitis) include symptoms such as headaches, vomiting, drowsiness and decreased level of consciousness, with or without fever
- infected VA shunts discharge organisms directly into the right cardiac atrium. This gives rise to intermittent fevers and signs of bacteraemia. Rarely, shunt nephritis may occur a long time (sometimes several years) after initial shunt surgery. It is a result of the formation and deposition of immune complexes on the glomeruli basement membranes, and is seen only in VA shunts
- infected VP shunts discharge organisms directly into the peritoneal cavity or may become distally infected without causing meningitis. Abdominal pain as a result of local inflammation may occur, as may local erythema over the shunt track. Rarely, the distal portion of the shunt may perforate the bowel, leading to peritonitis and abscess formation. Sometimes in such cases, polymicrobial ventriculitis, including anaerobes, can be found.
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
Use aseptic technique. Collect samples prior to antibiotic administration where possible.
Specimen requirements
When a shunt is removed all three portions should be sent in separate microbiologically approved sterile white top containers of the appropriate size. This will include the proximal catheter, a valve or reservoir, and a distal catheter.
CSF is usually obtained from the shunt reservoir.
Minimum volume
1-2ml
Limitations and restrictions
Samples sent to the laboratory 2 or more hours following collection risk disintegration of cells within the sample and therefore results will not be accurate.
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
The 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 to
CSF samples are not routinely testing for fungal pathogens. If fungal investigation is required, please contact the Consultant Microbiologist to discuss this prior to sending samples to the lab.
Additional tests may be requested for Mycobacteria sp. and bacterial PCR. These tests should be requested on a separate request form and a separate sample provided where possible.