Ventriculo-peritoneal shunt

Cerebral shunts are commonly used.

Indications for VP shunts include: congenital hydrocephalus, intracerebtal malignancies, spina bifida, craniosynostosis, Dandy-Walker syndrome , arachnoid cyst, and idiopathic Intracranial hypertension.

VP shunts are used to treat hydrocephalus, the swelling of the brain due to excess buildup of cerebrospinal fluid (CSF).

Ventriculoperitoneal shunting is surgery to relieve increased pressure inside the skull due to excess cerebrospinal fluid.

Procedure is performed in the operating room under general anesthesia.

A surgical incision is made made behind the ear and abdomen, with a skull opening and placement of a catheter in the brain ventricle.

Another catheter is placed under the skin behind the ear and moved down the neck and chest and into the abdominal (peritoneal) cavity.

A valve is placed underneath the skin behind the ear and is attached to both catheters.

When intracranial pressure builds in the ventricles, the valve opens, and excess fluid drains out of it into the belly.

Shunts may differ in construction and by the types of pumps used.

Complications mostly occur during childhood and diminish with adulthood.

Some complications require immediate revision.

If left untreated, cerebrospinal 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 with hydrocephalus or other related diseases.

Shunts consist of a valve housing connected to a catheter, the end of which is usually placed in the peritoneal cavity. 

A ventriculoperitoneal shunt running from a brain ventricle to the abdominal cavity. 

There a number of valve types.

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.

The distal end of the catheter can be located in any tissue with enough epithelial cells to absorb the incoming CSF. 

A difference in the pressure of the intracranial space and the peritoneal cavity is necessary for such a shunt to allow CSF flow from the intracranial to the peritoneal compartment.

Below are some common routing plans for cerebral shunts.

Frazier’s point-located on the parietal bone, above the lambdoid suture. More specifically, 3 to 4 cm lateral to the midline and 6 cm above the inion.

It is a common site for ventricular cannulation in the context of inserting a ventriculoperitoneal shunt for the treatment of hydrocephalus. 

A subgaleal shunt is a temporary measure used in infants who are too small or premature to tolerate other shunt types. 

Processes requiring shunting: 

Congenital hydrocephalus

A wide range of genetic abnormalities that could lead to hydrocephalus at birth. 0.04–0.08%/ births

Tumors located in the lateral or third ventricles, the posterior fossa, and intraspinal tumors. 

Post-hemorrhagic hydrocephalus: Bleeding into the ventricles of the brain, especially in infancy, can lead to blockage of CSF drainage and cause hydrocephalus.

Spina bifida: 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%/births incidence).

Congenital aqueductal stenosis, a genetic disorder which can cause deformations of the nervous system. 

Congenital aqueductal stenosis 

defect is commonly associated with intellectual disability, abducted thumbs and spastic paraplegia-(003%/births).

Craniosynostosis-occurs when the sutures of the skull close too early, fusing before the brain stops growing and increases ICP leading to hydrocephalus.(0.05%/births).

Inflammation and scarring caused by meningitis can inhibit CSF absorption.

Dandy–Walker syndrome , usually presents with a cystic deformity of the fourth ventricle, hypoplasia of the cerebellar vermis, and an enlarged posterior fossa: a genetically heritable disease. (0.003%/births).

Arachnoid cyst A defect caused when CSF forms a collection that is trapped in the arachnoid membranes, 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: middle fossa and the posterior fossa (0.05% births).

Idiopathic intracranial hypertension is a rare neurological disorder affecting approximately 1 in 100,000 people, most of whom are women of child-bearing age. 

IIH results in a raised intracranial pressure and can lead to permanent loss of vision.

Normal pressure hydrocephalus-Excess cerebrospinal fluid (CSF) occurs in the ventricles, and with normal or slightly elevated cerebrospinal fluid pressure

Shunt placement complications:

Many of the complications require immediate shunt revision.

Common symptoms of shunt placement often resemble the new onset of hydrocephalus such as headaches, nausea, vomiting, double-vision, alteration of consciousness, and damage to an individual’s short-term-memory.

Shunt complications are associated with headaches, nausea, vomiting, diplopia and altered level of consciousness.

Shunt failure rate 2 years after implantation has been estimated to be as high as 50%.

In the pediatric population, the shunt failure rate 2 years after implantation has been estimated to be as high as 50%.

Infection is a common complication that normally affects pediatric patients.

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. 

Infection is a more common complication of pediatric patients.

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 of <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.

Treatment of a CSF shunt infection generally includes removal of the shunt and placement of a temporary ventricular reservoir until the infection is resolved, along with antibiotics:  95% success rate.

Initial empiric  antibiotic therapy for CSF shunt infection should include broad coverage that includes gram-negative aerobic bacilli including pseudomonas and gram-positive organisms including Staph aureus and coagulase negative staphylococcus: combination of ceftazidime and vancomycin. 

Intrathecal aminoglycosides provides enhanced pseudomonas coverage, and meropenem and aztreonam are additional options that are effective against gram-negative bacterial infections.

Shunt failure includes 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 shunt can also become blocked at the distal end if the shunt is pulled out of the abdominal cavity, or from similar protein buildup. 

Other causes of blockage include overdrainage and slit ventricle syndrome.

Over drainage can occur when a shunt has not been adequately designed.

Overdrainage can lead to a number of different complications: when the CSF drains too rapidly, extra-axial fluid collection can occur, collapsing the brain on itself resulting in the collection of CSF or blood around the brain. 

This can cause severe brain damage by compressing the brain or forming a subdural hematoma.

Over drainage of CSF due to shunting can lead to acquired Chiari I malformation.

Common symptoms include major headaches, hearing loss, fatigue, muscle weakness and loss of cerebellum function.

Extra-axial fluid collection can be treated by shunt replacement or reprogrammed to release less CSF and the fluid collected around the brain will be drained.

Slit ventricle syndrome occurs when CSF slowly overdrains, over several years.

Slit ventricle syndrome is an uncommon disorder associated with shunted patients, but results in a large number of shunt revisions. 

The condition is often thought to occur during a period where overdrainage and brain growth occur simultaneously. 

With the slit ventricle syndrome the brain fills the intraventricular space, leaving the ventricles collapsed, brain compliance is decreased, preventing the ventricles from enlarging, thus reducing the chance for curing the syndrome. 

The collapsed ventricles can lead to obstruction, by affecting the shunt valve.

These effects of slit ventricle syndrome are irreversible.

Slit ventricle syndrome usually occurs several years after shunt implantation. 

Slit ventricle syndrome symptoms are often cyclical and will appear and then subside several times.

Slit ventricle syndrome symptoms can be alleviated by lying prone. 

In the case of shunt malfunction time or postural changes do not affect the symptoms.

An intraventricular hemorrhage can occur at any time during or after a shunt insertion or revision. 

Intraventricular hemorrhage can occur in nearly 31% of shunt revisions.

Intraparenchymal hemorrhages may be multi-focal in the pediatric population following ventriculoperitoneal shunting.

Hemorrhage can cause an impairment in shunt function, and lead to severe neurological deficiencies.

Intraventricular hemorrhage can occur in nearly 31% of shunt revisions.The flow rate in this system is controlled via a shunt valve.

Shunt malfunction with increased intracranial pressure can occur in pregnancy and especially in the third trimester.

Shunt malfunction in pregnancy improves spontaneously in the postpartum period.

Increased intraabdominal pressure can overcome pressure differences required for adequate CSF flow and can cause hydrocephalus.

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