Introduction
Ureteric stents are an indispensable component of modern urological practice. Knot formation is a rare complication but must be recognised to prevent ureteric injury. To date, 34 cases (26 papers) of knotted ureteric stents have been reported since its first description in 1989 (Supplementary Table 1)(1). Herein, we report an illustrative case where holmium:yttrium aluminium garnet Ho:YAG laser was utilised to remove stent encrustation and enabled stent removal using gentle traction. The optimal management for the retrieval of a knotted ureteric stent is contextual, but we provide a recommended treatment algorithm using a graded approach.
Case Presentation
A 31-year-old man presented with sudden-onset left flank pain, rigours, anorexia and vomiting. He had left nephrolithiasis that was managed conservatively, but he had no past medical history. He was haemodynamically stable and had an unremarkable abdominal examination with no evidence of peritonism or renal angle tenderness. Microscopic haematuria was noted on urinalysis. The provisional diagnosis was renal colic, and a computed tomography kidney, ureter and bladder scan demonstrated a left 8×6×6 mm3 proximal ureteric calculus with mild hydroureteronephrosis. Emergency ureteric stenting was undertaken due to intractable pain despite use of non-steroidal anti-inflammatory and opioid analgesia. An intraoperative retrograde pyelogram (RGP) demonstrated a thin distal left ureter with a proximal filing defect corresponding with the location of the ureteric calculus. Moderate difficulty was encountered traversing the obstruction during stent insertion. A 5-Fr multi-length Double-J stent was eventually deployed successfully. Completion intraoperative X-ray imaging demonstrated satisfactory stent placement.
During the definitive stone procedure, performed 6 weeks later, there was significant difficulty in retrieving the ureteric stent. Intraoperative fluoroscopy revealed a knot at the proximal J-coil of the ureteric stent (Figure 1). Gentle traction under fluoroscopic guidance was used to tease the knotted stent into the distal ureter; however, further traction was met with resistance, and the knot could not be moved beyond the vesicoureteric junction. Ureteroscopy demonstrated significant debris and heavy encrustation around a tight knot, resulting in a widened diameter that impeded stent extraction (Figure 2). Careful laser lithotripsy of the encrustation/debris reduced the diameter, increased the mobility of the distal knot and facilitated stent extraction with gentle traction. No contrast extravasation was identified on completion RGP to suggest ureteric injury. No residual collecting system calculi were identified on completion ureteropyeloscopy. The patient had an uncomplicated postoperative course, with no issues at the 6-month follow-up period. The patient provided informed written consent for the publication of the case.
Discussion
The mechanism of knot formation remains unclear. However, studies have demonstrated higher occurrence at the proximal end (only three cases reported at the middle or distal end), male preponderance (4:1) and association with excessive stent length and coil formation (2,3).
Multi-length stents are preferred because they are easier to use, reduce stent migration risk and cost-effective (4). However, they appear to knot more often with 18 of the 24 previous cases, that reported stent length, being multi-length stents. Studies have proposed that the increased length leads to excessive proximal coiling, which occurs after the stent abuts the wall of the renal pelvis (4,5). Subsequently, a knot forms when the stent passes through this open coil (6,7). Fixed-length stents may decrease knot occurrence, but have their own issues (4). By contrast, stent diameter does not appear to affect knot formation, as diameters ranging from 4.7 to 7 Fr have been observed (3).
Yamamoto et al. (8) suggested that knotting occurs during insertion, possibly due to excessive guidewire coiling within the renal pelvis, rather than during retrieval. Patient factors like the renal pelvis anatomy and presence of hydronephrosis or urolithiasis may further alter the configuration of the proximal J-coil during insertion, thereby predisposing to knot formation (3). Interestingly, an analysis of previous cases demonstrated that knot formation occurred more often in cases without hydronephrosis than with hydronephrosis (9).
Stent encrustation on knotted stents can add difficulty during stent retrieval, as it increases the knot diameter and prevents passage of a guidewire through the stent lumen (10). We postulate that encrustation increases the friction during retrieval, which impedes the uncoiling process and possibly precipitates knot formation. However, knots have occurred in stents without significant encrustation (10,11).
No clinical practice guidelines exist for the management of knotted stents. We present a recommended treatment algorithm for knotted ureteric stents based on the literature and our experience, summarised in Table 1. For instance, we recommend simple traction with real-time fluoroscopic guidance, which is successful in most cases. Traction can lead to tightening of the knot or ureteric avulsion, although no studies have reported avulsion (5).
If significant resistance is met during traction or the knot is tightened, attempts at straightening the knot should be pursued using a guidewire. This has been successfully completed using an Amplatz super stiff guidewire and straight tip guidewire (7,11).
If this is unsuccessful, possibly due to confounding stent encrustation that occludes the stent lumen, endoscopic extraction should be pursued, as it allows for visualisation of the knot and facilitates more precise traction, knot manipulation and/or application of the holmium:YAG laser (3,6,12,13). This requires general or spinal anaesthesia and adequate advancement of the ureteroscope to the level of the knot, which can be restricted by urethral strictures, obstructing urolithiasis or the stent itself in a narrow calibre ureter (10).
Holmium:YAG laser was first utilised to remove a knotted stent in 2011 (12). The laser can be used to fragment/sever the stent below the knot, fracture the knot itself or remove stent encrustation/debris (4,10,12,13). This technique is minimally invasive and reproducible and allows for direct visualisation, which reduces the occurrence of inadvertent ureteric damage (3,12). Excessive fragmentation of the ureteric stent should be avoided, as this requires removal using basket, graspers or percutaneous nephrostomy if endoscopic techniques fail (10,13).
Percutaneous nephrostomy is useful in patients who cannot undergo a general or spinal anaesthesia or if endoscopic removal is unsuccessful (2,3,9,10,14,15). The first case was performed in Australia after failure of traction and endoscopic retrieval (15). Other techniques have utilised a Terumo guidewire in a patient with steinstrasse, Amplatz guidewire through a dilated nephrostomy tract, and the use of a 26-Fr nephroscope via a superior caliceal puncture into the renal pelvis and upper ureter (2,3). Open removal procedures can be considered, if all other methods fail.
Ethics
Informed Consent: The patient provided informed written consent for the publication of the case.
Peer-review: Externally peer-reviewed.
Authorship Contributions
Surgical and Medical Practices: B.W.H.L A.J.N., D.R.A., A.J.M., Concept: A.J.N., D.R.A., A.J.M., Design: B.W.H.L, D.R.A., A.J.M., Data Collection or Processing: B.W.H.L, A.J.N., D.R.A., A.J.M., Analysis or Interpretation: B.W.H.L, A.J.N., D.R.A., A.J.M., Literature Search: B.W.H.L, A.J.N., D.R.A., Writing: B.W.H.L, A.J.N., D.R.A., A.J.M.
Conflict of Interest: No conflict of interest was declared by the authors.
Financial Disclosure: The authors declared that this study received no financial support.
