To the Editor: Ureterostenosis is one of the most common complications after kidney transplantation, with an incidence rate of 1.0–8.3% according to a relevant report.[1,2] This complication may cause postrenal obstruction, affecting the function of the transplanted kidney and increasing the risk of kidney loss. As for laparoscopic surgery, open surgery, or interventional treatment, the location and separation of the ureter may be inaccurate, even the ureter damage, the length of the ureter may be not enough, or the ureter may fail to pass through the segment of stenosis for unclear anatomical level, serious tissue adhesion, and special location for operation, thus causing failure of the operation. Therefore, treatment with efficacy and feasibility will be necessary to treat ureterostenosis after kidney transplantation. Magnetic compression anastomosis (MCA) is a recanalization method utilizing the attraction between anastomotic devices made of magnetic materials to compress the parietal layer or tissue of the viscera, thus causing local ischemia or necrosis.[3] MCA has been applied in the biliary tract, gastrointestinal tract, and vascular anastomosis preliminarily, with remarkable efficacy.[3,4] MCA was performed in the treatment of ureterostenosis after kidney transplantation based on these advantages that were reported previously.

Considering special factors such as magnet and magnetic field, the inclusion criteria of MCA were as follows: (1) The patient was diagnosed with definite ureterostenosis after kidney transplantation that needed pyelostomy for drainage; (2) The length of stenosis segment was ≤2 cm; (3) The patient signed the informed consent form and could cooperate with relevant treatment and reexamination during follow-up. Exclusion criteria: (1) Pregnant or lactating women accompanied with serious organ dysfunction, and patients with a psychological disease or active infection; (2) Patients with implants that might be disturbed by the magnetic field (e.g., cardiac pacemaker, metal denture, and internal fixation for fracture); (3) Patients who had to or might receive magnetic resonance imaging (MRI) in the near future; (4) The stenosis segment was too long (>2 cm), and the attraction between magnets could not meet the requirements for compression anastomosis; (5) The magnets could not be inserted because the diameter of ureter or urethra was excessively small. The study was reviewed and approved by the Ethics Committee of the First Affiliated Hospital of Xi'an Jiaotong University (No. XJTU1AF2021LSK-241). This study has been performed in accordance with the ethical standards of the Declaration of Helsinki. There were 10 cases who signed an informed consent form and were informed about the study and agreed to have their clinical information used in the reported research.

Patients with a definite diagnosis accompanied with decreased urine volume and significantly increased creatinine who could not receive operation within a short period of time, pyelostomy for drainage should be performed as soon as possible to relieve or eliminate the hydronephrosis and maintain the function of transplanted kidney, and at the same time, preoperative preparation for MCA should be done. Preoperative angiography is recommended for a preliminary understanding of the site, length, and degree of stenosis before MCA [Figures 1A and B]. The magnetic ring was of the third-generation rare-earth neodymium iron boron (nfeb) permanent magnet material, which was divided into daughter magnet (DM) and parent magnet (PM). The DM was of about 1.5 cm in length and 0.6 cm in diameter, and the PM was of about 1.5 cm in length and 0.8 cm in diameter. After anesthesia, a lithotomy position was taken, with perineum and kidney transplant areas disinfected and draped. A zebra guidewire was placed from the nephrostomy tube for the transplanted kidney, and the nephrostomy tube was removed. Guided by the guidewire, the pyelostomy channel was expanded to F20 for establishing the percutaneous kidney tract. Ureteroscopy found hydronephrosis in the kidney collective system. The DM was placed in the segment of ureterostenosis after kidney transplantation, and another ureteroscope was inserted into the bladder. The zebra guidewire was inserted into the ureter through the scar at the top wall of the bladder, and the PM was inserted until the magnets at both ends attracted each other to form a compression force. Then, the endoscopy was removed, and the nephrostomy tube was reinserted, as shown in Figure 1C. An abdominal X-ray was performed every week after surgery for observing the position of the magnets. After the magnets fell off, two F6 double-"J" tubes were placed through the anastomotic stoma. The recommended retention time was at least 3–6 months [Figure 1D].

Figure 1:

(A) Percutaneous nephrostomy for drainage of the transplanted kidney; (B) urography for transplanted kidney, with an arrow indicating stenosis site; (C) abdominal X-ray after MCA for observing the position of magnets; (D) two F6 double-"J" tubes placed after the magnets fell off. MCA: Magnetic compression anastomosis.

For all of the 10 cases, the operation process was smooth, and the estimated length of the stenosis segment: 1.46 ± 0.30 mm. Among nine cases, magnets fell off naturally 15.55 ± 2.74 days after MCA, and for one case, the magnets were removed 72 days after MCA (removed under endoscope). The follow-up time for all of the cases was >1 year. The double-"J" tubes were removed 3–6 months later. Three cases developed fever after the operation and were diagnosed with "urinary tract infection," which was improved by anti-infection treatment. Ureter re-ureterostenosis occurred in one case after the removal of the double-"J" tubes, who received another 3 months of retention, For the rest, no stenosis appeared again.

Usually, early ureterostenosis occurs 1–3 days after kidney transplantation, and it is directly related to surgical complications.[5] The main reasons for ureterostenosis include perirenal hematoma compression, ureteropelvic hemorrhage, bending angle for overlong ureter, overtight tunnel anastomosis of the bladder muscle layer, spermatic cord compression (for spermatic cord reservation), etc., which may be solved by open surgery. Furthermore, long-term ureterostenosis that usually occurs 3–6 months after operation is another challenge.[6] It may be caused by ureteral ischemic necrosis, ureteral calculus, fibrosis around the ureter for scar constitution, or chronic urinary tract infection, in which ureteral ischemic necrosis usually occurs at the anastomotic stoma as the most common cause of stenosis and obstruction.[7,8]

In recent years, magnetic surgery technology, including MCA, magnetic anchoring technology, magnetic navigation technology, magnetic levitation technology, magnetic tracer technology, and so on, has been developed rapidly and applied widely.[9] MCA takes advantage of the "non-contact" magnetic force of the magnet to compress the target tissue in a "non-penetrating" mode continuously, resulting in its ischemia-necrosis and recanalization. The recanalization time is mainly related to the magnetic force between magnets, the length and nature of the site for the compression site, etc. The recommended length for the stenosis segment is ≤2 cm. If the stenosis segment is longer than 2 cm, the operation was also recommended, but the recanalization may fail, or the recanalization time may be prolonged. The main steps for MCA are as follows: establishment of channels, implementation of compression surgery, continuous compression, and removal of magnets. When the pyelostomy channel and urethra were used as the paths for the placement of magnets, no additional trauma was caused. After the attraction between DM and PM, the distance between the magnets became smaller and smaller over time. During this period, close magnet monitoring, including X-ray examination (pelvic) and monitoring of urine volume change, should be carried out. The retention of the nephrostomy tube may reduce, even eliminate spontaneous urination through the primary urethra, and the increase or recovery of spontaneous urination indicates that the magnet ring may fall off (or eliminate from the body for a female). Among nine cases, magnets fell off naturally 15.55 ± 2.74 days after MCA, and for one case, the magnets were removed under endoscope 72 days after MCA due to re-ureterostenosis after open ureterovesical replantation 6 months ago as well as long and hard scar tissue between the magnets. In their study, the operation was performed successfully among nine cases, and another one case received re-stenting for re-ureterostenosis, the follow-up time for all of the cases was >1 year, no re-ureterostenosis occurred, the safety and effectiveness of the operation are confirmed. Compared with conventional surgical methods, MCA has many advantages, such as simple operation, minimal invasion, quick recovery, high success rate, high acceptability, and low cost. However, complications like reflux pyelonephritis, urinary tract infection, and anastomotic leakage occurred. The reason for this may be that MCA failed to follow the original anatomical structure in recanalization.

As a new breakthrough as an innovative therapy for ureterostenosis after kidney transplantation, as well as a model of "combination of medicine and industry," MCA has enriched relevant clinical treatment means. In this study, MCA for the treatment of ureterostenosis after kidney transplantation in China, proved the safety and feasibility of this treatment regimen, and also provided a new method or thought for the treatment of other diseases in the field of kidney transplantation. However, considering that the sample size of this study is small, the period for observation and follow-up is short, and there is no control group, the long-term effectiveness is still needed to be further observed.

Conflicts of interest

None.

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