Memokath Ureteral stenosis by mikeholy

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 Atlas of Surgery

   A novel long-term thermo-expandable ureteric metal stent:
                                 Memokath 051

 Papatsoris AG, Masood J, El-Husseiny T, Ndirika S, Junaid I, Buchholz N

    Department of Urology, Barts & The London NHS Trust, London, UK

Corresponding author: Mr. Noor Buchholz
Director of Endourology & Stone Services
Barts and The London NHS Trust
London, EC1A 7BE, UK
ph. +44 207 6018394, Fax +44 207 601 7844

                                           1 Atlas of Surgery

Double J stents have revolutionized minimal invasive management of malignant and
benign ureteric strictures. However, JJ stents are associated with several problems such as
encrustation (thus requiring 3–6-monthly changes), stone formation, pain, infection,
reflux, decreased ureteric peristalsis and migration. 1 Investigators have focused on the
development of the “ideal” stent that would have friendly maneuverability to the user,
stability after insertion, radiopacity, resistance to encrustation and infection, efficiency in
relieving intrinsic and extrinsic obstruction, long-term patency and low cost.2 In an
attempt to improve upon existing JJ stents, metallic versions were introduced such as the
novel long-term indwelling thermo-expandable Memokath 051T M stent.


The Memokath T M Stent (PNN A/S, Hornbaek/ Denmark) is a thermo-expandable nickel-
titanium alloy spiral stent. Since 1996, it is used as a prostatic and urethral stent for the
treatment of benign prostatic hyperplasia and urethral strictures, respectively. 3 More
recently, a ureteral version Memokath 051              was developed which shaft initially
expanded from 9.5Fr to a fluted end of14Fr, while the current version has a shaft
diameter of 10.5Fr and its fluted end expands to 22Fr. The available lengths are: 30, 60,
100, 150 and 200 mm, while double fluted ended stents can be manufactured in custom-
tailored lengths.

Being a spiral allows the Memokath to bend to adopt the natural curves of the ureter. The
resultant lack of outward pressure against the ureteric wall preserves peristalsis and
minimises the risk of secondary ischaemic damage to the ureter. Also, its titanium
component resists corrosion in the urinary tract. The Memokath TM stent has a thermo-
sensitive “shape memory” as it softens at < 10°C but returns to a pre-formed shape when
warmed to > 50°C, allowing easy insertion and removal. In addition, it has a closed tight
spiral structure which prevents urothelial in-growth, and thus again facilitates easy
removal if required. This is an advantage in comparison with previously used metallic
stents such as the Wallstent, which allow tissue in-growth and makes stent removal

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The Memokath 051            stent is inserted after the length and position of the ureteric
stricture has been determined through either retrograde or antegrade ureterography. 3 The
stricture is then marked between two metallic markers on the skin of the patient’s
abdomen. The distance between markers is measured and a stent of suitable length
chosen. This length must exceed the stricture length. Having passed a guide-wire across
the stricture, balloon catheters or graduated dilators can be used to dilate the stricture to
not more than F12. The Memokath 051 T M, mounted on its introducer, is aligned across
the stricture and the guide-wire removed. The working end of Memokath stent assembly
has a port for injecting hot water to induce stent expansion. Sterile water (5-20 ml)
preheated to 60°C is then flushed through the catheter, thus allowing the alloy to expand.
The proximal end opens to a funnel shape which then rests on the stricture anchoring the
stent. Once expansion has been observed no more hot water is necessary to inject. A
retrograde urogram is performed through the sheath to confirm correct positioning of the
stent and decompression of the upper tract. In addition, the distal end of the stent can be
visualized with a ureteroscope to confirm satisfactory positioning and to exclude
positioning of the stent in the bladder. If the lower segment of the Memokath lies in the
bladder, the theoretical possibility of encrustation is increased [VIDEO 1].

An antegrade version available for insertion through a nephrostomy tract is mounted in
reverse to enable identical positioning. Usually, the procedure takes 20-50 minutes,
patients leave the hospital the day of the procedure and most of them return to their daily
and working activities within a few days. Previous JJ stenting is not essential as with
other metallic ureteric stents.


To date we treated 42 renal units in 38 patients (20 females and 18 males), aged 23-84
years (median age 55.7) with Memokath 051 TM. Strictures were benign in 29 cases and
malignant in 9 cases (table 1), and bilateral in 4 patients (figure 1).

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Figure 1. Bilateral Memokath 051T M

Figure 2. Retrograde Memokath 051T M migration into the kidney

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   Benign strictures (29)

   o                Iatrogenic (post stone manipulation)           4

   o                Gynaecologic injury                            3

   §                          Uretero-vaginal fistula              2

   o                Pelvic inflammatory disease (BIL)              1

   o                Retroperitoneal/ para-aortic fibrosis          2

   o                Pelvic endometriosis                           1

   o                Crohn’s disease                                1

   o                Simple (idiopathic) strictures                12

   §                          in transplant kidney                 1

   o                Vesico-ureteric anastomosis stricture          5

   §                          in transplant kidneys                4

   §                          Bilateral after re-implantation      1

   o                Single kidneys                                    3

   o                Bilateral strictures                              4

   Malignant strictures (9)

   o                Rectum CA                                     2

   o                Cervix CA                                     3

   o                Prostate CA                                   2

   o                Colon CA                                      1

   o                Breast CA (retroperitoneal lymphadenopathy)   1

Table 1. Causes of benign and malignant strictures

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We did not experience any peri- or immediate postoperative complications. The average
hospital stay was 1.5 days and patients were discharged with antibiotics for 5 days. Our
follow-up included clinical examination, U&E’s, X-ray KUB and US of kidneys after 2
weeks, 3 months and then every 6 months. IVU and renal isotope studies were performed
if needed. In 2 patients a flexible ureteroscopy was performed after 1 year, which did not
reveal any ureteric hyperplasia into the Memokath stent.

The average indwelling time of an individual Memokath stent was 8 months. The overall
success rate was 84%. After a mean follow-up period of 17.5 months (1-44) there were
27 (65%) stents in situ. In 8 (19%) cases spontaneous resolution of the ureteric stricture
was revealed after a mean indwelling time of 8.5 months. The remainder 7 (16%) cases
were failures, which were managed with insertion of JJ stents and/or open surgery. The
causes of the failures were: stent encrustration in 4 (11%) cases, retrograde dislodgement
in 1 (3%) case with PUJ stenosis, renal failure in 1 (3%) case due to PUJ stenosis above
the Memokath and malignant obstruction in 1 (3%) case. In 36 (86%) cases no
Memokath exchange took place, while in 3 (8%) cases we performed one exchange, in 1
(2%) case two exchanges and in 2 (4%) cases we performed three exchanges. Taking into
account the Memokath exchanges, a total of 55 Memokath stents was inserted up to date.

A total of 16 complications were revealed after the insertion of the 55 Memokaths (29%).
Among these complications, 6 (11%) were minor involving UTIs, while in the remainder
10 (18%) stent manipulation or other surgery was required due to stent dislodgement (6
cases; 11%) or encrustration (4 cases; 7%). Regarding the UTIs, 2 patients needed
hospitalization for 3 and 5 days in order to receive iv antibiotics, while the other 6
patients with UTI were successfully treated with oral antibiotics only. Stent dislodgments
were retrograde in 2 cases and anterograde in 4 cases. The Memokath stents that migrated
into the kidney were removed with flexible ureteroscopy, while the stents that migrated
into the bladder were cystoscopically removed and exchanged. Regarding the 4 cases of
Memokath encrustration, in 3 cases patients were known stone formers, while the fourth
case involved a transplant anastomotic stricture. The former 3 encrustrations were
initially managed with ureteroscopy and stone fragmentation with the Lithoclast Master
in 2 cases, while in 1 case we wrongly used the Holmium laser as this resulted in stent
fragmentation as well [VIDEO 2]. These cases were eventually managed with open
                                            6 Atlas of Surgery

reconstructive operations (boari flap in 2 and ileum interposition in 1). In the transplant
patient, the encrusted Memokath stent migrated into the bladder and the stricture was
found resolved on retrograde studies. Regarding the 8 cases of spontaneous resolution of
the ureteric stricture, the Memokath stents were expulsed into the bladder in 7 patients,
while in 1 patient the stent was passed with urination. Only 4 patients reported lower
urinary tract symptoms. The 7 Memokath stents were easily removed from the bladder
and retrograde studies confirmed resolution of the ureteric stricture in all cases. Notably,
two cases involved transplant patients where the anastomotic stricture resolved.

Figure 3. Removal of a migrated Memokath 051T M with a balloon catheter


For the UK health system, we have developed a cost-comparison model between JJ and
Memokath stent insertion. 5 A JJ stent insertion including all costs (material, hospital
services, theatre, recovery etc.) comes to ~ 3000 €. Assuming 6-monthly stent changes
and 2 outpatient follow-ups with Xray per year, the total costs to treat a ureteric stricture
with JJ stents is ~ 6600 €/ year. Insertion of a Memokath 051           requires roughly the
same infrastructure. Additional costs arise from the stent itself at ~ 2300 €. Therefore,
Memokath 051 insertion comes to ~ 5300 €. Together with 3 follow-up visits in the first

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year with Xray the total cost is ~ 5700 €. Therefore, in the first year, the Memokath 051
is with ~ 900 € slightly less expensive than treatment with regular exchanges of JJ stent.
However, from the 2nd year Memokath patients will only require 2 yearly follow-up visits
with X-ray KUB at ~ 500 €. Therefore, from the 2nd year after stent insertion, the annual
savings through Memokath 051           is ~ 6000 €. These calculations do not take into
account any time off work or complications and resulting costs.


The successful usage of metallic stents in the vascular system and biliary tree has led
researchers to investigate their use in the urinary tract for the management of benign
prostatic hyperplasia, urethral strictures, detrusor-sphincter dyssynergia and more
recently for the treatment of ureteric strictures.2 Four types of ureteric metallic stents
have been studied:2 self expandable, balloon expandable, covered and thermo-expandable
shape-memory such as the Memokath stent. On the latter there is not much literature
available as yet. However, the data available correspond nicely with our own experience:

Kulkarni et al.6 presented their 4-year experience with 37 Memokath insertions in 28
patients with ureteric strictures. Ureteral obstruction was caused by malignancy in 18
cases and by recurrent benign disease in 10 cases. Upper tract decompression was
achieved in all except 2 patients with residual obstruction due to suboptimal stent
positioning. After a mean follow-up of 20 months (range 3 to 35), 13 patients had a total
of 15 functional stents (bilateral sites and reinsertion in 1 each) and 8 died of malignancy
progression with a total of 13 functional stents. No patient was hospitalized with stent
related symptoms, resulting in improved quality of life. Ureteroscopy that was performed
in 2 cases, 12 months after stent insertion for assessing ureteral obstruction due to
recurrent colorectal carcinoma revealed no evidence of endothelial hypertrophy or stent
encrustation. The authors suggest Memokath insertion for the management of malignant
strictures, especially when survival or cure is expected as well as in selected cases of
recurrent benign strictures.6,7

Klarskov et al.8 inserted 37 Memokath stents in consecutive 34 patients with benign (22
cases), post-radiation (5 cases) or malignant strictures (7 cases). Pre-insertion dilatation

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was impossible in one patient and difficult in two, all of whom had post-irradiation
strictures. Follow-up (median 14 months; range 3-30 months) visits took place after 1
month and thereafter every 3 months. Fifteen stents were in place and functioning with
no complications at death or the end of follow-up, while 22 stents were non-functioning.
Of these 22 stents, 10 had migrated and 12 were malfunctioning mainly because of
stricture length underestimation (successfully replaced in 4 cases). In 4 cases the stents
were occluded by stones after 1-10 months. No tissue in- growth was seen and stent
removal was easy, with the exception of one patient with stent calcification.

Boyvat et al.9 performed antegrade insertion of a Memokath stent in 4 transplant patients
with anastomotic ureter stenosis or complete occlusion. The follow-up (mean 20 months;
range 18-21 months) was performed with creatinine level measurements and
ultrasonography. During the follow-up one stent migrated within 10 days and was
removed cystoscopically, while another one was removed in the 14th month due to
persistent UTI and was replaced with a new one which remained patent. The authors
conclude that antegrade placement of the Memokath stent could be promising alternative
to balloon dilation, JJ stent insertion and open surgical intervention for anastomotic
stenosis or occlusion in kidney transplant recipients.

Arya et al.10 over a 3-year period inserted 13 Memokath stents in 11 patients with benign
ureteric strictures (due to radiation fibrosis, retroperitoneal fibrosis, ischaemic uretero-
ileal anastomosis and scarring after ureteroscopy, diathermy damage, extraluminal
endometriosis and stone passage). Contrast-medium studies were performed immediately
after insertion to confirm the stent position and ureteric patency. Other follow-up
investigations included isotope renography and X-ray KUB at 6-monthly intervals for the
first year, and then annually. The mean follow-up was 18 months (range 1.5–33). In 7 of
the 11 patients, ureteric obstruction was relieved and on follow-up there were no
Memokath stent-related complications. Four stents were removed at a mean of 16 months
(range 4-33), because of stent encrustation in 3 cases and migration in 1 case. Among the
cases of stent encrustation, 2 of these patients had a history of stone disease and recurrent
urinary tract infections.

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The Memokath 051T M stent seems to be an attractive cost effective treatment option for
both benign and malignant ureteric strictures. It has the advantages of immediate
decompression and relief of obstructive uropathy symptoms. It bears minimal risk for
bladder irritation, reflux and flank pain. Insertion, removal and/or exchange of the
Memokath 051T M stent is easy and it can be easily removed with a balloon catheter even
if it migrated into the kidney (figures 2,3) in contrast with previously used mesh metallic
stents.11 It is well tolerated by patients, who do not experience lower urinary tract
symptoms or loin pain. With the Memokath 051T M stent there is no need for frequent
replacement such as every three-six months. From our own experience, we discourage its
usage in active stone formers as well as the use of holmium laser in case of Memokath
encrustation. Interestingly, a 20% rate of spontaneous stricture resolution could be related
with the insertion of the Memokath stent, but further studies are warranted to prove this.


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Annual Meeting, London, 15-16/5/08.
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treatment of transplant kidney ureter stenosis or occlusion. Cardiovasc Intervent Radiol 2005; 28: 326-330.
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