Editors' ChoiceNeurology

Know the shunt flow

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Science Translational Medicine  02 Dec 2015:
Vol. 7, Issue 316, pp. 316ec208
DOI: 10.1126/scitranslmed.aad8026

Because no curative options exist, hydrocephalus treatment still relies on surgical placement of a shunt catheter into the brain’s ventricular space to divert cerebrospinal fluid (CSF) from the brain and relieve pressure. Although this low-tech solution has revolutionized care for hydrocephalus patients, it also suffers from fundamental flaws, as 50 to 60% of shunts fail within the first two years of implantation, mostly because of blockage of the catheter. Rather than monitoring shunt function on the basis of quantitative information, such as CSF pressure or flow through the catheter, patients and physicians rely on common neurological symptoms, such as nausea or headaches, for early signs of shunt malfunction.

To provide patients with objective measures of shunt malfunction, Pennell and co-workers developed an ultrasound-based, in-line flow sensor for CSF flow determination. The sensor determines flow through the catheter by measuring the transit time of ultrasound, which is modulated by flow if pulses are sent in the up- and downstream directions. In a pilot study comprising both pediatric and adult patients with externalized ventricular drains, the authors determined the accuracy of the flow sensor and report illustrative examples on how the mean and pulsatile information of the CSF flow waveforms can be used to differentiate a functioning shunt from one that is blocked. This differentiation is based on the interpretation of the mean flow through the catheter, as well as the pulsatility of the CSF flow waveform over a cardiac cycle, as the mean flow and pulsatility are both reduced as a blockage develops. The interpretation of such CSF flow waveforms might become less obvious once a flow sensor is implanted into ambulatory patients who constantly shift posture, which changes the intracranial pressure and CSF flow dynamics. Nevertheless, Pennell and co-workers have taken an important first step toward improving the lives of patients with hydrocephalus. With implanted catheters equipped to provide objective data on a shunt’s performance, the next step can now be taken.

T. Pennell et al., Noninvasive measurement of cerebrospinal fluid flow using an ultrasonic transit time flow sensor: A preliminary study. J. Neurosurgery Ped. 10.3171/2015.7.PEDS1577 (2015). [Abstract]

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