Cerebral shunt
Encyclopedia
Cerebral shunts are commonly used to treat hydrocephalus
, the swelling of the brain due to excess buildup of cerebrospinal fluid (CSF)
. If left unchecked, the cerebral spinal fluid can build up leading to an increase in intracranial pressure (ICP)
which can lead to intracranial hematoma, cerebral edema
, crushed brain tissue or herniation. The cerebral shunt can be used to alleviate or prevent these problems in patients who suffer from hydrocephalus or other related diseases.
Shunts can come in a variety of forms but all of them consist of a pump or drain connected to a long catheter, the end of which is usually placed in the peritoneal cavity
. The main differences between shunts are usually in the materials used to construct them, the types of pumps used, and whether the pump is programmable or not.
In addition to these four common locations for shunt drainage, the gallbladder
and ureter
can be suitable locations as well.
Shunt infection is a common problem and can occur in up to 27% of patients with a shunt. Infection can lead to long term cognitive defects, neurological problems and in some cases death. Common microbial agents for shunt infection include Staphylococcus epidermidis
, Staphylococcus aureus
, and Candida albicans
. Further factors leading to shunt infection include shunt insertion at a young age (<6 months old) and the type of hydrocephalus being treated. There is no strong correlation between infection and shunt type.
The symptoms of a shunt infection are very similar to the symptoms seen in hydrocephalus but can also include fever and elevated white blood cell counts.
Usually one of two types of overdrainage can occur. First when the CSF drains too rapidly, a condition known as extra-axial fluid collection can occur. In this condition the brain collapses on itself resulting in the collection of CSF or blood around the brain. This can cause severe brain damage by compressing the brain. Furthermore a subdural hematoma
may develop. Extra-axial fluid collection can be treated in three different ways depending on the severity of the condition. Usually the shunt will be replaced or reprogrammed to release less CSF and the fluid collected around the brain will be drained. The second condition known as slit ventricle syndrome occurs when CSF slowly overdrains, over several years. More information on slit ventricle syndrome appears below.
. It was previously thought that Chiari I Malformation was a result of a congenital defect but new studies have shown that overdrainage of Cysto-peritoneal shunts used to treat arachnoid cysts can lead to the development of posterior fossa
overcrowding and tonsillar herniation, the latter of which is the classic definition of Chiari Malformation I. Common symptoms include major headaches, hearing loss, fatigue, muscle weakness and loss of cerebellum function.
The condition is often thought to occur during a period where overdrainage and brain growth occur simultaneously. In this case the brain fills the intraventricular space, leaving the ventricles collapsed. Furthermore, the compliance of the brain will decrease, which prevents the ventricles from enlarging, thus reducing the chance for curing the syndrome. The collapsed ventricles can also block the shunt valve, leading to obstruction. Since the effects of slit ventricle syndrome are irreversible, constant care in managing the condition is needed.
can occur at any time during or after a shunt insertion or revision. The hemorrhage can cause an impairment in shunt function which can lead to severe neurological deficiencies. Studies have shown that intraventricular hemorrhage can occur in nearly 31% of shunt revisions.
Idiopathic Intracranial Hypertension
A rare neurological disorder affecting approximately 1 in 100, 000 people, most of whom are women of child baring age. IIH result in a raised intracranial pressure and can lead to permanent loss of vision.
Hydrocephalus
Hydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,...
, the swelling of the brain due to excess buildup of cerebrospinal fluid (CSF)
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
. If left unchecked, the cerebral spinal fluid can build up leading to an increase in intracranial pressure (ICP)
Intracranial pressure
Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...
which can lead to intracranial hematoma, cerebral edema
Cerebral edema
Cerebral edema or cerebral œdema is an excess accumulation of water in the intracellular or extracellular spaces of the brain.-Vasogenic:Due to a breakdown of tight endothelial junctions which make up the blood-brain barrier...
, crushed brain tissue or herniation. The cerebral shunt can be used to alleviate or prevent these problems in patients who suffer from hydrocephalus or other related diseases.
Shunts can come in a variety of forms but all of them consist of a pump or drain connected to a long catheter, the end of which is usually placed in the peritoneal cavity
Peritoneal cavity
The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall...
. The main differences between shunts are usually in the materials used to construct them, the types of pumps used, and whether the pump is programmable or not.
Types of valves
| Valve type | Description |
|---|---|
| Delta | Designed to prevent overdrainage. Remains closed until ICP reaches a predetermined level. Leaves shunted ventricle larger than the non-shunted ventricles. |
| Medium pressure cylindrical | Can lead to uneven drainage of ventricles. |
| Nulsen and Spitz | Contains two ball-valve units connected with a spring. Does not have an adjustable pressure setting. First mass produced valve used to treat hydrocephalus in 1956. |
| Spitz-Holter | Uses slits in silicone to avoid mechanical failure. |
| Anti-siphon | Prevents over drainage by preventing the siphon effect Siphon The word siphon is sometimes used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in the English language today, the word siphon usually refers to a tube in an inverted U shape which causes a liquid to flow uphill, above the surface of the reservoir,... . The device closes when the pressure within the valve becomes negative relative to the ambient pressure. Prevents overdrainage that might occur when a patient sits, stands or rapidly changes posture. |
| Sigma | The Sigma valve operates on a flow-control mechanism as opposed to the pressure-control system of other valves. The device can regulate CSF flow changes without being programmed or surgically changed. The first iteration was introduced in 1987. Valve operated in three stages to prevent over and under drainage. |
Shunt location
The location of the shunt is determined by the neurosurgeon based on the type and location of the blockage causing hydrocephalus. All brain ventricles are candidates for shunting. The catheter is most commonly placed in the abdomen but other locations include the heart and lungs. Shunts can often be named after the route used by the neurosurgeon. The distal end of the catheter can be located in just about any tissue with enough epithelial cells to absorb the incoming CSF. Below are some common routing plans for cerebral shunts.Shunt routing
| Route | Location of Fluid Drain |
|---|---|
| Ventriculo-peritoneal shunt (VP shunt) | Peritoneal cavity Peritoneal cavity The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall... |
| Ventriculo-atrial shunt (VA shunt) | Right atrium Right atrium The right atrium is one of four chambers in the hearts of mammals and archosaurs... of the heart |
| Ventriculo-pleural shunt (VPL shunt) | Pleural cavity Pleural cavity In human anatomy, the pleural cavity is the potential space between the two pleura of the lungs. The pleura is a serous membrane which folds back onto itself to form a two-layered, membrane structure. The thin space between the two pleural layers is known as the pleural cavity; it normally... |
| Lumbar-peritoneal shunt (LP shunt) | Peritoneal cavity Peritoneal cavity The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall... |
In addition to these four common locations for shunt drainage, the gallbladder
Gallbladder
In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....
and ureter
Ureter
In human anatomy, the ureters are muscular tubes that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually long and ~3-4 mm in diameter....
can be suitable locations as well.
Complications
There are a number of complications associated with shunt placement. Many of these complications occur during childhood and cease once the patient has reached adulthood. Many of the complications seen in patients require immediate shunt revision (the replacement or reprogramming of the already existing shunt). The common symptoms often resemble the new onset of hydrocephalus such as headaches, nausea, vomiting, double-vision, and an alteration of consciousness. Furthermore the shunt failure rate 2 years after implantation has been estimated to be as high as 50%.Infection
Infection is a common complication that normally affects pediatric patients because they have not yet built up immunities to a number of different diseases. Normally the incidence of infection decreases as the patient grow older, and the body gains immunity to various infectious agents.Shunt infection is a common problem and can occur in up to 27% of patients with a shunt. Infection can lead to long term cognitive defects, neurological problems and in some cases death. Common microbial agents for shunt infection include Staphylococcus epidermidis
Staphylococcus epidermidis
Staphylococcus epidermidis is one of thirty-three known species belonging to the genus Staphylococcus. It is part of human skin flora, and consequently part of human flora. It can also be found in the mucous membranes and in animals. Due to contamination, it is probably the most common species...
, Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...
, and Candida albicans
Candida albicans
Candida albicans is a diploid fungus that grows both as yeast and filamentous cells and a causal agent of opportunistic oral and genital infections in humans. Systemic fungal infections including those by C...
. Further factors leading to shunt infection include shunt insertion at a young age (<6 months old) and the type of hydrocephalus being treated. There is no strong correlation between infection and shunt type.
The symptoms of a shunt infection are very similar to the symptoms seen in hydrocephalus but can also include fever and elevated white blood cell counts.
Obstruction
Another leading cause of shunt failure is the blockage of the shunt at either the proximal or distal end. At the proximal end the shunt valve can become blocked due to the buildup of excess protein in the CSF. The extra protein will collect at the point of drainage and slowly clog the valve. The shunt can also become blocked at the distal end if the shunt is pulled out of the abdominal cavity (in the case of VP shunts), or from similar protein buildup. Other causes of blockage are overdrainage and slit ventricle syndrome.Over drainage
Over drainage occurs when a shunt has not been adequately designed for the particular patient. Overdrainage can lead to a number of different complications some of which are highlighted below.Usually one of two types of overdrainage can occur. First when the CSF drains too rapidly, a condition known as extra-axial fluid collection can occur. In this condition the brain collapses on itself resulting in the collection of CSF or blood around the brain. This can cause severe brain damage by compressing the brain. Furthermore a subdural hematoma
Subdural hematoma
A subdural hematoma or subdural haematoma , also known as a subdural haemorrhage , is a type of haematoma, a form of traumatic brain injury. Blood gathers within the outermost meningeal layer, between the dura mater, which adheres to the skull, and the arachnoid mater, which envelops the brain...
may develop. Extra-axial fluid collection can be treated in three different ways depending on the severity of the condition. Usually the shunt will be replaced or reprogrammed to release less CSF and the fluid collected around the brain will be drained. The second condition known as slit ventricle syndrome occurs when CSF slowly overdrains, over several years. More information on slit ventricle syndrome appears below.
Chiari I malformation
Recent studies have shown that over drainage of CSF due to shunting can lead to acquired Chiari I MalformationArnold-Chiari malformation
Arnold–Chiari malformation, or often simply Chiari malformation, is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils through the foramen magnum , sometimes causing non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid outflow...
. It was previously thought that Chiari I Malformation was a result of a congenital defect but new studies have shown that overdrainage of Cysto-peritoneal shunts used to treat arachnoid cysts can lead to the development of posterior fossa
Posterior fossa
Posterior fossa may refer to:* Posterior cranial fossa* Posterior intercondyloid fossa...
overcrowding and tonsillar herniation, the latter of which is the classic definition of Chiari Malformation I. Common symptoms include major headaches, hearing loss, fatigue, muscle weakness and loss of cerebellum function.
Slit ventricle syndrome
Slit ventricle syndrome is an uncommon disorder associated with shunted patients, but results in a large number of shunt revisions. The condition usually occurs several years after shunt implantation. The most common symptoms are similar to normal shunt malfunction, but there are several key differences. First the symptoms are often cyclical and will appear and then subside several times over a lifetime. Second, the symptoms can be alleviated by lying prone. In the case of shunt malfunction neither time nor postural position will affect the symptoms.The condition is often thought to occur during a period where overdrainage and brain growth occur simultaneously. In this case the brain fills the intraventricular space, leaving the ventricles collapsed. Furthermore, the compliance of the brain will decrease, which prevents the ventricles from enlarging, thus reducing the chance for curing the syndrome. The collapsed ventricles can also block the shunt valve, leading to obstruction. Since the effects of slit ventricle syndrome are irreversible, constant care in managing the condition is needed.
Intraventricular hemorrhage
An intraventricular hemorrhageIntraventricular hemorrhage
An intraventricular hemorrhage , often abbreviated "IVH," is a bleeding into the brain's ventricular system, where the cerebrospinal fluid is produced and circulates through towards the subarachnoid space...
can occur at any time during or after a shunt insertion or revision. The hemorrhage can cause an impairment in shunt function which can lead to severe neurological deficiencies. Studies have shown that intraventricular hemorrhage can occur in nearly 31% of shunt revisions.
Conditions requiring shunting
Below is a short list of known complications that can lead to hydrocephalus requiring shunting.| Diagnoses | Description | Incidence |
|---|---|---|
| Congenital hydrocephalus Hydrocephalus Hydrocephalus , also known as "water in the brain," is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head,... |
A wide range of genetic abnormailities that could lead to hydrocephalus at birth. | 0.04-0.08% |
| Tumor | A number of different tumors can lead to CSF blockage if they are located in certain areas. Some of these areas include the lateral ventricles, the posterior fossa, and intraspinal tumors. The tumors may be malignant or benign. | Unknown |
| Spina bifida Spina bifida Spina bifida is a developmental congenital disorder caused by the incomplete closing of the embryonic neural tube. Some vertebrae overlying the spinal cord are not fully formed and remain unfused and open. If the opening is large enough, this allows a portion of the spinal cord to protrude through... |
Specifically spina bifida myelomeningocele can cause the development of hydrocephalus because the cerebellum will block the flow of CSF in a development of Chiari Malformation II. | .125% |
| Congenital aqueductal stenosis | A genetic disorder which can cause deformations of the nervous system. The defect is commonly associated with mental retardation, abducted thumbs and spastic paraplegia. | .003% |
| Craniosynostosis Craniosynostosis Craniosynostosis is a condition in which one or more of the fibrous sutures in an infant skull prematurely fuses by ossification, thereby changing the growth pattern of the skull... |
Craniosynostosis occurs when the sutures of the skull close too early. The result of multiple sutures fusing before the brain stops growing is an increase in ICP leading to hydrocephalus. | 0.05% |
| Dandy-Walker syndrome Dandy-Walker syndrome Dandy–Walker syndrome , or Dandy–Walker complex, is a congenital brain malformation involving the cerebellum and the fluid filled spaces around it. A key feature of this syndrome is the partial or even complete absence of the part of the brain located between the two cerebellar hemispheres... |
Patients usually present with a cystic deformity of the fourth ventricle, hypoplasia Hypoplasia Hypoplasia is underdevelopment or incomplete development of a tissue or organ. Although the term is not always used precisely, it properly refers to an inadequate or below-normal number of cells. Hypoplasia is similar to aplasia, but less severe. It is technically not the opposite of hyperplasia... of the cerebellar vermis Cerebellar vermis The cerebellar vermis is located in the medial, cortico-nuclear zone of the cerebellum, residing in the posterior fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior surface of the cerebellum, dividing it into anterior and posterior lobes.... , and an enlarged posterior fossa. The condition is a genetically heritable disease. |
0.003% |
| Arachnoid cyst Arachnoid cyst Arachnoid cysts are cerebrospinal fluid covered by arachnoidal cells and collagen that may develop between the surface of the brain and the cranial base or on the arachnoid membrane, one of the three membranes that cover the brain and the spinal cord... |
A genetic defect caused when CSF rushes into ruptured arachnoid mater Arachnoid mater The arachnoid mater, literally from Latin "spider -like mother", is one of the three meninges, the membranes that cover the brain and spinal cord... . The resulting cyst can then block the normal flow of CSF from the brain resulting in hydrocephalus as well as other defects. The most common locations for an arachnoid cyst are the middle fossa Middle cranial fossa The middle fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest.... and the posterior fossa. The most common symptoms are nausea and vertigo. |
0.05% |
Idiopathic Intracranial Hypertension
A rare neurological disorder affecting approximately 1 in 100, 000 people, most of whom are women of child baring age. IIH result in a raised intracranial pressure and can lead to permanent loss of vision.