When there are concerns for ventriculoperitoneal shunt (VPS) malfunction, relying entirely on the head computed tomography (CT) scan and shunt series for ventriculoperitoneal shunt malfunction will miss 30% of shunt failure
When there are concerns for ventriculoperitoneal shunt (VPS) malfunction, relying entirely on the head computed tomography (CT) scan and shunt series for ventriculoperitoneal shunt malfunction will miss 30% of shunt failure: Excerpt from Avoiding Common Pediatric Errors
Author:
David Stockwell, MD
What to Do - Gather Appropriate Data
Perform a complete history and physical examination, evaluate the radiographic studies and their comparisons, and combine all of this information
to make an accurate diagnosis.
VPSs are a relatively common device in pediatrics. As with any artificial
device placed internally, the possibility of malfunctioning exists. Missing
the diagnosis of shunt malfunction may lead to permanent neurologic injury
or death. Unfortunately the diagnosis of shunt failure is not a simple task.
Commonly used techniques to diagnose shunt malfunction are a combination of the patient's history, clinical exam, and radiographic studies. Often,
however, the ultimate decision is based on the head CT and "shunt series."
This chapter will explain how relying solely on those results will result in
approximately one third of cases of shunt failure being missed.
Noninfectious shunt failure occurs due to obstruction, mechanical failure of the shunt (e.g., disconnection, fractured tubing, misplacement, or
migration of the shunt), overdrainage, cerebrospinal fluid drainage other
than from the shunt, loculations within the ventricular system, and abdominal causes. Timing of the malfunction may assist in diagnosing the type of
shunt failure. Obstruction of the shunt system can occur at any time after
shunt placement and at any point along the shunt. Early shunt malfunctions
are usually due to misplacement, disconnection, or migration of the shunt
components. Common causes for late shunt failure include tubing fractures,
shunt overdrainage, ventricular loculations, and erosion of the distal tubing
into a hollow viscus in the abdomen.
Radiographic evidence of shunt malfunction is typically observed either on plain radiographs or by CT scan. Plain radiographic images of the
entire shunt tract, the so-called shunt series, help identify a mechanical
disruption of the shunt. It will typically show broken tubing or disconnections. Common locations for fractures are near the clavicle or lower ribs.
Computed tomographic studies present evidence of increased ventricularsizeandrevealintraventricularcatheterlocation.Shuntfailureismanifest
on head CT scan by increasing ventricular size. It is imperative to compare
currentstudiesagainstabaselinestudyobtainedaftersuccessfulshuntplacement. Several studies note that current head CTs have been incorrectly read
as normal when compared to earlier head CTs because the comparison was
taken at another point of shunt failure.
When evaluating a head CT scan, it is important to realize that normal
ventricular size or even small ventricles does not rule out shunt dysfunction.
Forthisreason,CTandmagneticresonanceimagingscansshouldnotbeused
as the definitive diagnostic modality. Some of the causes of small ventricles
other than shunt failureinclude poorcompliance,overdrainage,slit ventricle
syndrome, intermittent shunt malfunction.
When a scan shows large ventricles, an effort should be made to find out
whether the ventricles have ever been smaller in size, thus usually implying
that the current shunt has failed. All previous scans should be reviewed and
compared with the current scan. Furthermore, it is crucial to know which
of the comparison scan represents normal shunt functioning. Finally, even
if the ventricles had never changed in size, the presence of large ventricles
still should raise the suspicion for shunt failure.
In patients with high clinical suspicion for shunt failure but nonconfirmatory radiographic studies, further studies could include shunt taps,
intracranial pressure monitoring, shunt patency studies, long periods of observation in the hospital, and even an occasional surgical exploration.
Evaluatingashuntmalfunctionisdifficult;certainlyneurosurgicalinput
should be requested early in the patient's evaluation. Unfortunately, the
radiographic studies that are the mainstay of evaluation are not infallible.
Suggested Readings
Browd SR, Ragel BT, Gottfried ON, et al. Failure of cerebrospinal fluid shunts: part I: obstruc
tion and mechanical failure. Pediatr Neurol. 2006;34(2):83–92.
Iskandar BJ, McLaughlin C, Mapstone TB, et al. Pitfalls in the diagnosis of ventricular shunt
dysfunction: radiology reports and ventricular size. Pediatrics. 1998;101(6):1031–1036.
Book Source Details
- Book Title: Avoiding Common Pediatric Errors
- Author(s): Anthony D Slonim MD, DrPH; Lisa Marcucci MD
- Year of Publication: 2008
- Copyright Details: Avoiding Common Pediatric Errors, Copyright © 2008 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Avoiding Common Pediatric Errors
Authors: Anthony D Slonim MD, DrPH; Lisa Marcucci MD
Publisher: Lippincott Williams & Wilkins
Copyright: 2008
ISBN: 0-7817-7489-6
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