Multiple pediatric hydrocephalus studies suggest that placement of a shunt catheter into a specific compartment of the lateral ventricles (i.e. frontal horn or occipital horn) leads to a lower risk of shunt failure. Putting the catheter into the best location and keeping them there, however, is difficult.
The HCRN ultrasound study was designed to see if the use of intraoperative ultrasound-guidance would result in accurate catheter placement, but the results were poor (Journal of Neurosurgery: Pediatrics, December, 2013). Using ultrasound, only 59% of catheters where in the targeted compartment on the post-operative scan. The rate of accurate placement in the comparison group, insertion by anatomical landmarks, was only 49%. In the ultrasound group it was clear that there was movement of the catheter between the ultrasound image obtained in the operating room and the first post-operative scan which was usually obtained the next day after surgery. The reason for this catheter movement between placement and post-operative scan was unclear, but movement occurred in a significant number of cases (33%).
Since the publication of the ultrasound study, the HCRN has continued to investigate the problems of catheter movement and poor catheter placement. In the August issue of the Journal of Neurosurgery: Pediatrics, we have published the results of a follow-up study where we try to identify factors that contribute to catheter movement and poor catheter placement. The study specifically looked at the following possible causes: surgeon, surgeon experience, patient age, size of the ventricles, thickness of the brain, shunt entry site, catheter length, and shunt hardware. The study shows that catheter movement is most likely to occur in patients less than six months of age. In fact, every case of catheter movement occurred in patients less than 6 months of age. This may be due to the high compliance or ‘softness’ of the immature brain which changes as the brain matures and myelinates. Poor catheter placement was also more likely to occur in young patients (< 6 months old), probably because of catheter movement, and to occur when the shunt catheter entry site was on the back of the head (posterior entry site) instead of on the front and top of the head (anterior entry site). Of course, it is not possible for the surgeon to significantly modify a patient's age at the time of treatment, however, the choice of entry site for the shunt catheter is almost entirely up to the surgeon. Approximately 50% of shunts are placed from a posterior entry site in the United States and Canada. The HCRN plans to continue to investigate the relationship between choices of entry site, accuracy, and shunt survival. Additional studies are in the works. Our goal is to take advantage of any possible opportunity to improve shunt function and reduce the number of shunt failures patients experience over the course of a lifetime. The complete publication is available for free courtesy of the Journal of Neurosurgery: Pediatrics, August 2014.