The Central Nervous System is made of all the nervous tissues which form the encephalon and the spinal cord. It is made of white and grey matter (nerves are excluded).
These noble tissues are essential to the human being functioning, as the encephalon ensures control over the whole body, but they are fragile and must be protected.
The Central Nervous System is protected, from the outside to the inside:
the cranium bones (for the encephalon) and the spinal canal (for the spinal cord) act like a “helmet”;
the meninges act like « a protective wrapping »;
- the dura mater, which is the outside layer; - the arachnoid; - the pia mater which is directly in contact with the central nervous system;
the CSF, or Cerebro-Spinal Fluid, which plays the role of a shock absorber.
The brain consists of two cerebral hemispheres (one right and one left), which meet in their lower midline part to form the diencephalon, which extends into the brain stem. The brain stem joins the spinal cord in its lower part.
Central Nervous System
Each cerebral hemisphere contains a cavity called the lateral ventricle. The two lateral ventricles take the shape of a crescent which is open anteriorly and which consists of three horns (frontal, temporal and occipital). They are connected in the midline to the underlying third ventricle through the foramen of Monro.
The diencephalon is the place where the two cerebral hemispheres meet, in which the 3rd ventricle lies.
The brainstem is located between the brain above and the spinal cord below. It consists of 3 parts, the mesencephalon (or midbrain), the pons and the spinal bulb (or medulla).
The 4th ventricle is delineated anteriorly by the posterior surface of the pons and posteriorly by the cerebellum. It communicates superiorly with the 3rd ventricle through the aqueduct of Sylvius and inferiorly with the ependymal canal and the sub-arachnoid spaces through the lateral foramina of Luschka and the median foramen of Magendie.
Anatomy of skull, brain and ventricles
Cerebro-spinal fluid is the transparent "gin clear" fluid that fills the cerebral ventricles. It bathes the brain and the spinal cord.
In addition to its mechanical protective role, CSF takes part in metabolic exchanges between the nervous system and the rest of the body.
Roles of CSF are:
Cleaning of waste due to cellular metabolism;
Absorption of shocks for the protection of the Central Nervous System.
CSF is produced in the ventricles by the choroid plexus at a rate of approximately 20 ml/h in adults (8 ml/h in infants).
The CSF circulates within the lateral ventricle, the 3rd ventricle and leave the 4th ventricle through the foramina, entering the sub-arachnoid spaces surrounding the brain and spinal cord. These sub-arachnoid spaces are fibrous tissues situated between the pia mater and the arachnoid, which behave like a sponge. Ventricles and foramina are cavities that have a role of reservoir for the CSF. There is permanently 125 ml to 150 ml of CSF in the ventricles.
The fluid returns to the venous circulation by absorption through small formations, the arachnoid villi (Pacchioni granules), a type of outgrowth from the arachnoid, through the dura mater and spaces in contact with the sagittal sinus at the midline of the brain.
Meninges and CSF absorption in sagittal sinus
With this cycle of production, circulation and absorption, under normal conditions, a perfect equilibrium exists between secretion and absorption of CSF.
The average CSF pressure in adults when lying down is 120-180 mm H2O (~10 mm Hg). The pressure is almost zero or even negative when standing up. The reference measurement of CSF pressure is measured at the level of the cerebral ventricles: this is intraventricular pressure. It is often called intra-cranial pressure (ICP).
II - What is hydrocephalus?
The term hydrocephalus indicates excess of fluid within the cranium. This is a pathological condition which occurs as a result of imbalance between the production and absorption of CSF. The equilibrium described above is disrupted.
Hydrocephalus only forms if the CSF is unable to leave the ventricular cavities or if its absorption is disturbed.
As the size of the cranium is fixed (except for children up to around 18 months of age in whom the fontanelles are still open), any increase in the volume of fluid within the ventricles affects the brain and leads to the development of neurological symptoms due to an increase in the Intracranial Pressure.
1 - Forms and types of hydrocephalus
Different forms of hydrocephalus may be distinguished:
Congenital, if it develops before or at birth;
Acquired, if it develops after birth, for example after a head injury, a meningitis, a cerebral haemorrhage or a neoplasic disease.
Hydrocephalus is commonly classified into two types:
Non-communicating or obstructive hydrocephalus;
Communicating or non-obstructive hydrocephalus.
Non-communicating hydrocephalus is caused by blockage of the circulation of CSF in the ventricular cavities. This blockage usually occurs at the level of the aqueduct of Sylvius and may also be seen in the foramen of Monro and other foramina. This type of hydrocephalus is commonly associated with clinical signs of raised intracranial pressure.
The major causes of non-communicating hydrocephalus are:
Congenital stenosis of the aqueduct of Sylvius;
Arnold Chiari Syndrome (Spina Bifida);
Tumours of the posterior fossa.
Communicating hydrocephalus occurs when the circulation of CSF around the brain is disturbed or if the absorption sites are non-functioning.
The major causes of communicating hydrocephalus may be grouped into two categories:
1 - Hydrocephalus due to excessive production of CSF: Choroid plexus papilloma (a very rare tumour); 2 - Hydrocephalus due to impaired re-absorption of CSF:
Idiopathic hydrocephalus, i.e. for which no cause can be found. This is commonly known as Chronic Adult Hydrocephalus (CAH) or, alternatively, Normal Pressure Hydrocephalus (NPH), as in this instance the hydrocephalus is usually associated with near normal intraventricular pressure;
Post-haemorrhagic hydrocephalus (head injury, rupture of an aneurysm, or arterio-venous malformation, and so on…);
Hydrocephalus of the premature infant (following intraventricular haemorrhage, etc).
2 - Clinical signs of hydrocephalus
The clinical manifestations of hydrocephalus occur as a result of ventricular dilatation and of the increase in pressure within the cranium.
These manifestations may differ between patients and as a function of age. The clinical signs for instance in infants and young children, whose cranial bones have not yet completely fused together, are different from those seen in adults.
The usual symptoms of hydrocephalus in infants include:
abnormal increase in head circumference;
dilatation of the veins on the surface of the cranium;
downward shift in gaze (sunset eyes), behavioural difficulties (irritability, drowsiness etc) or even seizures.
Depending on the cause, raised intracranial pressure may produce different signs in older children and adults. The major signs are:
visual disturbance (blurred vision, double vision etc) with papilloedema, which is seen when the fundus of the eye is examined;
consciousness disorders: drowsiness, progressive lethargy or even coma.
Other signs may be found and are systematically looked for by doctors. These include bradycardia or seizures.
The characteristic Hakim's Triad may be seen in normal pressure hydrocephalus, which is found mostly in adults:
psychiatric disorders, mimicking the appearances of dementia. This involves mostly slow and poor quality ideation and activity, with apathy and indifference, serious memory and orientation disturbance, particularly in time, loss of attention and unawareness of reality.
gait disorders, with instability. This is due to static abnormalities, which may develop into titubation. The person moves around slowly and with care and may, occasionally, walk on the spot. Turning around, or either starting or stopping suddenly leads to imbalance.
sphincter disturbance (incontinence++). On occasions, the person is incontinent of urine and sometimes faeces. It is not clear whether this is due to inattention, reduced awareness or urgency of micturition. The patient may pass urine anywhere and soil his clothing.
Although certain drugs may temporarily control communicating hydrocephalus, surgery is the only truly effective treatment.
CSF shunts have been performed for decades and still represent the most important advance made until now in the treatment of hydrocephalus when endoscopic treatment is not indicated or possible.
A CSF shunt involves establishing an alternative pathway for the movement of CSF in order to bypass an obstruction of the natural pathways.
The shunt is positioned to enable the CSF to be drained from the cerebral ventricles or sub-arachnoid spaces into another absorption site, the right atrium of the heart or the peritoneal cavity, through a system of small tubes known as catheters. A regulating device, also known as a valve, which may be more or less sophisticated, may be inserted into the pathway of the catheters. This drainage enables the excess CSF within the brain to be evacuated and, thereby, the pressure within the cranium to be reduced.
II - Constituents of a shunt
A CSF shunt system is made of:
A proximal catheter (inserted proximally into the cerebral ventricles or into the sub-arachnoid spaces and linked distally to either a reservoir or a valve). This catheter is closed at its proximal end and multi-perforated in order to enable the CSF to pass through. Many possible types and configurations are available, the mostly widely used being the straight and right angle ventricular catheters.
A reservoir (optional) which may be attached to the valve. When present, the reservoir may be used to assess the patency of the shunt and to access the CSF for injections and/or samples.
A unidirectional valve (or anti-reflux valve, i.e. a valve which prevents the flow of CSF towards the ventricles once the fluid has passed through the valve). Many types and configurations are available. The valves for hydrocephalus are designed to work at different pressures, depending on the patient, in order to avoid excessive drainage of CSF.
An anti-siphon device (optional), which may be attached to the valve. The anti-siphon device theoretically allows sudden increases in the differential pressure between the proximal and distal parts of the shunt to be corrected when subjects move from lying down to standing up.
A distal catheter (linked proximally to the valve and inserted distally into the peritoneal cavity or into the entrance to the right atrium of the heart). Again, many types and configurations are available. The distal tip is usually open and multi-perforated in order to facilitate the flow of CSF into the peritoneal (or cardiac) cavity.
Shunts are made from materials which have been shown to be well tolerated by the body, such as silicone, polysulphone or stainless steel.
The entire shunt system is positioned under the skin.
In obstructive hydrocephalus, the tip of the proximal catheter must imperatively be placed within the ventricular system and is known as the ventricular or proximal catheter.
In non-obstructive hydrocephalus, the proximal catheter is placed either in the ventricles (ventricular catheter) or in the sub-arachnoid space, at the level of the lumbar spinal column (lumbar catheter).
III - Different types of shunts
From these clinical features, the neurosurgeon will decide to insert one of the three CSF shunt systems from a choice of the three following types of implantation:
Ventriculo-Peritoneal Shunt (V-P): The CSF is shunted from the cerebral ventricles to the peritoneal cavity where it is reabsorbed into the blood through the peritoneum, the membrane which lines the gastro-intestinal organs.
Ventriculo-Atrial Shunt (V-A): The CSF is shunted from the cerebral ventricles into the right atrium of the heart. The CSF is then shunted directly into the blood circulation.
Lumbo-Peritoneal Shunt (L-P): The CSF is shunted from the lumbar sub-arachnoid spaces to the peritoneal cavity.
Insertion of a CSF shunt is a surgical procedure performed in the operating room under general anaesthesia. Neurosurgeons will choose the most appropriate operating method and valve for each patient depending on their experience.
Standard valves for hydrocephalus work at constant pressure or resistance. It is the neurosurgeon who chooses the type and pressure of valve which he will insert before implantation, depending on the patient's clinical characteristics and further investigations.
Standard shunt valve manufacturers generally offer three different calibrations of each of their models; either a low pressure model, a medium pressure model or a high pressure model. Although in most cases the choice will be correct at the time the system is implanted, shunting the patient's CSF changes the patient's clinical condition and in a significant number of cases the neurosurgeon has to change the valve, replacing it with a valve which operates at a different pressure. Repeated surgeries are not without danger for the patient. The solution to this problem is to implant a valve which has several different pressure settings covering the entire desired pressure range and which can be adjusted to change the pressure as desired, without re-operating the patient, i.e. non-invasively. This is the concept underlying the adjustable pressure valve.
The Sophy® valve was the first adjustable pressure valve routinely implanted in the World. Together with other adjustable valves, it has produced results which clearly demonstrate that adjustable valves are a major step forward in the treatment of hydrocephalus patients.
The Sophy® Valve
In 2004, Sophysa introduced Polaris® the latest edition of adjustable valves. Based on the same successful principle than Sophy®, Polaris® features a patented self-locking mechanism which prevents unintentional dysadjustment during everyday life and MRI exposure to magnetic fields.
Polaris® represents then the ultimate standard for safety of adjustable valves in hydrocephalus treatment.
The Polaris® Valve
The originality of both the Sophy® and Polaris® valves resides in the possibility of modifying their operating pressure by simple external adjustment.
It indeed allows the neurosurgeon to adjust the CSF drainage flow according to the patient's requirements, without the need for surgical re-intervention. Depending on clinical and tomodensitometric (CT) MRI findings, it offers the neurosurgeon the facility to quickly relieve under-drainage or over-drainage symptoms by changing the operating pressure.
Either with Sophy® or Polaris®, the pressure adjustment is painless. The pressure setting may be changed non-invasively using the appropriate adjustment kit. It is carried out by the magnetic action of a special magnet, which is part of an adjustment kit and which the neurosurgeon places on the patient's skin, just above the valve.
The Sophy® Adjusment Kit & The Polaris® Adjusment Kit
Thanks to the wide range of pressures it offers, the Sophysa Adjustable Pressure Valves allow most cases of hydrocephalus to be treated and equilibrated, regardless of its cause. It is also indicated for use when the pressure setting may need to be changed over time.
The Sophysa Adjustable Pressure Valves allow the patient to live his daily life without hospitalization, by simply observing a few specific precautions as well as the surgeon's recommendations.
"Thanks to Polaris®, my physician can treat me without always having to stay at the hospital"
I - Specificities of a treatment with a Polaris® Valve
Most of hydrocephalic patients will have to keep their CSF shunt throughout their whole life. As treatment is a lengthy process, patient surveillance will be pursued over a long period of time. Both the patient and his family will be required to participate actively in this surveillance.
Post-operative precautions need to be taken and regular medical consultations are recommended in order to detect possible complications.
Depending on the patient's clinical condition, an ophthalmological exam, a cranial CT Scan, an MRI or X-Rays of the shunt system, for example, will be asked for.
Unlike any other adjustable valve, the Polaris® valve has been designed to give you a normal daily life. Indeed, since Polaris® is insensitive to any everyday magnetic fields as well as to direct shocks, specific precautions to be taken with this implant are reduced to the maximum.
"I like Polaris® because it lets me to do whatever I want."
Tests have shown that magnetic properties of the Polaris® valve, and therefore its adjustment, were not significantly affected by even repeated exposures to MRI up to 3 Teslas.
If your pathology requires a follow-up with MRI examinations, Polaris® will ensure you that your valve will not experience any dys-adjustment during the procedure.
II - When should I consult my physician?
Even if the risk of complication is low, the patient or his family needs to know that certain complications may arise from the surgery.
The main complications of shunts are obstruction, infection and overdrainage. These complications require prompt attention from the patient's physician.
1 - Obstruction
The most common complication is obstruction, which can occur at any point of a ventriculo-atrial or ventriculo-peritoneal shunt.
The ventricular catheter can be obstructed by a blood clot, cerebral tissue, or even tumor cells.
The tip of the ventricular catheter can also become embedded in the choroid plexus or ventricular wall, either directly or following collapse of the walls due to over-drainage.
In a ventriculo-atrial shunt, the cardiac catheter can be colonized by thrombus, while the development of clot around the catheter can lead to pulmonary embolism.
The peritoneal catheter can be obstructed by peritoneum or loops of intestine.
Loss of patency of a shunt may also be due to obstruction by fragments of cerebral tissue or biological deposits (protein deposits, etc.).
Obstruction of the shunt leads to loss of control of hydrocephalus, rapidly reflected by recurrence of the symptoms and signs of raised intracranial pressure.
Symptoms and signs vary from one patient to another and over time.
In infants and young children, the symptoms may consist of an abnormal increase in the size of the skull, swelling of the fontanelles, dilatation of scalp veins, vomiting, irritability with loss of attention, downward displacement of gaze and sometimes convulsions.
In older children and adults, the raised intracranial pressure due to hydrocephalus is responsible for headaches, vomiting, visual disturbances, diplopia, drowsiness, slowed movements, gait disorders, psychomotor retardation, possibly causing total disability.
Shunt obstruction can also lead to CSF leakage around the catheter and subcutaneous collection. If obstruction is confirmed, the shunt should be removed.
2 - Infection
Chronic shunt dysfunction can lead to leaking of CSF along the shunt, increasing the risk of infection.
Local or systemic infection is another possible complication of CSF shunt systems. It is generally secondary to colonization of the shunt by cutaneous bacteria. However, as for any foreign body, the shunt can be colonized by any local or systemic infection. This infection may present in the form of erythema, oedema and cutaneous erosion along the path of the shunt.
Prolonged, unexplained fever may also be due to infection of the shunt system.
Septicemia, in a context of deterioration of the general state, may arise from shunt infection.
The shunt system should be removed and specific treatment should be introduced in the case of infection.
3 - Overdrainage
Overdrainage can lead to collapse of the ventricles (slit ventricles) and the development of subdural haematoma.
In children, depression of the fontanelles, overlapping of skull bones, or even acute craniostenosis or the development of communicating hydrocephalus into obstructive hydrocephalus as a result of stenosis of the aqueduct of Sylvius may occur.
In addition to various symptoms such as vomiting, auditory or visual disorders, drowsiness, adults may also present headaches occurring in the upright position and resolving in the supine position.
Depending on the clinical and CT findings, the neurosurgeon can correct the symptoms and ventricular size by varying the operating pressure of the Sophy® or Polaris® Adjustable Pressure valve. However, immediate drainage of a subdural haematoma may be indicated.
4 - Others
Failure of a shunt system may also be due to disconnection of its various components:
The ventricular catheter can migrate inside a lateral ventricle. The peritoneal catheter can migrate in the peritoneal cavity in response to intestinal peristalsis and an atrial catheter can migrate in the right side of the heart as a result of blood flow.
An abdominal viscus may also be perforated or occluded by the peritoneal catheter.
Bodily growth may progressively lead to expulsion of the catheters from their site of insertion. These disorders require immediate surgery.
Cases of skin necrosis over the implantation site have also been reported.
In the case of implantation on the skull, vibrations due to CSF flow may be perceived.
Cases of silicone allergy have been described.
Cases of epilepsy after ventricular shunting procedures has been reported.
Cases of axial rotation of the valve by the patient have been reported, while implanted on the chest. Such rotation induces reverse lecture of the pressures and a risk of catheter obstruction.
The ruby ball can be maintained in off centering position on its seat by protein deposit or cells accumulation. The consequences of such situation can be:
- A lack of flow regulation of the valve inducing a risk of over-drainage. - An impaired anti-reflux function.
Rotor blockage by protein deposit or cells accumulation can make adjustment impossible with the magnet.
III - Warnings and cautions
The pressure settings should always be checked in case of shock on the implantation site.
Changing pressure settings must only be performed by a neurosurgeon.
Patient must be advised that carrying his Patient Identification Card is important and necessary for the follow-up of the clinical conditions.
Patients undergoing MRI exposure should be advised that they might feel a small yet harmless effect due to MRI.
The pressure settings should always be checked before and after MRI exposure, or after strong magnetic field exposure.
Patient must be advised that in the case of implantation on the skull vibrations due to CSF flow may be perceived.
Patients with implanted valve systems must be kept under close observation for symptoms of shunt failure.
IV - Do I have to own any particular documents?
The answer is Yes: you have to keep your Patient Identification Card (PIC) with you.
Each Sophy® and Polaris® valve has been strictly controlled at each step of the manufacturing process. As each Sophy® and Polaris® valve characteristics is unique, an individual serial number is engraved in the body of each valve. This serial number is recorded in the Patient Identification Card which has been given to you by the neurosurgeon during your stay at the hospital. You should carry your PIC with you at all times, as it provides information concerning the implanted device (reference, pressure setting …) which is important and necessary for your medical follow-up.
Warning: This information should not be used as a substitute to a medical advice.