because of their widespread use , complications secondary to stent placement have also increased , such as stent encrustation , stent fragmentation , stone formation , and recurrent urinary tract infections . knot formation within the body or coiled portion of the ureteral stent is an extremely rare condition , with less than 15 cases reported in the literature . nevertheless , this condition may lead to legal and medical problems for urologists , health institutions , and also for patients . the authors report a rare case of knotted stent ( ks ) complicated by an obstructive acute renal failure and urosepsis , in a 32-year - old man with a solitary functioning kidney . a 32-year - old male with solitary left functioning kidney was admitted with complaints of lumbar pain , which radiated to the groin , burning urination , fever , and moderate dyspnea that had persisted for 2 days . prior to this presentation patient had under gone ureteroscopy for the treatment of ureteral stone , following which ureteral stent was left in place . laboratory findings on admission showed the following : serum creatinine 44 mg / dl , blood urea nitrogen 14.7 mg / dl , hemoglobin level of 10 g / dl , c - reactive protein 95 mg / l , and total white blood cell count of 14000/mm with 88% polymorphs . plain - film radiograph of abdomen revealed entire double j stent coiled in the left renal pelvis . in our institution the urologist and the surgical report , of the previous ureteroscopy , confirmed that the stent was placed without problem after ureteroscopy . kub x - ray performed after the insertion of the stent confirmed its good placement . renal ultrasonography revealed moderate hydronephrosis with hyperechoic intrapelvic stent . the patient was admitted with a diagnosis of oliguric acute renal failure and urosepsis due to obstructive ks . a 7-f ureteral catheter was inserted , under local anesthesia , to relieve the renal obstruction [ figure 1 ] . after 3 days , the urosepsis was relieved with drainage and antibiotic therapy , and the patient recovered from the acute renal failure with serum creatinine of 1.8 mg / dl and , blood urea nitrogen 20.7 mg / dl . when the patient was stable , ureteroscopy was performed . under spinal anesthesia , in the rigid ureteroscopy position , the right lower limb was kept in the lithotomy position , and the left limb bent in the lowest position . a hydrophilic guidewire was inserted in the ureteral catheter and coiled in the renal pelvis . an 8-f rigid ureteroscope was advanced beside the guidewire through urethra , bladder , and then the left ureter . the stent end was grasped with a basket and progressively extracted under fluoroscopic guidance . when the stent knot had reached the proximal ureter , a 7-f ureteral catheter was inserted on the guidewire until it was in the renal pelvis . on the fourth postoperative day , a plain x - ray film of the abdomen shows the original coiled jj stent with formation of a complete knot ( black arrow ) . an additional ureteral stent was inserted for rapid decompression of infected solitary kidney ( white arrowhead ) . the first report on the ks in literature was by groeneveld in 1989 . sometimes , the stent may knot inside the ureter , representing a therapeutic challenge with the potential risk of ureteral avulsion . conservative retrieval remains difficult in patients with solitary kidney , ureteric implantation , or uretero - intestinal anastomosis . flam et al . , reported two cases a 4-year - old and 86-year - old patient , respectively . according to literature , many different ureteral stent configurations are available , including single -j , double - j , and multi - length stents . some authors have hypothesized that excessive length stent , as well as , coil configuration increase the likelihood of knot formation . most of these knots involve the proximal end of the stent near the coil , but any part of the stent can be involved . quek et al . , reported a case in which the knot was formed in the middle of the stent while eisner et al . depicted a patient who had knots in two separate indwelling stents ks comes to notice when the patient 's symptoms reappear , during incidental imaging , or acute renal function with urosepsis , like in our patient . given the potential morbidity of both percutaneous and open procedure , we opted for a retrograde ureteroscopy after initial placement of retrograde ureteral catheter , to achieve adequate urinary drainage , and antibiotic therapy for urosepsis . , after failure of ureteroscopic extraction at initial attempt , inserted a second ureteral stent alongside the ks to allow the passage of a 9.5f ureteroscope 1 week later . no guidelines exist for successful management of ks.[46 ] various methods of treatment like combinations of retrograde ureteroscopy , percutaneous removal , and open surgery have been used for retrieval of these knotted stents.[137 ] table 1 summarizes the main advantages and inconvenient disadvantages of each technique . the standard clinical approach to management of ks is ureteroscopic removal when it is feasible with simple , gentle traction , both under direct vision and fluoroscopy . this traction can be immediate or delayed after initial placement of ureteral stent to promote dilation of the ureter below the ks for two or three days . the occurrence of resistance to moderate traction during ureteroscopy or hematuria requires stopping the maneuver to avoid ureteral injury . braslis et al . , achieved successful percutaneous extraction of dysfunctioning stent while sighinolfi et al . , used 3 days of continuous staged traction on the stent tied at the leg with a common catheter strip at the distant coil allowing its spontaneous expulsion . report the successful use of flexible ureteroscopy with holmium laser in treating a case of a retained double j stent . in this case , the laser was found helpful in breaking the center of the knot and removing the stent in two pieces . failure of mini - invasive approach results in open removal . in our patient , due to potential morbidity related to percutaneous approach , we chose the retrograde approach , both to treat obstruction of the urine flow and to promote ureteral dilation in a poorly compliant patient . retrograde approach is less invasive and has a lower risk of bleeding compared with percutaneous surgery . the close follow - up of stented patients is valuable for the early detection of morbidity or complications . ureteric stent monitoring is essential and should include regular monthly urine cultures , monitoring of serum creatinine levels , and x - ray kub .
the insertion of indwelling ureteric stents is a routine procedure in urology practice . 
 complications secondary to the insertion of these stents have also increased , such as stent encrustation , stent fragmentation , stone formation , and recurrent urinary tract infections . 
 knot formation within the renal pelvis or in the coiled portion of the ureteral stent is an extremely rare condition , with less than 15 cases reported in literature . 
 the authors report a rare case of knotted stent , complicated by an obstructive acute renal failure and urosepsis , in a patient with a solitary functioning kidney .