Ventriculoperitoneal Shunt

Anatomy and Physiology

The ventricles of the brain are a communicating network of cavities located within the brain parenchyma. The ventricular system is composed of two lateral ventricles, the third ventricle, the cerebral aqueduct, and the fourth ventricle. The choroid plexus in the ventricles produce CSF, which fills the ventricle and the subarachnoid space in a constant cycle of production and reabsorption.[2][4][5][6] The CSF is then absorbed into the cerebral venous circulation through the Pacchionian (arachnoid)granulations. Any block or obstruction in this pathway will produce obstructive hydrocephalus and if permanent will require a shunt. Sometimes, these granulations become obstructed from blood products or high protein and will not function adequately producing communicating hydrocephalus.

Placement of a cerebral shunt and its location is determined based on the surgeon's preference. It may be placed through a frontal approach into the anterior horn of the lateral ventricles or though a parieto-occipital approach into the trigone or occipital horn of the lateral ventricle. The catheter placed into the cerebral ventricle is called the proximal shunt (ventricular catheter) implying proximity to the brain. The most preferred proximal shunt location is on the right lateral ventricle as any complication will not be associated with the dominant hemisphere. If there is asymmetry, then the larger ventricle is used. The distal catheter can be placed in the abdomen (peritoneal cavity), heart via a cervical venous access, chest cavity (pleura), or rarely into the ureter or the bladder if all previous sites have been used. In all cases, however, the distal end of the catheter can be located in any tissue with cells capable of absorbing the incoming CSF.

A subgaleal shunt is a temporary measure used in infants who are too small or premature to tolerate other shunts of have difficulty with peritoneal absorption. The surgeon forms a pocket beneath the subgaleal space and allows the CSF to drain from the ventricles, creating a fluid-filled swelling on the infant's scalp. As the child grows, these shunts are later converted to a permanent shunt type.[7][8][9]

Indications

Most VP shunts are placed to treat the hydrocephalus. Disorders that typically requiring shunting include the following:

• Congenital hydrocephalus after aqueductal stenosis is a genetic disorder which can cause deformations of the nervous system and is associated with mental retardation, abducted thumbs, and spastic paraplegia
• Tumors leading to CSF blockage of the lateral ventricles, third ventricle, and those in the posterior fossa blocking the cerebral aqueduct or fourth ventricle
• Communicating hydrocephalus secondary to meningitis or subarachnoid hemorrhage
• Myelomeningocele causes the development of hydrocephalus because the flow of CSF is altered due to hindbrain malformation
• Craniosynostosis occurs when the sutures of the skull close too early with sutures fusing before the brain stops growing and in rare occasions can cause hydrocephalus
• Dandy-Walker syndrome presents with a cystic deformity of the fourth ventricle, hypoplasia of the cerebellar vermis, and an enlarged posterior fossa
• Arachnoid cysts are a defect caused when CSF forms a collection that is trapped in the arachnoid membranes resulting in a block of the normal flow of CSF resulting in hydrocephalus
• Idiopathic intracranial hypertension is a rare neurological disorder affecting approximately 1 in 100,000 people, usually women of childbearing age, causing a rise in intracranial pressure which can result in permanent loss of vision
• Normal-pressure hydrocephalus caused a classic triad of memory problems/dementia, gait dysfunction, and urinary incontinence.

Contraindications

Absolute contraindications include:

• Infection over the entry site
• Infection of the CSF
• Allergy to any of the catheter components (silicone)[10][11][12]

Relative contraindications include:

• altered coagulation function
• high CSF protein
• CSF with blood

Equipment

A VP shunt is placed in the operating room under general anesthesia by a neurosurgeon.

Equipment needed to perform the procedure includes:

• Shunt system (ventricular catheter, peritoneal catheter, and valve)
• Valve (small, medium, or high-pressure)
• Programmable valve
• Specimen tubes for CSF
• Drill for the burr hole
• Shunt passer
• Image-guided navigation system (only for small ventricles)

Personnel

Neurosurgeon

Anesthesiologist

Nurse (circulating and technical)

Preparation

Brain magnetic resonance imaging (MRI) or computed tomography (CT) scan is reviewed for the planning of the shunt and the proper placement of the proximal catheter. All patients need appropriate preoperative workup and informed consent for surgery and general anesthesia. The patient is placed supine. For a parieto-occipital approach, the head is tilted to the contralateral side of the shunt placement. Preoperative antibiotics are given and the patient is dressed in sterile conditions.

Technique or Treatment

• Shave the hair away from the head incision site (some surgeons use minimal shaving)
• Clean the skin with an antiseptic
• Apply a sterile fenestrated drape over the incision sites (head, neck, chest, and abdomen)
• Fenestrated drape the patient
• Make a "U or C" shaped skin incision over the entry point where the burr hole is to be performed for the introduction of the ventricular catheter. If the frontal approach will be used, then Kocher’s point is used which is an entry point that is 11 cm superior and posterior from the nasion, 3 cm lateral to midline along the mid pupillary line, and 1 to 2 cm anterior to the coronal suture; catheter should then be passed to a depth of 5-5.5 cm.[13]  For a parieto-occipital approach, Keen’s point is used which is approximately 2.5 to 3 cm superior and posterior to the pinna and the catheter should then be passed to a depth of 4 to 5 cm or until reaching the trigone of the ipsilateral lateral ventricle, but sometimes it is aiming toward the frontal horn of the lateral ventricle.[13] Alternatively, Dandy's point can be used which is 3 cm above the inion and 2 cm left or right to the midline.[13]
• Burr hole is performed at the desired entry point and the dura incised. A small entry point in the cortex is coagulated and incised.
• Ventricular catheter is introduced directed into the ventricle and cut to the appropriate pre-measured length
• CSF samples are collected
• The ventricular shunt is connected to the valve and secured with a silk tie.
• An incision in the abdomen is done to access the peritoneal cavity; the site depends on the surgeon's preference and can be done in the upper quadrant or the midline
• Shunt passer is used to pass the peritoneal distal catheter between both incisions.
• Peritoneal catheter is connected to the valve and secured with a silk tie.
• After good distal CSF flow at the peritoneal catheter, it is introduced into the peritoneal cavity.
• Wounds are closed in anatomical layers
• The CSF sample is sent to the laboratory for cell count, glucose, protein, gram stain, and culture

Complications

Complications include the following:

• Infection due to skin flora entering the shunt, usually from Staphylococcus epidermidis
• Intracerebral or intraventricular hemorrhage
• Malposition
• Abdominal perforation during placement 
• Shunt erosion of the skin with exposure of the system
• Shunt over drainage (slit ventricles)[14][15][16]
• Shunt nephritis[17][18]
• Shunt disconnection
• Shunt obstruction
• Subdural hematomas
• Abdominal CSF collections (pseudocyst or CSFoma)[16]
• Shunt breakage at any point
• Catheter perforation of viscera and rarely extrusion through the anus[19][20][21]
• Inguinal hernia
• Seizures

In those cases of malfunction, the shunt has to be assessed for proper function. The following technique is used:

• Clean the skin with an antiseptic
• Apply a sterile fenestrated drape over the incision site
• Insert a small (23 ga) butterfly needle perpendicular to the skin into the reservoir
• Evaluate for spontaneous CSF filling the line of the butterfly needle
• Measure the opening pressure using a manometer
• Aspirate CSF with syringe
• Collect 5 mL of CSF and place into sterile specimen containers
• Withdraw the needle from the reservoir
• Gauze applied to site
• Send the cerebrospinal fluid sample for cell count, glucose, protein, gram stain, and culture

Complications of a shunt tap are:

• Bleeding from subcutaneous vessels during the tap
• Cerebrospinal fluid leak from the puncture site
• Ventricular collapse due to rapid aspiration of CSF, especially in slit ventricles
• A misplaced tap can result in the sectioning of the tubing or the reservoir.

Clinical Significance

Ventriculoperitoneal shunts are used to treat hydrocephalus and divert CSF from the lateral ventricles into the peritoneum. Tapping a shunt is performed for both diagnostic and therapeutic reasons (evaluate for infection or malfunction). A VP shunt is one of the high impact advances made in neurosurgical patient care. 

Evaluation

Patients with shunts are evaluated for evidence of signs or symptoms related to complications or malfunction. Acute symptoms of malfunction/infection are: headache, lethargy, diplopia, nausea and vomiting, seizure, irritability, poor feeding, head enlargement when sutures are open, tense fontanelle, fever, neck rigidity. Shunt system has to be assessed manually for proper function and visible for evidence of redness or swelling along the shunt tubing. Shunt X rays are done to evaluate the integrity of the system. CT scan or MRI is done to evaluate the size of the ventricles. 

Outcome

VP shunt can be lifesaving, but the eventual outcome depends on the reason why the shunt was inserted. For benign disorders, most patients have a good outcome. However, for malignant tumors, the outcomes are usually poor; often these patients die from other causes unrelated to the shunt. The complication rates of VP shunts range from 2-20%. In addition, shunt revision is required in about 5-10% of neonates and young children.[22][23](Level V)

Enhancing Healthcare Team Outcomes

There is no question that VP shunts have saved many lives, but these devices are not without complications. The shunt has to be monitored for infection and malfunction. The abdomen has to be monitored for peritonitis secondary to shunt infection. While the neurosurgeon is always involved in the care of patients with hydrocephalus, it is important to consult with an interprofessional team that includes a pediatrician, and a general surgeon. Any unusual finding by the primary physician has to be immediately reported back to the neurosurgeon. The nurses are also vital members of the interprofessional group as they will monitor the patient's clinical signs and assist with the education of the patient and the family. In the postoperative period for pain, or for shunt infection; the pharmacist will ensure that the patient is on the right analgesics and appropriate antibiotics. The radiologist also plays a role in determining the cause of the malfunction. Without providing a proper history, the radiologist may not be sure what to look for or what additional radiologic exams may be needed. Before the patient is discharged, the family has to be educated on the early identification of shunt failure and how to monitor the child's improvement. In some cases, a home care nurse may be required to pay regular visits to ensure that the VP shunt is functioning without problems.[24][25] (Level V)