Double-J ureteric stent encrustations: clinical study on crystal formation on polyurethane stents

To evaluate the crystalline composition of encrustations on double-J ureteric stents in order to prevent their formation on the base of urolithiasis prophylaxis.

40 patients had a polyurethane double-J ureteric stent inserted between June 1994 and March 1995. Group 1 comprised 22 stone formers whose stents were placed in support of endourological treatment or extracorporeal shock wave lithotripsy of renal or ureteric calculi. Group 2 comprised 18 patients whose stents were inserted for advanced and obstructive malignancy (n = 8) or as an adjunct to reconstructive surgery or endourological techniques (n = 10). After removal, stents were examined for encrustation and obstruction. A biochemical semiquantitative analysis was performed for deposits > 5 mg, and smaller sediments were examined with a polarizing optical microscope.

The incidence of encrustation was significantly higher (p = 0.009) for stone formers. In addition, in this group indwelling times of encrusted and obstructed stents were significantly shorter (p = 0.03 and 0.02, respectively). No particular relationship was found between the incidence of encrustation and indwelling times for stone formers. Conversely, for patients without urolithiasis, indwelling times were significantly longer for encrusted or obstructed stents than for unaffected ones (p = 0.05 and 0.02, respectively). Biochemical and optical analyses of encrustations mainly revealed calcium oxalate, calcium phosphate and ammonium magnesium phosphate. Calcium oxalate was the main crystalline phase, especially in the absence of urinary infection.

Calcium oxalate represents the principal component of double-J ureteric stent encrustations. Thus, prophylaxis of encrustation may consist of preventive measures usually applied in cases of recurrent idiopathic calcium oxalate urolithiasis.