Introduction
•
Although many consider shunting a relatively simple
procedure, problems with CSF shunts are common, costly, and sometimes debilitating. Within the first year, shunts fail at extraordinary rates of up to 40% and show nearly a 10%
infection rate.
•
Adult patients shunted in early childhood have a particularly high incidence of noncommunicating (intraventricular)
hydrocephalus in our experience
Introduction
VALVE DESIGN AND TERMINOLOGY
•
Probably the most important component of a shunt system is the valve.
•
Hydrocephalus is a heterogeneous disorder, with a wide range of intracranial pressures, ventricular compliance, and CSF
profiles across patients
•
The main challenges arise from problematic patients, such as those suffering from headaches, subdural hematomas,
repeated shunt obstructions, slit ventricle syndrome caused
by chronic overdrainage, and so on
Differential Pressure Valve
•
The basic building block of most shunt valves is a differential pressure “check valve” mechanism.
•
The basic design of John Holter continues in some form more than half a century after its development.
•
In most current valve designs, it consists of a tiny ball situated
on a ring, with a spring pushing the ball downward on thering. CSF passes through the ring, elevating the ball if the
pressure exceeds the pressure exerted by the spring. This
creates a one-way flow mechanism because reverse
flow will not occur as the ball sits down onto the ringDifferential Pressure Valve
•
Opening of this valve mechanism depends on the differential pressure across the ring. For example, if the spring is exerting downward pressure of 100 mm H
2O, CSF will flow if the
difference between the inlet and outlet pressures is greater
than 100 mm H
2O, regardless of whether the inlet pressure is
positive or negative.Differential Pressure Valve
• A common misconception is that the valve opening pressure must be lower than the ventricular pressure (as measured at the time of surgery) for CSF to flow down the shunt.
•
In a study of patients with normal-pressure hydrocephalus (NPH), intracranial pressure was statistically lower at all head-of-bed elevations compared with preoperative values, even with the valve set at 200 mm H
2O opening pressure.
•
For example, despite a mean preoperative intracranial
pressure of 164 ± 64 mm H
2O, the mean postoperative
intracranial pressure was 125 ± 69 mm H
2O (P = .04
Differential Pressure Valve
• This demonstrates that use of a low-pressure valve
setting is not necessary and results in excessive CSF
drainage in many patients
Differential Pressure Valve
Differential Pressure Valve
Adjustable ("Programmable") Valves
• these valves are not truly programmable and are better considered as merely adjustable valves
• Adjustable valves arose from the realization that fixed- pressure differential pressure valves result in either
overdrainage or underdrainage in a significant number of adult patients
• Another justification for the routine use of adjustable
valves is based on the range of “final” valve opening
pressures when these valves are used
Adjustable ("Programmable") Valves
Adjustable ("Programmable") Valves
Adjustable ("Programmable") Valves
• Arguments that these valves are unreliable, or
malfunction more frequently than fixed valves do, are
not supported by any clinical study
Adjustable ("Programmable") Valves Drawback
1. Perhaps the biggest drawback is cost. Currently, adjustable valves are two to three times more costly compared with fixed-pressure valves, and there is no clinical study comparing cost-effectiveness.
2. Another drawback of adjustable valves has been MRI
compatibility. To date, two manufacturers (Sophysa Polaris and Aesculap proGAV) have designed a locking mechanism that in
theory prevents resetting of the valve when the patient is brought in and out of the MRI scanner
Siphon-Control and Anti-Siphon Devices
Siphon-Control and Anti-Siphon Devices
• ASDs are add-on devices, meaning that they are used in
conjunction with (immediately distal to) a differential pressure valve mechanism. These devices have been used clinically for more than 30 years
• In general, the device is based on a membrane that is mechanically coupled to the subcutaneous tissue overlying it.
• The pressure differential between the internal valve lumen and the atmosphere, transmitted across the skin and ASD membrane,
determines the flow-pressure characteristics of the ASD device.
Siphon-Control and Anti-Siphon Devices
• When the intraluminal pressure becomes significantly negative (relative to atmospheric pressure), the membrane is drawn inward- interacting with other fixed components of the ASD and thereby creating an increased pressure gradient.
• This phenomenon, better termed gravity-dependent drainage, occurs as the result of gravity-driven CSF flow down the distal catheter when the patient is in the upright position.
• Our intracranial pressure studies in idiopathic NPH patients, aswell as those of others,suggestthat gravity-dependent drainage is likely to playa lesser role in the etiology of overdrainage complications.
Siphon-Control and Anti-Siphon Devices
• For some hydrocephalus patients, the presence of an ASD is detrimental.
• This so-called low-pressure hydrocephalus syndrome, of which the incidence has not been quantified but is presumed to be less than 5%, occurs both in childhood and in adults.
• In our experience as well as that of others, the addition of an ASD can be effective in patients with clinically symptomatic
overdrainage.
Siphon-Control and Anti-Siphon Devices
Dr. Mohammad Hallajnejad
Flow Restriction Devices
• Another approach taken to counteract shunt overdrainage is the incorporation of a CSF flow restriction mechanism.
• The premise is that shunt overdrainage occurs as a result of an excessive rate of CSF drainage.
• It follows that by limiting the maximum CSF flow rate, overdrainage should be averted.
Flow Restriction Devices
Gravitational Devices
• As discussed earlier, gravity-induced CSF flow (commonly referred to as siphoning) is considered by many to be the primary cause of overdrainage.
• To offset the negative pressures generated by the long hydrostatic column, the gravitational (also termed hydrostatic) device
interposes a very high differential pressure valve while the patient is in the upright position.
Gravitational Devices
Gravitational Devices
Shunt Overdrainage
•
This term means different things to different people. In our view, it is a condition that is (1) caused by excessive CSF drainage or intracranial hypotension and (2) of clinical significance.
•
Overdrainage typically is manifested as either
• postural headaches (with or without nausea or other ill feelings) or
• imaging evidence of pathological subdural fluid collections
Shunt Overdrainage
• Overdrainage symptoms are equivalent to a post–lumbar puncture or “spinal” headache.
• We know from the lumbar puncture literature that depending on needle size and design, the incidence of post–dural puncture
headaches is 1% to 30%.
• Presumably, most subjects after lumbar puncture experience some period of intracranial hypotension, but only a minority are
sensitive to the state. This means that the mere presence of negative intracranial pressure is not pathognomonic of
overdrainage
Shunt Overdrainage
Shunt Overdrainage
• The patient will have clearly recognized that the headache or other symptoms occur within minutes of assuming an upright position and are alleviated immediately with recumbency.
• Intracranial pressure monitoring is not needed in such cases.
• Furthermore, postural headaches can occur in the setting of
unchanged ventricle size, with a reduction in ventricle size, or with the presence of subdural fluid collections
• If postural headaches are mild, conservative measures such as hydration can often bide the patient over until the body re- equilibrates and the symptoms abate spontaneously.
Shunt Overdrainage
• Increasing the valve opening pressure (by at least 30 mm H2O) usually alleviates postural headache symptoms within 1 hour of the intervention.
• The use of adjustable valves obviates the need for a shunt revision in most of these cases
• In the situation in which the patient is already at the maximum valve opening pressure of an adjustable valve (or has a fixed pressure or other valve), a shunt revision is typically
required either to add an ASD or gravitational device or, with the latter scenario, to change the valve to an adjustable valve with a higher range of pressures
Shunt Overdrainage
• Less commonly, headache may not be the main symptom of shunt overdrainage.
• Some patients complain of only nausea, whereas others have difficulty concentrating.
• For patients who have new-onset headaches not present before the shunt operation, there should be a clinical suspicion of
overdrainage even if there is no clear postural relationship
Shunt Overdrainage
• In general, overdrainage headaches do not occur in a delayed manner.
• In other words, a patient who has been doing fine for months will not spontaneously present with overdrainage symptoms.
• Exceptions to this rule might include new subdural fluid collection and inadvertent shunt adjustment (such as with an MRI)
Shunt Overdrainage
• The development of subdural fluid collections is a second possible manifestation of shunt overdrainage.
• Subdural hygroma (also known as effusion) formation is relatively common in the shunted NPH population.
• Small subdural hygromas (<5 mm) are usually asymptomatic and are often associated with improvement in NPH symptoms because they occur only in conjunction with reduction of the ventricular system.
Shunt Overdrainage
• As a result, the presence of a subdural hygroma is not by itself diagnostic of shunt overdrainage.
• Expanding or large subdural hygromas are more worrisome and, many would agree, are risk factors for the development of acute hemorrhage (subdural hematoma).
• A non–trauma-related subdural hematoma in a shunted patient is obviously an overdrainage presentation
Shunt Overdrainage
• It is our observation that shunted patients undergoing a contrast- enhanced MRI study sometimes show diffuse pachymeningeal enhancement—the same finding that is used to diagnose
spontaneous intracranial hypotension.
• Given that most shunts generate some degree of intracranial hypotension, this enhancement pattern is not necessarily indicative of clinical overdrainage.
• If postural symptoms are present, however, the finding may support an overdrainage diagnosis.
Shunt Overdrainage
• “Slit” or collapsed ventricles are typically a manifestation of chronic overdrainage.
• Clearly, not all patients with slit (or unilateral slit) ventricles are symptomatic, but it is generally agreed that this state increases the risk of ventricular shunt obstruction.
• The apposition of the ventricular catheter to the ventricular wall increases the chance of ingrowth of ependymal cells or choroid plexus
• The incidence is unknown but represents about 5% of the non-NPH evaluations in our clinic.
• The syndrome occurs more commonly in patients who have been shunted for many years, either as an adult or in childhood.
Shunt Overdrainage
• In addition, it is our observation that a significant proportion of patients with adult slit ventricle syndrome have previously
unrecognized noncommunicating hydrocephalus.
• Common symptoms of adult slit ventricle syndrome include intermittent headaches that become more frequent and intense over time.
• The etiology of these intermittent headaches has been unclear but may be related to periods of insufficient CSF drainage.
Shunt Overdrainage
• In addition, collapse of the ventricular system lowers intracranial compliance, further amplifying elevations in intracranial pressure during shunt underdrainage.
• At shunt revision, the typical intraoperative finding is nearly total but not complete obstruction of the ventricular catheter (typically only one or two holes are patent).
• Left untreated, the symptoms may progress to more continuous headaches, presumably due to completed mechanical obstruction of the shunt system.
• Therefore, the slit ventricle syndrome is actually an underdrainage syndrome created by a preceding period of overdrainage.
Shunt Overdrainage
• Significant hearing loss is an uncommon complication of CSF shunting.
• One small prospective study showed a significant increase in the mean threshold in most frequencies and the pure tone average after VP shunt placement
• In our experience, the hearing loss is reversible with valve pressure adjustments
Underdrainage
• In many cases, shunt underdrainage is easy to recognize.
• This includes patients who were obviously symptomatic from
hydrocephalus and then fail to improve after shunt surgery or see a return of their symptoms with clinical deterioration.
• Similarly, interval enlargement of the ventricles is diagnostic of underdrainage.
Underdrainage
•
It is the patient in whom the association between clinical findings and ventriculomegaly is uncertain and fails to improve after shunt surgery (or only minimally improves) who represents a clinical challenge.
•
This is especially problematic in NPH patients because there always exists some doubt in the diagnosis. As a result, the failure to improve might be attributed to an incorrect
diagnosis (an underrecognized weakness of many NPH
clinical studies).
Underdrainage
• For example, what if there is no clinical improvement in a patient with suspected NPH despite the valve’s being brought down to its lowest setting?
• After confirming shunt patency, many might consider such a patient a “nonresponder” and therefore by inference misdiagnosed.
• For patients in this scenario who remain with significant
ventriculomegaly, the low-pressure hydrocephalus state should be considered.
• For these patients, clinical improvement strongly coincides with reduction in the ventricular size, and only with significant negative intracranial pressure does reduction in the ventricular size occur.
Not surprisingly, this state occurs with higher incidence in patients with ASDs
Underdrainage
• In NPH, if imaging reveals a reduction in ventricular size, a patient should be considered a nonresponder if no clinical improvement occurred.
• Downward adjustments in valve opening pressure are unlikely to benefit the patient and instead increase the risk of subdural
hematoma.
Underdrainage
• If underdrainage is suspected, shunt obstruction is always a consideration.
Underdrainage
• For example, if there is an ASD, remove it. If the patient has a fixed- pressure valve or a flow-restricting valve, change it to an adjustable differential pressure valve (no ASD).
• It is our observation that ventriculoatrial shunts provide more drainage than ventriculoperitoneal shunts do, and therefore we offer a shunt
revision to a ventriculoatrial shunt as well.
Valve Selection
• There are no evidenced-based guidelines to support any recommendations.
• On the basis of peer-reviewed published clinical studies and our large experience, we see no reasonable justification for not using an adjustable valve for NPH.
• Although adjustable valves are not the panacea, the use of a
nonadjustable valve for the treatment of NPH exposes the patient to an unacceptable underdrainage or overdrainage risk
Valve Selection
• The second decision in valve selection is choosing the initial opening pressure.
• About 2% will have clinical overdrainage despite a valve pressure setting of 200 mm H2O, and the other 2% will have underdrainage at a setting of 30 mm H2O.
• In our practice, for NPH patients the valve is initially set at 200 mm H2O unless they are of short stature, in which cases settings as low as 140 mm H2O are used. The opening pressure is sequentially lowered, typically by 30 mm over 2 to 3 weeks to effect
Valve Selection
• We recommend that younger, non-NPH patients receive even higher opening pressure settings (upper opening pressures of 300 or 400 mm H2O) or, alternatively, that an ASD, flow-limiting device, or gravitational device be incorporated in series with the “standard”
adjustable valve (30 to 200 mm H2O).
Shunt Configuration
• For routine shunt placement, we prefer a frontal (precoronal) ventricular puncture shunt rather than a posterior or occipital shunt.
• A retrospective analysis of shunt operations from the U.K. Registry study demonstrated that frontal catheters were adequately placed in 67% of cases, whereas occipital catheters were adequate in 52%.
• Moreover, we typically use frameless stereotaxis for the shunt
ventricular catheter placement in patients with a bifrontal distance (maximum distance of lateral frontal horns) of less than 40 mm to increase the chances of optimal catheter placement.
• The tip of the catheter should reside just anterior to the ipsilateral foramen of Monro to keep it away from the choroid plexus.
Shunt Configuration
• If the ventricles are large, the catheter is first positioned orthogonal to the skull, then angled slightly about 5 degrees anteriorly before the freehand insertion. The ideal depth is typically 6 cm of catheter at the dura.
• As a general rule, every shunt incision should be carefully planned so that it does not directly overlie a shunt component.
• Failure to do so increases the risk of skin breakdown.
• We routinely place a modified titanium bur hole cover (one sector removed) over the frontal bur hole site after the catheter is situated.
This prevents dimpling of the skin into the bur hole, which can result in poor cosmesis and sometimes discomfort
Shunt Configuration
• Some neurosurgeons routinely use ventricular endoscopy to assist ventricular shunt placement. A multicenter trial demonstrated no benefit from this strategy.
• In our opinion, endoscopy is not a substitute for stereotaxis.
• A poor initial trajectory may not be remediable by attempted endoscopic catheter placement
Shunt Configuration
• Distal Site
• If the patient is not obese and has no history (or probability) of peritoneal adhesions, a ventriculoperitoneal shunt is offered.
Otherwise, a ventriculoatrial shunt is recommended.
• There is a growing literature on laparoscopy-assisted peritoneal catheter placement for obese patients and patients with peritoneal adhesions.
• For the very cases in which laparoscopy is indicated, a ventriculoatrial shunt can usually be performed instead.
• As a result, we have used laparoscopic assistance in only two cases during a 14-year period
Shunt Configuration
• Ventriculoatrial Shunt Technique
• We routinely use a modified percutaneous technique.
• With use of a sterile intraoperative ultrasound unit to visualize the needle cannulation of the internal jugular vein, only a 5-mm
incision is needed.
• We use an 8 French peel-away vascular access kit and fluoroscopic visualization to place the tip of the catheter at the distal superior vena cava (we still use the term ventriculoatrial shunt for
simplicity).
• We avoid placement of the catheter in the atrium to minimize the risk of sinus arrhythmias.
Ventriculoatrial Shunt Technique
• We routinely use a modified percutaneous technique.
• With use of a sterile intraoperative ultrasound unit to visualize the
needle cannulation of the internal jugular vein, only a 5-mm incision is needed.
• We use an 8 French peel-away vascular access kit and fluoroscopic visualization to place the tip of the catheter at the distal superior vena cava (we still use the term ventriculoatrial shunt for simplicity).
• We avoid placement of the catheter in the atrium to minimize the risk of sinus arrhythmias.
• The perception that the infection rate is higher with ventriculoatrial
shunts in comparison to ventriculoperitoneal shunts is not supported by the literature.
Ventriculoatrial Shunt Technique
Ventriculoatrial Shunt Technique
• Shunt Nephritis
• One concern is shunt nephritis, an immune complex–mediated glomerulonephritis that results from long-term, subacute
bacteremia (typically an indolent species, such as Staphylococcus epidermidis).
• During the last 15 years, with placement of more than 250
ventriculoatrial shunts, we have seen one case of documented shunt nephritis. This condition is not unique to ventriculoatrial shunts, having been reported in ventriculoperitoneal shunts as well.
• Patients present with fever of unknown origin and microscopic hematuria.
Ventriculoatrial Shunt Technique
• It underscores the importance of a shunt tap in shunted patients in whom another obvious source of infection cannot be identified.
• Shunt cultures should be kept in the incubator for at least 5 days to identify indolent bacterial forms
Ventriculoatrial Shunt Technique
• The percutaneous ventriculoatrial shunt approach is performed in a specific order.
• Once the components are tunneled and situated, the patient is placed in Trendelenburg position for the ultrasound-guided placement of the distal (“atrial”) catheter.
• Once this has been accomplished and the table returned to the neutral position, the dura is incised and the ventricular catheter is inserted.
• This order eliminates CSF loss while the patient is in the Trendelenburg position.
• The final assembly of the ventriculoatrial shunt is at the retroauricular
incision site, where the distal valve is connected to the proximal portion of the atrial catheter. This has to be done last because the atrial catheter has to be cut to the correct length based on the localization of the distal tip.
Percutaneous Ventriculoatrial shunt
Ventriculoperitoneal Shunt Technique
• For most cases, we mark an incision about 4 to 5 cm below the costal margin and centered at the lateral border of the rectus omusculature
• Typically, the mini-laparotomy can be accomplished easily with a horizontal incision of 3 cm or less.
• The (appendectomy) retractor is used for exposure in the pre-rectus fascia space only.
• After the superficial rectus fascia is opened transversely, the rectus muscle separated vertically in a muscle-sparing fashion, an open Cushing forceps is all that is needed to provide exposure of the deep rectus fascia.
• This fascia is picked up with two Crile hemostats, and a 3- to 4-mm incision
• is made with Metzenbaum scissors.
Ventriculoperitoneal Shunt Technique
• Pulling up on these hemostats brings this deep fascial plane superficial to the rectus muscle, thereby allowing the approach by such a small skin incision.
• In about half the cases, the peritoneum is adherent to this fascial layer, and the peritoneal cavity will be encountered.
• In the other cases, the peritoneum can be picked up with two mosquito hemostats and incised with the Metzenbaum scissors;
• the peritoneum cavity can then be confirmed by gently probing with the Penfield 4 instrument.
• Closure is performed in layers, with a single 3-0 absorbable suture
reapproximating the deep fascia (we do not use a purse-string suture) and interrupted 3-0 absorbable sutures in the superficial fascia and dermis layers.
Ventriculoperitoneal Shunt Technique
Ventriculoperitoneal Shunt Technique
• Challenges occur when a thick preperitoneal fat layer is encountered or if the omentum is large and it is difficult to confirm entrance into the peritoneal cavity.
• More troublesome is encountering peritoneal adhesions.
• If this occurs, a larger exposure may be required to be able to digitally explore the peritoneal space.
• As noted before, a ventriculoatrial shunt is a better choice in patients suspected of having peritoneal adhesions.
Ventriculoperitoneal Shunt Technique
• One of the known complications of ventriculoperitoneal shunts is retraction of the peritoneal catheter into the subcutaneous pocket underlying the wound.
• In this case, a laparoscopic technique proposed by Nfonsam and coworkers is appealing in that the shunt tunneler penetrates the peritoneum under laparoscopic visualization away from the open incision sites.
INFECTION AVOIDANCE
• Nearly every prospective pediatric population shunt study has reported an infection rate of approximately 8%.
• Less information is available about infection rates for adults.
• There are clearly multiple contributing factors for shunt infections, but given the highest incidence within the first month of surgery, the
"contamination" most likely occurs at the time of the shunt surgery.
INFECTION AVOIDANCE
• Meta-analyses sUPE0rt the routine use of perioperative intravenous antibiotics.
• We routinely use cephazolin (Ancef), although an
argument could be made for an antibiotic with better central nervous system penetration.
• We routinely remove the hair (with clippers) over the surgical areas once the patient is under anesthesia.
• Our rationale is that there is greater assurance that the surgical
preparation solution will cleanse and make contact with all surfaces exposed after draping if the hair has been removed.
• We routinely clip the hair enough to create at least a l-cm margin around all wounds.
INFECTION AVOIDANCE
• Use of a razor to shave the scalp is not necessary and possibly
contraindicated because it causes microabrasions that expose more skin flora.
INFECTION AVOIDANCE
• For "healthy" patients undergoing a primary, uncomplicated shunt operation, we basically employ only these measures.
• For other patients, we use a tailored approach. Before every shunt operation, we investigate the risk factors for shunt infection. This includes any of the following:
1. malnourishment, 2. diabetes mellitus,
3. open sores or wounds,
4. hospitalization of more than 24 hours, 5. shunt revision within 3 months,
6. immunosuppression (including steroids).
INFECTION AVOIDANCE
• If possible, a shunt operation should be
postponed for patients with active infection, such as a urinary tract infection, until the
infection is resolved.
• In many cases, it is prudent to enlist the aid of an infectious disease consultant.
INFECTION AVOIDANCE
• Certain "high-risk" patients undergo more extensive preoperative skin preparation.
• These patients include:
1. intensive care unit patients with an external ventriculostomy, 2. patients with a history of a shunt operation within 30 days, 3. patients with a tracheostomy,
4. patients with a history of problematic skin infections.
• After clipping of the hair as described earlier, all adhesive residues along the track are removed with an adhesive remover solvent.
• This is particularly important in neurosurgical intensive care unit patients who have had ventriculostomies, electroencephalographic leads, or recent craniotomies.
INFECTION AVOIDANCE
• These adhesive residues are not removed by the standard sterile preparation, and in our opinion, the space underlying them may be contaminated by virulent nosocomial organisms.
• Once the adhesive residue is removed, we gently cleanse the skin with a mild detergent before a final surgical "sterile" preparation with Betadine or chlorhexidine.
INFECTION AVOIDANCE
• Clinical studies strongly support the routine use of antibioticimpregnated catheters.
• An analysis by Eymann and colleagues70 suggests that, despite the incremental implant costs associated with the use of antibiotic
impregnated catheters, the overall reduction in infection-related costs made their use cost beneficial.
• We routinely use antibiotic impregnated catheters for all shunt operations.
INFECTION AVOIDANCE
• A third tier of antimicrobials is the instillation of intrathecal (intraventricular) antibiotics at the time of the shunt operation.
• This better addresses the possibility of CSF “contamination” at the time of surgery.
• Many of the common skin bacteria associated with shunt infections, such as coagulase-negative staphylococci and Propionibacterium acnes, are highly sensitive to antibiotics, and therefore giving a high concentration of intraventricular antibiotics is likely beneficial.
• Since, we have routinely used intrathecal antibiotics for all higher risk shunt operations (as defined previously).
• The antibiotic solution (tobramycin 8 mg and vancomycin 10 mg in 6 mL of saline) is prepared by the hospital pharmacy in a sterile hood.
INFECTION AVOIDANCE
• A wound breakdown or CSF leak increases the risk for (or is a sign of) shunt infection.
• The importance of planning the incision sites and configurations, so as to not overlie any shunt hardware, cannot be overemphasized.
We do not use monopolar electrocautery (and avoid any coagulation) on skin incisions.
• Meticulous closure of the wounds is also important. For scalp
wounds, after an interrupted layer of absorbable galeal sutures, we routinely close the skin using a 3-0 (or 4-0) running vertical
mattress suture to best appose and align the skin edges.
• Although usually straightforward, shunt placement carries one of the highest complication rates among neurosurgery operations.
• Attention to detail and careful planning and surgical technique can mitigate many risk factors
Shunt Allergies
• True shunt allergies are rare.
• CSF often demonstrates persistent eosinophilia (3% to 36%), with negative cultures.
• Recurrent shunt failure is a common presentation.
• Pathologic examination of the ventricular catheter often
demonstrates mechanical obstruction by inflammatory
debris consisting of eosinophils and multinucleated giant cells.
• There are documented cases of immune responses to unpolymerized silicone in the literature.
Shunt Allergies
• There are several management strategies.
• One is to consider an endoscopic third ventriculostomy and to remove the offending shunt.
• A second is to use a shunt system devoid of silicone, such as a polyurethane shunt system (Medtronic, Goleta, CA).
• We favor the use of hyper extruded silicone components (Medtronic).
• According to the manufacturer, many shunt allergies arise from a reaction to the oils used during the silicone manufacturing. A
second extrusion cycle apparently effectively removes these oils that are othenvise present in trace amounts
RECOMMENDATIONS FOR SPECIFIC CHALLENGING SCENARIOS
• High Protein Concentration or Cell Count in the Cerebrospinal Fluid
• High CSF protein concentration alone does not appear to increase the incidence of shunt obstruction.
• It is the cell count (which is often associated with a high protein concentration) that is more problematic.
• Ideally, the fewer the total cells (specifically white blood cells) the better.
• Issues such as pleocytosis chronicity must be considered; therefore, it is not possible to assign an arbitrary cutoff point for cell number.
• For example, in a patient with coccidioidomycosis meningitis, you may have to accept CSF cell counts in the hundreds
RECOMMENDATIONS FOR SPECIFIC CHALLENGING SCENARIOS
• Patient Undergoing Anticoagulation or Antiplatelet Therapy
• We make every effort to normalize the clotting profile before shunt implantation.
• Aspirin is stopped at least 8 days before surgery, whereas clopidogrel (Plavix) is stopped 14 days before surgery.
• Warfarin (Coumadin) therapy is reversed and, if necessary, enoxaparin (Lovenox) is temporarily prescribed and then discontinued 24 hours before surgery.
• A normal partial thromboplastin time and international normalized ratio are documented before skin incision.
RECOMMENDATIONS FOR SPECIFIC CHALLENGING SCENARIOS
• Patient Undergoing Anticoagulation or Antiplatelet Therapy
• After surgery, warfarin can be restarted as early as 3 to 5 days postoperatively.
• It is critical to maintain a tightly controlled international normalized ratio
• Aspirin or clopidogrel is restarted 7 to 10 days after surgery.
• In our opinion, combined aspirin-clopidogrel is contraindicated after shunt surgery because of the high risk of subdural hematoma.
RECOMMENDATIONS FOR SPECIFIC CHALLENGING SCENARIOS
• The Hemicraniectomy Patient
• Management of hydrocephalus in a patient with a hemicraniectomy is challenging.
• This hypercompliant state is prone to both shunt underdrainage and overdrainage situations in the same patient, depending on body
position.
• If possible, it is advisable to perform the cranioplasty before the
shunt placement or as soon as possible if a shunt is already present.
• During this cranioplasty, we place multiple central dural tack-up sutures every 2 cm.
• Failure to do so greatly increases the risk of an epidural hematoma once the shunt is placed (or if it is already present).
RECOMMENDATIONS FOR SPECIFIC CHALLENGING SCENARIOS
• Shunt Operations Associated with Other Procedures
• For patients undergoing a lengthy craniotomy (such as for tumor resection), we avoid placing a shunt at the same operation.
• There is typically a higher CSF cell count at the time, and the longer operative time increases the risk of shunt infection.
Continuity Care of the Pediatric Hydrocephalus into Adulthood
• The transition from the pediatric to the adult neurosurgeon can be very stressful for the patient and family because a lifelong bond is seemingly broken.
• Based on our experience, the following observations and recommendations are offered:
• (1) Shunt failure in early adulthood in a patient who has not had a shunt revision since early childhood is frequently a highly
challenging scenario.
• Shunt underdrainage and overdrainage are frequent, and therefore the combination of adjustable DPV and gravitational valves should be considered.
• (2) Always assess for the potential use of ETV. Long-term shunting does not necessarily equate to shunt dependence.
Continuity Care of the Pediatric Hydrocephalus into Adulthood
• (3) Seek guidance from pediatric neurosurgery colleagues, preferably the referring one if possible.
• In a small retrospective study, 10% of pediatric patients had become shunt independent before adulthood.
• Twenty-two percent of shunts remained intact without revision for up to 35 years (mean functional intactness of 23 years).
• Seventy-five percent of patients worked on a daily basis, and 45%
lived independently.77
ROLE OF ENDOSCOPIC THIRD VENTRICULOSCOPY
• There exists a controversy regarding the efficacy of ETV in adult patients with extraventricular (“communicating”) hydrocephalus, particularly in NPH.
• In a 2008 multicenter clinical trial, Gangemi and colleagues
reported a nearly 70% rate of (marginal) clinical improvement, with a low complication rate, in patients with communicating NPH
treated with ETV.
• This study was criticized because their patients had not
systematically undergone a lumbar drainage trial preoperatively, and therefore the extent of expected improvement was not known.
• In a recent randomized clinical trial comparing ETV to VP shunt for NPH, Pinto and associates reported that VP shunt is a superior
method because it had better functional neurological outcomes 12 months after surgery.
ROLE OF ENDOSCOPIC THIRD VENTRICULOSCOPY
• As mentioned previously, evidence of physical ventricular
obstruction should be sought in all patients to assess whether ETV is an option.
• Even if the ETV results in shunt independence, theoretically the conversion of ventricular to extraventricular hydrocephalus should lower the risk for subdural hematoma formation by more evenly equalizing the intraventricular and subarachnoid pressures
following the ETV.
• With regard to ETV technique in adults, principally it is the same.10 Video 31-3 demonstrates the technique we use.
Dr. Mohammad Hallajnejad
Dr. Mohammad Hallajnejad