Ventriculoperitoneal Shunts

Introduction

The function of cerebrospinal fluid is not entirely understood.

However, cerebrospinal fluid is believed to be an ultrafiltrate of blood that cushions the brain. It allows for removal of metabolic products and the proper environment for neuro- transmission. 

Most CSF is produced by the choroid plexus in the lateral, third and 4th ventricles. It moves from the point of production secondary to differences in pressure, by cilia action, blood vessel pulsation, and respiratory variations. After production, it passes from the lateral ventricle through the paired foramina of Monro into the third ventricle. CSF is resorbed in the superior sagital sinus by arachnoid villous activity in a process of active transport that is affected by CSF pressure. 

Hydrocephalus

  1. Overproduction of CSF- unusual and caused only by choroid plexus papilloma
  2. Blockage of the normal flow of CSF.
    1. Communicating or Absorptive- blockage of the resorption of CSF in the arachnoid villi, basal cisterns, or subarachnoid space. The ventricles are patent and all 4 are enlarged. 
    2. Non-communicating- Obstruction proximal to the foramina of Lushka and Magendie at the outlet of the 4th ventricle.
      1. Tumors 
      2. Cysts 
      3. Infection and hemorrhage 
      4. Congenital malformations 
      5. Aqueductal stenosis
  3. The best treatment for hydrocephalus is the placement of a extracranial shunt from the ventricles to an outside absorptive surface (i.e., ventriculoperitoneal, ventriculo-atrial, ventriculopleural, etc.)

Shunts

  1. Shunts usually consist of three parts
    1. Proximal end that is radiopaque and is placed into the ventricle. This end has multiple small perforations.
    2. Valve- this allows for unidirectional flow. Can adjust various opening pressures. Usually has a reservoir that allows for checking shunt pressure and sampling CSF
    3. Distal end that is placed into the peritoneum or another absorptive surface by tracking the tubing subcutaneously

vp_shunt_belly_large.jpg

Surgical insertion of a VP shunt. http://dannymiller.typepad.com/blog/2009/08/due-date.html

Shunt malfunctions

  1. Median survival of a shunt (before need for revision) in a child under 2 years of age is 2 years; over two years of age is 8 - 10 years. 
  2. Signs and symptoms include headache, malaise, general not feeling well, vomiting, mental status alterations, increased blood pressure, head circumference increase, Cushings triad, bulging fontanel, sixth nerve palsy signs, Macewen's sign, changes in gait, and personality changes. There may also be an increase of seizures and a complaint of neck pain.  The parents often know that something is wrong.  Teachers may state that there has been a change of school performance 
  3. Obstruction- most often the proximal tip is obstructed with cells, choroid plexus, or debris. May also have kinking of the tubing and migration of the distal end.
    1. Diagnosis by suspicion based on signs and symptoms and confirmed by CT scan of the head or shunt tap or lumbar puncture for CSF pressure elevation (ALWAYS RECORD A PRESSURE WHEN DOING AN LP!!!!).
  4. Infection-
    1. signs include fever, meningeal signs, vomiting, signs and symptoms of shunt malfunction, abdominal pain, and peritonitis. 
    2. There may be evidence of purulent material around the shunt insertion site and redness along the shunt tract 
    3. Most common organisms are S. epidermidis and S. aureus. Also gram negative organisms. 
    4. Diagnosis by positive blood cultures, shunt fluid cultures, or lumbar puncture cultures. Also the presence of greater than 10 cells in the fluid is suggestive of infection.

Infection peaks in the first few weeks after a shunt insertion. Infection years after shunt placement is rare unless the skin is broken over the tubing.

Treatment of Malfunctions

  1. Antibiotics including Vancomycin and Gentamycin
  2. External Ventricular Drainage
  3. Removal of the shunt.
  4. Disconnections and breakage of tubing are another cause of malfunction, though less common than occlusion.
  5. Migration into the scrotum, perforation of the bowel wall, and intussuseption are all rare complications in the peritoneum

In a child with a ventriculoperitoneal shunt, the shunt is statistically unlikely to be the cause of any specific problem. However, if family members suspect shunt malfunction or no other cause for fever, malaise, behavioral change, etc., can be found (i.e., ear infection), careful and diligent evaluation of the shunt is mandatory.

References

  1. The Shunt Book. Drake and St. Rose 1996.
  2. Madikians A. and Conway E.E. Cerebrospinal Fluid Shunt Problems in Pediatric Patients. Pediatric Annals October 1997.
  3. Iskander B.J. et al. Pitfalls in the Diagnosis of Ventricular Shunt Dysfunction: Radiology Reports and Ventricular Size. Pediatrics. 1998

Back to Table of Contents