Radiation risk due to shunted hydrocephalus and the role of MR imaging-safe programmable valves

The Evolution of Ventriculoperitoneal Shunt Valves and Why They Fail

This article reviews the historical progression of ventriculoperitoneal shunt valve designs with the goal of providing an understanding of their functionality and failure mechanisms. While shunting is the predominant treatment for hydrocephalus, the statistics of overall shunt failure remain high, and valve failure is responsible for a significant percentage of revision surgeries. Therefore, this review spans valve evolution from an engineering perspective with an emphasis on discussing potential failure mechanisms and patient-specific valve selection. Information is provided on the importance of valves in hydrocephalus treatment with discussion on each class of valves and their advantages and shortcomings. Substantial development over decades has significantly improved valve functionality, and ongoing research continues to provide more robust valves and shunt systems for hydrocephalus management.

Mild traumatic brain injury in children with ventricular shunts: a PREDICT study

OBJECTIVE

Current clinical decision rules (CDRs) guiding the use of CT scanning in pediatric traumatic brain injury (TBI) assessment generally exclude children with ventricular shunts (VSs). There is limited evidence as to the risk of abnormalities found on CT scans or clinically important TBI (ciTBI) in this population. The authors sought to determine the frequency of these outcomes and the presence of CDR predictor variables in children with VSs.

METHODS

The authors undertook a planned secondary analysis on children with VSs included in a prospective external validation of 3 CDRs for TBI in children presenting to 10 emergency departments in Australia and New Zealand. They analyzed differences in presenting features, management and acute outcomes (TBI on CT and ciTBI) between groups with and without VSs, and assessed the presence of CDR predictors in children with a VS.

RESULTS

A total of 35 of 20,137 children (0.2%) with TBI had a VS; only 2 had a Glasgow Coma Scale score < 15. Overall, 49% of patients with a VS underwent CT scanning compared with 10% of those without a VS. One patient had a finding of TBI on CT scanning, with positive predictor variables on CDRs. This patient had a ciTBI. No patient required neurosurgery. For children with and without a VS, the frequency of ciTBI was 2.9% (95% CI 0.1%-14.9%) compared with 1.4% (95% CI 1.2%-1.6%) (difference 1.5% [95% CI -4.0% to 7.0%]), and TBI on CT 2.9% (95% CI 0.1%-14.9%) compared with 2.0% (95% CI 1.8%-2.2%) (difference 0.9%, 95% CI -4.6% to 6.4%).

CONCLUSIONS

The authors' data provide further support that the risk of TBI is similar for children with and without a VS.

Epidermal electronics for noninvasive, wireless, quantitative assessment of ventricular shunt function in patients with hydrocephalus

Hydrocephalus is a common and costly neurological condition caused by the overproduction and/or impaired resorption of cerebrospinal fluid (CSF). The current standard of care, ventricular catheters (shunts), is prone to failure, which can result in nonspecific symptoms such as headaches, dizziness, and nausea. Current diagnostic tools for shunt failure such as computed tomography (CT), magnetic resonance imaging (MRI), radionuclide shunt patency studies (RSPSs), and ice pack-mediated thermodilution have disadvantages including high cost, poor accuracy, inconvenience, and safety concerns. Here, we developed and tested a noninvasive, skin-mounted, wearable measurement platform that incorporates arrays of thermal sensors and actuators for precise, continuous, or intermittent measurements of flow through subdermal shunts, without the drawbacks of other methods. Systematic theoretical and experimental benchtop studies demonstrate high performance across a range of practical operating conditions. Advanced electronics designs serve as the basis of a wireless embodiment for continuous monitoring based on rechargeable batteries and data transmission using Bluetooth protocols. Clinical studies involving five patients validate the sensor's ability to detect the presence of CSF flow (P = 0.012) and further distinguish between baseline flow, diminished flow, and distal shunt failure. Last, we demonstrate processing algorithms to translate measured data into quantitative flow rate. The sensor designs, fabrication schemes, wireless architectures, and patient trials reported here represent an advance in hydrocephalus diagnostics with ability to visualize flow in a simple, user-friendly mode, accessible to the physician and patient alike.

Noninvasive measurement of cerebrospinal fluid flow using an ultrasonic transit time flow sensor: a preliminary study

OBJECT Mechanical failure-which is the primary cause of CSF shunt malfunction-is not readily diagnosed, and the specific reasons for mechanical failure are not easily discerned. Prior attempts to measure CSF flow noninvasively have lacked the ability to either quantitatively or qualitatively obtain data. To address these needs, this preliminary study evaluates an ultrasonic transit time flow sensor in pediatric and adult patients with external ventricular drains (EVDs). One goal was to confirm the stated accuracy of the sensor in a clinical setting. A second goal was to observe the sensor's capability to record real-time continuous CSF flow. The final goal was to observe recordings during instances of flow blockage or lack of flow in order to determine the sensor's ability to identify these changes. METHODS A total of 5 pediatric and 11 adult patients who had received EVDs for the treatment of hydrocephalus were studied in a hospital setting. The primary EVD was connected to a secondary study EVD that contained a fluid-filled pressure transducer and an in-line transit time flow sensor. Comparisons were made between the weight of the drainage bag and the flow measured via the sensor in order to confirm its accuracy. Data from the pressure transducer and the flow sensor were recorded continuously at 100 Hz for a period of 24 hours by a data acquisition system, while the hourly CSF flow into the drip chamber was recorded manually. Changes in the patient's neurological status and their time points were noted. RESULTS The flow sensor demonstrated a proven accuracy of ± 15% or ± 2 ml/hr. The flow sensor allowed real-time continuous flow waveform data recordings. Dynamic analysis of CSF flow waveforms allowed the calculation of the pressure-volume index. Lastly, the sensor was able to diagnose a blocked catheter and distinguish between the blockage and lack of flow. CONCLUSIONS The Transonic flow sensor accurately measures CSF output within ± 15% or ± 2 ml/hr, diagnoses the blockage or lack of flow, and records real-time continuous flow data in patients with EVDs. Calculations of a wide variety of diagnostic parameters can be made from the waveform recordings, including resistance and compliance of the ventricular catheters and the compliance of the brain. The sensor's clinical applications may be of particular importance to the noninvasive diagnosis of shunt malfunctions with the development of an implantable device.

Age- and gender-specific estimates of cumulative CT dose over 5 years using real radiation dose tracking data in children

BACKGROUND

It is necessary to develop a mechanism to estimate and analyze cumulative radiation risks from multiple CT exams in various clinical scenarios in children.

OBJECTIVE

To identify major contributors to high cumulative CT dose estimates using actual dose-length product values collected for 5 years in children.

MATERIALS AND METHODS

Between August 2006 and July 2011 we reviewed 26,937 CT exams in 13,803 children. Among them, we included 931 children (median age 3.5 years, age range 0 days-15 years; M:F = 533:398) who had 5,339 CT exams. Each child underwent at least three CT scans and had accessible radiation dose reports. Dose-length product values were automatically extracted from DICOM files and we used recently updated conversion factors for age, gender, anatomical region and tube voltage to estimate CT radiation dose. We tracked the calculated CT dose estimates to obtain a 5-year cumulative value for each child. The study population was divided into three groups according to the cumulative CT dose estimates: high, ≥30 mSv; moderate, 10-30 mSv; and low, <10 mSv. We reviewed clinical data and CT protocols to identify major contributors to high and moderate cumulative CT dose estimates.

RESULTS

Median cumulative CT dose estimate was 5.4 mSv (range 0.5-71.1 mSv), and median number of CT scans was 4 (range 3-36). High cumulative CT dose estimates were most common in children with malignant tumors (57.9%, 11/19). High frequency of CT scans was attributed to high cumulative CT dose estimates in children with ventriculoperitoneal shunt (35 in 1 child) and malignant tumors (range 18-49). Moreover, high-dose CT protocols, such as multiphase abdomen CT (median 4.7 mSv) contributed to high cumulative CT dose estimates even in children with a low number of CT scans.

CONCLUSION

Disease group, number of CT scans, and high-dose CT protocols are major contributors to higher cumulative CT dose estimates in children.