Hydrocephalus ("Water on the Brain")

For a host of different reasons, during pregnancy or, with diminishing likelihood, at any subsequent point in time, a disturbance in the balance of production and evacuation of fluid in the brain and vertebral canal may arise. The many functions of this fluid such as pressure compensation, cushioning against hard jolts and regulation of certain biochemical exchange processes are then impaired and may bring about symptoms. These symptoms change in the course of a child's growth and neurological development. In case of a rapid increase in fluid, these symptoms often point to an increase in pressure and can lead to headaches and vomiting, clouding of consciousness or even stupor. During infancy, an increase in pressure can still be compensated by the dehiscence of the elastically connected cranial bones and is manifested in overly rapid head growth. In case of mild but prolonged pressure increases, vision can be impaired even without noticeable headaches. Beginning changes in the pressure-sensitive optic nerves can be diagnosed by an experienced ophthalmologist in the fundus of the eye.

Abbildung 1: Liquorshunt (ventrikulo-peritoneal)

Abbildung 1: Liquorshunt (ventrikulo-peritoneal)

Treatment of hydrocephalus first took a positive turn in the 1960s with the invention of the valve-regulated shunt. Today, with timely treatment and close monitoring, the prospects for maintaining the intellectual and motor skills that a child brings with it into the world are good.Currently, when treating a patient with a CSF shunt (ventriculoperitoneal [Fig. 1] or ventriculoatrial), we primarily use gravity-assisted valves which, in terms of their characteristics, approach the natural drainage processes. Despite all the technical advances, shunt systems must sometimes be partially or completely replaced due to failure by means of a repeated operation. In most cases, adjustable valves combined with anti-siphon mechanisms can be used to avoid having to re-operate in cases of over or underdrainage and instead performing a valve readjustment. It is essential for us to consistently combat the risk of shunt infections during the operation. This can be accomplished using a strict antiseptic operative protocol as well as tube systems impregnated with antibiotics. If a mechanical obstruction is present in the narrower cerebrospinal fluid canals, the flow can be re-opened with a small endoscopic procedure or the obstruction can be bypassed.

 

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Ventriculocisternostomy (endoscopic ventriculostomy)

Abbildung 2: Schematische Zeichnung der internen und externen Nervenwasser- (Liquor-) Räume wie den Nervenwasserkammern (Ventrikel) und dem Subarachnoidalraum. Bei Engstellung oder Verschluss der Verbindungen zwischen 3. Ventrikel und 4. Ventrikel sowie dem Subarachnoidalraum (rote Kreise) kann eine endoskopische Behandlung erwogen werden.

Figure 3: Endoscopic view of the foramen of Monro, the anatomical opening between the lateral ventricle and the third ventricle.

Abbildung 3: Endoskopische Sicht auf das Foramen Monroi, die anatomische Öffnung zwischen dem Seitenventrikel und dem 3. Ventrikel.

Abbildung 4: Der Boden des 3. Ventrikels (1) begrenzt nach dorsal durch die sog. Corpora mamillaria (2) und nach frontal durch das Infundibulum (3).

Ventriculocisternostomy is the most frequently performed endoscopic operation used to treat hydrocephalus. The typical indication for this is aqueductal stenosis as well as a closure of the drainage paths at the exit of the fourth ventricle (Fig. 2). Causes of this may include changes subsequent to hemorrhages in the ventricular system or infections. Moreover, an obstruction may be caused by a tumor. Very rarely a congenital disorder is the cause of aqueductal stenosis (Bickers-Adams syndrome). Under these conditions, there is an obstruction blocking CSF flow from internal to the external cerebrospinal fluid spaces. The goal of a ventriculocisternostomy is to create a bypass circuit thus making it possible for the cerebrospinal fluid drainage into the external CSF spaces to flow out into the subarachnoid space.

In order to perform a ventriculocisternostomy, it is necessary to use an endoscope in which, in addition to an optical channel, there is an operative channel through which surgical instruments are introduced. Furthermore, there should be two additional channels for continuous rinsing and for drainage. During the surgical procedure, typically, a right frontal cut and, depending on the how the bone presents, a drill hole in the calvarium are made. An incision is made in the dura mater and the cortex surface is exposed. After a small opening has been made in the surface of the tissue, the endoscope is inserted perpendicular to the surface thereby puncturing the lateral ventricle in the right hemisphere of the brain. Through the optical unit, the middle portions of the lateral ventricle with the plexus choroideus and the foramen of Monro are now visible to the surgeon

which makes it possible for him to make the connection to the third ventricle (Fig. 3). Here the tip of the endoscope is inserted so that it is now possible to view the floor of the third ventricle. This is bounded by the anatomical landmarks of the corpora mamillaria and the infundibulum (Fig. 4). A blunt instrument can now be inserted through the operative channel and and pushed forwarded until a perforation of the floor can be achieved. The instrument is then removed and a Fogarty catheter with an inflatable balloon measuring approx. 5 cm in diameter at its end is inserted. The opening created can be expanded with this catheter. The catheter is now removed and, after checking to make sure that the perforation was successful without any signs of bleeding, the endoscope is carefully removed. The opening in the dura mater is closed and the skin sutured in two layers. By means of this procedure, a CSF bypass circuit has been created allowing the CSF to flow directly from the lateral ventricles via the third ventricle into the subarachnoid space. The closure at the level of the aqueduct or the exit of the fourth ventricle is thus bypassed.

The success rate of this procedure is generally approx. 80%. If the procedure is successful, it is unnecessary to implant a foreign object such as a ventriculoperitoneal shunt which is known to carry with it the risk of various complications over the long-term. A relative indication for a ventriculocisternostomy in this context is obstructive hydrocephalus in children in their first year of life since in their case the success rate of this treatment is only 20-30%.

We should not fail to mention that such a procedure is also associated with complications. In addition to the general risk such as wound healing disorder, infections or CSF fistulae, first and foremost there is the risk of a secondary hemorrhage about which the patient must be informed. Not least because an important brain artery is located underneath the third ventricle, the  basilar artery which may not be injured under any circumstances. For this reason, the surgeon must have sufficient experience in order to perform this procedure.

Ventriculocisternostomy has now become a procedure which is often used and which, with appropriate experience, has a very low rate of complications. Further monitoring of the patient is also necessary even without a shunt since, similar to with a shunt, reobstruction as a result of closure of the created channel may arise. Compared to the case of a shunt, however, the risk of reobstruction is considerably lower.

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Aqueductoplasty

Other operations, e.g. aqueductoplasty, are also performed to treat patients with hydrocephalus. This involves the expansion of the CSF channel between the third and fourth ventricle. The procedure must be performed with the utmost care since the aqueduct is located in the region of the brain stem in which, among other things, the patient's eye movements and alertness are controlled. Therefore, there are only limited indications for performing this procedure, i.e. isolation of the fourth ventricle in which only a short segment of the aqueduct is closed. This means that the fourth ventricle is isolated from the CSF circulation and, as a result of the CSF production which nonetheless takes place there, the ventricle expands resulting in compression of the brain stem and the cerebellum. The treatment consists in enabling circulation of the CSF by opening the aqueduct. The outflow from the internal CSF spaces (ventricles) is then achieved by combining the procedure with a ventriculocisternostomy or with a ventriculoperitoneal shunt. From a technical point of view, the procedure is performed in a manner similar to a ventriculocisternostomy. The drill hole site is however a bit more frontal and during the inspection of the third ventricle, the surgeon uses the anatomy in the rear portion which is funnel-shaped and ends in the aqueduct. Using a catheter, the short-segment closure can now be opened. The surgeon must decide intraoperatively whether a ventricular catheter needs to be left in as a stent in order to maintain the opening. This prevents the opening from re-closing. This stent is attached either to a shunt or a Rikham reservoir in the region of the calvarium so that undesired displacement can be prevented. Alternatives to this procedure include either perforating the fourth ventricle from the outside with a ventricular catheter and simultaneously connecting this catheter to a shunt or opening the skull in the region of the transition between the cerebellum and the cervical spine in order to make it possible to open the exits of fourth ventricle using microscopic technique. The latter procedure is, on the one hand, highly complex and on the other hand it cannot be performed on every patient.

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Computer-Assisted Endoscopy

Abbildung 5: Navigationsbildschirm zur Planung der Endoskopführung und der Platzierung des Ventrikelkatheter.

Abbildung 6: Navigierte Neuroendoskopie. Der Operateur verfolgt das Kamerabild des Endoskopes. Parallel wird die Position auf dem Bildschirm der Navigation angezeigt.

If in the case of a patient with hydrocephalus, there is an internal drainage obstruction from individual ventricle compartments associated with an anatomic abnormality of the CSF system, combining endoscopy with a  navigation system can be quite helpful. At Charité, over the last few years we have used this method on children more and more often. The situation to avoid here is one in which due to missing anatomical landmarks, orientation in the CSF spaces is no longer possible. The navigation system used here consists of a computer which stores the preoperative image data. In addition, markers are affixed to the patient's skin which are also visible in the MRI images. This allows the position of the patient's head to be localized in the operating room with the aid of an infrared camera (Fig. 5). The camera also recognizes certain instruments, including the endoscope, if it has markers on it (Fig. 6). Similar to a car's navigation system, the position of the endoscope in the patient's head can be conveyed to the surgeon based on the MRI data which basically serve as a map. This permits a better orientation.

In some cases, however, there is the problem in the event that a large amount of CSF is lost during the operation that the image data acquired prior to the operation no longer match the intraoperative situation. This must continuously be verified by the surgeon. The situation can also be improved through continuous compensation of the fluid loss by rinsing with appropriate drainage.

The aim of this operating technique is to permit drainage systems which are as simple as possible in case of complicated anatomical situations associated with hydrocephalus. This means CSF drainage through a shunt should be performed using the smallest possible number of catheters. On the one hand, the aim of this is to reduce the rate of of long-term complications due to obstructions, for example, and on the other hand to facilitate the diagnosis of the dysfunction during necessary revision operations.

It should also be noted that this procedure is very technically complex and fortunately is only required in a small percentage of patients. However, especially in severe cases, this procedure allows for noticeable improvement in treatment.

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Summary

As a rule, patients with hydrocephalus are treated with a CSF shunt when, despite expanded CSF spaces, said spaces are communicating with one another. Endoscopic surgery is used primarily in case of an internal obstruction of CSF outflow. Most often, a ventriculocisternostomy is performed in which the flow of the CSF from the internal CSF spaces into the subarachnoid space through the opening of the floor of the third ventricle. Other procedures such as aqueductoplasty or navigated endoscopy can, in case of specific indications, enable an improvement in treatment of hydrocephalus. Overall, today endoscopic surgery can no longer be ignored as a complementary procedure in treating hydrocephalus.

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