Radiopacity and hounsfield attenuation of cystine urolithiasis: case series and review of the literature

Establishment and application of a nomogram diagram for predicting calcium oxalate stones in patients with urinary tract stones

This retrospective study aims to examine the correlation between calcium oxalate (CaOx) stones and common clinical tests, as well as urine ionic composition. Additionally, we aim to develop and implement a personalized model to assess the accuracy and feasibility of using charts to predict calcium oxalate stones in patients with urinary tract stones. A retrospective analysis was conducted on data from 960 patients who underwent surgery for urinary stones at the First Affiliated Hospital of Soochow University from January 1, 2010, to December 31, 2022. Among these patients, 447 were selected for further analysis based on screening criteria. Multivariate logistic regression analysis was then performed to identify the best predictive features for calcium oxalate stones from the clinical data of the selected patients. A prediction model was developed using these features and presented in the form of a nomogram graph. The performance of the prediction model was assessed using the C-index, calibration curve, and decision curve, which evaluated its discriminative power, calibration, and clinical utility, respectively. The nomogram diagram prediction model developed in this study is effective in predicting calcium oxalate stones which is helpful in screening and early identification of high-risk patients with calcium oxalate urinary tract stones, and may be a guide for urologists in making clinical treatment decisions.

Endoscopic Stone Composition Identification: Is Accuracy Improved by Stone Appearance During Laser Lithotripsy?

OBJECTIVE

To evaluate if videos during laser lithotripsy increase accuracy and confidence of stone identification by urologists compared to still pictures.

METHODS

We obtained representative pictures and videos of 4 major stone types from 8 different patients during ureteroscopy with holmium laser lithotripsy. A REDCap survey was created and emailed to members of the Endourological Society. The survey included a picture followed by the corresponding video of each stone undergoing laser lithotripsy and additional clinical information. Each picture and video included multiple-choice questions about stone composition and response confidence level. Accuracy, confidence levels, and rates of rectification (change from incorrect to correct answer) or confounding (correct to incorrect) after watching videos were analyzed.

RESULTS

One hundred eighty-seven urologists responded to the survey. The accuracy rate of stone identification with pictures was 43.8% vs 46.1% with videos (P = .27). Accuracy for individual stones was low and highly variable. Video only improved accuracy for 1 cystine stone. After viewing videos, participants were more likely to rectify vs confound their answers. Urologists were more likely to be confident with videos than pictures alone (65.4% vs 53.7%, respectively; P <.001); however, confident answers were not more likely to yield accurate predictions with videos vs still pictures.

CONCLUSION

Stone identification by urologists is marginally improved with videos vs pictures alone. Overall, accuracy in stone identification is low irrespective of confidence level, picture, and lithotripsy video visualization. Urologists should be cautious in using endoscopic stone appearance to direct metabolic management.

Non-contrast computed tomography characteristics in a large cohort of cystinuria patients

Purpose

Cystine stones are widely considered hard and difficult to treat. Hounsfield Units (HU) are used in other stone types to estimate ‘hardness’ and treatments based on that finding. Our objective was to report mean HU of cystine stones in vivo in a large case series of cystinuria patients and assess for differences in genotype.

Methods

A prospective case series of cystinuria patients referred to a specialist centre was analysed. CT imaging was assessed by two independent radiologists to determine in vivo attenuation of cystine calculi. Mean HU was compared for both cystinuria genes (SLC3A1 and SLC7A9) using an independent t-test.

Results

164 adult cystinuric patients were identified (55% male), median age 43 years (range 18–80). Median follow up was 31 months (IQR 10–62). Genetic data available for 153/164 (93%) demonstrated 97 SLC3A1 (63%) and 55 (36%) SLC7A9 mutations (39 homozygous, 16 heterozygous) and one heterozygous for both SLC3A1/SLC7A9. 107 patients had CT images available demonstrating calculi. Median HU across the cohort was 633 (5th to 95th centile 328–780). There was no difference in mean HU between SLC3A1 and SLC7A9 genotypes (p = 0.68) or homo and heterozygous SLC7A9 (p = 0.70). Mean HU correlated with stone size (Pearson correlation coefficient = 0.51, p < 0.001).

Conclusion

In this large single centre cystinuria cohort, mean HU was low for stones that are difficult to treat. Calculi of < 800 HU should prompt consideration of a cystinuria diagnosis. Attenuation was not associated with genotype, and distinct ‘smooth’ and ‘rough’ stones were not observed. Calculi with HU > 1000 are unlikely pure cystine, and in a known cystinuric would suggest conversion to another stone type.

Electronic supplementary material

The online version of this article (10.1007/s00345-020-03509-0) contains supplementary material, which is available to authorized users.

A single center's experience in pediatric cystine stone disease management: what changed over time?

The authors aimed to evaluate the factors affecting clinical outcomes of cystine stone disease in children and to understand the change in disease management over time. Between January 1991 and September 2017, the demographic and clinical data of pediatric patients with documented cystine stone disease were retrospectively analyzed. Patients with at least 12-month follow-up were included. Disease management and clinical outcomes were compared between the first and second 35 patients managed during the study's time frame. A total of 70 patients were included. The female to male ratio was 30/40. The mean age and follow-up period was 29.8 ± 40.1 months and 106.5 ± 56 months, respectively. The mean initial procedure number to treat the first stone episode was 2.4 ± 1.6. Single stone and single affected site were significant predictors for stone clearance. Overall, patients underwent a mean of 5.5 procedure during their follow-up. Recurrence was detected in 71.4% (50/70) of patients. Residual fragments and non-compliance to medical treatment after the initial intervention were significant predictors for recurrence within shorter interval period. 31.4% (22/70) of patients had renal atrophy during follow-up. They were older at the initial diagnosis and had average urine pH lower than 7.5. The first 35 patients had more open procedures. Still, they had more recurrence rate and tend to have more renal atrophy. As a conclusion, cystine stone disease has a recurrent course in children. Stone and fragments entirely removed (SaFER) concept with all minimally invasive methods available and strict follow-up should be the basis for any management plan.

How should patients with cystine stone disease be evaluated and treated in the twenty-first century?

Cystinuria continues to be one of the most challenging stone diseases. During the latest decades our knowledge of the molecular basis of cystinuria has expanded. Today 160 different mutations in the SLC3A1 gene and 116 in the SLC7A9 gene are listed. The full implications of type A, B or AB status are not yet fully understood but may have implications for prognosis, management and treatment. Despite better understanding of the molecular basis of cystinuria the principles of recurrence prevention have remained essentially the same through decades. No curative treatment of cystinuria exists, and patients will have a life long risk of stone formation, repeated surgery, impaired renal function and quality of life. Therapy to reduce stone formation is directed towards lowering urine cystine concentration and increasing cystine solubility. Different molecules that could play a role in promoting nucleation and have a modulating effect on cystine solubility may represent new targets for cystinuria research. Investigation of newer thiol-containing drugs with fewer adverse effects is also warranted. Determining cystine capacity may be an effective tool to monitor the individual patient's response. Compliance in cystinuric patients concerning both dietary and pharmacological intervention is poor. Frequent clinical follow-up visits in dedicated centres seem to improve compliance. Cystinuric patients should be managed in dedicated centres offering the complete range of minimal invasive treatment modalities, enabling a personalized treatment approach in order to reduce risk and morbidity of multiple procedures.