The value of colour Doppler imaging in assessing flow through ventriculo-peritoneal shunts

So far, Doppler ultrasonography has had little application in paediatric neurosurgery. The incidental observation of normally invisible CSF flow from the peritoneal end of a ventriculo-peritoneal (V-P) shunt on colour Doppler during a conventional abdominal ultrasound examination in one of our patients suggested that colour Doppler imaging might be of potential interest. Using a 10-5 MHz broad-band linear array transducer, conventional 2D and Doppler (spectral and colour-coded) ultrasonography was performed in 17 patients with V-P shunts, who were aged 3 months to 12 years. In all, 20 examinations were performed, because 2 patients had repeat examinations before and after shunt revision. In 13 examinations (65%) CSF flow was identified through the shunt tube. Flow velocities between 5 and 7 cm/s were measured. No flow was seen in 7 examinations (35%), 3 of which (15%) were performed before revisions for a blocked shunt. Further in vitro studies with simulated shunt/ventricular system model demonstrated that although clear CSF is not ultrasonically visible, the presence of particulate matter, such as choroid plexus debris, can generate a satisfactory Doppler signal with the probe insonating over the length of the tubing. In the presence of clear CSF, turbulence generated at junction points of the shunt system or at the exit of the peritoneal tube can be visualised well with Doppler ultrasonography, presumably due to generation of microbubbles. The clinical implications for the management of shunt obstruction are discussed.