Complications of Hydrocephalus

Shunt malfunction

Most cases of shunt malfunction are due to occlusion(blockage) of the proximal ventricular catheter. In these instances pumping of the shunt will show a valve that is slow to refill, or does not refill at all. An imaging (CT or MRI) scan which shows ventricles large enough so that if the shunt were working properly, the valve should have refilled promptly.
In a majority of cases infection is cause of shunt malfunction when a distal malfunction is suspected. A preoperative CSF specimen from a shunt tap should be obtained to exclude this possibility. The more proximal system can be tested by insuring free flow of CSF, whereas the distal system can be tested by runoff using a manometer.
The symptoms of over-drainage can be very similar to those of under-drainage though there are important differences. Headaches, dizziness and fainting occur and are often worse after getting up from lying down are the symptoms of under-drainage, whereas the headaches caused by high CSF pressure are often worse on waking, before rising in the morning. However the best way to diagnose the problem, having recognised that one exists, is to measure the CSF pressure over 24 hours.

Symtoms of malfunction:

The signs and symptoms of shunt malfunction, are the same as for hydrocephalus itself, headache, nausea, vomiting, irritability, change in behavior or intellectual performance, etc.

Malfunction in Infants:

Enlargement of the baby's head
Fontanelle is full and tense when the infant is upright and quiet
Prominent scalp veins
Swelling along the shunt tract
Vomiting
Irritability
Sleepiness
Downward deviation of the eyes
Seizures

Malfunction in Toddlers:

Head enlargement
Vomiting
Headache
Irritability and/or sleepiness
A loss of previous abilities (sensory or motor function)
Seizures

Malfunction in Children and Adults:

Vomiting
Headache
Vision problems
Irritability and/or tiredness
Personality change
Seizures
Difficulty in waking up or staying awake

How is a shunt malfunction diagnosed?

In most cases of shunt malfunction, the diagnosis is obvious because of the obvious signs of elevated intracranial pressure, including headaches, vomiting and lethargy. In about 30% there will be only subtle signs of deterioration, with neuropsychologic, cognitive and behavioral symptoms heralding their shunt dysfunction.

In infants an ultrasound examination can be used as a diagnostic tool if the skull has not yet fused, a CT scan is used for diagnosing older children and adults. The size of the ventricles can be compared to "normal values" for the sizes of the ventricles. The persons size, age and growth progress(in children) will give indication to whether the ventricles are to large.
Once there is a suspicion of a shunt malfunction a CT scan or MRI scan is used to compare the ventricular size and show the most definitive signs of a malfunction. This is only useful if a previous scan can be used for comparison. In cases where the symptoms of a shunt malfunction are present but the scanning shows no evidence then a shunt tap is the next test.
A shunt tap is performed after washing the skin over the shunt with a sterile antibacterial solution. After placing a small needle through the skin into the shunt, the spinal fluid pressure can be measured, fluid withdrawn to test for infection and fluid can also be withdrawn to see if symptoms improve temporarily.

Shunt Occlusion(blockage)

There is a heightened risk of shunt blockage in the first few months following placement. The proximal end (the end within the ventricle of the brain) is the most likely to be blocked, it is usualy chloroid plexus or blood generated from the placement of the catheter which causes the blockage.

The catheter exerts a suction effect, this can draw choroid plexus, blood and debris towards the holes in the catheter and contributes to obstruction. Newer shunt designs, such as those with siphon control devices or flow regulated valves may alleviate this cause of late shunt occlusion.
Distal end occlusions are less common than proximal. If the shunt used has a distal slit valve, progressive debris accumulation may lead to its occlusion. Ventriculo-atrial shunts may occlude due to thrombus formation if the distal end migrates out of the atrium. Ventriculo-peritoneal shunts will malfunction if the peritoneum loses its absorptive capacity. This will typically present an increasing abdominal girth, an abdominal ultrasound will show intraperitoneal fluid collection.

Preventing Proximal Catheter Obstruction.

To prevent proximal catheter blockage the catheter needs to lie anterior to the foramen of Monroe, occipital placement with a catheter long enough to reach the front of the ventricular system or a frontal catheter placement will help.
It is important to design the incision so that no part of the shunt hardware or shunt system lays under the incision line. The use of the frontal catheter placement is sometimes useful when there is the symptomatic slit ventricle syndrome. The occipital placement needs to be far enough posteriorly so that one does not risk placing the catheter through the internal capsule. When an error in placement of the ventricular catheter has been made, and this is detected on the postoperative scan, an assessment as to how the patient is doing should be made before deciding on elective revision. Suboptimally placed ventricular cathethers do not have to be automatically revised.

There are two situations, however, which have a high incidence of leading to shunt failure, and elective revision should be considered.
The first is the situation where the catheter is barely in the ventricle, so that when ventricular decompression occurs the catheter would actually become intraparenchymal.
The second situation is a catheter that is located in the anterior part of the temporal horn where subsequent shunt occlusion is very likely to occur.

Intraventricular endoscopes can be used to accurately place ventricular catheters, and fenestrate cysts and comunicate loculated ventricles. Intra-operative ultrasound can also be used to assist catheter placement and locate cysts.

When blockage of a ventricular catheter is found, the catheter is usually adherent to the choroid plexus. It can be difficult to remove. These malfunctions are usually associated with the quick development of elevated intracranial pressure so that a rapid shunt revision should be performed shortly after the patient arrives at the hospital. The revision is performed, replacing the occluded catheter with a right angle ventricular catheter of an appropriate chosen length. This is then connected to the rest of the shunt assembly with a single straight connector.
In cases where the ventricular catheter is stuck, several maneuvers may help free the catheter and avoid intraventricular hemorrhage from overly aggressive pulling on a stuck ventricular catheter.
First, the ventricular catheter can be grasped with a hemostat and rotated. This may free the catheter from the underlying choroid plexus, and there may be a sudden give in the resistance. If the twisting of the catheter does not free it, the next step is to place the stylette down the shunt catheter and touch the Bovie cautery to the stylette. This sometimes will coagulate the choroid plexus at the tip of the catheter and release it. If there is still firm resistance, the catheter should be left in place, a new burr hole placed next to the existing one, and a new ventricular catheter utilized. Intraventricular endoscopy may be particularly useful in this situation. The adherent choroid plexus can be coagulated and freed from the ventricular catheter Using the working channel of the endoscope.
If a proximal revision needs to be performed in the face of relatively small ventricles, there are special considerations that will ensure the safety of this operations. It usually occurs in the setting of shunt dependency where the ventricles were slit-like when the patient was well, but have dilated only slightly with the shunt malfunction. It is frequently wise to place a tube at a frontal site leaving the blocked occipital catheter in place.

A second alternative is to attempt to slide a new ventricular catheter down the same tract following the removal of the old ventricular catheter. No attempt should be made at placing the catheter with a stylette or brain needle, since it may veer off the tract and be difficult to hit the small ventricle. If the catheter does not find its way into the ventricle, then a single attempt with a brain needle or stylette in the ventricular catheter can be made to try and cannnulate the small ventricle. If this is unsuccessful, however, repeated attempts should not be made, and the operation should be aborted. The patient should be watched closely for signs of elevated intracranial pressure, as well as serial CT scans, and a proximal shunt revision subsequently performed when the ventricle has dilated. In this setting it may then be useful to utilize the frontal shunt placement, where it can be easier to hit a small ventricular system.
If a proximal revision is performed, and on placing the new ventricular catheter, blood- tinged CSF is obtained, then an effort should be made to clear the ventricular system of this bleeding which is coming from the choroid plexus. The new catheter should be attached to a three way stopcock and irrigated with saline until it begins to clear. This often requires patience, as it may require up to 20 minutes of gentle irrigation with saline. Once the CSF does clear, a new ventricular catheter should be placed so that there is no risk of a catheter being left in place which is occluded with a blood clot. These patients obviously need to be watched closely for signs of shunt failure within the first few hours after a revision, in which case a temporary ventriculostomy may be needed until the blood clears.

Complications of Distal Shunt.

Most distal malfunctions that are not associated with a short catheter are due to shunt infections.
In the face of a distal malfunction, one should look carefully at the CSF prior to shunt revision to make sure an infection is not present. The presence of an abdominal pseudocyst detected on abdominal ultrasound or CT scanning should be considered a shunt infection until proven otherwise.
It is especially important to allow the fluid to be analyzed in the laboratory for a longer period of time than usal to look for diptheroids, which may not grow on the culture medium in the first two days.
Distal shunts have been known to erode into various abdominal viscera. There are reports of shunts eroding into the intestine, the bladder, the vagina and even protruding from the anus. Most of these complications were seen with the spring loaded distal shunt tubing, which now should be avoided.

Disconnection or Fracture of the Shunt

The second most common cause of shunt failure is disconnection or fracture of the shunt. Disconnection may occur at any site of connection along the course of the tubing. This is usually related to improper technique (loose ligature) or excessive strain along the shunt tube between two points of fixation. The incidence of disconnection has been decreased by the introduction of one-piece shunts. Shunts are made from silicone rubber. Silicone is very flexible but may deteriorate with time after implantation. Calcification of the outer wall of the shunt may produce fixation of the shunt to the subcutaneous tissue, most commonly in the neck or along the chest. This fixation may lead too stretching of the tube and result in fracture or disconnection. Palpation along the shunt tubing may not reveal the fracture as the examiner will feel a firm, fibrous sheath that envelopes the shunt. Definitive diagnosis is made by visualizing the disconnection or fracture on radiographs of the shunt. Mechanical shunt malfunction will usually present with the classic signs symptoms of increased intracranial pressure: headaches, nausea , vomiting and possibly papilledema. Infants will demonstrate irritability, full fontanel and rapidly increasing head circumference. Diagnosis is confirmed by comparing a radiograph study (cranial ultrasound, CT, MRI) obtained while the child is symptomatic with baseline study obtained previously and documenting an increase in the size of the ventricles. If the diagnosis of shunt malfunction remains unclear or a previous study is unavailable for comparison., a shunt function study is performed. The test demonstrates the prescence or absence of flow within the shunt by injection of a small amount of Technetium (a radioisotope) into the reservoir of the shunt and following its flow using scintillation detectors.

Over-drainage

Over-drainage is a more difficult problem,a change of valve to a higher pressure cannot be relied upon to cure it, though it appears to do so in some cases. Studies have shown that the use of an 'antisyphon device', a small button inserted into the shunt tubing, will often solve the problem, but this does not always work. Some shunts have these built-in, but neurosurgical opinion varies as to whether they should be used. To change a valve pressure it is necessary to remove the valve and insert another. A relatively new shunt, the 'programmable' or adjustable shunt, is intended to allow adjustment of the working pressure of the valve without operation. The valve contains magnets which allow the setting to be changed by laying a second magnetic device on the scalp. This is undoubtedly useful where the need for a valve of a different pressure arises, but the adjustable valve is no less prone to over-drainage than any other and it cannot be used to treat this condition.

It has long been believed that a raised protein level in the CSF will block the shunt, and in babies with hydrocephalus shunting has been delayed until the protein level has fallen. Recent research has shown that a raised CSF protein level has no ill-effect on shunt function, nor does it increase the risk of infection, and there is now no reason to delay unless blood is also present.

Over-drainage may lead to a variety of problems such as subdural hematoma, post-shunt craniosynostosis and slit ventricle syndrome. As postural changes and patient height are partially related to the overdrainage, these problems, with the exception of craniosynostosis, are seen mostly in children and adolescents rather than infants.
Subdural Hematoma
Both subdural hematoma formation and the occurrence of post-shunt craniosynostosis are caused by "craniocephalic disproportion." In pediatrics, this is the result of a large head created by a hydrocephalic brain. The head is unable to decrease in size to the same extent that the brain does when the hydrocephalus is treated, and this creates a space between the inner surface of the skull and the outer surface of the brain. A subdural hematoma is formed when the veins bridging between the brain and skull become stretched and tear. This may occur spontaneously or be the result of relatively trivial injury. Some hematomas may be asymptomatic, filling the space created by decompression of the hydrocephalus and resolve spontaneously. If the hematoma is causing symptoms (headaches, vomiting, somnolence) treatment options include a craniotomy and evacuation of the hematoma or placement of a shunt into the subdural space. Craniosynostosis Post-shunt craniosynostosis is the result of apposition and overlapping of the cranial sutures in an infant following decompression of hydrocephalus. Surgical intervention is usually not necessary, but, when indicated, requires a reshaping of the entire skull.

Slit Ventricle Syndrome

The slit ventricle syndrome is usually seen after the shunt has been in place for several years and is characterized by chronic or recurring headaches and slit-like ventricles shown by CT. The slit ventricle syndrome is not a single pathologic entity, but is a symptom complex with several etiologies. The evaluation and management of the slit ventricle syndrome requires a systematic and comprehensive approach. The initial step in the evaluation of the slit ventricle syndrome is to ensure patency of the shunt using the radioisotope shunt function study discussed above. If the shunt is occluded, a shunt revision is performed. If the shunt is functional, the next step is to monitor the intracranial pressure. This is achieved by placement of a small fiberoptic transducer into the outer surface of the brain and measurement of pressure over several hours to days. The child or parents record when the headaches occur and this correlated with their pressure recordings. Consistently high intracranial pressure or frequent waves of high pressure of a functioning shunt implies a reduction of the buffering reserve normally afforded by CSF. Increased intracranial pressure, which would result from increases in intracranial pressure, which would result from increases in intracranial blood volume, is normally prevented by increased absorption of CSF. A constant decrease in the amount of CSF in the intracranial space (from over shunting) precludes this protective mechanism and allows increased intracranial pressure and headaches with increases in blood flow. These children invariably have a relatively small head circumference and thick skull. The preferred treatment is a cranial expansion. This will increase the intracranial volume and allow for the normal changes in blood flow. Headaches may occur with evidence of low intracranial pressure, a condition termed intracranial hypotension. These headaches usually occur in the upright position and are relieved by lying down. They are due to overdrainage by the shunt and are treated by the addition of an antisiphon device to the shunt system. It is hoped that use of the newer shunt systems, which are less likely to cause overdrainage, will reduce the incidence of these complications.

Under-drainage

Under-drainage, in which the fluid is not removed quickly enough and the symptoms of hydrocephalus return, is one of the commonest problems. It is usually due to blockage of the upper or lower tubes of the shunt tissue, though it can be due to the shunt breaking or its parts becoming disconnected from each other. It is rarely due to the valve itself, which usually continues to function in the same way for years. Pressure may sometimes build up rapidly, resulting in loss of consciousness, and treatment is required as an emergency. However, in most cases the onset is more gradual, and can follow a minor illness such as a cold. Headaches increase in frequency and severity, often worse on waking in the morning. Vomiting and dizziness also occur, and sometimes other symptoms which vary from patient to patient. In these cases the parents or carers will be able to recognise the symptoms from previous episodes. Specialist hospital staff are now fully aware of the various presentations of 'blocked shunt' but non-specialists and family doctors may not be.
Shunt blockage can also have much more subtle consequences and the headaches may be infrequent, the main problem being behavioural deterioration. In older children this might take the form of increased irritability, 'laziness', poor or disruptive school performance or even more antisocial activity. This may be very difficult to distinguish from the usual teenage angst but, if there is any reason to suspect that the deterioration in behaviour is not 'normal', assessment must be carried out by an experienced educational psychologist with a knowledge of hydrocephalus. The basis for the effects of high CSF pressure have been explained in the previous article. If the shunt is to blame, a dramatic improvement can result from appropriate treatment, though this form of shunt problem is particularly difficult to diagnose. It may be necessary to monitor CSF pressure, often over 24 hours. This can be done using a pressure monitor in the scalp connected to a recorder. In this way pressure can be recorded during sleep and changes in posture. Scans to show the size of the ventricles are particularly useful if they can be compared to previous scans, though in someone with clear symptoms of either high or low CSF pressure they may also serve to support the diagnosis.
In the case of over-drainage, the shunt allows CSF to drain from the ventricles more quickly than it is produced. If this happens suddenly, usually soon after the shunt is inserted, then the ventricles in the brain collapse, tearing delicate blood vessels on the outside of the brain and causing a haemorrhage ('subdural haematoma'). This can be trivial or it can cause symptoms similar to those of a stroke. The blood may have to be removed, and in some cases if this is not done it may be a cause of epilepsy later. If the overdrainage is more gradual, the ventricles collapse gradually to become slit-like ('slit ventricles'). This often interferes with shunt function causing the opposite problem, high CSF pressure, to reappear, but unfortunately the slit ventricles do not always increase in size again, producing the situation where there is very high CSF pressure with headache, vomiting etc but very small ventricles on scan.

Epilepsy

Epilepsy has been associated with shunt-treated hydrocephalus. Though is not thought to be directly related to the placement of the shunt, but to the cause the hydrocephalus.

Infection

The rate of shunt infection is about 10-15%, and 95% of infections will occur in the first 5 days after surgery.

Symptoms:

The signs of shunt infection may include fever, neck stiffness, light sensitivity (also called photophobia), headaches, or signs of shunt malfunction. Shunt infections can present with signs of meningitis and ventriculitis. In addition, signs of septicemia or peritonitis can be seen, depending on the type of shunt. The shunt may be reddened along its course under the skin, or the wounds may be reddened and/or draining pus. Most commonly the bacteria responsible are those that reside normally in the skin of the patient - Staphylococcus species, distal shunt malfunctions frequently accompany shunt infections. In VA shunts blockage due to infection is rare, and many months or years can go by before the infection becomes apparent. During this time there will be tiredness, irritability, poor appetite, various aches and pains, skin rashes and other signs but all of these can be due to common disorders. A blood test will usually reveal anaemia and this is an important though, on its own, not a specific indication of infection. Blood cultures and even CSF cultures can be negative. Later, blood may appear in the urine due to secondary kidney damage.

Diagnosis:

Diagnosis is made by culture of the wound if there is drainage, or, more commonly, by culture of the cerebrospinal fluid within the shunt. Fluid is sampled by insertion of a needle into a reservoir in the shunt. The major risk is low (approximatley one percent), it makes us consider carefully the indications for each tap. Factors such as time from the last surgery and the presence of other possible sources of the fever are taken into consideration.

Causes:

Most shunt infections are caused by either Staph-epidermidis or auerus. Both bacteria normaly found on the skin and are presumably implanted at time of surgery. Infection usually becomes apparent within the first few months following surgery: 50 percent by two months and 90 percent by six months after surgery.

Occurance:

Shunt infections occure with an incidence of 2-8% of each shunt operation being associated with a postoperative shunt infection.
As recently as eight years ago, a review article about shunt infection stated that the expected infection rate ranged between 10-20 percent.
Overall, between 5 and 15% of shunts can be expected to become infected over the life of the shunt. Of these infections, 70% are diagnosed within one month after surgery and close to 90% by six months. There are, however, late shunt infections which can occur after six months of a shunt procedure.

Treatment:

The treatment of shunt infections is somewhat controversial. The standard treatment is to remove all of the shunt hardware system, usually done within 2 days of the diagnosis, and treat with appropriate antibiotics. Approximately 10 days later, a new shunt system can be placed. While the child is on the systemic antibiotics, a temporary ventriculostomy may be necessary to control the hydrocephalus.
Once the infection is cleared, we will place the new VP shunt in the same site, unless there are skin abnormalities which would necessitate placing the shunt on the opposite side. After a shunt has been externalized for approximately 7 days, and CSF cultures have cleared, then a completely new VP shunt is placed, and antibiotics are continued for an additional two days. The antibiotics can then be discontinued.
If, however, there are signs of peritonitis, or distal shunt malfunction, then the shunt should be removed quickly. A septic child may be too great an anesthetic risk until the vital signs have stabilized.
In cases where a nonfulminating shunt infection is diagnosed within the first month after a shunt insertion, an attempt can occasionally be made to treat the shunt infection with intravenous and intrathecal antibiotics without removing the shunt system. The families need to understand that this method of treatment may fail, and that ultimately the shunt would have to be removed. This method, however, does provide a way of saving the shunt system and successfully treating many early shunt infections. This method of treatment, however, must be abandoned if cultures do not become sterile within several days, or if more aggressive signs of infection are noted.
Antibiotics have not been shown to be of benefit for this purpose, and other measures often have only a temporary effect, though obviously the care and expertise of the surgical team is one of the most important factors in reducing the rate of infection to a minimum. However, even in the best of hands infection still occurs. One of our recent developments has been a process which makes shunts resistant to bacterial infection, and we hope that the current clinical trials will show that it is capable of reducing shunt infection by more than 80%.