The distribution of crystalline material in obstructed stents--in need for intra-luminal surface modification?

Usually, hampered urine flow and failing of Seldinger technique leads to the explanation "obstructed ureteral stent" with no further clarification where exactly the obstructions are located. If stent obstruction is caused by intra-luminal biofilm and/or crystal deposits, the need of biofilm reducing coatings on the stent's inside has to be discussed. We investigated 59 stents from patients in whom acute hydronephrosis and/or acute pyelonephritis required stent replacement and/or usage of Seldinger technique failed. The stents were investigated by X-ray and, after longitudinal cutting, by light-microscopy for occurrence of obstructing material. The inside of 25% of the samples was lined with a thick film composed of blood clots and tiny non-aggregated crystals. Only in these samples X-ray investigation showed a positive result for massive inner encrustations, which in fact may be responsible for stent occlusion. 48% of the stents contained few small domains composed of blood clots and crystals. 27% of the stent samples showed no alteration. 75% of the "obstructed" stents showed no significant inner deposits. Obstruction of urine transport and failure of Seldinger technique occurred due to other reasons. Thus, coating of the stent's inner surface may be overrated