Role of stents in open ureteral surgery

Stent extrusion on the external surface of the transplanted kidney: unusual occurrence

Here we present the case of a 40-year-old man, who underwent deceased donor renal transplantation. Towards the end of this operation, open-ended double J stent was inserted in the transplanted kidney. Modified Lich-Gregoir ureterovesical anastomosis was performed. Prior to the abdominal closure, it was discovered that proximal end of the stent had pierced the renal parenchyma and extruded on the external surface of the transplanted kidney. We contemplated removing the stent and reinserting it but decided against that due to various reasons. The stent was left as such. The patient was managed conservatively with satisfactory outcome in the postoperative period. To the best of our knowledge, this is first such report of conservative management of stent extrusion in transplanted kidney in the literature.

Mathematical formulation for computing the performance of self expanding helical stents

Stents are cylindrical devices implanted inside pathologic tubular passages within the body. The stents, which are made of metal or plastic, keep the passage open for flow (of blood, urine, air etc.) by applying radial pressure on the passage walls. In most cases the stents are selected empirically for each application. We introduce here a mathematical formula for computing the radial pressure induced by self expanding helical stents. The formula was verified experimentally for an urological stent using a special device. The results correlate well with the theoretical predictions (R = 0.997; y = 1.017 x -0.06 kg; SEE = 0.034, for forces and R = 0.9988; y = 1.04 x +8.7 mmHg; SEE = 25.3 for pressures). This formula can potentially serve as an analytical tool for selecting the most suitable stent for a given application.