Abstract

With a reported 33,000 shunt placement procedures performed in the US annually, and

a lifetime revision rate approaching 50%, abdominal radiologists must be familiar with the

typical imaging appearance of an array of shunt complications. Complications related to the

peritoneal portion of the shunt have been reported in up to 25% of patients.1

More than 40,000 CSF shunts are placed annually in the United States, the majority of

which are for the treatment of hydrocephalus. Shunt failure occurs in 40–50% of patients

during the first 2 years after shunt surgery. Therefore, radiologists should be familiar with the

radiologic manifestations of shunt malfunction and complications.2

These include ventriculoperitoneal (VP) shunts, lumboperitoneal (LP) shunts, and

ventriculoatrial (VA) shunts. In VP shunts, a catheter is inserted into a non-draining ventricle

and tubing is then tunneled subcutaneously down the thorax before being tunneled into the

peritoneal cavity. In LP shunts, a catheter is inserted into the thecal space between two

adjacent lumbar vertebras before being tunneled subcutaneously around the abdomen and

into the peritoneal cavity. VA shunts, which are rarely created, have a similar origin as a VP

shunt, however rather than being tunneled into the peritoneal cavity, the shunt is terminated

in the right atrium of the heart and contains no intra-abdominal portion.2

Shunts typically consist of three major components:

• An inflow (proximal or closer to the inflow site) catheter, which drains CSF from the

ventricles or the subarachnoid space; this tube leaves the brain through a small hole in the

skull and then runs for a short distance under the skin.

• A valve mechanism, which regulates differential pressure or controls flow through the shunt

tubing; this device is connected to the proximal catheter and lies between the skin and the

skull, usually on top of the head or just behind the ear.

• An outflow (distal or farther away from the inflow site) catheter, which runs under the skin

and directs CSF from the valve to the abdominal (or peritoneal) cavity, heart or other suitable

drainage site

Other shunt components may include reservoirs and/or chambers for CSF sampling or

injecting medications or dyes, on/off devices, anti-siphon or other flow-compensating

devices, or auxiliary catheters to modify performance or adapt the basic system to the

patient’s specialized needs. In selected cases (such as when cysts or subarachnoid fluid

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collections are drained), a shunt may not contain a valve or a very low resistance valve may

be used.

Catheters and tubing

Catheters and tubing divert CSF from the site where there is an excess volume of CSF

to a location within the body where the CSF will be absorbed. The proximal catheter

(ventricular or lumbar catheter) drains excess CSF from the ventricles or the spinal lumbar

sac through rows of small holes at its origin Distal catheters are typically placed in the

abdominal (or peritoneal) cavity, but may also be placed in the heart, pleural cavity (lungs)

and other suitable locations where CSF is drained into the bloodstream. The type of shunt

system is named by the inflow and outflow locations, e.g. if the proximal catheter is in the

ventricle and the distal catheter is in the peritoneal cavity it is called a ventriculo-peritoneal

(VP) shunt.3

Valve mechanisms

To assure that the rate of flow through the shunt is controlled, a valve is placed in the

tubing system.Most valves operate on the principles of change in differential pressure

(DP)—the difference between the pressure at the proximal catheter tip and the pressure at the

drainage end. Neurosurgeons select a DP valve based upon the age of the patient, the size of

the ventricles, the amount of pressure, and other important clinical factors. Most

commercially available fixed DP shunts are provided in three to five ranges: low, medium or

high pressures (and very low and very high), depending on their response to the pressure

differential between the shunt’s upper and lower ends.3,4

Examples of valves

ProGAV Adjustable shunt OSV II® Flow Regulating V

2

Antechambers/Reservoirs

An antechamber is a sampling chamber or reservoir located under the skin between the

inflow catheter and the valve. They can be used to sample CSF in the shunt, inject drugs into

the brain through the proximal catheter, and measure pressure. In addition, these “bubbles”

can be felt through the skin and pumped manually to help keep the shunt open. In general, if

one pushes on the reservoir and it does not spring back, then there might be an obstruction in

the proximal catheter because the reservoir is not filling with CSF. On the other hand, if the

reservoir feels rather stiff and more force is needed to depress it, then the distal catheter may

be clogged. Some clinicians recommend pumping the reservoir periodically to help keep the

shunt open.

Connectors

Short plastic tubes are used to connect catheters with tubing, tubing with valves or

accessories, etc. Typically, such connectors require the surgeon to secure them with a suture

tie during surgery and are weak points that can become loose and disconnect the catheter

Overdrainage Control Devices

Ideal shunt pressure-flow characteristics must match the patient’s specific needs.

However, postural(standing, sitting, or lying down) and vasogenic (blood flow) influences

modify shunt function. Standing posture causes a siphon or sucking effect, essentially

“pulling” fluid out of the brain or lumbar region when the patient stands. During the night,

there are periodic, small increases in blood volume in the head. This nocturnal cerebral

vasogenic wave activity occurs several times a night during sleep. Similar blood volume

increases occur when the patient strains, as during a cough or a bowel movement. These

volume increases, in turn, “push” CSF out of the ventricles through the shunt. The terms

“siphoning”,“overdrainage” and “overshunting”, (often used interchangeably) are not the

same. Siphoning is a purely postural phenomenon.

Overdrainage and overshunting refer to shunting CSF in excess of that required and

may be caused by postural and vasogenic effects. A variety of siphon and overdrainage

regulating devices have been developed to mitigate the effects of CSF overdrainage.

Siphon-resistive devices (SRD

These so-called anti-siphon or siphon-control devices incorporate a silicone membrane

that closes when conditions favoring postural overdrainage are present. Siphon-resistive

devices react to hydrostatic pressure across the two ends of the catheter and close the valve

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(by increasing the valves opening pressure) when the patient assumes a vertical posture. Such

devices tend to create a positive intracranial pressure in the standing position

VP shunts are the most common type of CSF shunts used, accounting for 97.7% of

shunts placed for nontumoral hydrocephalus in one study of over 700 patients 2. VP shunts

are composed of a proximal ventriculostomy catheter, a pressure sensitive valve and reservoir

to regulate CSF flow, and a distal catheter terminating in the peritoneal cavity.Modern shunts

are most commonly placed in the peritoneum, right atrium, or pleural space.

Ventriculoperitoneal shunts are preferred by most neurosurgeons because of fewer

complications and the relative ease of peritoneal access.2

Ventriculoatrial shunts are generally preferred when ventriculoperitoneal shunting is

contraindicated. The right atrium is typically accessed percutaneously via the facial,

subclavian, or internal jugular vein and proper placement may be ensured with the use of

real-time transesophageal echocardiography. The primary disadvantage of ventriculoatrial

shunts is the risk of serious intravascular complications. Ventriculopleural shunts are rarely

used for long-term shunting because of the high incidence of hydrothorax. The most common

uses are temporary CSF drainage during management of ventriculoperitoneal or

ventriculoatrial shunt infection and decompression of acute hydrocephalus before removal of

an obstructing tumor.3

Table 1: Most common shunt systems

Shunt Pathway Shunt type CSF Inflow Location CSF Drainage Location

Ventriculo-peritoneal VP Ventrivle Peritoneal Cavity

Ventriculo-atrial VA Ventricle Right Atrium of the heart

Ventriculo-pleural VPL Ventricle Pleural cavity

Lumbo-peritoneal LP Lumbar Spine Peritoneal cavity

VP shunts have a high failure rate, with up to half of patients needing shunt revisions.

Patients with abdominal complications often present with vague abdominal symptoms, but

can present with emergent neurologic symptoms related to shunt failure and increased

intracranial pressure.The incidence of ventriculoperitoneal shunt failure ranges from 25% to

40% at 1 year and 63% to 70% at 10 years.5 Failure rates with ventriculoatrial and

ventriculopleural shunts are slightly higher. Symptoms with the highest positive predictive

value include nausea and vomiting and decreased level of consciousness. Seizures, diplopia,

and weakness are less frequent presentations.Neurologic examination may show papilledema,

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focal deficits, hyperactive reflexes, and ataxia 6. In children, a bulging fontanelle or splaying

of the cranial sutures may be observed. These complications have been traditionally divided

into either mechanical or biological category. Mechanical complications are related to an

intrinsic shunt malfunction such as shunt discontinuity, leak, obstruction, or migration, while

biological complications, such as infection, abscess,pseudocyst, and hematoma.

Discussion

Biological complication

Shunt infection is the most common form of biologic complication of CSF shunting .Timing

of infection seems to affect which organism is cultured, with skin flora such as coagulase-

negative Staphylococcus and S.aureus occurring earlier in the postoperative period. Later

however, Streptococcus and Gram-negative species such as Pseudomonas become more

common due to intra-abdominal complications such as bowel perforation and peritonitis.

Ventriculoperitoneal (VP) shunt is one of the commonest procedures in neurosurgical

practice. A significant problem encountered in shunt procedures is infection, with infection

rate ranging from 2 to 27%, often with poor outcome. Shunt associated infections are most

frequently (65%) caused by coagulase negative Staphylococcus (CoNS).5,7,8 Gram negative

bacteria are the next most frequent pathogens, accounting for 19% to 22% of cases.5

Peritonitis

Clinically, patients with peritonitis present with signs and symptoms of infection including

abdominal pain may undergo a contrast-enhanced abdominal computed tomography (CT) to

exclude abscess formation. Patients with peritonitis will often show diffuse, hyperenhancing

peritoneal thickening, and may display inflammatory stranding of the mesenteric fat, with a

variable amount of infected fluid present.4

Abscess

Abdominal abscess is another known complication of CSF shunting to the peritoneal cavity.

Radiographs typically will not demonstrate an abscess within the abdomen, unless there is air

within the abscess causing an air fluid level which is distinct from bowel. The CT appearance

is similar to abscess of other etiologies, with a walled-off collection measuring simple or

complex fluid attenuation with a thickened, enhancing rim, and possible internal septations.

Depending on the causative bacteria, gas may be present in the abscess.

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Two different VP shunt patients A and B presented with symptoms of abdominal infection

including abdominal pain, nausea, and vomiting. Contrast-enhanced CT demonstrates

enhancing irregular thick-walled pelvic fluid collections(open arrows) surrounding the

abdominal portion of the VP shunt (white arrows) consistent with abscesses.

Ultrasound (USG) appearance is similar to other abscesses;a thick-walled hypoechoic or

anechoic fluid collection which may be multiloculated. There is an absenceof internal

vascularity on doppler, however the rim will be echogenic and often show increased vascular

flow on color doppler.

CSF pseudocyst

On abdominal radiographs, CSF pseudocyst, if large,may cause mass effect on adjacent

bowel loops or hydronephrosis if the collection compresses the ureters. On US, a CSF

pseudocyst has imaging characteristics of a cyst, with a hypoechoic to anechoic center, with a

thin echogenic outer wall. There may be low-level internal echoes secondary to internal

debris and/or septations,and the shunt tubing may be identified within it. There will be no

internal color flow on doppler.9 On CT, a CSF pseudocyst has an appearance of a thin-walled

mass measuring simple fluid attenuation, this is in contrast to an abscess which is typically

thick walled and will show secondary signs of inflammation such as adjacent fat stranding

and reactive lymphadenopathy. The collection may have areas of increased attenuation from

internal debris. The shunt tubing can be seen entering the collection, and its distal tip is

typically found terminating within the pseudocyst.6

6

Axial CT images through the abdomen and pelvis of a patient with VP shunt and abdominal

pain demonstrates A a large thin-walled pelvic fluid collection causing abdominal distention

consistent with CSF pseudocyst (open arrows) with shunt identified within it (white arrow),

and B mass effect from the CSF pseudocyst on the ureter with resultant bilateral

hydronephrosis (asterisks). The shunt is seen coursing through the anterior abdominal

subcutaneous tissue at this level (white arrow).

Infected pseudocyst in a patient who had many shunt revisions and developed

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Hematoma

Hematomas form as a result of vascular injury during surgical placement of the CSF shunt.

On USG, a hematoma within the abdominal wall will have marked heterogeneous

echogenicity, variable through transmission, local mass effect, and no internal color flow on

doppler imaging. The catheter tubing may be seen within or adjacent to the collection. On

CT, a hematoma will initially show intermediate to high attenuation in the acute phase; the

attenuation diminishes in the subacute phase There may be hemorrhage of varying age or

hematocrit levels visible within a single hematoma, in which case there may be layering or

admixing higher and lower attenuation within the collection.7,9

Patient status post recent VP shunt placement was found to have a new abdominal mass on

physical exam. US demonstrates a heterogeneous complex collection with subtle increase

through transmission and no internal flow on color doppler at the site of the palpable

abnormality, consistent with a hematoma.

Calcification

Rarely, shunt tubing may become encrusted with calcium. On abdominal radiographs, the

encrusted catheter will have a calcific density similar to bone, making it appear more

radiodense than the non-calcified tubing. The tubing will also appear thickened, as the

calcification accumulates on the external surface of the tubing.8

8

Calcium encrustation of the outer proximal abdominal portion of this VP shunt

Neoplastic metastases to the peritoneal cavity

The most common solid malignancies in the pediatric population are CNS tumors, frequently

resulting inhydrocephalus which requires CSF shunting there are reported cases of patients

with primary CNS neoplasms presenting with peritoneal metastasis, thought to have spread

via the VP shunt. These patients will present with US or CT findings of solid peritoneal

implants 4,10.

Mechanical complications

Obstruction/disconnection

Physiologic shunt obstruction and other mechanical failures may coexist.CT exams can

reveal specific causes such as catheter disconnect, catheter fracture, valve disconnect, or

catheter migration. In contradistinction to a CSF pseudocyst, CSF may acutely leak in the

setting of catheter fracture or disconnect. Catheter disconnection is more common at the

ventriculostomy reservoir or valve, while fracture is more common in the neck due to

movement 9. These areas should be carefully inspected on imaging studies.

9

Coronal CT images of the same patient as in Fig. 9b with LP shunt demonstrates

disconnection of the shunt tubing, A the tip of the shunt is identified (open arrow) and B

isdiscontinuous with the valve mechanism in the left flank(white arrow).

l

connectors (arrow) caused by a non-barium-impregnated plastic sleeve

skull radiograph shows a gap between the metalli

CSF leaks

CSF leaks occur secondary to mechanical disconnection or failure of catheter tubing, leading

to extravasation of CSF near the failure site. Nuclear medicine shunt studies reveal

accumulation of radiotracer at the failure site. As a result of the leak, radiotracer is not seen

spilling into the peritoneal cavity. Similarly, CSF can accumulate at the failure site on CT,

which can be confirmed with CT myelography7,8

10

CSF leak on a NM shunt study A with accumulationof radiotracer in the patient’s flank at 60

min (open arrow), without spill into the peritoneal cavity. B On CT myelography,iodinated

contrast material accumulates in the right flank collection, confirming the nuclear medicine

findings (white arrow).

Migration

Over time, shunt tubing can migrate within the abdomen due to patient motion. Shunt tubing

has been reported to perforate bowel in 0.1–0.7% of patients.10 The exact mechanism is

unclear but several etiologies have been suggested in the literature including the use of trocar

technique during placement, silicone allergy, fibrous sheath formation, tubing stiffness, and

local erosive pressure.10 The mortality rate associated with bowel perforation due to a shunt is

as high as 15% , in part due to the development of CNS infection. Abdominal VP shunt

tubing can retract out of the peritoneal cavity back into the subcutaneous tissues resulting in

catheter malfunction and a focal subcutaneous CSF collection. When shunt tubing migrates

into encapsulated organs such as the liver or spleen it can result in a subcapsular CSF

collection causing shunt malfunction. Shunt tubing has migrated to such unexpected

locations as the mouth, umbilicus, bladder, vagina, anus, and scrotum.4,5

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Valve malfunction and abdominal ascites

CSF drainage into the peritoneum is regulated via valve mechanism spliced directly into the

shunt tubing. Patients with valve malfunction will present with symptoms related to over or

underdrainage of CSF. For a shunt to work properly, the peritoneum must also be able to

absorb the CSF which is being produced. Patients typically present with increasing

abdominal distension, in the absence of liver, kidney, or cardiac disease. A contributing

factor in these cases may be an elevated CSF protein, altering absorption rates of the

peritoneum.4

Two axial CT images obtained on a patient with VP shunt demonstrating, A a subcutaneous

fluid collection with shunt tubing coiled within it (open arrow), and B the distal shunt tip

(white arrow) is seen retracted into the subcutaneous fluid collection (open arrow).

Orphaned/abandoned shunt

During shunt revision, the intra-abdominal portion of the malfunctioning shunt can be

disconnected and left in place to simplify the revision procedure, when not contraindicated

secondary to infection. This distal retained shunt tubing is often referred to as an abandoned

or orphaned shunt.4

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Conclusion

CSF shunts are commonly used to successfully treat hydrocephalus. VP shunts represent the

vast majority of shunts placed today. These shunt catheters can malfunction leading to a host

of complications attributed directly or indirectly to these shunts. As we have illustrated

above, mechanical and biological complications often are intertwined, and may present in

tandem. It is important for the abdominal radiologist to be familiar with the array of

abdominal complications associated with CSF shunts and to recognize distinguishing imaging

features of these complications and the clinical implications they present.

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DAFTAR PUSTAKA

1. Bondurant CP, Jimenez DF (1995) Epidemiology of cerebrospinal fluid shunting. Pediatric Neurosurg 23(5):254–258. doi:10.1159/000120968

2. All authors: Mallinckrodt Institute of Radiology, 510 S Kingshighway Blvd, St. Louis, MO 63110.

3. Chung JJ, Yu JS, Kim JH, Nam SJ, Kim MJ (2009) Intraabdominal complications secondary to ventriculoperitoneal shunts: CT findings and review of the literature.

4. Coley BD, Kosnik EJ (2006) Abdominal complications of ventriculoperitoneal shunts in children. Semin Ultrasound CT MR 27(2):152–160. doi:10.1053/j.sult.2006.01.009

5. Wells DL, Allen JM (2013) Ventriculoperitoneal shunt infections in adult patients. AACN Adv Crit Care 24(1):6–12. doi:

6. Pernas JC, Catala J (2004) Case 72: pseudocyst around ventriculoperitoneal shunt. Radiology 232:239–243.

7. P. McAllister, PhD and Marvin Sussman, PhD Shunt Systems for the Management of Hydrocephalus

8. Wang BH, Hasadsri L, Wang H (2012) Abdominal cerebrospinal fluid pseudocyst mimicking full-term pregnancy. J Surg Case Rep 2012

9. Boch AL, Hermelin E, Sainte-Rose C, Squouros S (1998) Mechanical dysfunction of ventriculoperitoneal shunts caused by calcification of the silicone rubber catheter. J Neurosurgery

10. Rickert C (2003) Extraneural metastasis of pediatric brain tumors. Acta Neuropathol 105(4):309–327. doi:10.1007/s00401-002-0666-x

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