Endoscopic third ventriculostomy
An endoscopic third ventriculostomy (ETV) is sometimes performed as an alternative to a shunt for hydrocephalus. It involves introducing an endoscope through the skull and brain into the ventricles. A ventricular endoscope is a thin tube which contains a light source to illuminate inside the cerebral ventricles as well as an optic system for taking the light back to the video camera which is connected to the outer end of the ventricular endoscope. It is introduced through the brain into the ventricular system. The endoscope is then navigated from the lateral ventricle through the foramen of Munro into the third ventricle. A ventriculostomy is then performed. This involves creating a small hole in the bottom of the brain allowing CSF to bypass any obstruction to CSF outflow.
After the endoscope has been removed, a Rickham reservoir might be inserted. This will allow drainage of CSF if the ventriculostomy were to close, and would also allow for testing of the CSF circulation. Some neurosurgeons leave a Rickham reservoir in the site of the burr hole in all patients.
What are the indications for ETV?
The most common procedure for which it is used is obstructive hydrocephalus, particularly when there is an obstruction at the level of the aqueduct. Apart from the anatomy of the CSF circulation problem and the underlying condition, age is an important factor. There is a decrease in the long-term success of ETV in children under 6 months of age. However, a trail of ETV may still be indicated to avoid a CSF shunt.
In some cases, in addition to an ETV, other additional procedures may also be performed. Aqueductoplasty involves directly opening the aqueduct when it is blocked. This is not always indicated or possible. The area around the aqueduct is particularly sensitive and needs to be treated with great care. However, if there is a thin membrane within the aqueduct or aqueduct web, this may be a suitable indication for aqueductoplasty.
In some instances, there may be an intraventricular cyst which may need to be fenestrated. Fenestration basically means making an opening in the wall of a cyst. A cyst is a fluid filled cavity. Within the ventricular system this may have quite a thin wall. Opening that wall of the cyst or fenestrating the cyst may restore normal CSF circulation.
If there is a tumour within the ventricle causing an obstruction, this may be either biopsied or in some cases, removed.
What are the risks of ETV?
When introducing an endoscope into the brain there is a small risk of introducing an infection despite the use of sterile conditions and prophylactic antibiotics. An infection within the CSF is termed meningitis. An infection of the brain is termed encephalitis. In the vast majority of cases, should this occur, it can be treated with antibiotics.
By passing the endoscope through the brain there is a small risk of causing a haemorrhage, i.e., bleeding within the brain or within the ventricular system. This may be of no consequence, or it may be very serious, or even cause death. This risk of a life-threatening haemorrhage or a haemorrhage that causes a stroke which results in paralysis or other neurological deficits is very low.
The floor of the third ventricle is usually quite thin. Various techniques are used to make the hole in the ventricle and the technique is dependent on the neurosurgeon. The floor of the third ventricle contains structures important for memory and that have a role in hormone regulation. Although they are normally no clinical consequences of making the hole in the floor of the third ventricle, there is a small risk.
Under the floor of the third ventricle is a large and important artery called the basilar artery. It must be stressed that this may also happen with CSF shunts and overall is extremely rare. It is one of the structures about which neurosurgeons are most concerned when performed the ventriculostomy, as puncturing it or one of its branches can result in death or other serious complications. This is of course very rare, but is still a risk of the procedure.
Like CSF shunts, ETVs are not without failure. The ventriculostomy can close which may cause a recurrence of symptoms or symptoms of raised intracranial pressure such as headache, vomiting, blurred or double vision, and lethargy leading to drowsiness and coma. Several late deaths after ETV have been reported in the literature. These are presumably due to closure of the ventriculostomy and acute hydrocephalus. It must be stressed that this may also happen with CSF shunts and overall is extremely rare.
Although the ETV may be technically successful, the ventriculostomy may still not resolve the CSF circulation problem in all cases. An assessment of the chances of the success of the ventriculostomy depends upon the patient’s age and the underlying condition. A proper assessment needs to take these factors into account and can normally be provided to you by your neurosurgeon.
The operation involves making an incision, and therefore the normal risks of any surgery apply. These include, but are not limited to, the risks of infection of the wound, bleeding, CSF leakage and wound dehiscence. A scar will inevitably form but this is behind the hairline.
The procedure normally takes in the order of 20-40 minutes including all surgical parts of the procedure. It requires a general anaesthetic which has its own set of risks.
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.
In some cases, a stereotactic scan will need to be performed. This scan is loaded into the image guidance system to help the neurosurgeon guide the endoscope to into the ventricle or towards the tumour if present.
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 are 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. If they are well, 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. The average length of stay in hospital is 2-5 days.
What follow-up is required after surgery?
The scalp is normally closed using skin clips. In children, a dissolving suture is 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. At that time further follow-up scans may also need to be arranged.