Reviews of the Cook Medical Resonance Stent | Which Medical Device

Features

A recent development is the ‘Resonance^TM’ metallic double- pigtail ureteric stent that is formed by a tight spirally coiled metal wire of a special alloy (COOK, Ireland) (Fig. 1), which aims to prevent tumour in-growth and resist encrustation, thereby providing primary patency rates over longer periods of time.

This device was initially designed for cystoscopic retrograde insertion by urologists, and we now have some experience for percutaneous (antegrade) placement of this ‘ResonanceTM’ metallic ureteric stent for the management of patient with malignant ureteric obstruction. It is hoped that these stents can remain ‘in situ’ for 12 months before stent change is necessary. This would obviate the need for regular stent changes and offer significant benefit for these patients with limited life expectancy. 

Design/construction

The ‘ResonanceTM’ stent (COOK, Ireland) is a continuous, unfenestrated all-metal double pigtail ureteric stent with no end or side holes and has an internal safety wire that is welded to both closed ends (Fig. 1), therefore it is deployed through a long sheath rather than over a guidewire. It is made of MP35N® alloy which is a composite of non-magnetic nickel-cobalt-chromium-molybdenum. This metal alloy is corrosive resistant, MRI compatible and has ultrahigh tensile strength.

In Use

For the one-stage procedure, an antegrade approach is performed by puncturing a dilated interpolar calyx using a 19G sheathed needle under ultrasound guidance. A nephrostogram is performed to outline the collecting system. Fig. 2 shows a left tight distal ureteric stricture caused by recurrent cervical cancer.  A J- tip guidewire (85cm, COOK) is inserted into the collecting system, over which a 6F manipulation catheter (Torcon Blue, 6F, 55cm, COOK) is used to cannulate the ureter. A hydrophilic-coated guidewire (Hiwire, 150cm, COOK, Ireland) is used to negotiate the stricture so that the 6F manipulation catheter can be passed over the wire into the bladder. The guide-wire is exchanged for a superstiff Amplatz guidewire (Boston Scientific, MA) and the catheter is removed. A co-axial system of catheter/sheath is then passed over the wire - an inner 5F ureteric catheter and an outer 9F introducer sheath (COOK, Ireland) (Figs.3 a, b). Both the guidewire and the inner ureteric catheter are then removed leaving the tip of the outer sheath in the bladder and a 6F ‘ResonanceTM’ metallic ureteric stent (COOK, Ireland) is then inserted through the introducer sheath into the bladder using a plastic pusher at the proximal end.

Once the distal pigtail has formed in the bladder, it is important to check the proximal end to avoid pushing the ureteric stent too far in, as there is no retrieval thread/ mechanism with this deployment kit (Figs. 4a, b). Once the proximal end is placed within the calyx, the final step is to remove the introducer sheath over the pusher whilst holding the pusher in a constant position. When the introducer sheath reaches a marked site on the pusher, there is then only the proximal pigtail left inside the sheath at that point (Fig. 5). Further removal of the sheath over the pusher allows the formation of the final pigtail in the collecting system (Fig.6).

This new ‘Resonance ^TM’ metallic double- pigtail ureteric stent consists of a tight spirally coiled metal wire (COOK, Ireland) and aims to prevent tumour in-growth. It functions as a conventional double-pigtail ureteric stent with better primary patency rate and a one year in-dwelling life span. It has no end hole, and the urine drains primarily around the outer aspect of the spiral coiled metal, although if pressure within the urinary system increases urine can enter the internal lumen of the coil and then drain outwards once a low pressure system is encountered (beyond the stricture).

Results so far

In our experience, the anchorage with the guide wire and inner ureteric catheter allows very tight malignant strictures to be negotiated by the wider bore introducer sheath. The introducer sheath allows insertion of the metallic double pigtail ureteric stent with ease. Although there is no retrieval mechanism, this has proven not to be a problem with careful planning and placement. There are commercially available snares and other retrieval devices available to us if there is a need to retrieve a malpositioned ureteric stent. 
 
To date, we have demonstrated that despite the fact that this stent has a different deployment mechanism to other antegrade stents we have used hitherto, it can be inserted with relative ease after an initial learning curve. . All the stents at the time of exchange were changed via a cystoscopic approach with relative ease by the urologists. Some urologists prefer to pass a guidewire alongside the stent as this stent does not have an end hole for cannulation by the guidewire whilst others prefer to remove the stent before reinsertion of the stent retrogradely.  Here is an example of one stent that was removed in our institution at 1 year had remained patent on imaging and was free of any significant stent encrustation at the time of removal (Fig. 7). However, in patients known to be recurrent stone formers, there is a risk of developing encrustation around the stent as happened in one of our patients (Fig. 8). Therefore careful patient selection is important when choosing the type of stent and these patients will require closer monitoring regarding their stent status.  

Our initial experience with ‘Resonance^TM’ metallic ureteric stent indicates that they may provide adequate long term urinary drainage (up to 12-months) in patients with malignant ureteric obstruction but without significantly bulky pelvic disease. This obviates the need for regular stent changes and would offer significant benefit for these patients with limited life expectancy. 

In addition, for this selected group of patients, not only does this stent improve their quality of life, but also provides a cost efficient service. The cost of this stent including the deployment kit is £600 (870 Euros) in our centre and for most conventional plastic stents, at least 2 –3 stent changes per year are required for each patient. Each visit, including the theatre time, anaesthetic support and overnight hospital stay amounts to about £2000 (2900 Euros) on average per visit. 

Summary

Despite of the initial higher cost of the individual stent when compared with conventional plastic stents, we consider that the ‘Resonance TM’ stent (COOK, Ireland) is a useful and valid alternative for patients with malignant disease who require long term urinary drainage. 

Acknowledgement: The ‘Resonance ^TM’ metallic ureteric stents were provided by COOK, Ireland.

Dr Tze Wah
Consultant Interventional and Uroradiologist
St James Hospital
Leeds, UK