Non-invasive pediatric ureteral stent removal with the use of a novel magnetic bead
Rodolfo A. Elizondo, MD1, John Chen, BS2, Valerie Pinillos, BS2, Margaret Watkins, BS2, Eric Yin, BS2, Allen Zhao, BS2, Esther J. Kim, MD3, Gene O. Huang, MD1, Chester J. Koh, MD, FACS, FAAP1.
1Texas Childrens Hospital, Houston, TX, USA, 2Rice University, Houston, TX, USA, 3Baylor College of Medicine, Houston, TX, USA.
Background
Ureteral stents are often utilized after minimally invasive (robotic or laparoscopic) surgery for ureteropelvic junction obstruction (UPJO) in children. To avoid the inadvertent premature removal of the stent, the dangler string on the stent is often removed to avoid any external tubing or strings in pediatric patients. However, in children, this necessitates a subsequent cystoscopic stent removal under general anesthesia. We hypothesized that a non-invasive solution that utilizes a novel electromagnet and a bead attached to the indwelling ureteral stent would allow for removal of the stent without the use of cystoscopy or anesthesia.
Methods
An undergraduate engineering senior design team collaborated with a pediatric urologist to develop a novel electromagnet and a coated neodymium bead that could be attached to the string on the distal portion of a ureteral stent. 3D-printed models of the bladder and ureters were created to observe the movement of the bead and removal of the ureteral stent. Simulated soft tissue testing with bologna to approximate the features of skin and muscle were conducted to evaluate the compression of tissue planes between the magnet and bead. Paint tests (beads coated with paint) to evaluate the paint markings / striations during removal were performed to identify the key tissue contact points of the bead during the removal. Time trials and shake tests were performed in 3D-printed male and female urethra models. Cost estimates between the non-invasive method and cystoscopic removal of the stent were compared.
Results
Magnetic removal of the bead in the 3-D printed urinary tract model showed adequate movement of the bead with subsequent stent removal. Only mild tissue compression in the simulated tissue model was seen during the magnetic removal process that is expected to be pain-free. An average of 3.4 paint markings / striations were seen during passage of the bead through the 3D model. There was a significant difference in the removal time trials between the female and male urethra models (p=0.015). Shake tests did not result in displacement of the stent. Magnetic stent removal is estimated at 1/3 of the costs associated with cystoscopic stent removal in children (charges: $906 vs. $2,600, respectively).
Conclusion
A novel magnetic stent removal system can provide an alternative method for safe and cost-efficient non-invasive removal of ureteral stents in the pediatric population. Testing to date shows reliable removal of the bead and stent in 3D-printed models. Further steps on the device development pathway are needed for future clinical use. This solution may encourage the future use of indwelling ureteral stents without external tubing and strings in pediatric patients
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