Allium stent for the treatment of a malignant ureteral stenosis: A paradigmatic case

Introduction

The management of ureteral obstruction as a result of benign or malignant conditions can be challenging. To date, chronic ureteral stenosis can be managed with a double J stent or a percutaneous nephrostomy tube, which allows a safe urinary drainage. However, they need to be replaced every few months, and they can be subject to several side effects, such as stent intolerance, infection, encrustation, and obstruction (1, 2).

Metallic stents have tried to overcome these problems, showing promising results in comparison to traditional stents. However, undesirable complications were still associated with these stents, such as urothelial hyperplastic reactions, encrustation, or migration (2, 3). Thanks to the advances in biomaterials, a new generation of biocompatible stents has been developed, to prevent tissue ingrowth into the lumen and early encrustation. Their design, different from the classic double-pigtail stents, should mitigate the irritating effects that lead to a scarce patient tolerance, especially after a long indwelling period. Among these, the Allium ureteral stent (URS; Allium Medical Solutions Ltd, Caesarea, Israel) is a self-expanding stent made of a nitinol skeleton and a polymeric cover that has shown to be an effective choice to treat chronic ureteral stenoses and fistulas, with a good patient tolerability (4-7). We present a paradigmatic case where Allium URS was the optimal choice to treat a malignant ureteral stenosis in a 69-year-old patient intolerant to double-J stent.

Case description

Allium URS stent

It is a self-expanding stent made of a super-elastic nickel-titanium (nitinol) skeleton and a biocompatible polymeric cover (Fig. 1A). The metal component provides radial and longitudinal strength, while the polymer bio-inertness to prevent tissue ingrowth into the lumen and early encrustation (1, 4). The main body has a high radial force and longitudinal flexibility, with softer ends. The Allium URS comes mounted on a dedicated 8-10 Fr delivery system (Fig. 1B), which is hollow like a ureteral catheter, allowing urine drainage. Once released, the Allium URS opens up to 24-30 Fr; its length varies from 10 to 12 cm. Some stents are equipped with a 5 mm anchor connected to the main body. Each end of the stent has three radiopaque markers essential for its correct placement under fluoroscopy. Visual markers can be helpful during cystoscopic maneuvers (Fig. 1C).

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Fig. 1

Allium URS stent and delivery system.

Surgical procedure

Good endourological and radiological facilities are mandatory for the correct placement of Allium URS and similar devices. The procedure was performed under general anesthesia. The double-J was removed and the left ureter contrasted retrogradely through a ureteral catheter, showing the known stenosis of around 6 cm in length, from the uretero-pelvic junction (UPJ) to the lumbar tract of the ureter (Fig. 2A). A 0.035 Terumo guidewire was introduced up to the renal calyxes. We chose not to pass a ureteral balloon dilator over the site of stenosis, considering that the pre-existing double-J stent had left enough space to insert the Allium URS. Under fluoroscopic guidance, using the guidewire, we positioned a 12 cm, 30 Fr self-expanding Allium URS in the stenotic segment, taking care not to cross the UPJ (Fig. 2B). The stent was released and its gradual self-expansion was clearly visible under fluoroscopy, with passage of contrast medium inside it (Fig. 2C). Successively, we started to gently retract the 10 Fr delivery system. As a certain amount of tension was felt during retraction, in order to avoid to dislodge the stent, we left the delivery system in place, waiting for the maximal expansion of the Allium URS, achievable within 24 hours. The day after, an abdominal radiography confirmed the correct placement of the stent and the delivery system was easily removed, together with the bladder catheter. Bed rest for the first postoperative 24 hours is essential to avoid the displacement of the stent.

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Fig. 2

Intraoperative fluoroscopy showing the ureteral stenosis and the deployment of the Allium URS.

Follow-up

At 1 month, the patient was well and the irritative urinary symptoms had disappeared, with a significant improvement in her quality of life. A reno-vesical ultrasound ruled out hydronephrosis, while another abdominal radiography showed that the Allium URS was correctly positioned (Fig. 3). The situation was the same after 6 months, at the last follow-up.

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Fig. 3

One-month abdominal radiography showing the correct placement of the Allium URS.

Conclusions

The management of chronic ureteral obstruction, due to benign or malignant conditions, can be challenging. New-generation metallic stents represent an interesting alternative to conventional drainage techniques such as nephrostomy tube or double-J, aiming to solve the obstruction in a single procedure while avoiding side effects such as tissue erosion, infection, and tube encrustation necessitating frequent replacement (2, 4). Thanks to the advancements in biomaterials, the design and structure of metallic stents has greatly improved in the last years, accommodating to ureteral dynamics while ensuring lumen patency by providing direct wall support.

In particular, Allium URS is made of a super elastic nickel-titanium alloy that guarantees a strong radial force while keeping it flexible. On the contrary, a new biocompatible polymer completely covers the stent to prevent tissue ingrowth and early encrustation. Clinical experience has shown that larger lumen stents and metal-containing stents are not free from encrustation, even if they do so at a much slower rate (1, 8). The bio-inertness of the polymer covering the Allium URS should enhance its ability to resist encrustation. This was confirmed by an accelerated encrustation model conducted on Allium URS, showing a 80% surface coverage after 6 weeks, but with only minimal effect on stent lumen and no lumen closure. The same in vitro study suggested that greater encrustation may occur on the ends of the stent that protrude into urine-filled cavities, where the outer stent surface is exposed to urine (1). In our patient, this was one reason more to avoid the protrusion of the Allium URS in the renal pelvis during its placement in the lumbar ureter. According to the aforementioned study, the encrustation build-up is more evident in the mid-section of the stent rather than in the ends, going along with the concept of segmental stents designed to just bridge the stenotic tract without significantly extending beyond it (1).

According to the recent literature, Allium URS are safe and effective but not devoid of side effects, including migration, residual pain, upper tract dilation, and infection (4-7). Only a few series have been published in the literature, all showing the effectiveness and safety of these stents. Moskovitz et al reported 49 cases with a mean indwelling time of 17 months, observing migration in seven (14.2%) patients, and occlusion in only one stent (4). In a series by Guandalino et al, 36 patients were treated with Allium URS for ureteral stenosis or fistulas, with an overall efficacy of 52.8%. Stent migration, intolerance, and infection were reported 18.9%, 8.1%, and 10.8% of cases, respectively (5). The biggest series up-to-date, published by Bahouth et al, evaluated 92 patients treated with Allium URS worldwide. During a mean follow-up of 27 months, only one stent was obstructed, while stent migration was seen in 11 patients (7). In all series, no problems were reported during stent removal, even after a long indwelling period. In our case, no complications were experienced during the first 6 months of follow-up. Moreover, all the irritative symptoms disappeared thanks to the design of the stent that is only 12 cm long and does not protrude into the bladder. Replacement of the stent, if needed, is scheduled after another 24-30 months.

To correctly place the Allium URS, good endourological and radiological facilities are mandatory. The need for an associated ureteral dilatation with a ureteral balloon must be taken in consideration in cases of tight stenosis: in our patient, the ureteral stenosis allowed the passage of the device without the need of ballooning. However, as we felt a certain tension during the retraction of the delivery system, we decided to leave it in place, waiting for the maximal radial expansion of the stent. We were able to do that, as the delivery system is designed like a normal ureteral catheter, being hollow inside and allowing urine drainage. The next day, the delivery system was easily removed without tension. In all cases, however, it is advisable to maintain the patient at bed rest for 24 hours after the procedure, to limit the risk of stent dislodgement as much as possible.

Other metallic stents have been developed in the last years, such as Memokath, Uventa, and Resonance; all have different features in the attempt to reduce the risk of side effects while maximizing their durability and biocompatibility. The results reported in the literature generally seem to be quite similar to these of Allium URS, even if a proper comparison between devices has not been made yet.

In our opinion, new-generation metallic stents such as Allium URS represent a useful therapeutic option in complicated scenarios of chronic ureteral stenosis, in patients who cannot have or do not want reconstructive surgery and would be dependent on frequent double-J or nephrostomy replacement procedures. The correct patient selection is essential: the ureteral stenosis must be short enough and well localized to be covered by the length of the stent. This device is particularly useful in patients who do not tolerate the double-J stent, as we can avoid both the reflux and the irritative symptoms due to the tail of the double-J protruding into the bladder. When selecting a patient for the placement of Allium URS, we also have to consider the cost-effectiveness of the procedure. It has been suggested that a minimum of two double-J replacement procedures must be avoided in order to achieve an economic benefit from the placement of Allium URS, which (considered alone) is way more expensive than an ordinary double-J stent (6). All these things considered, the ideal candidate for Allium URS could be an oncological patient with an acceptable prognosis and life expectancy, with a localized malignant ureteral stenosis.

This report represent a paradigmatic case of a patient who can benefit from such a device, which allowed to treat the ureteral obstruction, solve the irritative urinary symptoms, and avoid frequent accesses to the operatory room to replace the double-J.