CSF dynamics, shunt recent advances

1. Shunts For Hydrocephalus
By: Dr. Shahnawaz Alam
Moderated By: Dr. Vikas C. Jha

2. Introduction:
• Hydrocephalus(HCP) frequently occurs as a consequence of complex congenital
anomalies or as a complication of prematurity.
• It results from an accumulation of CSF within the ventricular system of the brain and,
with the possible exception of overproduction of CSF in the case of the very rare tumor
derived from the choroid plexus, it is always related to an obstruction of flow.
• After SAH from head trauma, bleeding from aneurysms, or neonatal IVH, many patients
develop a mild degree of HCP that is diagnosed by imaging studies but later may be
found to resolve or stabilize without intervention.
• HCP is indisputably associated with developmental delay, cerebral palsy, neurological
deficits, and cognitive disorders.

3. • Thorough understanding of the cause-and-effect relationship of HCP to brain
dysfunction rather than as a result of the cause of HCP itself is essential in making
treatment decisions for this relatively common condition.
• Unfortunately, this understanding is often elusive or completely unknown and decisions
must be based on predictions of risk.
• Treatment of HCP must be individualized in a variety of ways. The specific risks to brain
function and development must be assessed as a function of the severity of the
hydrocephalus itself, the sensitivity of the brain of the individual patient, and the
pathophysiologic mechanisms that have created the condition.
• It is also necessary to communicate to the patient or family the expected outcome of
the available treatments, including continued observation.
• The clinician’s definition of successful treatment and the patient and family’s definition
of success of the treatment of this most chronic of diseases must correlate closely.

4. Epidemiology
• The management of hydrocephalus with CSF shunts is the MC neurosurgical
problem encountered in the pediatric age group.
• 73% of patients in the International Society for Pediatric Neurosurgery (ISPN)
database who presented for first-time shunt insertion (774 patients) were 6
months of age or less at time of insertion.
• Furthermore, the median corrected age of patients entered in the shunt design
trial (SDT) was 55 days.
• In the endoscopic shunt insertion trial (ESIT) the median corrected age of patients
was less than 3 months.

5. • Using data from US based on epidemiologic databases, including discharge diagnoses,
procedure codes, and Bureau of Census data obtained from interviews and estimates
from shunt manufacturers, Bondurant et al. studied the economic impact of
hydrocephalus on the health care industry.
• In the US 69,000 discharges/year were related to HCP, and 36,000 initial shunt
procedures were performed. Furthermore, there were 14,000 shunt revisions,
representing 42% of the total number of shunt procedures performed.
• They estimated that the cost of care for patients requiring shunts was more than $100
million; almost half of that cost was for shunt revision.
• The cost of caring for adults and children with hydrocephalus in the United States has
been estimated to be $1 billion.

6. CSF Dynamics:
• CSF is produced by two mechanisms. Both sources of CSF
flow into the ependymal-lined spaces (ventricles and
central canal of the spinal cord), pass through a series of
channels, and exit the ventricular system via the foramina
of the fourth ventricle, which is through the foramina of
Luschka (paired) and Magendie (single).
• The CSF then flows by bulk flow into the spinal
subarachnoid space and up over the convexities of the brain
to be absorbed into the large intracranial venous sinuses.
CSF pathway

7. Hydraulic model of the physics of
CSF flow as a circuit diagram
• A hydraulic circuit of the circulation of CSF
as it is produced from arterial blood at
arterial blood pressure within the choroid
plexuses and within the substance of the
brain and spinal cord as a byproduct of
metabolism of CNS.
• When the CSF reaches the distal recesses of
the pathway, it either distends the
container, as in the lumbar theca where
distension occurs by displacement of the
epidural veins, or is absorbed into the
venous sinuses.

8. • Physiologic studies of ICP and its relationship to pressure in the dural venous sinuses
consistently show a 5 to 7 mm Hg pressure differential between ICP and pressure in
the dural venous sinuses.
• This difference suggests that a valvular mechanism restricts flow between the CSF
pathways and the dural venous sinuses.
• The absorption of CSF does not require energy; there are several alternative pathways
for the absorption of CSF, including otherwise unrecognized lymphatic drainage into
the cervical lymphatic chain and paranasal sinuses and flow outward with the
cranial and spinal nerves.
• Wherever CSF is absorbed, it finally returns to the right atrium via the superior
vena cava.
• Portnoy et al. shown that the cortical veins also play a significant role in
maintaining normal ICP. Cortical veins join the dural venous sinuses at such an
angle that a valvular mechanism is created. Similar to the valvular mechanism
between the CSF and dural venous sinuses, the cortical veins maintain a
pressure differential of 5 to 7 mm Hg within the intracranial compartment.

9. • Arterial blood enters the intracranial compartment into the choroid plexuses where
CSF is produced by an energy-requiring process. This CSF is produced at a pressure of
5 to 7 mm Hg or normal ICP.
• Most of the CBF, which represents ~20% of total cardiac outflow, flows through the
cerebral circulation system and provides oxygenation and nutrition to the brain. It
enters the brain at the level of arterioles, which are the primary resistance elements
to control CBF. These vessels are responsible for cerebral autoregulation.
• Because of CNS metabolism, 20 to 50% of CSF is produced. It flows through the white
matter to pass through the ependymal surface into the ventricles where it mixes with
choroidal CSF.

10. • CSF flows through a series of channels and eventually reaches the intracranial
venous sinus. From there it flows into the superior vena cava and eventually
returns to the heart as venous blood to complete the circuit.
• CSF is produced at a rate of ~0.3 cc/min, and CBF is ~1000 cc/ min. Therefore, CSF
dynamics represent a very small component of total ICP dynamics.
• The final important factor in defining normal CSF dynamics relates to the bipedal
nature of humans and the amount of time that they spend in an erect position.
Humans are subject to hydraulic forces when they assume an erect position. The
venous blood in the cortical veins and dural venous sinuses rapidly drains into the
jugular veins.

11. • When a person assumes an erect position from a lying position, the CSF in the head
tends to drain into the spinal subarachnoid space. After overcoming an intrinsic
resistance to accept the drainage of the intracranial CSF, the lumbar thecal sac
distends but at the expense of the dural venous sinuses.
• Jugular veins are unique among the venous structures in the body because they have
no valves. Theoretically, when a person assumes an erect position, the jugular veins
and dural venous sinuses drain until they are empty or until they have reached a
degree of negativity consistent with the distance between the height of the head and
the height of the right atrium.

12. • As soon as the pressure within the jugular veins in the neck becomes the same as
atmospheric pressure, the veins collapse and flow through these structures ceases.
At the point where jugular vein pressure becomes negative, all CBF diverts to the
azygos vein, which exits the skull and is known to have valves.
• Thus, the natural CSF pathway contains a valvular mechanism for the absorption of
CSF. The inlet (CSF pathway) and outlet (dural venous sinuses) are linked
geometrically. They move together so that the absolute pressure differential
between the two compartments remains the same regardless of the body’s
position. In this scenario, normal ICP in a recumbent position is between 5 and 15
mm Hg. In the erect position it is -5 to +5 mm Hg relative to atmospheric or right
atrial pressure.
• Therefore, the major challenge in the management of hydrocephalus is to
recreate the natural dynamics of CSF physiology.

13. Noncellular components
 In normal adult CSF, there are 0–5
lymphocytes or mononuclear cells per
mm3, and no polys (PMNs) or RBCs.
 In the absence of RBCs, 5–10 WBCs per
mm3 is suspicious, and >10 WBCs per
mm3 is definitely abnormal.

14. Comparison of Pediatric and Adult Hydrocephalus
• There are significant differences between the pathophysiology of hydrocephalus in
children and in adults.
• In adults, the causes of hydrocephalus are limited; it is related to a tumor, a
hemorrhage, or infection in most cases.
• After shunting and improvement in the patient’s clinical condition, the size of the
ventricles may or may not decrease, depending on the patient’s age and chronicity of
the condition.
• If an adult is shunted the ventricles may decrease in size or stay the same. If the ven-
tricles respond by decreasing in size after a shunt is placed they will definitely increase
in size at the time that the shunt fails. It is therefore possible to diagnose shunt failure
on the basis of change in ventricular size.

15. • Complex birth defects in infants lead to unusual patterns of obstruction and unusual
sets of symptoms at the time of shunt failure.
• In spina bifida, there are four potential sites of obstruction. Each site of obstruction
can lead to unique modes of presentation initially and at the time of shunt failure.
Potential sites of obstruction to the
flow of CSF in patients with spina
bifida

16. 1. Closure of the aqueduct of Sylvius from upward herniation of the cerebellum
through an incompetent tentorium leads to overt hydrocephalus at birth and
rapid progression of symptoms and ventriculomegaly at the time of shunt
failure.
2. Obstruction of the outlet foramina of the fourth ventricle can lead to hand
dysfunction, and scoliosis related to syringomyelia.
3. Obstruction to CSF flow from the spinal to cortical subarachnoid space can
lead to insidious shunt failure with ventriculomegaly and few signs of
increased ICP. In this situation the patients can be found on routine
neuroimaging studies to have significant unexpected ventricular dilatation
with no overt symptoms. These patients will often have exhibited a decline in
school performance, severe behavioral disturbances, and staring spells.
4. Finally, infants with the Chiari II malformation can have venous hypertension
due to the presence of the torcula at the level of the foramen magnum. These
patients will have hydrocephalus in infancy; however, later in life, they develop
a form of pseudotumor with severely increased ICP without ventriculomegaly.

17. Diagnostic Tests
• The decision to treat hydrocephalus is usually precipitated by the observation of
ventricular enlargement.
• In the baby with an open fontanel, ultrasound will quite readily determine if there is
obvious ventriculomegaly. The addition CT or MRI scans will vary depending on the
center and the clinical characteristics of the patient being considered.
• Most surgeons prefer a CT scan or an MRI prior to shunt insertion to assess the
morphology of the ventricles (including cysts and compartments) and the condition
of the surrounding brain.
• The exception is hydrocephalus associated with myelomeningocele; some surgeons
will shunt these patients based on the ultrasound alone.

18. • VM may be due to hydrocephalus or atrophy of surrounding brain tissue. The
differentiation between these two conditions is crucial when deciding to place a shunt.
• Increasing head circumference or signs of raised intracranial pressure (ICP) make the
differentiation straight forward.
• The radiographic parameters that suggest hydrocephalus rather than atrophy have been
nicely summarized: (1) dilated temporal horns, (2) enlarged anterior and posterior
recesses of the third ventricle, (3) downward displacement of the floor of the third
ventricle, (4) dilatation and rounding of the frontal horns, (5) effacement of the sulci,
and (6) periventricular interstitial edema.
• In addition, inferiorly displaced cerebellar tonsils seen on sagittal MRI may indicate
raised intracranial pressure.

19. HCP is suggested when either:
1. size of both temporal horns (TH) is ≥2 mm in width; in the absence of HCP, TH
should be barely visible), and the sylvian & interhemispheric fissures and cerebral
sulci are not visible OR
2. both TH are ≥2mm,and the ratio FH> 0:5 (where FH is the largest width of the
frontal horns, and ID is the internal diameter from inner-table to inner-table at this
level

20. Other features suggestive of hydrocephalus:
1. Ballooning of frontal horns of lateral ventricles (“Mickey Mouse” ventricles) and/or
3rd ventricle (the 3rd ventricle should normally be slit-like).
2. Periventricular low density on CT, or periventricular high intensity signal on T2WI on
MRI suggesting trans-ependymal absorption of CSF (note: a misnomer: CSF does not
actually penetrate the ependymal lining, proven with CSF labeling studies; probably
represents stasis of fluid in brain adjacent to ventricles).
3. Used alone, the ratio:
4. Evans ratio: ratio of FH to maximal biparietal diameter (BPD) measured in the same
CT slice: >0.3 suggests hydrocephalus.
5. Sagittal MRI may show thinning of the corpus callosum (generally present with
chronic HCP) and/or upward bowing of the corpus callosum.

21. Indications for a Shunt
• Ventriculomegaly either in a baby who presents with irritability, vomiting, a full
fontanel, splayed sutures, and increasing head circumference, or in an older child who
presents with headache, vomiting, and papilledema, poses no therapeutic dilemma.
Such children have raised intracranial pressure in need of treatment.
• Other children, however, often present with milder symptoms, signs, or unimpressive
imaging studies. In these patients, the decision is more difficult.
• Some authors feel that asymptomatic mild or moderate ventriculomegaly does not
need treatment. The definition of symptomatic, therefore, becomes very important.
• McLone et al define compensated hydrocephalus as untreated hydrocephalus that is
clinically and radiographically stable. Children with a stable clinical course and ventricle
size who are older than 5 years may be followed without a shunt, but do require
frequent testing of their intellectual development.

22. • Children who are less than 5 years old, and particularly those less than 3 years old,
who have anything more than mild hydrocephalus should be shunted.
• This younger group is difficult to assess for intellectual development, and mere
attainment of developmental milestones is insufficient to determine ultimate
intellectual function. Measurement of lumbar opening pressure may be helpful in
some cases.
• MRS has been suggested as a method of differentiating atrophy from hydrocephalus.
• Brain lactate levels were more commonly elevated and N-acetylaspartate/creatine
ratios were low in children with atrophy compared with those with hydrocephalus.
• Documentation of a progressive problem is a key factor in the decision. This may
include progressive developmental or cognitive delay. The most difficult decision is in
the young child with compensated hydrocephalus and moderate to severe
ventriculomegaly.

24. Disease-Specific Considerations
1. Post-traumatic Ventriculomegaly
 Marmarou et al. followed 75 patients whose head injuries resulted in a GCS of 8 or
less. Based on the size of the frontal horns, the ICP, and the resistance to CSF
absorption (measured with a lumbar infusion test), they classified patients as having
normal intracranial pressure, benign intracranial hypertension, atrophy, normal
pressure hydrocephalus, or high pressure hydrocephalus.
 They advocated shunting patients in the last two groups; 4 of 15 such patients
were shunted. All four improved one level on the GCS.
 SAH on the baseline scan was more common (70% versus 16%) in patients with
hydrocephalus.

25. 2. Posterior Fossa Tumor
• Routine pre-op shunting of tumor patients is no longer common practice because
many patients remain shunt free after tumor removal.
 Dias and Albright reported a series of 58 patients with posterior fossa tumors and
HCP. 25 patients were shunted preoperatively, 17 had EVDs and 16 had no
preoperative ventricular catheterization. 24of the 33 patients not initially shunted
remained shunt free at long term follow-up. Using a Cox regression model two factors
were associated with shunt insertion: subtotal tumor resection and incomplete dural
closure at surgery.
 Lee et al. studied 42 children (<20 years old) with newly diagnosed posterior fossa
primitive neuroectodermal tumors who did not have shunts at the time of surgery
and who survived the perioperative period. 17 patients (40%) required a shunt by 4
weeks postoperatively and an additional 2 patients required late shunting at the time
of tumor recurrence. The shunted group was younger (5.4 years versus 10 years), had
more severeHCP, and had more extensive tumors.
• At present, a shunt should be withheld in the pre-op phase, unless a significant delay
between presentation and surgery is expected. Even then a temporary EVD or a third
ventriculostomy may be preferable to a shunt. Many children with a posterior fossa
tumor have resolution of their HCP with tumor removal alone.

26.  Sainte-Rose et al. have reported their results from management of HCP in a
consecutive group of 206 children with posterior fossa tumors. Only 4 of 67 patients
(6%) who underwent preoperative third ventriculostomy developed progressive
hydrocephalus requiring treatment, compared with 22 of 82 patients (28%) who had
conventional treatment preoperatively.
 This is interesting; however, in our opinion it does not justify the risk of doing a
preoperative third ventriculostomy in all posterior fossa tumor patients,
because a significant number will not need any treatment for HCP. An ETV may
be considered for patients who appear drain dependent after tumor removal,
but in our experience, most of these patients eventually require a VP shunt.

27. 3. Myelomeningocele
• Several studies are available regarding the timing of shunting in children with a
myelomeningocele. The reported advantages of simultaneous shunt insertion and
back closure are a shorter hospital stay and a decreased incidence of back wound
problems.
• However, the disadvantages of simultaneous surgery are an increase in the infection
rate and the failure rate of the shunt. There is also the risk of committing some
children to a shunt who may have not needed one.
• At present, both approaches are used, and a clear advantage of one over the other
has not been demonstrated.

28.  Caldarelli et al. compared simultaneous shunting to delayed shunting in 89 children
with myelomeningocele treated between 1980 and 1994. One-year failure rates in the
simultaneous and delayed shunt insertion groups were 31% and 47%, respectively;
infection rates were 23% and 7%. Six patients had a shunt inserted first and underwent
delayed back closure; 5 of them (83%) had a shunt infection.
 At the University of Pittsburgh, 69 new myelomeningocele patients underwent back
closure and either simultaneous (n = 21) or delayed (n = 48) shunt placement between
1987 and 1993.17 The two groups were similar in terms of head circumference, but no
other comparative information is given. There were 8 children with CSF leak from the
lumbar wound in the delayed group and none in the simultaneous group. The rate of
obstruction, however, was higher in the simultaneous group, so the overall
complication rate was not significantly different between the groups. The infection rate
was not different between the groups (1 of 21 and 2 of 48). The authors concluded that
simultaneous repair led to shorter hospitalizations and lower back wound morbidity.

29. Shunting
• The shunt was a technical miracle, providing life-saving treatment and a near-normal
existence for a large number of patients, the need to keep the shunts working and
without complication created an entirely new set of challenges.
• Since the invention of the first implantable shunt valve by Nulsen and Spitz almost 50
years ago, there have been innumerable innovations and new designs of shunt
equipment to treat pediatric and adult HCP.
• Shunts have made a dramatic impact on a previously devastating disease. Despite the
rational and seemingly more physiological designs of these new devices,
complications related to shunts continue to plague.
• The goals of the treatment of hydrocephalus:
1. To decrease ICP and therefore save the patient’s life;
2. To protect the brain from deterioration in neurologic function;
3. To maintain open CSF pathways to allow the free flow of CSF among various compartments;
4. To create an environment of CSF production, absorption, and flow that most closely mimics
the natural dynamics of the CSF; and
5. To minimize the need for intervention throughout the life of the patient.

30. • These devices have numerous mechanisms to prevent overdrainage, including the
collapse of a membrane at a stage when the pressure falls below atmospheric
pressure (anti-siphon devices, Integra, Plainsboro, NJ; siphon-control devices
including the Delta and Strata Valves, Medtronik PS Medical, Minneapolis,
Minnesota), devices that restrict the flow of CSF to slow flow (Orbis-Sigma and
Elekta-Cordis Horizontal-Vertical Valves; Medtronic PS Medical, Minneapolis,
Minnesota; and Codman Siphonguards, Codman & Shurtleff, Raynham,
Massachusetts), and various forms of gravity compensating devices (GAVI and HV
Valves [Integra, Plainsboro, New Jersey], and the CRX Diamond Valve [Phoenix
Biomedical Corp., Valley Forge, Pennsylvania].

31. Shunt versus Third Ventriculostomy
• Unfortunately, patient selection remains a challenge because there is no simple, non-
invasive test to assess adequacy of CSF absorption.
• In general, patients who have late-onset hydrocephalus from aqueductal stenosis do the
best after third ventriculostomy, presumably because they had normal CSF absorption
prior to blockage at the aqueduct.
• The surgical goal is to create an opening in the floor of the third ventricle between the
infundibular recess and the mammillary bodies. This creates a free-flowing
communication between the ventricular system and the basal subarachnoid spaces.
• Endoscopic third ventriculostomy is an option for ~25% of children with hydrocephalus.
The remaining majority, however, will still require a shunt.

32. Schematic diagram demonstrating the foramen of
Monro and the surrounding structures.
• The trajectory of the endoscope for ETV, with the fenestration between
the mammillary bodies and the infundibular recess.
• The surgeon must keep in mind the proximity of critical vascular
structures to the floor of the third ventricle, including the basilar artery
and perforating arteries in the interpeduncular cistern.
Superior view of the floor of the lateral ventricles
• Note that in the right lateral ventricle, the
thalamostriate vein is to the right of the choroid
plexus.
• Also note that the fornix forms the superior and
anterior boundary of the foramen of Monro.

34. Equipment
• VP shunts are composed of three basic
elements: a ventricular catheter, a
valve, and a peritoneal catheter. There
are many variations of each of these
components available on the market.

35. 1. Ventricular Catheter
• Barium impregnated Silastic tubes that enter the ventricle are available in several
configurations. Several different transverse diameters are available, but the
difference is primarily in the wall thickness because the internal diameter is almost
identical.
• Right-angled ventricular catheters are also available, but they are somewhat limiting
because the intracranial length is fixed. If right angled catheters are used, it is
necessary to have several catheters of different lengths available for different clinical
situations.
• Another consideration is whether the ventricular catheter should be a separate or
integral part of the valve mechanism. When the ventricular catheter is inserted, if
bleeding occurs, it is best to allow drainage of fluid through the ventricular catheter
prior to attaching it to the valve. With an integral ventricular catheter and valve, this
is not possible; the blood and cellular debris can potentially occlude the valve
immediately.

36. 2. Valves
• Most modern valves can be grouped into several categories based on their
hydrodynamic characteristics, differential pressure valves, siphon-resisting valves,
flow-regulating valves, and adjustable valves.
Differential Pressure Valves
• It has been available for the longest amount of time, and surgeons have accumulated
the most experience with this type of valve.
• These valves open when the pressure difference across the valve exceeds a
predetermined threshold. The valve then remains open, and during this time it has a
very low resistance to flow.
• When the pressure difference drops below the predetermined threshold, the valve
closes again and flow stops.
• When the patient is in the upright position, a large differential pressure between the
head and the abdomen develops from the long column of water in the shunt tubing.
The valve therefore opens, and fluid flows until the pressure in the head is excessively
negative. This phenomenon is called siphoning, and it is thought to be responsible for
over-drainage and its associated complications.

37. A schematic diagram illustrating the siphoning effect in patients with
shunts
Valve dynamics predominate in the supine position; hydrostatic effects predominate in the
upright position.

38. In a standard differential pressure valve, flow
increases rapidly once the opening pressure is
exceeded.

39. • The differential pressure valves are available in low, medium, and high opening
pressures. In general, low-, medium-, and high-pressure valves refer to opening
pressures of ~5, 10, and 15 cm of water, respectively.
• Unfortunately, however, there are no uniform standards for these designations, and
the manner in which the pressure is measured is variable.

40. Siphon-Resisting Valves
• The Delta valves (Medtronic Neurosurgical, Goleta, California) contain a device that
is designed to reduce flow as the patient assumes the upright position (i.e., when
siphoning occurs).
• Similar mechanisms are available as separate components that can be added to
other shunt systems (e.g., V. Mueller Heyer-Schulte anti-siphon device [Integra,
Plainsboro, New Jersey] and Medtronic Neurosurgical siphon control device).
Delta (Medtronic
Neurosurgical, Goleta,
California) valve consists
of a standard differential
pressure valve (diaphragm
type) followed by an anti-
siphon device to reduce
the effects of gravity when
the patient is upright.

41. Flow-Regulating Valves
• The Sigma valve (Medtronic Neurosurgical, Goleta, California) consists of a flexible
diaphragm that moves along a piston of variable diameter resulting in three pressure
flow stages.
1. The valve functions similar to a differential pressure valve.
2. In stage two, as the ventricular pressure increases, the diaphragm descends along the piston
whose diameter progressively enlarges. This reduces the flow orifice and dramatically
increases the resistance to flow. A very small increase in flow rate results despite a
progressive increase in pressure.
3. Stage three is a high pressure safety release mechanism that results in open flow when the
pressure in the ventricular catheter reaches ~40 cm of water. The diaphragm at this point is
beyond the end of the piston and resistance is very low.
The Cordis-Orbis Sigma
(Medtronic Neurosurgical,
Goleta, California) valve is a
flow-limiting valve.

42. Externally Adjustable Valves
• Recently, shunt systems incorporating an adjustable valve have been developed, which
enable the surgeon to make non-invasive alterations in the valves pressure/flow profile
as the patient’s clinical course changes.
• Unlike traditional valves, however, programmable valves may be percutaneously
adjusted using an external magnet or a special programming tool that works via a
magnetic field.
• This may be advantageous in patients with normal pressure hydrocephalus, in
patients with arachnoid cysts, and in patients with complications caused by acute
or chronic over-drainage such as subdural hygromas, chronic subdural
hematomas, and the slit ventricle syndrome.
• In pediatric patients, closure of the sutures, attainment of erect posture, growth,
and aging are all additional situations in which the opening pressure of the valve
might require adjustment.

43. Programmable shunt valve
designs
Both the Strata (Medtronic
Neurosurgical, Goleta,
California) (A) and the Codman-
Medos (Codman & Shurtleff,
Raynham, Massachusetts) (B)
valves allow percutaneous
adjustment of the valve
pressure using an external
magnetic tool.

52. • A randomized clinical trial did not demonstrate any survival benefit of the Codman-
Medos (Codman & Shurtleff, Raynham, Massachusetts) programmable valve over
standard valves.
• Although a clear advantage to adjustability has not yet been demonstrated in terms of
shunt survival, many surgeons find this feature desirable in an attempt to relieve
symptoms, maintain large ventricles, or deal with small fluid collections.
• The ability to adjust the valve pressure noninvasively, and thus potentially minimize
subsequent operative manipulations of the shunt system, may warrant the increased
expense and complexity of the programmable system.

53. 3. Reservoir
• A reservoir is very commonly used; it may be incorporated as part of the valve or
added separately. It is usually placed near the valve or at the burr hole.
• It is useful for access to the CSF for diagnosis of infection and occasionally for removal
(or attempted removal) of CSF in emergent situations.
4. Peritoneal Catheter
• Peritoneal catheters are also Silastic and impregnated with barium to make them
radiopaque. The length is suitable for adult insertion, but the catheter can be
shortened for use in the child if necessary.
• In most cases, a full-term baby can accept nearly the full length, so elective
lengthening is unlikely to be necessary. The catheters have an open distal end, and
some have distal ports on the side.
• Peritoneal catheters are also available with a closed distal end and slits in the side of
the tubing (distal slit valves), which function in a differential pressure fashion.

54. Antibiotic-Impregnated Shunt Systems
• Recently, an antibiotic-impregnated shunt system was evaluated in a prospective,
randomized clinical trial to determine if it reduced the incidence of shunt infections
compared with standard shunts.
• After a median follow-up of 9 months, 10 of 60 in the control group and 3 of 50 in the
antibiotic-impregnated shunt group developed infections (p = .08).
Choosing the Appropriate Equipment
• The amount of evidence that is available for choosing shunt equipment is limited.
Probably the best advice is for a surgeon to become familiar with one system and use it
consistently.
 A multi-center trial has compared a differential pressure valve, a siphon-resisting valve
(Delta valve; Medtronic Neurosurgical, Goleta, California), and a flow-regulating valve
(Orbis-Sigma valve; Medtronic Neurosurgical, Goleta, California) for children with newly
diagnosed hydrocephalus. No significant difference was found in the time to first shunt
failure among the three systems.

55. Surgical Technique
Positioning
• The patient is positioned under GA
with the head rotated to the side
opposite of the proposed shunt. The
neck should be extended with a bolster
under the neck and shoulder so that
there is almost a straight line between
the scalp and abdominal incisions

56. Ventricular Catheter Placement
Head Entry Site
• The ventricular catheter may be inserted through a posterior parietal or a coronal burr
hole. The relative merits of these two have been debated in the past. Data from a
nonrandomized study with 10-year follow-up from Pittsburgh suggested improved shunt
function following coronal placement.
 A randomized trial compared these two entry sites. At 14-months follow-up, 59% of the
shunts inserted through an anterior burr hole continued to function throughout the
study compared with 70% of shunts inserted through a posterior burr hole. This
difference was not statistically significant, however, and the authors concluded that
anterior placement did not offer any advantage over posterior placement.
• Recently, anterior placement has been supported by some surgeons as the preferable
method when endoscopic insertion is being performed. An anterior approach may allow
better visualization of the foramen of Monro and catheter placement through an
intraluminal endoscope.

57. • Its disadvantage is that it usually requires an additional skin incision behind the ear
because it is difficult to make a direct subcutaneous tract from the coronal incision to the
site of the distal catheter.
• The scalp incision should be placed such that the shunt hardware does not lie directly
underneath it, particularly in younger patients with thin scalps. This helps to reduce the
risk of erosion of the shunt through the incision. If a linear incision is desirable, it should
be of sufficient length so the tissue can be retracted and the burr hole made medial or
lateral to the incision. A curvilinear incision is another possible option.
• When making the opening in the dura, care should be taken to make the opening just
large enough to allow passage of the ventricular catheter. This will decrease the chance of
CSF leak around the tubing. One method to create a small dural opening is to place a
small brain needle against the dura and apply low-intensity monopolar coagulation to the
needle.

58.  Pre-op patient positioning. (a)
Patient supine with head rotated to
left. Anatomical landmarks: anterior
fontanelle, incision, and midline are
marked. (b) Scalp incision showing
dura overlying anterior fontanelle.
 Tunneling between coronal and
retro-auricular incision. (a)
Coagulation of the soft tissues
performed to facilitate passage of
the plastic sheath. (b) Hemostat
used to pull plastic sheath through
incision to avoid excessive
dissection.
 Illustration of the mini-laparotomy
technique for distal peritoneal tube
placement. Hemostat forceps are
used to localize individual layers of
the abdominal cavity until the
peritoneum is reached. A small
incision is made in the peritoneum
until bowel or omentum is
visualized.

59. Location of the Tip
• To minimize the chances of proximal obstruction, the ventricular catheter tip should
be placed away from the choroid plexus.
• Most surgeons choose the frontal horn, but based on their review of 1719
hydrocephalic patients in Toronto and Paris, Sainte-Rose et al prefer the atrium. In
their series, the likelihood of ventricular catheter obstruction was lower when the
catheter was placed posteriorly in the atrium of the ventricle via an occipital route.
 In a randomized trial, Steinbok et al. compared placement of the ventricular
catheter tip on the ipsilateral and contralateral sides of the ventricular system.
When the surgeon’s intention was to place the catheter in the contralateral
ventricle, 29% of patients developed ventricular asymmetry in follow-up compared
with 48% with ipsilateral placement. When the analysis was based on the final
location of the catheter (despite the surgeon’s intentions), the asymmetry was seen
in 23% of the contralateral catheters and 54% of the ipsilateral catheters. There was
no difference, however, in the shunt-revision rate in the two groups.

60. Loculated Hydrocephalus
• This relatively uncommon entity occurs when the ventricular system becomes obstructed
by septations or cysts that develop congenitally or after hemorrhage, infection, or surgical
trauma.
• It is particularly difficult to deal with, as there can be numerous septations within the
ventricular system that inhibit the drainage of cerebrospinal fluid.
• These patients sometimes end up with multiple intracranial catheters and/or multiple
shunt systems. Complex shunt systems (incorporating 3-way connectors or consisting of
multiple linear shunt systems) have been shown to have a much higher failure rate than
simple, linear shunts.
• With the currently available endoscopic equipment, it is often advantageous to attempt
fenestration of the septations or the septum pellucidum to allow communication between
the loculated compartments.
• Endoscopic fenestration can help reduce the rate of shunt revision, simplify existing shunt
systems, and in some cases, avoid placement of shunts.
• MRI provides the necessary anatomic detail, but a CT dye study remains the best
preoperative imaging study to verify lack of communication with the ventricular system
and delineate CSF compartments.

61. Adjuncts to Placement
Ultrasound
• In a child with an open fontanel, ultrasound provides an excellent means by which to
visualize the ventricular system and observe the ventricular catheter as it is being
inserted.
• A small amount of movement of the catheter is sometimes helpful; when this is done,
the surgeon can usually identify the position of the catheter with respect to the
ventricular system.
Endoscopy
• Endoscopes are now available that fit into the lumen of the ventricular catheter. These
allow visualization of the ventricular system as the catheter is being inserted. The goal
when using such equipment is to place the catheter away from the choroid plexus,
which is thought to decrease the incidence of obstruction.

62. Distal Catheter Placement
Peritoneum
• This is the preferred location of the distal catheter and the most commonly used. The
rationale for this preference is that it is technically easy to gain access to the peritoneal
cavity, and the peritoneum is extremely effective in absorbing CSF.
• It may be accessed via an open, small laparotomy at which time the peritoneum is
identified and opened for catheter placement. A purse string suture is placed around
the catheter as it enters the peritoneum.

63. Alternate Distal Sites
• Children with multiple abdominal operations, active abdominal infection (including
necrotizing enterocolitis in the preterm infant) or chronically elevated intraabdominal
pressure may require extraperitoneal shunt insertion.
• These incudes : Atrium/Pleural Cavity/Gallbladder
Postoperative Care
• Children are usually placed with the head slightly elevated.
 Sainte-Rose et al. recommended wrapping of the head with light compression to the
cranial wound to minimize the collection of CSF around the shunt in the early
postoperative days.

64. Shunt Failure
Epidemiology of Malfunction
• Many articles have been written on shunt malfunction. They report a remarkably
consistent failure rate of 30 to 40% within the first year.
 DiRocco et al. published the results of a cooperative survey of ISPN members. 38
neurosurgical centers submitted data on 773 patients. 220 (29%) patients required a
shunt reoperation in the first year.
 Although a univariate analysis of risk factors for shunt failure was performed
with data gathered over a vague time period, the findings were as follows:
1. 34% of shunts inserted at emergency surgery failed compared with 29% of shunts
inserted electively;
2. failure rates were the same for surgeons and residents;
3. unconscious patients had a 40% failure rate compared with 30% when consciousness
was not impaired;
4. distal shunt insertion by open laparotomy had a 32% failure rate compared with 24%
failure rate when a trocar was used;
5. infection rate was 6.7% for patients who received prophylactic antibiotics and 4.5%
for the patients who did not receive prophylactic antibiotics; and
6. the failure rate for shunts inserted in the first 6 months of life (35 to 47%) appeared
to be substantially higher than that for children over 6 months of age (14%).

65.  In a detailed review of his extensive experience, Piatt et al. reported on 727 shunt
operations over a 13-year period.
 Among the 671 simple linear shunts, the failure rate was 32% at one year. Simple
shunts had better survival than complex shunts. Age was a significant risk factor
for failure, with children less than 2 years of age being at higher risk than older
children.
 Another interesting finding was that revision of a shunt after a short interval (less
than 6 months) resulted in a higher risk of failure than that of new shunts or
shunts revised after a longer interval.
 The etiology of the hydrocephalus, the duration of the operation, the time of day
of the surgery, and the presence or absence of epilepsy did not have a significant
effect on the risk of shunt failure.

66. Types of Failure
1. Obstruction
• Obstruction to flow can occur at any point along the shunt system; however, it most
commonly occurs at the ventricular catheter. It is MC mechanical complication of shunts,
accounting for 63.2% of mechanical complications in DiRocco’s survey.
• When the type of shunt failure was looked at over time, proximal obstructions and
infections were more common soon after insertion; distal obstructions and disconnections
were more common in late failures.
• Obstruction of the valve is much less common and usually occurs very soon after shunt
insertion or proximal shunt revision. Presumably, valve obstruction is due to cellular
debris or blood that gets into the ventricular catheter, passes into the valve, and obstructs
the valve.

67. 2. Disconnection and Migration
• Although rare, it is possible for the components of a shunt system to disconnect or for the
whole system to move distally so that the ventricular catheter slides out of the ventricular
system. These complications tend to occur soon after shunt surgery, and they are easily
detected on plain radiographs.
3. Fracture
• Fracturing of shunt tubing is almost always a late complication. It is usually observed in
tubing that has been in place for a long time that has become calcified and has
subsequently cracked.
• Commonly, the patient’s shunt will function for a while after the fracture, because CSF will
pass through the fibrous sheath that usually surrounds the shunt tubing.
• Eventually, though, CSF flow fails and the patient presents with shunt malfunction.
• Fractured tubing most commonly occurs in the neck. In one large series, fractures were
observed in 60 of 2065 shunt procedures (3%).

68. Numerous types of shunt complications can occur including shunt fracture (A) and (B),loculated CSF
collections (C),over-drainage leading to subdural collections (D) or slit ventricles (E), and abdominal
pseudocysts (F).

69. 4. Over-drainage : it may either be seen as extra-axial fluid collections or classified as slit
ventricle syndrome(SVS).
Extra-Axial Fluid Collections :
• With the collapse of the ventricular system, extra-axial fluid and/or blood can
accumulate. It usually occur soon after insertion of a new shunt in an older child with
large ventricles.
• Management of these collections can be very difficult; two primary approaches have
been used: (1) decrease or stop the overdrainage, usually by changing the shunt valve
to one with more resistance or to one with a siphon-resisting device, or (2) drain the
extra-axial fluid.
• The second approach may be accomplished by a burr hole and a temporary drain or by
inserting a subdural catheter and connecting it to the existing shunt system below the
valve. This latter option results in drainage of the extraaxial fluid with little or no
resistance.
• In the recent years, use programmable valves in high-risk patients can be done. It
should begin with the valve pressure set toward the higher end (e.g., Codman-Medos
at 150; Strata at 2.0), and then gradually reduce the valve pressure over many months.

70. Slit Ventricle Syndrome :
• Characterized by symptomatic very small ventricles in a delayed fashion after shunt
insertion.
• Their most common complaint is headache. Typically, the symptoms are repetitive or
cyclical in nature and consist of intermittent headaches, nausea or vomiting, and other
signs consistent with elevated intracranial pressure. The symptoms are often related to
posture; patients may report improvement after a period of recumbency. An acute
presentation is also possible with lethargy and coma.

71. Management :
• Even though only a small percentage of children with shunts will develop SVS, their
management is complex.
• Conservative approaches that are appropriate in many cases include observation and
medical therapy.
• In a review by Walker et al, 13 of the 31 (42%) patients with the clinical diagnosis of SVS
were managed successfully without surgical intervention. This approach is reasonable if
the patient’s symptoms are infrequent and do not prevent participation in daily activities.
Antimigraine therapy has appeared as an alternative first step in several articles and
reviews.
• If conservative measures are not sufficient, several surgical approaches have been
described.

72. • In some situations, ICP monitoring may be helpful. Low pressure during symptoms may
respond to upgrading the existing valve, adding a siphon-resisting component,
changing to a flow- control valve, or changing the setting of an adjustable valve.
• Management of patients with high pressure during symptoms is more problematic.
Although cranial expansion and subtemporal decompression have been advocated in
the past, currently shunt revision is preferred.
• Revising the ventricular catheter in such patients can be difficult. Several technical
options have been suggested: (1) dilate the ventricular system under close observation
and ICP monitoring, followed by reinsertion of the ventricular catheter; (2) use
endoscopy, fluoroscopy, or stereotaxis during the revision; or (3) perform an
endoscopic third ventriculostomy.
• Despite these maneuvers, managing such patients remains one of the most difficult
and frustrating tasks in pediatric neurosurgery.

73. 5. Other complications: Loculation/ Infection
6. Mortality
 Sainte-Rose et al. observed a 1.05% mortality rate directly related to shunt failure in
1719 patients over a 10-year period.
• The mortality rate of 12.4% at 10 years has been reported in a series of 907 patients in a
recent study by the Toronto group.
• The only risk factor for death was a history of shunt infection.
Follow-Up of Shunted Patients
• Following shunt insertion or revision, patients are usually reassessed within the first 2 or
3 months and then annually.
• In general, a CT scan is used and babies who start out with ultrasound are converted to
CT scan when their fontanels close.

74. Shunt Revision
• It is probably the most common operation done by pediatric neurosurgeons.
• It is also important for the surgeon to be aware of the shunt system that the patient has in
place so that the appropriate replacement needs are facilitated.
• In addition, the surgeon needs to be familiar with the different flow characteristics
inherent to different shunt systems to interpret the shunt function intraoperatively.
• The preference is to begin by opening the cranial wound, separating the ventricular
catheter above the valve, and assessing the spontaneous flow (or lack thereof) out of the
ventricle.
• Distal runoff through the valve and peritoneal catheter is also assessed with manometry.
Interpretation of the latter maneuver requires knowledge of the valve in place and its
usual expected flow characteristics. If poor runoff is obtained, it is important to then
remove the valve and test the peritoneal catheter by itself to detect blockage within the
valve.

75. • For patients with good runoff but poor flow from the ventricular catheter, the first
maneuver is to remove the old ventricular catheter.
• The ventricular catheter is commonly stuck, and its removal using a Bugbee wire can be
very effective. Passing the Bugbee wire into the ventricular catheter should be done with
care so it is not advanced beyond the tip of the catheter into the brain. The coagulating
and/or the cutting current may be used to free up the adhesions within the ventricular
catheter. The catheter is then gently withdrawn.
• The new system should be available quickly so that the surgeon can insert it without
allowing much CSF to escape. This is particularly important when the ventricles are small.
• Endoscopes are now available that will fit down the ventricular catheter and can
conveniently be used in shunt revision surgery. The goal in such cases is to place the new
catheter in a position away from the site where the old catheter was stuck.

76. • If a valve is being replaced, it is most commonly replaced with one of the same flow
characteristics unless the preoperative decision was to change the valve characteristics.
This is usually not the case for shunt obstruction but may be appropriate in suspected
over-drainage.
• When there is a distal blockage, the whole peritoneal catheter should be replaced from
the valve down to the abdomen. Cutting across the peritoneal tubing at the abdominal
scar and attaching a new piece of tubing at that point with a straight connector results
in the shunt being fixed at this point and predisposes it to subsequent disconnection or
fracture.
• The peritoneal catheter may be replaced using the tunneler for shunt insertion or can
be pulled through the same tract using the old peritoneal catheter or a guide wire.

77. Complications
• Acute complications from insertion of the proximal catheter include hemorrhage
and neurological injury.
• Intra-parenchymal hemorrhage related to shunt surgery occurs in ~1% of cases and
is more common if the old ventricular catheter is removed.
• Hemiparesis is possible if the catheter traverses the internal capsule, but in most
cases this deficit is transient.
• Abdominal visceral or vascular injury can occur after placement of a peritoneal
shunt. Perforation of viscera can occur either at the time of shunt insertion or later
from erosion of the tubing through the visceral wall. Perforations of the stomach,
small and large bowel, bladder, and uterus have been reported.

78. • Pseudocysts are loculated pockets filled with unabsorbed CSF. The cyst wall is a
peritoneal serous membrane thickened by chronic inflammatory tissue rather than by
formed mesothelial tissue, thus a pseudocyst. A low-grade shunt infection with
Staphylococcus epidermidis or Propionibacterium acnes has been identified as the
causative factor in 30 to 100% of pseudocysts; most series reporting a rate of at least
60%.
• In addition to infection, multiple previous abdominal operations and chronically
elevated CSF protein have been identified as risk factors for the formation of
pseudocysts. They usually occur in a delayed fashion, even up to years after the last shunt
operation, and can cause abdominal pain, distention, vomiting, fever, and poor appetite.
• The vast majority of patients with pseudocysts do not show symptoms of shunt
malfunction. Treatment of the pseudocyst requires removal of the peritoneal catheter, at
which time fluid from the pseudocyst can be aspirated in a retrograde manner through
the catheter, and the CSF and tip can be cultured. The pseudocyst typically subsides after
the peritoneal catheter is removed; a laparotomy is rarely required.

79. • With pleural shunts, pulmonary parenchymal injuries, pneumothoraces, and effusions
are the most common complications. Most of these complications can be managed
with observation alone. If pleural effusions become large and symptomatic, serial
thoracentesis or removal of the distal catheter may be necessary.
• Distal components of ventriculo-atrial shunts can cause thrombosis around the tip,
with or without pulmonary embolus. This complication has been reported in up to 40%
of patients with atrial shunts.
• Craniosynostosis is a rare complication of CSF shunting that occurs only in patients
who were shunted before 6 months of age. Surgery is warranted if the child is
developing well and the alterations in the cranial vault are cosmetically significant, or if
there is evidence of raised intracranial pressure in the presence of a working shunt. In
such cases, cranial vault reconstruction may be necessary.

80. Shunt Removal
 Whittle et al. studied 46 children with arrested hydrocephalus.
 30 children had shunts placed previously and at the time of review appeared to be
shunt independent. The diagnosis of shunt independence meant that (1) the shunt
had been clipped or removed, or (2) an isotope shunt study confirmed shunt
blockage and serial neuroradiographic studies had confirmed that HCP was not
progressing.
 All of these patients underwent intracranial pressure monitoring and 24 of the 30
(80%) patients with apparent shunt independence demonstrated intermittent or
persistent intracranial hypertension. 6 of 30 (20%) had normal ICP tracings. Based
on the ICP recordings, all 24 patients had their shunts re-established.
• True shunt independence in children who have had shunts in place is uncommon; thus,
great caution should be exercised in concluding that a child’s shunt does not need to be
fixed. Long-term vigilance with a very low threshold for re-evaluation is warranted, as late
deterioration after a period of apparent compensation and/or shunt independence has
been documented.

81. Late Outcome after Shunt Placement
• Late outcome after shunt placement depends in part on the etiology of the
hydrocephalus.
 Sgouros et al. reviewed 70 patients shunted between 1974 and 1978 who were
followed for a minimum of 16 years.
 Patients were excluded who died before age 16 years or who had tumors or post-traumatic
hydrocephalus. The average age at follow-up was 19.1 years; the average age at shunt
insertion had been 5.1 months (all 2 years or less). 33 of the 201 (16%) shunt-related
operations were performed on the children after the age of 16 years (26 shunt malfunctions
and 7 infections).
 For children with myelomeningocele, 50% attended normal schools and 40% were in special
school settings for the physically handicapped; 10% had mental handicaps that prevented
normal education.
 Patients with meningitis and intraventricular hemorrhage had the worst outcomes, with 30%
and 40% mentally handicapped rates. Two thirds of all patients were socially independent but
living with parents (age-related), 17% were dependent, and the remaining patients were
either independent or married.
 Of the whole population, 14% were either unemployable or required specially structured
work environments. In this study, there were two late deaths and four major complications
related to shunt malfunction and infection.

82. Conclusion
• When deciding that hydrocephalus needs treatment, repeated assessments over time
may be necessary to demonstrate a progressive problem.
• In difficult cases, ICP monitoring may be helpful.
• When choosing shunt equipment, the surgeon should become familiar with one system
and use it consistently.
• After shunt insertion, baseline images should be obtained immediately postoperatively
and at 3 and 12 months.
• Placing the ventricular catheter tip away from the choroid plexus may reduce the
chance of proximal shunt obstruction.

83. THANK YOU
References:
• Youmans and Winn neurological surgery 7th edition
• Ramamurthi & Tandon's textbook of neurosurgery 3rd edition
• Osborn Brain Imaging ; 2nd edition
• Principles and Practice of Paediatric Neurosurgery 2nd edition by A. Leland Albright
• Paediatric Neurosurgery: Tricks of the Trade By Alan R. Cohen