Pearl in a seashell: epitaxy of solitary cystolith on the leftover curl of a double j stent – a case report

Abstract

Introduction and importance:

Epitaxy is a process of stone formation in an intricate pattern of layers over a nidus. This case report highlights rare phenomenon of cystolith formation through epitaxy on a leftover curl of double j stent (DJ stent), emphasizing the importance of careful post-removal assessment and management to prevent complications.

Case presentation:

A 30-year-old male presented with dysuria and intermittent urination for 1 month. He had a history of ureterolithotripsy and DJ stent insertion 3 years ago, with a difficult stent removal a year prior. Examination revealed suprapubic tenderness, and lab tests showed normal blood count and renal function, with some red and white blood cells in urine. Imaging revealed a >5 cm bladder stone associated with a leftover DJ stent curl. After stabilizing the patient, cystolithotomy was performed, removing large stone, and stent curl. The stent curl likely served as the core for stone formation. The patient recovered well during follow-up visits.

Clinical discussion:

Ureteral stents, developed over a century ago, are widely used in urology, particularly after upper tract stone procedures. However, prolonged use of DJ stent can lead to complications, including encrustation, breakage, and stone formation, especially calcium phosphate stones. There are many conditions that lead to stone formation on DJ stents like urinary tract infections, metabolic disorders, recurrent stone disease, and prolonged indwelling time of stent inside the urinary system.

Conclusion:

Careful monitoring and management of foreign bodies in the bladder are crucial to prevent vesical stone formation. Timely removal of DJ stents is essential to avoid encrustations and ensure complete elimination, preventing future nidus-related stones. Proper handling of impacted DJ stents is vital during treatment.

Introduction

Roh et al's^[1^] epitaxy is a process of stone formation in an intricate pattern of layers over a nidus. The crystal deposition leading to a bladder calculus is a common urological diagnosis. There are many reasons behind their primary formation in the urinary bladder like bladder outlet obstruction, urinary tract infection (UTI), and neurogenic element. They also develop on foreign bodies left over in urinary systems like any leftover part of double j stent (DJ stent). There are many types of ureteral stents that are in use however DJ designed stent first introduced by Finney in 1978 is most commonly utilized^[2^]. Ureteral stents-related complications are globally known since the tremendous increase in their use in urological procedures since last decades. These complications can be lumbar pain, UTIs, hematuria, encrustations, and calcifications of ureteral stents. These stents can also get fragmented, obstructed, or migrated and can make situation difficult for their removal^[3^].

HIGHLIGHTS

• This case illustrates the rare occurrence of cystolith formation through epitaxy on the leftover curl of a double j stent (DJ stent), highlighting the importance of post-removal assessment to prevent complications.

• The case emphasizes the potential risks associated with prolonged use and difficult removal of DJ stents, including stone formation and encrustation, which may require surgical intervention.

• The report underscores the significance of timely removal of DJ stents to avoid complications such as encrustation and vesical stone formation, ensuring complete elimination of foreign bodies from the bladder.

The formation of stone over stents are considered related to complex processes like formation of biofilms by bacterial colonization, stents related factors, patient related factors, and epitaxy.

Vesical stones themselves can present with any of the following symptoms pain penile region, suprapubic discomfort, and dysuria, intermittency of urine, hematuria, and urinary retention^[4,5^]. Kaul et al^[6^] usually diagnosed on x-ray radiography, ultrasonography, and plain computed tomography for complex cases. Various treatment modalities are used for vesical stones depending on the size of the stones and the clinical expertise and urological equipment available. Small vesical calculi usually of 1–2 cm stones are manageable with cystolitholapaxy while stones more than 2 cm in size are manageable with percutaneous cyst lithotripsy or open cystolithotomy^[6^].

Epitaxy is the formation of stone in the form of layers over some time but the complete encasement of the curl of DJ stent inside the calculus is a novel finding and less data available on formation of such intricate stone formation with layered formation of three cores with innermost of uric acid, middle one of calcium oxalate and outermost calcium phosphate around DJ stent in radial layers around a curl of DJ stent which was retrieved by open cystolithotomy. This case report has been reported in line with the SCARE criteria^[7^].

Clinical presentation

A written informed consent was obtained from the patient based on the journal’s policies for the publication of this case information and accompanying investigation.

Case history/examination

A 30-year-old male presented with dysuria and intermittency of urine for 1 month. He has a history of right-sided ureterolithotripsy for right-sided mid-ureteric stone and DJ stent insertion 3 years ago. He also had a history of difficult removal of that forgotten DJ stent 1 year back. The patient did not have any comorbidity. On examination, his suprapubic region was mildly tender on deep palpation and the rest of the examination was unremarkable.

Differential diagnosis

The formal diagnosis at the time included bladder stone (bladder calculus), post-surgical complications, Chronic UTI, bladder tumor or malignancy, interstitial cystitis, bladder pain syndrome, and bladder outlet obstruction.

Investigations

The routine laboratory investigations demonstrated hemoglobin 11 gm/dl white blood cell (WBC) count of 7000 × 10⁹/L, platelet count of 254 000 × 10⁹/L, urine examination shows 10–20 red blood cells, 5–10 WBCs, and renal function tests were within normal range and the rest of the laboratory investigations were unremarkable. The Urine complete examination showed 3–4 pus cells and 3–4 RBCs with all other parameters within normal limits. The culture and sensitivity test were negative for any growth of bacteria. X-ray pelvis demonstrated a spherical shape radiopaque shadow in the urinary bladder region (Fig. 1). His ultrasound shows a solitary 5.2 × 3 cm oval-shaped stone in the urinary bladder with no other stone or hydronephrosis in either kidney (Fig. 2). Computed tomography scan (CT scan) shows a large oval shape calculus of about 5.1 × 3.2 cm (Fig. 3).

Figure 1.

Plain x-ray KUB depicting epitaxy of a solitary cystolith on the left-over curl of DJ stent.

Figure 2.

Ultrasound bladder showing 5 cm foreign body.

Figure 3.

CT KUB showing stone inside urinary bladder.

Treatment intervention

After complete optimization of the patient, due to huge size and smooth of stone endoscopic removal was avoided and his cystolithotomy was done, and the stone was retrieved (Fig. 4). The stone was broken into pieces and a curl of forgotten DJ stent made up of a synthetic polymer polyurethane was found inside the stone just like a pearl is formed in the sea shell and urologically we can call it a curl in a vesical stone (Fig. 5). The case was retrospectively reviewed to find out the reason behind such formation and it could be hypothesized that the curl was left inside the urinary bladder or kidney by the surgeon during the removal of an encrusted DJ stent in toto and that curl served as a nidus for this layer-by-layer formation of stone over this curl (Fig. 6) (Table 1). During the patient’s recovery period after surgery, the healthcare team closely monitored their progress to promote proper healing and prevent any potential issues. The patient received effective pain management with paracetamol 500 mg taken orally twice a day for 5 days. To prevent infection, ceftriaxone 1 gm was administered intravenously twice a day for 5 days. On the second day after surgery, the urethral catheter was removed and the patient had normal urinary output. With no signs of discomfort or health concerns, the patient was discharged on the second postoperative day with a clean bill of health. The follow-up period was uneventful. However, in order to investigate further about the formation of stone the curl of DJ stent was sent to laboratory for bacterial culture and it was found heavily loaded with the colonies of E. coli, and pseudomonas bacteria and the chemical analysis of the stone depicted calcium oxalate 62% calcium phosphate 25% and uric acid 13%, respectively. The patient was advised that he should regularly go for his metabolic profile after every 6 months and use adequate levels of citrates and regularly monitor his pH of urine and keep in contact with his urologist.

Figure 4.

Removal of stone by open cystolithotomy.

Figure 5.

Broken DJ fragments retrieved after breaking stone.

Figure 6.

Flowchart depicting steps of events in vesical stone formation.

Table 1.

Sequence of events leading formation of vesical stone over foreign body through epitaxy

No of steps	Diagnosis	Management
Step 1	Patient presented with right flank pain due to right side mid-ureteric stone.	Right side ureteroscopy done and double j stent placed.
Step 2	Patient forgot stent for 2 years and presented with flank pain and dysuria due to severely encrusted forgotten stent right side.	Attempted to remove that forgotten encrusted stent and majority of stent removed but a part of stent left inside.
Step 3	Dysuria and intermittency of urine 1 month due to large vesical stone diagnosed at presentation.	The case studied retrospectively and no definitive reason identified behind why a part of stent remained inside. However, hypothesis can be made probably the upper curl remained inside later came down and served as nidus for epitaxy.
Step 4	Epitaxial formation of stone over a left-over curl of DJ stent developed in urinary bladder.	Open cystolithotomy.

Discussion

The vesical stone formation is ancient pathology known to mankind and its formation is not only dependent on the left-over curl of DJ stent or any other foreign body. There are a lot many reasons behind stone formation like malnutrition, dehydration, and metabolic disorders. Epitaxy is a radial formation of stone layer by layer over a nucleus that can be any crystal or any foreign body. The mechanisms behind formation of encrustations over stents are not clearly defined and the world is still in the search of an ideal stent. This case study emphasizes on finding the reasons behind formation of such intricate stones and the importance of meticulous handling of stents during their removal and insertion.

More than a hundred years ago, Shoemaker made a ground-breaking contribution by documenting the first use of a ureteral catheter, which heralded the advent of ureteral stents in the treatment of numerous urological conditions. DJ stents are used widely in urological systems for ensuring drainage post-operatively after managing upper tract stone disease. With the passage of time these stents have evolved into many types in the context of design, material, the coating used over them and indwelling time. They are available in different shapes like single J, double j, magnetic tip, pig tail, and meshed shapes^[8^]. The material of the stents is broadly divided into two categories synthetic and biodegradable stents and the most common synthetic stents used are made up of silicon and polyurethane. The biodegradable stents are mostly made up of polylactic acid and polyglycolic acid. The metallic stents are also used for long-term placement. The coatings used over them are of different types like drug-eluting, anti-fouling, anti-microbial, and lubricating and their major purpose is to save stent from encrustations and blockage^[9,10^].

Usually, DJ stents are kept for 6 weeks but can also be placed longer depending on the indications^[11^]. The short-term indications are usually after post-ureteroscopy in managing ureteral stones, in reconstructive urological procedures like pyeloplasty or to prevent ureter from trauma in abdominal or gynecological procedures. The long-term placement is usually required in malignant encasement or in retroperitoneal fibrosis^[12^].

The exact mechanism behind formation of encrustation is unclear and there are many studies in literature who worked to find the correlation between DJ stent and encrustation development like Singh et al^[13^] in their study on encrusted polyurethane ureteral stents found that encrustations are attributed to multifactorial reasons like long indwelling time, sepsis, chronic infections, congenital anatomical renal abnormalities, and recurrent stone formation history. Similarly, Tunney et al^[14^] studied pattern of encrustation formations on five different kind of stents materials in hydroxyapatite and struvite urine models. He utilized scanning electron microscopy and atomic absorption spectroscopy techniques to find that the silicon stent is least prone to encrustations and as the time passed it becomes more resistant to encrustations in comparison to other materials like Siltek, percuflex, and polyurethane^[14^]. In another study by Tomer et al^[15^] narrated encrustations are formed due to two main reasons one is due to elevated levels of minerals in urine like calcium, oxalate, and phosphorus and other reason is urease producing bacteria like proteus, Klebsiella keep levels of pH high and led to formation of struvite stones but there are many risk factors that contribute in the development of encrustations over stent^[15^] (Table 2).

Table 2.

Risk factors associated with stent encrustation and stone formation

No	Risk factors
1	Indwelling time [R9]
2	Bacterial colonization [R10]
3	Urinary tract infections [R10]
4	Diabetes mellitus [R12]
5	Chronic renal failure [R12]
6	Pregnancy [R12]
7	History of stone disease [R8]
8	Malabsorptive disorders [R8]
9	Low health education [R6]
10	Noncompliance of patients [R6]

Similarly, Kawahara et al^[16^] narrated that ureteral stent patency, length, and position didn’t correlate with risk of encrustations but caliber of stent has strong correlation as he found more encrustations in 6fr caliber stent than 7fr stent. Whereas the presence of severe mineral deposition can compromise the stent tensile length facilitating its rupture during removal and can induce ureteral damage and avulsion as well^[17^].

These stents have various complications if left over for a longer time in the renal system like encrustations, breakage of stents, and stones formation over the stents. These complicated stents are difficult to remove and during their retrieval, there is a great chance that their some parts may remain inside the kidney or bladder which later serves as a nidus for further stone formation. These stents were initially utilized to address complications related to the urinary tract, such as ureteral or renal calculi, as well as during renal transplant and upper urinary tract reconstructive surgeries. Various surgical techniques, including endourological, laparoscopic, robotic, and traditional methods, were employed in these procedures. From a therapeutic perspective, ureteral stents played a vital role in alleviating obstructive uropathy and offered a conservative treatment option for trauma affecting the upper urinary tract^[18,19^]. The incidence of vesical stone formation is less than 5% globally and its prevalence is higher in the Middle East and developing world probably due to dietary factors. The vesical stone formation is attributed to bladder outlet obstruction, prostate disease, and UTIs. Foreign bodies like Foley catheters, DJ stents, and supra-pubic catheters can also play a role in the formation of vesical stones via infection or encrustations. Bladder augmentation surgeries, urethral strictures, and radiation exposure also serve as predisposing factors for the formation of primary bladder stones^[20^].

Some kidney stones also pass through ureters in the bladder and later layers develop over them in the urinary bladder same as over a retained foreign body. These stents when forgotten for a longer duration inside serve as a nidus for stone formation mostly these stones are calcium phosphate stones. The other bladder stone types are of uric acid, calcium oxalate, and struvite in origin. The bladder stones which are formed in acidic pH are uric acid, calcium oxalate, and cysteine for which the alkalinizing agent can be used as initial therapy to manage and prevent further stone formation like potassium citrate and sodium bicarbonate^[21^]. Epitaxy is a phenomenon of layer-by-layer growth of stone over a nucleus and many such vesical calculi are reported with laminated creation of such stones without the presence of any foreign body^[1^]. This phenomenon for such vesical stone formation is proposed by many authors like Lonsdale^[22^] narrated that epitaxy is a geometrical biomineralization of different compounds in a specific layered pattern over one another most commonly the calcium phosphate and calcium oxalate deposit over uric acid crystals in intricate fashion to make large stones in which the outer layers are mostly of phosphate crystals. In another study by Meyer et al^[23^] documented calcium oxalate monohydrate crystals served as nidus for the deposition of calcium phosphate crystals investigated by electron microscopy. Similarly, Grover et al^[24^] found in their experimental study that calcium phosphate crystals can serve as nidus for calcium oxalate stone formation in un-diluted human urine samples. Hence it shows that crystals can attract crystals to make such intricate stones with or without a foreign body and the mechanisms behind such attractions are less well understood and less data is available to find any correlation between encrustation development via epitaxy.

However, there are also cases reported in which stones are formed over Foley catheters, DJ stents, and over-displaced intra-uterine contraceptive devices^[25^]. The smaller stones are removed through cystolitholapaxy and larger stones more than 2 cm are managed with cystolithotomy. Encrusted DJ stents mostly pose difficulty in their retrieval and are vulnerable to breakage and their broken parts can left behind which later serve as a nidus for such novel findings we just reported.

It is recommended that all the risk factors should be considered before DJ stent placement and in high-risk stone formers stents should be replaced after 6 weeks. The patients with ureteral stents should be regularly monitored for their stent indwelling time and record should be maintained in register. The patients should be educated about the importance of ensuring adequate hydration, and to promptly seek medical advice for UTIs. The study signifies about understanding the complex relation of stents, stones, and epitaxy and emphasize on staying vigilant regarding endo-stents-related complications.

The future demands a biodegradable stent which is resistant to encrustations and if left forgotten no second procedure should require for its removal, moreover surface coatings should resist bacterial colonization and mineral deposition. The artificial intelligence-related software should be installed in patient’s cellular phones to regularly remind them of their stent removal time. Further research is required to find the exact relation and mechanism of epitaxial deposition of different compounds over DJ stent as less data is available in literature.

The limitation of this study is that less data is available on stone formation through epitaxy on DJ stent to compare with our case and we didn’t find some investigational record due to retrospective nature of the study.

Conclusion

The primary formation of vesical stone over a foreign body is not uncommon and it demands meticulous monitoring and handling of such foreign structures during their management. Their timing of removal should be respected so that encrustations or stone formation can be avoided moreover their complete removal should be ensured so that the patient can be prevented from any future sequel of nidus-related vesical stone formation.

Ethical approval

Ethical approval was not applicable as this was a case report. However, the written consent to publish the clinical data of the patient was given and is available on request.

Consent

Written informed consent was obtained from the patient for the publication of this case report and the accompanying images.

Sources of funding

The authors declare that no financial support was received for this work, and no funding was provided for the conduct of this case report.

Author’s contribution

Conceptualization, project administration, supervision, visualization, writing – original draft: R.N.A.; writing – original draft; data curation, writing – review and editing: A.A.; writing – original draft; data curation, review and editing: I.U.H.; writing – original draft; validation, writing – review and editing: S.I.; conceptualization, methodology, writing – review and editing: W.I.; visualization, writing: R.I.K.; methodology; project administration; writing – review and editing: A.A.; writing – original draft, visualization: M.Z.

Conflicts of interest disclosure

The authors declare no conflict of interest.

Research registration unique identifying number (UIN)

This is not applicable, as we obtained written informed consent from the patient for the case report instead.

Guarantor

Aymar Akilimali.

Provenance and peer review

Not invited.

Data availability statement

Upon reasonable request, we are willing to provide all patient data relevant to the case report that is in our possession.