Current computed tomography techniques can detect duct of Bellini plugging but not Randall's plaques

Skeletal and extraskeletal disorders of biomineralization

The physiological process of biomineralization is complex and deviation from it leads to a variety of diseases. Progress in the past 10 years has enhanced understanding of the genetic, molecular and cellular pathophysiology underlying these disorders; sometimes, this knowledge has both facilitated restoration of health and clarified the very nature of biomineralization as it occurs in humans. In this Review, we consider the principal regulators of mineralization and crystallization, and how dysregulation of these processes can lead to human disease. The knowledge acquired to date and gaps still to be filled are highlighted. The disorders of mineralization discussed comprise a broad spectrum of conditions that encompass bone disorders associated with alterations of mineral quantity and quality, as well as disorders of extraskeletal mineralization (hyperphosphataemic familial tumoural calcinosis). Included are disorders of alkaline phosphatase (hypophosphatasia) and phosphate homeostasis (X-linked hypophosphataemic rickets, fluorosis, rickets and osteomalacia). Furthermore, crystallopathies are covered as well as arterial and renal calcification. This Review discusses the current knowledge of biomineralization derived from basic and clinical research and points to future studies that will lead to new therapeutic approaches for biomineralization disorders.

Automatic detection of calcium phosphate deposit plugs at the terminal ends of kidney tubules

Kidney stones are a common urologic condition with a high amount of recurrence. Recurrence depends on a multitude of factors the incidence of precursors to kidney stones, plugs, and plaques. One method of characterising the stone precursors is endoscopic assessment, though it is manual and time-consuming. Deep learning has become a popular technique for semantic segmentation because of the high accuracy that has been demonstrated. The present Letter examined the efficacy of deep learning to segment the renal papilla, plaque, and plugs. A U-Net model with ResNet-34 encoder was tested; the Letter examined dropout (to avoid overtraining) and two different loss functions (to address the class imbalance problem. The models were then trained in 1666 images and tested on 185 images. The Jaccard-cross-entropy loss function was more effective than the focal loss function. The model with the dropout rate 0.4 was found to be more effective due to its generalisability. The model was largely successful at delineating the papilla. The model was able to correctly detect the plaques and plugs; however, small plaques were challenging. Deep learning was found to be applicable for segmentation of an endoscopic image for the papilla, plaque, and plug, with room for improvement.

Sensitivity of Noncontrast Computed Tomography for Small Renal Calculi With Endoscopy as the Gold Standard

OBJECTIVE

To compare the sensitivity of noncontrast computed tomography (CT) with endoscopy for detection of renal calculi. Imaging modalities for detection of nephrolithiasis have centered on abdominal x-ray, ultrasound, and noncontrast CT. Sensitivities of 58%-62% (abdominal x-ray), 45% (ultrasound), and 95%-100% (CT) have been previously reported. However, these results have never been correlated with endoscopic findings.

METHODS

Idiopathic calcium oxalate stone formers with symptomatic calculi requiring ureteroscopy were studied. At the time of surgery, the number and the location of all calculi within the kidney were recorded followed by basket retrieval. Each calculus was measured and sent for micro-CT and infrared spectrophotometry. All CT scans were reviewed by the same genitourinary radiologist who was blinded to the endoscopic findings. The radiologist reported on the number, location, and size of each calculus.

RESULTS

Eighteen renal units were studied in 11 patients. Average time from CT scan to ureteroscopy was 28.6 days. The mean number of calculi identified per kidney was 9.2 ± 6.1 for endoscopy and 5.9 ± 4.1 for CT (P <.004). The mean size of total renal calculi (sum of the longest stone diameters) per kidney was 22.4 ± 17.1 mm and 18.2 ± 13.2 mm for endoscopy and CT, respectively (P = .06).

CONCLUSION

CT scan underreports the number of renal calculi, probably missing some small stones and being unable to distinguish those lying in close proximity to one another. However, the total stone burden seen by CT is, on average, accurate when compared with that found on endoscopic examination.

Metabolic diagnosis and medical prevention of calcium nephrolithiasis and its systemic manifestations: a consensus statement

BACKGROUND

Recently published guidelines on the medical management of renal stone disease did not address relevant topics in the field of idiopathic calcium nephrolithiasis, which are important also for clinical research.

DESIGN

A steering committee identified 27 questions, which were proposed to a faculty of 44 experts in nephrolithiasis and allied fields. A systematic review of the literature was conducted and 5216 potentially relevant articles were selected; from these, 407 articles were deemed to provide useful scientific information. The Faculty, divided into working groups, analysed the relevant literature. Preliminary statements developed by each group were exhaustively discussed in plenary sessions and approved.

RESULTS

Statements were developed to inform clinicians on the identification of secondary forms of calcium nephrolithiasis and systemic complications; on the definition of idiopathic calcium nephrolithiasis; on the use of urinary tests of crystallization and of surgical observations during stone treatment in the management of these patients; on the identification of patients warranting preventive measures; on the role of fluid and nutritional measures and of drugs to prevent recurrent episodes of stones; and finally, on the cooperation between the urologist and nephrologist in the renal stone patients.

CONCLUSIONS

This document has addressed idiopathic calcium nephrolithiasis from the perspective of a disease that can associate with systemic disorders, emphasizing the interplay needed between urologists and nephrologists. It is complementary to the American Urological Association and European Association of Urology guidelines. Future areas for research are identified.

Genome-Wide Gene Expression Profiling of Randall's Plaques in Calcium Oxalate Stone Formers

Randall plaques (RPs) can contribute to the formation of idiopathic calcium oxalate (CaOx) kidney stones; however, genes related to RP formation have not been identified. We previously reported the potential therapeutic role of osteopontin (OPN) and macrophages in CaOx kidney stone formation, discovered using genome-recombined mice and genome-wide analyses. Here, to characterize the genetic pathogenesis of RPs, we used microarrays and immunohistology to compare gene expression among renal papillary RP and non-RP tissues of 23 CaOx stone formers (SFs) (age- and sex-matched) and normal papillary tissue of seven controls. Transmission electron microscopy showed OPN and collagen expression inside and around RPs, respectively. Cluster analysis revealed that the papillary gene expression of CaOx SFs differed significantly from that of controls. Disease and function analysis of gene expression revealed activation of cellular hyperpolarization, reproductive development, and molecular transport in papillary tissue from RPs and non-RP regions of CaOx SFs. Compared with non-RP tissue, RP tissue showed upregulation (˃2-fold) of LCN2, IL11, PTGS1, GPX3, and MMD and downregulation (0.5-fold) of SLC12A1 and NALCN (P<0.01). In network and toxicity analyses, these genes associated with activated mitogen-activated protein kinase, the Akt/phosphatidylinositol 3-kinase pathway, and proinflammatory cytokines that cause renal injury and oxidative stress. Additionally, expression of proinflammatory cytokines, numbers of immune cells, and cellular apoptosis increased in RP tissue. This study establishes an association between genes related to renal dysfunction, proinflammation, oxidative stress, and ion transport and RP development in CaOx SFs.

Kidney stones

Kidney stones are mineral deposits in the renal calyces and pelvis that are found free or attached to the renal papillae. They contain crystalline and organic components and are formed when the urine becomes supersaturated with respect to a mineral. Calcium oxalate is the main constituent of most stones, many of which form on a foundation of calcium phosphate called Randall's plaques, which are present on the renal papillary surface. Stone formation is highly prevalent, with rates of up to 14.8% and increasing, and a recurrence rate of up to 50% within the first 5 years of the initial stone episode. Obesity, diabetes, hypertension and metabolic syndrome are considered risk factors for stone formation, which, in turn, can lead to hypertension, chronic kidney disease and end-stage renal disease. Management of symptomatic kidney stones has evolved from open surgical lithotomy to minimally invasive endourological treatments leading to a reduction in patient morbidity, improved stone-free rates and better quality of life. Prevention of recurrence requires behavioural and nutritional interventions, as well as pharmacological treatments that are specific for the type of stone. There is a great need for recurrence prevention that requires a better understanding of the mechanisms involved in stone formation to facilitate the development of more-effective drugs.

Endoscopic and Pathologic Characterization of Papillary Architecture in Struvite Stone Formers

OBJECTIVE

To describe the endoscopic characteristics of renal papillae in struvite stone formers (SFs).

MATERIALS AND METHODS

From 2009 to 2014, patients undergoing percutaneous nephrolithotomy were prospectively enrolled in our study. Endoscopic analysis and biopsy of papillae were performed to demonstrate the presence and percentage surface area (SA) of Randall's plaque or ductal plug. Comparison with idiopathic calcium oxalate (CaOx) SF and non-SF controls was performed.

RESULTS

We identified 29 struvite SFs to compare with 90 idiopathic CaOx SFs and 17 controls. On endoscopic mapping, 28 struvite SFs (97%) demonstrated Randall's plaque and 9 (31%) had plugging. The average mean SA of Randall's plaque in struvite SF (1.5 ± 1.4%) was less than CaOx SFs (3.7 ± 4.3%, P  =  .0018) and similar to controls (1.7 ± 2.7%, P  =  .76). Average mean plug SA was similar between struvite SFs, CaOx SFs, and controls. On metabolic assessment, 83% of struvite SFs had at least one urine abnormality, with urinary uric acid and oxalate levels significantly higher among struvite SFs compared to controls (P  =  .002). Despite lack of active urinary tract infection, interstitial inflammation was more prevalent in struvite SFs compared to CaOx SFs (43.5% vs 7.3%, P  =  .0001).

CONCLUSIONS

Our findings suggest a limited role for Randall's plaque in struvite stone formation. Struvite SFs have less plaque formation than CaOx SFs, but demonstrate evidence of severe parenchymal inflammation compared to other SFs. The role of this prominent interstitial inflammation requires further study.

Endoscopic and histologic findings in a cohort of uric acid and calcium oxalate stone formers

OBJECTIVE

To characterize the endoscopic and histologic renal papillary lesions in a cohort of uric acid (UA) stone formers (SF).

METHODS

Data were prospectively obtained during percutaneous nephrolithotomy between 2009 and 2013. Renal papillae were endoscopically analyzed to quantitate surface area occupied by plaque or plug, and biopsies were obtained. UA SF were compared with non-SF controls and patients with >50% calcium oxalate (CaOx) in the absence of UA.

RESULTS

There were 23 UA SF; of which 19 stones (83%) were admixed with CaOx and 4 (17%) were pure. Compared with CaOx SF and controls, UA SF had a higher prevalence of diabetes and obesity, greater serum creatinine and UA levels, lower estimated glomerular filtration rate and urine pH, and elevated UA supersaturation. Characteristics of UA SF were compared with 95 CaOx SF and 19 controls. Overall, 23 (100%) UA SF had endoscopic plaque and 13 (57%) plugs. Endoscopically, UA SF displayed a greater incidence of plugging (57% vs 45% vs 11%; P = .006) relative to CaOx SF and controls. Likewise, UA SF had a greater percentage surface area of plugging (0.1 vs 0.0; P = .002) and plaque (2.0 vs 0.9; P = .006) than controls but similar amounts to CaOx SF. Histologic plugs were similar in UA and CaOx SF, although CaOx SF demonstrated greater interstitial inflammation on endoscopic biopsy.

CONCLUSION

UA and CaOx SF have similar amounts of plaque, whereas UA SF have more endoscopic but not histologic collecting duct plugs. These data suggest an overlap between the pathogenesis of UA and CaOx stones. The anchoring site for UA stones remains uncertain.