Cerebral shunt

A cerebral shunt , cerebral shunt or liquorshunt is a medical hose system (usually an implant ) that is used for hydrocephalus , but is also used for pseudotumor cerebri (intracranial hypertension), especially since the symptoms are similar. By a cerebral shunt (in most cases peritoneal shunt ventriculo ), excess cerebrospinal fluid from the brain chambers body internally, for example, in the abdominal cavity discharged to the intracranial pressure to a normal value to reduce. It is usually a thin plastic tube that, with the interposition of a valve , drains the cerebral fluid from the head, under the skin, behind the ears and along the neck into another body cavity (abdominal cavity or atrium of the heart).

If a cerebral shunt is not used because, for example, the protein levels in the CSF are too high after a shunt infection, the use of a Rickham reservoir can alternatively be considered for small children in order to drain CSF and thus temporarily reduce intracranial pressure when puncturing several times a day to stabilize.

introduction

In hydrocephalus there is either a resorption disorder of the cerebrospinal fluid , an occlusion of the connections between the cerebral ventricles or the spinal canal or an overproduction of cerebrospinal fluid. Resorption disorders usually result from intracerebral bleeding (ICB) involving the ventricles (intraventricular cerebral haemorrhage - IVH) in newborns. The arachnoid villi in the area of the spinal nerve exits and the venous blood conductors in the dura mater (sinus durae matris) stick together due to the proteins contained in the blood and block CSF absorption. As a result, the intracranial pressure (Intracranial Pressure, ICP for short, brain pressure) rises , in a newborn, the skull grows disproportionately because the cranial sutures are not yet firmly connected. In this case, a liquorshunt is the method of choice. Through a shunt system, the liquor is drained from the ventricles inside the body, for example into the abdomen, and the intracranial pressure is reduced to a normal value. In general, hydrocephalus goes hand in hand with the destruction of brain tissue due to the overpressure situation in the skull. Increased intracranial pressure causes the loss of brain tissue . Brain tissue that has already disappeared is irretrievably lost, but the progress of the process can be stopped by a cerebral shunt.

Working principle

A shunt system has the task of draining CSF from a defined intraventricular pressure (IVD) and at the same time ensuring that not too much CSF is drained and thus overdrainage occurs. The pressure in the patient's abdomen (intraperitoneal pressure, ID) and the hydrostatic pressure (HD), i.e. the pressure difference that results from the height difference between the ventricular system and the abdomen of the sitting, lying or standing patient, must also be taken into account . To calculate the intraventricular pressure, the following formula applies, where OD represents the opening pressure of the valve. The specification H ₂ O designates a unit of pressure as "cm water column".

Intraventricular pressure (IVD) = intraperitoneal pressure (ID) + opening pressure of the valve (OD) - hydrostatic pressure (HD)
IVD = ID + OD - HD

Example:

The patient lying down has:

an abdominal pressure of 0 cm H ₂ O,
an opening pressure of the valve of 10 cm H ₂ O and, since it is located,
a hydrostatic pressure of 0 cm H ₂ O.

Implemented on the formula

IVD = ID + OD - HD

surrendered

IVD = 0 + 10 - 0 = 10 cm H ₂ O.

The same patient is now standing upright. He has:

an abdominal pressure of 0 cm H ₂ O,
an opening pressure of the valve of 10 cm H ₂ O and
a hydrostatic pressure of 50 cm H ₂ O.

Implemented on the formula

IVD = ID + OD - HD

surrendered

IVD = 0 + 10 - 50 = -40 cm H ₂ O.

Here the patient experiences overdrainage while standing.

Example two thus also shows the major disadvantages of single-stage shunt valves. The patient either experiences overdrainage while standing or overpressure in the ventricles while lying down. The situation is made more difficult by the fact that obese patients have a higher intraperitoneal pressure than lean patients.

Types of shunt systems

A basic distinction is made between ventriculo-atrial (VA) and ventriculo-peritoneal (VP) shunt systems. In the rarely indicated VA shunt systems, the liquor is drained into the right atrium . In the most frequently indicated VP shunt systems, liquor is drained into the abdominal cavity ( peritoneum ). External ventricular drainage (e.g. a Codman drain) is also indicated for certain indications, e.g. after a shunt exploration due to a shunt infection . However, external drainage can only be used temporarily, as the risk of new infections is much higher than with internal drainage.

Construction of shunt systems

Shunt systems basically consist of the following components:

Ventricular catheter
Borehole diverter (with or without pumping chamber / reservoir)
Distal catheter
Valve systems
Atrial or peritoneal catheter

Ventricular catheter

The ventricular catheter actually drains the cerebral ventricles. It is a silicone tube that is rounded off at the end and is provided with small holes in the end area so that liquor can enter the tube from the ventricles. After a hole has been drilled (usually in the back of the frontal bone), one of the two lateral ventricles is punctured with the catheter.

Borehole diverter / borehole reservoir

The ventricular catheter is usually connected directly to a borehole diverter or a borehole reservoir. The borehole diverter sits on the ventricular catheter and angles the catheter by 90 degrees so that the connector adjoining it is parallel to the top of the skull. Alternatively, there are borehole reservoirs that enable a CSF puncture for ICP measurement and CSF diagnostics directly on the ventricles. There are also pumping chambers that allow a stuck valve to be flushed out. Combinations of both are also offered. Newer devices (consisting of a reservoir and pumping chambers) also contain a check valve that prevents a sudden increase in pressure in the ventricles when pumping. The use of reservoir, pumping chambers or a combination of both is individual, depending on the indication.

Distal catheter

The distal catheter is often connected directly to the deflector / reservoir / pump chamber. It connects the ventricular catheter and deflection unit with the actual shunt valve.

Shunt valve

The shunt valve is used to regulate the ICP and is often a combination of different valve types. Today's valve systems are usually implanted behind the ear. Due to its design, a shunt valve also prevents the backflow of liquor and thus also prevents liquids from entering the ventricular system from the peritoneal space. Thus, the shunt valve always represents an infection barrier.

Atrial and peritoneal catheters

The atrial catheter guides the CSF from the valve into the right atrium of the heart, the peritoneal catheter into the abdominal cavity. The respective silicone tubes of the distal as well as the peritoneal or atrial catheter have an outer diameter of about 2.3 millimeters and are pulled through under the skin. A shunt implantation requires a maximum of three to four small skin incisions.

Historical valve types

Today there are about 130 different types of valves on the world market, but they are all based on four basic types of shunt valves. Together with the types offered in different pressure levels, the neurosurgeon can now choose between around 450 different valves.

Basics, technical valve principles

To achieve a differential pressure between the cerebral chambers and the discharge point (today mostly the abdominal cavity), three different types of valves are still used today. This does not mean the hydraulic mode of operation of valves, but rather the technical implementation. The first valves were the so-called slit valves, in which the stiffness of the material (silicone) defines the pressure at which the valve opens. The situation is similar with diaphragm valves; here it is the rigidity of the material (silicone) against warping that defines the opening pressure. The ball-cone principle is used in all modern valve types, in which the opening pressure is not determined by the closing element itself, but by a spring that can be set much more precisely.

Ball-cone valves

With this type of valve, a ball pressed into a metal cone by a spring closes the liquor passage. The spring tension determines the opening pressure of the valve. If the CSF pressure on the ball is higher than the spring force with which the ball is pressed into the cone, the valve opens and the CSF can pass. These valve designs usually work very precisely and reliably. The most well-known representative of this type of valve is the Cordis-Hakim standard valve.

Diaphragm valve

In the case of a membrane valve, a membrane made of highly flexible silicone presses against a rigid ring-shaped opening and thereby closes the liquor passage. If a defined pressure is exerted on the membrane, the membrane is deformed and the liquor can pass through the opening. The flexibility and pretension of the membrane determine the opening pressure of the valve. The disadvantage of this type of valve is the so-called silicone memory effect . The silicone membrane changes its physical properties in the course of use, which also changes the characteristics of the valve. It depends very much on the silicone base material used, how pronounced and how quickly the silicone memory effect comes into play. Well-known representatives of this valve type are the Heyer-Schulte valves.

Slit valve

The slot valve again has two different basic shapes. With the simple (linear) slit valve there are several incisions near the closed end of a silicone tube. If the pressure is low, the silicone lips press against each other and liquor cannot pass through. If the pressure increases, the slits separate and liquor can pass through.

Other designs are cross slots or duckbill slots, which, however, basically fulfill the same function. As with the diaphragm valve, the silicone memory effect also comes into play here. Another disadvantage is that the sometimes very small slits to the liquor passage can very easily become blocked.

Simple differential pressure valves

All the presented basic types were developed between the fifties and seventies of the twentieth century. For the first time an effective possibility of hydrocephalus therapy had been created with these valves. What all types have in common, however, is that they always have only one static pressure level that is suitable for the patient lying down. If the patient is sitting or standing, the hydrostatic pressure difference inevitably leads to overdrainage of the ventricular system. Since overdrainage can lead to significant complications, these valves must be assessed as out of date if they are implanted without additional valves.

From a technical point of view, all valves are differential pressure valves.

In order to avoid overdrainage, more and more shunt types were increasingly developed in the early 1970s, but they still make use of the findings with the basic types presented.

Modern valve types

During the development of the modern shunt valves, four main paths were taken from which

the adjustable valves,
the self-adjusting valves,
the anti-siphon valves and
the gravitation controlled valves

have emerged. The latter two are often grouped together under the collective name of hydrostatic valves , as they take into account the hydrostatic pressures in standing or sitting patients.

Adjustable valves

The adjustable valves are essentially based on the ball-cone technique, in which a ball is pressed into a cone with a spring. In contrast to the static ball-cone valve, the preload of the spring can be changed with the adjustable valve with the help of a rotating armature. Bar magnets sit on the armature, with the help of which the armature can be adjusted from the outside with a matching bar magnet or a rotating magnetic field and the preload of the spring can be changed. As a result, the valve can be set very differently to the requirements of the patient without the need for intervention. With the first generations of these valves, which were introduced in 1983, it was shown again and again that magnetic fields already occurring in the home, such as those of headphones, were sufficient to adjust the valve. With the first generations of these valves, an X-ray examination was also required immediately after an MRI to check the setting of the valve. However, valves available today are designed to be resistant even to a 3 Tesla magnetic field from an MRI. A kind of compass is used today to check the settings, which is held over the valve and shows the current pressure level. The adjustable valve per se is not suitable to prevent overdrainage while sitting or standing. Adjustable valves are often referred to as "programmable shunts", but this designation is not entirely correct, as it suggests a function that the valve cannot fulfill.

Self-adjusting / self-regulating valves

Self-adjusting or flow-controlled valves are based on the consideration that only as much liquor has to be removed per unit of time as is actually produced. For this purpose, a shunt valve was presented for the first time with the Cordis Orbis Sigma valve , which discharges a constant amount of cerebrospinal fluid per unit of time regardless of the differential pressure at the shunt ends. With a conventional valve, an increased differential pressure would also increase the amount of liquor to be removed. This is achieved by providing an elastic membrane with an opening which is more or less narrowed by a conical plunger. If the patient is lying down, the differential pressure between the ends of the shunt is low and thus the pressure on the membrane is low: The membrane is only slightly stressed, at this point the conical plunger is relatively thin and a moderate amount of liquor can be drained off. If the patient is sitting upright or standing, the differential pressure increases dramatically. The pressure on the membrane increases and it deforms in the direction of a point of the conical plunger with the largest diameter, the liquor drainage is exposed to a comparatively greater resistance and the lumen is correspondingly reduced. Another emergency pressure level has been implemented in the event of a life-threatening increase in intracranial pressure. Here the membrane is deflected to such an extent that there is no longer any obstruction from a plunger and large quantities of liquor can flow away.

Evaluation of self-adjusting / self-regulating valves

As a reminder: The underlying idea of this type of valve is that no more liquor is removed than is produced per unit of time. If this value could be precisely defined, the concept would make sense. Most valves assume a value of 20 milliliters per hour and try to keep this value approximately independent of the differential pressure. However, this is also the main disadvantage of these systems: CSF production varies considerably over the course of a day. There are times when significantly more than 20 milliliters of liquor is produced per hour, and there are also times when this amount is clearly undercut. It is also known that CSF production decreases with age. So there are always times in the daily rhythm with too high and too low ICP. Risks also arise with this type of valve in the treatment of normal pressure hydrocephalus in connection with B waves. These describe a short-term increase in the blood volume in the head, the pressure increase of which cannot be adequately compensated for in the case of hydrocephalus and can therefore lead to very high pressure peaks. Flow controlled valves are conceptually incapable of preventing this. Due to their design, these types of valves also tend to clog.

Anti-siphon valves

The anti-siphon valve (ASD = anti-siphon device) is based on the functional principle that a suction effect occurs on the shunt valve when the patient is standing or sitting upright. As a result, a membrane comes to rest on a plastic component and thus prevents the flow of liquor. If there is no longer any suction, the very elastic membrane can move back and allow the liquor to flow again. Since anti-siphon valves always have to be combined with conventional valve types, it did not take long before complete solutions were available on the market. The best-known representatives are the Heyer-Shulte or PS Medical Delta valves.

Evaluation of anti-siphon valves

The critical point of these valves is the use of atmospheric pressure as a reference pressure on the side facing away from the liquor. In the laboratory and immediately after the implantation, this is not a problem. This only occurs after the scarring is complete. Since the valves are mostly located in the subcutaneous fatty tissue, the reference pressure increases considerably after the scarring. This also explains the fact that the valves initially worked excellently and, once the scarring was complete, caused problems that led to the valves being completely closed. After initially adequately avoiding overdrainage, symptoms of overpressure developed after a few weeks: the hydrocephalus returned. From today's perspective, these valves are therefore no longer up-to-date, as the risk of a shunt failure is too high.

Gravity controlled valves

In the case of gravitation-controlled valves, a distinction is made between the counterbalancer and the switcher types. The first developed Counterbalancer based similar to a lift, in which a counterweight to the actual car exists on the balance of forces. If the adult patient stands up, the pressure on the valve is about 50 centimeters of water column. A ball-cone combination opposes this weight with a corresponding resistance. Only when the pressure increases, the balls are lifted out of the cone and the excess liquor can pass through. If the patient lies down, however, the balls fall out of the cone and the liquor can pass through. With the Cordis-Hakim-Lumbar valve , such a type of valve was created for the first time. However, this type of valve, patented as early as the 1970s, was only offered for lumboperitoneal drainage.

With the Miethke Shunt Assistant, Christoph Miethke developed a valve for the peritoneal discharge for the first time, which realized an opening pressure that was directly dependent on the posture. While the Miethke Shunt Assistant is just an additional valve, both the Cordis-Hakim-Lumbar-Valve and the Miethke PaediGAV represent an "all-in-one" solution that meets the needs of both the lying and the straightened consider standing patients.

Another valve that set a posture-dependent opening pressure was the Sophysa AS valve made in France . The functional principle was based on an armature that repeatedly aligns itself downwards and thereby changes a spring preload by lengthening or shortening the effective lever arm, which thus presses a ball into a cone to different degrees. Unfortunately, this construction was unsuccessful, because the effect was dependent on the direction of the erection and the implantation position. In the case of randomly unfavorable movements, it was not possible to lower the opening pressure, which resulted in dangerous underdrainage. For this reason, this type of valve is no longer implanted today. The first and so far only clinically successful "switcher type" is the Miethke dual-switch valve , about which numerous very positive reports can be found in the specialist literature, especially for patients with normal pressure hydrocephalus.

Switcher or counterbalancer

Counterbalancers compensate the hydrostatic pressure more aggressively than switchers. Counterbalancers should therefore be used more in patients with whom the risk of overdrainage is assessed as very high. Switchers are to be preferred in patients for whom permanent and sufficient CSF drainage is important for optimal therapy. In any case, the correct implantation location and the correct position in relation to the body axis are important.

Adjustable gravitational valves

The currently most modern valve type is the combination of adjustable valves and gravitational valves. In this way, on the one hand, the position-dependent adapting mode of operation of the valve is ensured and, on the other hand, an adaptation of the mode of operation to individual patient needs is possible. While adjustable valves in combination with an additional gravitational unit ensure adjustment in the same direction only for the lying and standing position, the Miethke-proSA valve makes it possible for the first time to adjust the valve characteristics separately. While the opening pressure can remain at clinically favorable low values when lying down, for example, adaptation to growth-related changes in the standing posture, regardless of the lying position, is possible for the first time with the proSA valve.

Shunt Complications

Compared to the entire spectrum of pediatric and neurosurgical operations, the shunt operation does not have the highest degree of technical difficulty. Nevertheless, due to the peculiarities of this particular clinical picture, shunt complications such as "overdrainage", "underdrainage" and "infection" can occur.

Underdrainage

In the case of underdrainage, if the shunt is already implanted, too little CSF is drained through the shunt system. Causes can be

a defective valve,
a misaligned valve,
a blocked or incorrectly draining tube (e.g. a child has grown and the tube no longer ends in the abdomen),
a hose torn off the valve.

The result of underdrainage is an increase in intracranial pressure. The shunt must then be relocated (valve and / or hose) or the valve must be adjusted if it is an adjustable valve.

Overdrainage

With overdrainage, more liquor is drained through the shunt system than is produced. This doesn't need to be anything bad to begin with, especially if it only occurs temporarily. Large meta-analyzes show that only around 20 percent of overdrained patients ever notice anything (the numbers vary between four and 70 percent!). The body is quite capable of compensating for certain forms of overdrainage on its own. Symptoms only appear where this does not succeed.

The following symptoms of overdrainage can be classified:

With overdrainage syndrome , patients primarily suffer from headache, nausea and dizziness. The symptoms are very similar to those of overpressure. Only the fact that they predominantly appear when standing up / standing up and disappear again when lying down enables the demarcation to excess pressure. Imaging procedures (CT or MRI) can rarely make reliable diagnoses.

Slit ventricles per se have no disease value. However, the name explains the width of the ventricles that have collapsed due to overdrainage. They are typically seen on CT or MRI in overdrain syndrome .

In subdural hematoma or effusions is fluid retention (usually liquorähnliche fluids) between them as a result of collapsing ventricle (Schlitzventrikel) mater dura and arachnoid form, to compensate for the collapse of the ventricle produced by the negative pressure. If smaller venous vessels tear out in the process, the spaces, which are normally only the width of the capillary gap, are filled with blood.

In the slit ventricle syndrome (SVS) (ger .: slit ventricle syndrome ) is a difficult to diagnose consequence of the drainage that occurs more likely in children than in adults. If overdrainage occurs in a standing patient, the ventricles collapse and the ventricle walls close the perforated shunt tip (stage 1). Due to the suction of the overdrain, the tissue lining the ventricular wall also penetrates into the holes of the ventricular drain. In the second stage, all holes are closed and no liquor can pass the drainage. After a certain time or after lying down, the ventricles inflate again and the tissue parts that close the perforation of the catheter emerge from the catheter. Liquor can pass again (stage 3) and is drained. Between stage 3 and stage 2 there can be a long back and forth without the patient noticing anything or only experiencing very brief symptoms. At some point, however, stage 2 can pass into stage 4: Then the openings of the ventricular catheter are so tightly closed with tissue that there are overpressure symptoms with all their consequences. The shunt is irreversibly blocked and action must be taken quickly. The insidious thing is that the SVS in the MRI or CT is usually completely normal and is therefore very difficult to diagnose. In addition, the constant to and fro between stages 2 and 3 can scar the ventricular walls and become rigid. This makes imaging diagnostics even more difficult.

When Shuntversagen and the clogging of the ventricular catheter is the lack of proper shunt function. With a blocked ventricular catheter - usually caused by the slit ventricle syndrome (see above) - the openings of the catheter tip are blocked by tissue in the ventricular walls, so that CSF can no longer be drained and total shunt failure inevitably occurs. The result is overpressure symptoms. Another form of shunt failure is exactly the opposite: smaller pieces of tissue or blood clots that are transported away by the ventricular catheter can become lodged in the shunt valve and either block the flow of CSF in the valve or cause permanent CSF drainage. Overpressure or overdrainage are the respective consequences.

When enlarged sinuses , thickened skull bones , the craniosynostosis and craniostenosis is it's shunt complications, are related to an over-drainage in pediatric hydrocephalus. The overdrainage creates a suction inside the skull, which can lead, among other things, to thickened skull bones or enlarged paranasal sinuses. With craniosynostosis, the skull sutures that may still be open in a child, depending on their age, close prematurely due to the suction effect of the overdrainage. If all cranial sutures are affected, the brain can no longer grow and in addition to the microcephalus, intracranial pressure symptoms inevitably occur. Usually, however, only the sagittal suture located above (arrow suture) is affected. Since the skull can no longer grow in width, the mass of the brain is compensated for by increasing the length of the skull. Such malformations of the skull are generally referred to as craniostenoses.

The constriction of certain parts of the ventricle is a particularly pronounced form of overdrainage. The resulting suction effect can lead to certain brain areas being moved out of their normal position and lying in the skull differently than normal. For example, if the two lateral ventricles are narrowed in the form of a slit, the brain stem slips upwards and, under certain circumstances, the connection between the III. and IV. ventricle - the aqueduct measuring only 0.75 millimeters - bend and thus close it. Since shunts are usually located in the lateral ventricles, liquor can no longer pass from the IV. Ventricle via the aqueduct and the III. Ventricle drain towards the shunt. The liquor accumulates in the fourth ventricle. Imaging techniques reveal both the narrowed lateral ventricles and the distended fourth ventricle.

Therapy of overdrainage

In principle, asymptomatic overdrainage does not have to be treated. In the case of mild symptoms such as headaches, conservative therapy should be carried out first. The patient should lie flat for several days and drink plenty of fluids. If this remains unsuccessful, operative measures may be indicated. If the patient has an adjustable valve, this can be readjusted if necessary. If the patient only has one conventional valve, another gravitation-controlled valve can be implanted to prevent overdrainage in an upright posture. The implantation is usually carried out problem-free with local anesthesia in the existing shunt system. In serious cases, a temporary total closure of the shunt system may be indicated. To do this, a metal clamp or suture is placed around the silicone tube and the shunt is closed. If the symptoms are permanently resolved, the clip is removed again and the shunt is open again.

Therapy for the consequences of overdrainage.

If manifest consequences have already occurred, such as a craniosynostosis or a subdural hematoma, the consequences of overdrainage must usually also be treated. Sealed cranial sutures can, for example, be treated very successfully with a sutturectomy, in which the sealed sutures are again surgically opened. A subdural hematoma - if it is not encapsulated - is usually broken down by the body itself. If, on the other hand, the hematoma is encapsulated, it may also have to be drained by applying an external drainage system.

Shunt infection

Shunt infections occur on average in 5 percent of cases. In the literature, however, up to 12 percent have been reported, and there are also reports that speak of 1 percent of the cases. That sounds very unsettling at first, but one must always keep in mind that the shunt is a foreign body with no blood supply, and bacteria can easily settle on the surface of the silicone tubes. These bacteria (such as Staphylococcus epidermidis) can continue to form a film of mucus, which makes them practically non-vulnerable for antibiotic treatments. The worst consequence of a shunt infection can be the involvement of the meninges or other organs. In any case, the shunt can no longer be saved and must be explanted. A new shunt can only be implanted again when the shunt infection has completely healed. Alternatively, in such a case, an external ventricular drainage can be used temporarily.

history

The breakthrough in modern hydrocephalus therapy came in 1949. Frank Nulsen developed a ball-cone valve that was first implanted in May of the same year by Eugen Spitz in Philadelphia. The engineer Ted Heyer and Robert Pudenz developed the first transverse slot valve in 1955. Philadelphia-born engineer John D. Holter, meanwhile, waged a desperate battle against time for the life of his son, who had congenital hydrocephalus. In the record time of a few weeks he developed the first double-slit silicone valve, which should be considered the hydrocephalus valve par excellence and which should bring shunt therapy to neurosurgical acceptance. It was again Eugen Spitz who implanted the valve for the first time in March 1956. In the summer of the same year, mass production of the system known as the Spitz-Holter valve began. In 1958 the watchmaker Rudi Schulte, who had emigrated from Germany, met Pudenz and Heyer and improved their slit valve. His own development followed in 1960, the Schulte diaphragm valve. Also in 1958, Ames developed its distal-slit valve, which was intended for ventriculoperitoneal implantation. In the 1970s, Raimondi improved the system and eventually sold it as the Raimondi Uni-Shunt .

literature

Beate Will: Contribution to growth conditions in hydrocephalus - a quantitative study ; Medical Faculty of the Ernst-Moritz-Arndt University in Greifswald, 2001
Martin Moser: Localization and extent of intracranial bleeding in premature infants as influencing factors on the course of posthemorrhagic ventricular dilatation ; Human medicine at the Justus Liebig University Giessen, 1998
Alfred Aschoff: In-vitro testing of hydrocephalus valves ; Habilitation thesis; Heidelberg, 1994