Failure of ureteral stents subject to extrinsic ureteral obstruction and stent occlusions

Amitay-Rosen, Tal; Nissan, Alon; Shilo, Yaniv; Dror, Ishai; Berkowitz, Brian

doi:10.1007/s11255-021-02810-0

Cited by 13 publications

(9 citation statements)

References 22 publications

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“…Based on previous modeling studies, 9,12,13 it could be anticipated that the number of active side-holes would increase as a result of these physiological curvatures and asymmetries, due to local fluid pressure variations between the stent and ureter lumens driving the fluid into/out of the stent. 13 Similar considerations apply to the stent geometry, which was modeled as straight in the present study but would also present curvatures once deployed in a patient. (b) The study was conducted with the model oriented horizontally.…”

Section: Resultsmentioning

confidence: 93%

“…These findings are also consistent with earlier numerical investigations showing that, in the absence of occlusions of the ureter or stent, the total flow rate partitions between the stent and ureter lumens on the basis of their relative cross-sectional areas. 13 …”

Section: Resultsmentioning

confidence: 99%

“… 12 Stents with smaller diameter had superior drainage performance, including within ureter models presenting mild-to-severe stenoses. Further investigations on the function of side-holes and urine flow distribution in the stented ureter have been carried out in a CFD study by Amitay-Rosen et al 13 Their numerical model replicated either a circumferential occlusion of the ureter or an external pressure applied on one side of the ureter wall. A comprehensive analysis of the urine flow field and pressure levels in the renal compartment was carried out for a range of stent occlusions.…”

Section: Introductionmentioning

confidence: 99%

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The accumulation of particles in ureteric stents is mediated by flow dynamics: Full-scale computational and experimental modeling of the occluded and unoccluded ureter

et al. 2022

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Ureteric stents are clinically deployed to restore urinary drainage in the presence of ureteric occlusions. They consist of a hollow tube with multiple side-holes that enhance urinary drainage. The stent surface is often subject to encrustation (induced by crystals-forming bacteria such as Proteus mirabilis) or particle accumulation, which may compromise stent's drainage performance. Limited research has, however, been conducted to evaluate the relationship between flow dynamics and accumulation of crystals in stents. Here, we employed a full-scale architecture of the urinary system to computationally investigate the flow performance of a ureteric stent and experimentally determine the level of particle accumulation over the stent surface. Particular attention was given to side-holes, as they play a pivotal role in enhancing urinary drainage. Results demonstrated that there exists an inverse correlation between wall shear stress (WSS) and crystal accumulation at side-holes. Specifically, side-holes with greater WSS levels were those characterized by inter-compartmental fluid exchange between the stent and ureter. These “active” side-holes were located either nearby ureteric obstructions or at regions characterized by a physiological constriction of the ureter. Results also revealed that the majority of side-holes (>60%) suffer from low WSS levels and are, thus, prone to crystals accumulation. Moreover, side-holes located toward the proximal region of the ureter presented lower WSS levels compared to more distal ones, thus suffering from greater particle accumulation. Overall, findings corroborate the role of WSS in modulating the localization and extent of particle accumulation in ureteric stents.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The accumulation of particles in ureteric stents is mediated by flow dynamics: Full-scale computational and experimental modeling of the occluded and unoccluded ureter

et al. 2022

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“…In this context, detailed quantitative discussions of the impact of percent stent occlusion on urine flow appear elsewhere. 14 , 15 These studies 14 , 15 demonstrate, in particular, that in the presence of external ureteral obstructions, stent lumen occlusion of >90% in even small regions along a stent can lead to significant increases in renal pressure, thus indicating the inability of the stent to conduct urine efficiently.…”

Section: Discussionmentioning

confidence: 98%

Imaging and Chemical Analysis of External and Internal Ureteral Stent Encrustation

Amitay-Rosen¹,

Dror²,

Shilo³

et al. 2022

RRU

Self Cite

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Introduction Ureteral stents are effective in alleviating flow disruptions in the urinary tract, whether due to ureteral stones, strictures or extrinsic ureteral obstruction. However, significant stent encrustation on the external and/or internal stent lumen walls can occur, which may interfere with stent functioning and/or removal. Currently, there is only limited, generally qualitative, information on the distribution, mineral structure, and chemical content of these deposits, particularly in terms of stent lumen encrustation. Objective To quantify, in an initial investigation, external and internal encrustation in representative, intact ureteral stents. The study investigates possible correlations between patterns of external and internal encrustation, determines mineral structure and chemical composition, and examines the potential for stent lumen obstruction even in the absence of external stent wall encrustation. Study Design High-resolution, laboratory micro-computed tomography (micro-CT) was used to non-destructively image external and internal stent encrustation in four representative stents. X-ray diffractometry (XRD) and scanning electron microscopy–energy dispersive x-ray spectroscopy (SEM-EDS) enabled parallel analysis of mineral structure and chemical content of samples collected from external and internal encrusted material along the distal, proximal and mid-ureteral stent regions. Results Extensive stent lumen encrustation can occur within any region of a stent, with only incidental or minor external encrustation, along the entire length of the stent. External and internal encrusted materials in a given stent are generally similar, consisting of a combination of amorphous (mostly organic) and crystalline mineral deposits. Conclusion Micro-CT demonstrates that significant stent lumen encrustation can occur, which can lead to partial or full stent lumen occlusion, even when the exterior stent wall is essentially free of encrusted material.

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“…In a physiological scenario however, the ureter displays a number of patient-specific curvatures and strictures [ 45 ], and the stent may be in contact with the inner ureter wall in some regions. On the basis of earlier investigations [ 69 ], it could be inferred that the number of ‘active’ side holes may increase due to these physiological curvatures or asymmetries, because of local fluid pressure gradients established between the stent and ureteral lumens. These pressure differences may also locally enhance fluid flow through a porous stent wall.…”

Section: Discussionmentioning

confidence: 99%

Computational simulation of the flow dynamic field in a porous ureteric stent

Yang

Mosayyebi

Carugo

2022

Med Biol Eng Comput

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Ureteric stents are employed clinically to manage urinary obstructions or other pathological conditions. Stents made of porous and biodegradable materials have gained increasing interest, because of their excellent biocompatibility and the potential for overcoming the so-called ‘forgotten stent syndrome’. However, there is very limited characterisation of their flow dynamic performance. In this study, a CFD model of the occluded and unoccluded urinary tract was developed to investigate the urinary flow dynamics in the presence of a porous ureteric stent. With increasing the permeability of the porous material (i.e., from 10−18 to 10−10 m2) both the total mass flow rate through the ureter and the average fluid velocity within the stent increased. In the unoccluded ureter, the total mass flow rate increased of 7.7% when a porous stent with permeability of 10−10 m2 was employed instead of an unporous stent. Drainage performance further improved in the presence of a ureteral occlusion, with the porous stent resulting in 10.2% greater mass flow rate compared to the unporous stent. Findings from this study provide fundamental insights into the flow performance of porous ureteric stents, with potential utility in the development pipeline of these medical devices. Graphical abstract

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Failure of ureteral stents subject to extrinsic ureteral obstruction and stent occlusions

Cited by 13 publications

References 22 publications

The accumulation of particles in ureteric stents is mediated by flow dynamics: Full-scale computational and experimental modeling of the occluded and unoccluded ureter

The accumulation of particles in ureteric stents is mediated by flow dynamics: Full-scale computational and experimental modeling of the occluded and unoccluded ureter

Imaging and Chemical Analysis of External and Internal Ureteral Stent Encrustation

Computational simulation of the flow dynamic field in a porous ureteric stent

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