Use of a Memokath™ 045 temperature-controlled memory alloy stent for treating upper renal calyx calyceal neck atresia: a case report

Abstract

Renal calyceal neck atresia is a rare disorder. There is no clear guidance for standard treatment of this condition. The Memokath™ 045 temperature-controlled memory alloy stent is commonly used in the treatment of urethral strictures, but it has not been used for treating calyceal neck atresia. We present a case of a 44-year-old female patient with left lumbar pain who underwent two stages of treatment to resolve calyceal neck atresia located at the upper calyx of her left kidney. The first procedure was transurethral ureteroscopy combined with percutaneous recanalization of the left upper calyx calyceal neck atresia. One 6 F internal stent and one 8 F internal stent were placed, and she was discharged with a left nephrostomy tube. After her urinary tract infection was fully resolved, the patient returned for the second procedure of percutaneous upper renal calyx calyceal neck metal stent implantation. The temporary stents and nephrostomy tube were successfully removed. Our findings suggest that the Memokath™ 045 temperature-controlled memory alloy stent is an effective choice for treating calyceal neck atresia.

Background

Renal calyceal neck atresia refers to a micturition disorder where there is an obstruction or absence of the connection between the calyces and the renal pelvis. This is a rare congenital condition and is sometimes caused by calyceal diverticulum. ¹ Renal calyceal neck atresia can also be an acquired condition caused by ureteric stones or recurrent infections. A complication after pyelolithotomy or renal parenchymal lithotomy in treating complex renal calculi can also be the cause of calyceal neck atresia.^2,3 Calyceal neck atresia can result in urine buildup and increased pressure in renal calyces and tubules, which may lead to complications, such as infection, inflammation, renal tissue ischemia, and even loss of kidney function. The common treatments for calyceal neck atresia include ethanol ablation of the kidney, long-term nephrostomy, calyceal atresia recanalization, and laparoscopic/partial nephrectomy to remove the calyceal atresia.

It should be noted that calyceal neck atresia poses great challenges to operations and postoperative recovery because of its specific location, sometimes resulting in treatments failing to achieve the desired efficacy. The emergence of new devices and materials has led to more options for better management of calyceal neck atresia. In this report, we present a case of a patient who suffered from calyceal neck atresia at the upper calyx of the left kidney and was treated with stenting using a Memokath™ 045 temperature-controlled memory alloy stent. We found that placing the stent with this material successfully resolved the problem, greatly improving the quality of life of the patient. The reporting of this study conforms to the CARE guidelines. ⁴

Case presentation

Patient

A 44-year-old female patient who had a history of right renal atrophy and gallstones sought medical attention for left lumbar pain. The patient had a history of left renal calculi that was treated with percutaneous nephrolithotomy and flexible ureteroscopy for transurethral lithotripsy. She was found to have left upper calyx stenosis in 2020, which was not resolved after percutaneous nephrolithotomy to expand the stenosis. In March 2021, the patient underwent open kidney exploration on the left kidney, in which the operation was terminated intraoperatively because of severe perirenal adhesions. In July 2021, percutaneous nephrolithotomy combined with ureteroscopy was performed, during which calyceal neck atresia at the upper calyx was located. However, recanalization was not successful. The patient was discharged with a nephrostomy tube fixed through the left upper calyx with a daily urine drainage of 500 to 1000 mL.

The patient visited our hospital for further treatment in August 2021. Upon admission, a physical examination showed tenderness in the left kidney area. Blood tests showed an elevated creatinine concentration of 280 µmol/L, while urine tests showed a high white blood cell count of 15,123/µL and a high bacteria count of 7763/µL. A computed tomography scan showed that the right kidney was atrophied, while the left kidney had mild hydration (Figure 1). Taking into account the patient’s history, physical examination findings, and laboratory results, the diagnosis of left renal upper calyceal neck atresia, right renal atrophy, urinary tract infection, and chronic renal insufficiency was considered. We decided that further treatment to correct the atresia should be performed because the patient had an atrophic right kidney that functioned poorly but the left kidney had a functional upper calyx. After consulting with the patient, we devised a treatment plan into two stages. In the first stage, we planned to perform transurethral ureteroscopy on the left kidney to determine the location and recanalization of the calyceal atresia in the upper calyx. At the same time, we planned to establish adequate drainage and infection control. In the second stage, we planned to perform percutaneous metal stenting at the upper calyx neck with a thermal memory alloy stent. Informed consent for treatment was obtained from patient. Antibiotic treatment was administered before the operation.

Figure 1.

Computed tomography scan shows right renal atrophy, gallstones, postoperative left nephrostomy, and left ureteral stent placement.

Operative procedures

At the first stage, after the patient underwent general anesthesia. She was placed in the prone position, and a new 14 F nephrostomy tube was placed and fixed with a ballon after the original channel was dilated to 16 F. A 3-mL mixture of contrast agent and methylene blue was injected through the tube. The nephrostomy tube was then clamped shut. The patient was changed to the oblique supine lithotomy position. A Wolf 8.0/9.8 ureteroscope (Richard Wolf GmbH, Knittlingen, Germany) was then advanced into the urethra and reached to the bladder. One ureteral stent from a previous intervention was identified and removed. The ureteral orifice was identified when the ureteroscope was inserted for the second time, and the ureteroscope was advanced into the upper segment of the left ureter under the guidance of a 3 F ureteral catheter. The blue dye was not observed throughout the renal ureter or kidney, which indicated that there was a blockage. A 5 F ureteral catheter was placed along a zebra guidewire. Retrograde angiography showed mild effusion in the middle and lower calyces but no development in the upper calyx, suggesting that the blockage was at the upper calyx. The possibility of ureteral duplication was excluded (Figure 2).

Figure 2.

Antegrade and retrograde angiography images show upper calyx calyceal neck atresia of the left kidney.

Repeated attempts of retrograde recanalization were not successful. Two zebra guidewires were retrogradely passed under fluoroscopic guidance into the suspected atretic calyceal neck. A 16 F Peel-away sheath (CREATE MEDIC Corporation, Yokohama, Japan) was inserted along the original nephrostomy channel to establish a percutaneous renal channel. A Wolf 8.0/9.8 ureteroscope was advanced into the left renal collecting system to examine the upper calyces to locate the blockage. The retrogradely placed zebra guidewires were not found in the upper calyces, and the suspected atresia site was located. A metal probe was used to penetrate the atresia site and smoothly passed through the calyceal neck under the guidance of the guidewires in the antegrade direction. The retrogradely inserted zebra guidewires were observed afterwards. Antegrade angiography showed a clear image for each calyx of the left kidney, indicating that the blockage was resolved. Two Bard internal stents (6 F and 8 F) (C.R. Bard Inc., Covington, GA, USA) were advanced over the guidewire and positioned across the calyceal neck, with the proximal end in the upper calyx and the distal end in the bladder under the guidance of fluoroscopy. No active bleeding was observed. One 14 F left renal balloon gastrostomy tube was placed along the zebra guidewire and fixed with a skin suture. A volume of 3 mL of contrast reagent was injected into the ballon, and the stents were confirmed to be in proper positions with fluoroscopy (Figure 3).

Figure 3.

Angiography images show recanalization of upper calyx calyceal neck atresia of the left kidney by a superior and inferior combination.

The patient tolerated the procedure well and the postoperative recovery was uneventful. She was discharged with instructions for stent care and follow-ups.

2. The patient returned for the second stage of treatment after her urinary tract infection was fully resolved. The procedure was performed under general anesthesia. After a F16-Foley catheter (CREATE MEDIC Corporation) was inserted into the bladder, the patient was placed in the prone position. A 0.032-inch zebra guidewire was inserted into the proper position along the original percutaneous renal channel. An incision was made on the skin and a fascial dilator was used to dilate the incision to F24. A corresponding Peel-away sheath was indwelled to establish a percutaneous renal channel. A Wolf 12 F nephroscope (Richard Wolf GmbH) was advanced into the left renal collecting system through the channel. Vision was kept clear by flushing with a motor control center perfusion pump. Two previously placed stents were located and pulled out. An attempt to pass the guidewire through the stents was not successful, which indicated that the stents were blocked internally. However, passing the zebra guidewire along the side of the stents through the calyceal neck was successful. The stents were then removed. The suprarenal calyceal neck was dilated with a 24 F balloon directed by fluoroscopy, and the calyceal neck length was measured under the direct vision of the nephroscope. Under the combined guidance of fluoroscopy and nephroscopy, a temperature-controlled memory alloy stent (Memokath™ stent, model 045TW, inner diameter: 20 F, outer diameter: 24 F, outer diameter after expansion of both ends: 42 F, length: 10 mm; PNN Medical A/S, Kvistgård, Denmark) was placed at the calyceal neck. Sterile water at 55°C was used to pass through the metal stent to allow it to expand. This stent was observed under direct vision through the nephroscope, and fluoroscopy showed that the stent had gradually expanded and anchored to the desired position. A ureteroscope was used to directly observe the metal stent. The contrast agent diatrizoate meglumine was injected through nephrostomy tube, and fluoroscopy clearly showed calyces in the left kidney. We confirmed again that the alloy stent was placed at the appropriate position, and the stent was expanded and opened well at both ends. A F16 minimally invasive nephrostomy tube was placed as routine practice, and it was fixed with 4-0 silk thread and connected to a drainage bag (Figure 4).

Figure 4.

Angiography images show percutaneous balloon dilatation of left upper calyceal neck stenosis and metal stent placement in the second-stage operation.

Postoperative course

The patient had an uneventful postoperative recovery. No complaint of abdominal distension or pain was reported. She developed no fever, constipation, or diarrhea. The cystostomy drainage was unobstructed. A physical examination showed stable vital signs. The abdomen was soft, without tenderness or rebound tenderness. The patient reported no percussion pain in either kidney area. The nephrostomy tube was removed before the patient was discharged from the hospital. The patient returned to the hospital for regular postoperative follow up examinations at 6, 8, and 10 months. She was free of urinary tract infection, and her creatinine concentrations were between 180 and 200 µmol/L, which are nearly less than half of the creatinine concentrations before the first operation.

Discussion

Renal calyceal neck atresia is a rare disorder with a complex nature. There have been few reports on the treatment of calyceal neck atresia, and lack of consensus and guideline for its diagnosis and treatment makes it a clinical challenge. Reaching a definitive diagnosis of calyceal neck atresia preoperatively is difficult. However, the diagnosis of calyceal neck atresia can be made by using a guidewire in the attempt of going through the suspected atresia location with endoscopy or by injection of methylene blue solution through a ureteral catheter to observe whether the fluid can be observed in the calyx during the operation. ⁵

Depending on the severity of calyceal neck atresia , treatment options of this condition can range from close monitoring and managing symptoms to surgical intervention to correct the blockage. If renal function is lost but there is no empyema infection, percutaneous nephrolithotomy with absolute alcohol injection or conservative treatment are the usual choices. ⁶ In extreme cases, if the affected kidney develops pyonephrosis, removal of the affected kidney can be an option if the contralateral kidney functions well.

In the present case, the patient had an atrophic right kidney while her left kidney was generally functional. Despite the atresia, there was no obvious signs of dilated effusion or signs of infection in the left upper calyx. The large drainage volume through the calyceal fistula indicated a functional calyx. Therefore, the options of partial nephrectomy, injection of absolute alcohol into the upper calyx, or conservative treatment were not good choices for the patient. Percutaneous nephrostomy drainage can alleviate symptoms and preserve the function of the kidney. ⁷ However, long-term catheter placement may result in recurrent urinary tract infections and reduced quality of life.

The treatment plan that we designed for the patient was to perform intracavitary calyceal neck atresia recanalization and metal stent placement in two steps. The first procedure aimed to locate the position of calyceal neck atresia and recanalize it. At the same time, we aimed to fully resolve her urinary tract infection by placing temporary stents and a nephrostomy tube to achieve adequate drainage. The most important steps are to clarify the position of the calyceal neck atresia, followed by the risk of massive bleeding and false passage formation when the calyceal neck atresia is recanalizing. The second procedure aimed to place a temperature-controlled memory alloy stent at the calyceal neck to achieve long term internal drainage and remove the requirement for a nephrostomy tube. The main consideration during stent insertion is to ensure precise positioning and selection of the appropriate length.

The Memokath™ 045 is a type of stent that is usually used in the treatment of urethral strictures, but it has not been reported to be used in treatment of calyceal atresia.^8,9 This stent is made of a thermo-expandable nickel-titanium alloy, which can change its shape in response to different temperatures. Once the stent is placed in the proper position, it can adapt to the shape required for the destination by changing its temperature, thus providing a comfortable fit. Besides the use of this stent in the treatment of urethral strictures, a case of successful use in treatment of ileal conduit stomal stenosis has also been reported. ¹⁰ The adverse reactions associated with Memokath™ stent implantation are relatively minor, and they include stent migration, pain or discomfort, stone deposition, recurrent stenosis during stent retention, and stent migration. ¹¹

In this present case, we chose the Memokath™ 045 stent for a long-term solution for the patient’s calyceal neck atresia. This stent was placed in the calyceal neck, where the atresia was located, with its two ends containing inverted bulges positioned in the calyceal neck and renal pelvis, respectively. The structure of this metal stent can effectively prevent stent displacement, enabling its long-term use.

The patient’s creatinine concentrations greatly improved in all postoperative follow-ups. The metal stent placement replaced the requirement for a nephrostomy tube, which greatly improved the quality of life of the patient. In addition, this stent placement diminishes the risk of restenosis following dilation. ¹² Our experience indicates that this metal stent placement is a good minimally invasive treatment for patients with calyceal neck atresia and good calyceal function.