CSF Shunts for Hydrocephalus
What is a shunt?
A shunt is essentially a tube that drains fluid from one part to another. The fluid in this case is cerebrospinal fluid (CSF). Most shunts consist of three basic components: a proximal catheter, a valve and a distal catheter. There are various combinations of these components.
The most common type of a shunt is the ventriculoperitoneal (VP) shunt. With a VP shunt the proximal catheter is passed through an area of the brain and into the ventricle via a small burr hole. Depending on the size of the ventricles this can be performed with or without the assistance of stereotaxy. CSF drains via the valve to the distal catheter which allows CSF to drain into the peritoneal cavity. The peritoneal cavity is a large area within the abdomen which contains the bowel and other organs, The end of the shunt sits within this space and the fluid is absorbed by the lining of the peritoneal cavity back into the blood stream.
In some cases, particularly when there may be adhesions in the peritoneal cavity from previous abdominal surgery, the distal end of the shunt may be placed in into a vein. This is called a ventriculoatrial shunt. Other alternatives include the pleural space around the lung or even into the gallbladder.
Another site used to drain CSF is the lumbar space. This is used when there is no obstructive hydrocephalus and is more commonly used in cases of idiopathic intracranial hypertension. The lumbar space is accessed through the back of the lower spine with the proximal or lumbar catheter sitting within the space around the nerve roots. These shunts are also usually connected to a valve and peritoneal catheter. Shunts may also be placed into arachnoid cysts or syrinx cavities in the spinal cord in some cases.
There are many types of valves available on the market. Most valves open in response to a certain pressure differential. The pressure at which they open varies. Some are fixed pressure valves although programmable valves where the setting can be changed using a special magnet in the office are also commonly used, particular in NPH. The valve used will vary depending on the condition, age of the patient and the preference of the surgeon.
Related conditions to CSF Shunts
How is a shunt procedure performed?
A shunt is inserted under a general anaesthetic. For most shunts two small incisions are made. One to insert the proximal catheter and another to insert the end of the distal catheter. The operation takes less than one hour.
For a ventriculoperitoneal shunt the incision is usually made above and behind the right ear and a small burr hole made. A pocket is created just below this for the valve. The valve and distal catheter are then passed underneath the skin in the subcutaneous tissues to a second small catheter in the right upper quadrant of the abdomen. The ventricular catheter is then inserted into the ventricle. CSF is obtained and sent for testing. The ventricular catheter is connected to the valve. The end of the distal catheter is observed for CSF flow before it is inserted into the peritoneal space. The wounds are then closed, and the patient recovered.
What are the risks associated with a shunt?
The risks are dependent on the type of hydrocephalus or related condition that is being treated as well as type of shunt being implanted.
There are general risks associated with this type of surgery. These risks include those normally associated with surgery such as bleeding or infection, DVT or pulmonary embolism and the risks associated with a general anaesthetic. Surgery in or around the brain also has specific risks such as neurological deficit from stroke or haemorrhage. This is rare.
Shunts, as mentioned, are a tube and therefore have the potential for blockage. When a shunt is inserted for obstructive hydrocephalus, this may lead to raised intracranial pressure and the shunt may need to be revised urgently to alleviate the pressure and blockage. In other types of hydrocephalus such as normal pressure hydrocephalus, it may mean a return of symptoms. Revision of the shunt will be required but is less urgent.
Shunts are also a foreign material and therefore are more prone to infection. Infection can be serious and may require temporary removal of the shunt. The proximal and distal catheters are often impregnated with antibiotics that then leach out over a few moths which may prevent some infections.
Patients with NPH are often older have other morbidities. They are therefore more prone to other complications. In addition, overdrainage of CSF may cause a collection of blood over the surface of the brain called a subdural. This risk can be reduced, although not eliminated, by the use of a programmable valve and adjusting the shunt down as needed.
Prof Owler will discuss these risks in more detail at you consultation and answer any questions that you may have.
What happens before surgery?
Prior to surgery, patients may be asked to attend a preadmission clinic. This will involve routine blood tests and for some patients an ECG and chest X-ray. Patients that have significant co-morbidities or illness may require extra assessment.
When do I stop my blood thinning medication?
Patients who are on aspirin or clopidogrel should cease those medications 7 days before surgery. For patients who are on warfarin, management will depend on the original reason for their warfarin. Some patients will require early admission and be started on heparin, for example, patients with mechanical heart valves. Others will just need to stop taking warfarin 2 days before surgery. The INR will be checked before surgery.
Other anticoagulants, for example, Eliquis or Xarelto will also need to be ceased prior to surgery and this will be planned with Prof Owler and, if needed, your cardiologist
What about other medications?
Other medications should be continued including those usually taken on the morning of surgery. These medications should be taken with a sip of water even though the patients may be nil by mouth otherwise. If you are in any doubt, then please contact Prof Owler’s rooms or the hospital.
Patients with a history of diabetes will need to have their medications managed depending on the nature of their condition and fasting times. Some diabetic medications will need to be ceased prior to surgery but this will be planned prior to surgery with Prof Owler and his anaesthetist.
How long do I need to fast for before surgery?
All patients undergoing a general anaesthetic will need to fast. That is, they should have nothing to eat or drink for around 8 hours prior to surgery. Failure to comply with this may necessitate cancellation of the procedure as it may expose the patient to significant risk. As most patients are admitted on the day of the surgery, the hospital will contact them to inform them of the time for admission, likely time of surgery and the required fasting times on the day before the surgery.
What do I need to bring to hospital with me?
Most patients are admitted to hospital on the day of the surgery. Patients need to ensure that their latest X-rays, CT scans and MRI scans are with them when they come to hospital. These scans are the surgeon’s road map and without them the operation cannot proceed. Except in rare circumstances, patients are responsible for these films, and are normally given back to them at the time of consultation.
What occurs after the surgery?
At the end of the operation, most patients are recovered, that is woken-up and the breathing tube removed just like any other general anaesthetic. The patient is then assessed in terms of their neurological function and transferred to the intensive care unit or high dependency area where they closely observed. After a few hours the patient can normally start to eat and drink.
Either on the same day or the next day the patient will undergo a CT scan of the brain to check the position of the ventricular catheter and ensure there are no other issues. If they are well then, they are transferred to a normal ward bed. Observations are still performed but less frequently. Depending on the patient’s condition and their clinical progress most patients are discharged home. Some patients, especially older patients with iNPH may undergo a period of rehabilitation. The average length of stay in hospital is 4- 7 days.
What follow-up is required after surgery?
The scalp and abdomen are normally closed using skin clips. In children a dissolving suture us usually used. Skin clips need to be removed 7-10 days after the surgery and patients are asked to return to their GP for removal of the clips. This also provides an opportunity for the wound to be reviewed by their doctor
Patients are encouraged to return to see Prof Owler around 4-6 weeks after the surgery to ensure that the recovery is proceeding as planned and discuss any concerns. An appointment will be made for you shortly after the procedure has been performed.
Important Information
This information was provided to assist you. While it has been prepared to provide accurate information the practice and techniques of surgery will differ between surgeons. Likewise, the information is a generalisation in relation to the surgery and will vary between patients depending on the individual and their pathology. This information cannot cover all aspects of the surgery especially in relation to surgical risks and should not be considered an exhaustive explanation. Please contact Prof Owler’s office if there are any further concerns or questions.
