Cystic renal masses: accurate Bosniak classification requires adequate renal CT

Validation of the updated Bosniak classification (2019) in pathologically confirmed CT-categorised cysts

INTRODUCTION

The updated Bosniak classification in 2019 (v2019) addresses vague imaging terms and revises the criteria with the intent to categorise a higher proportion of cysts in lower-risk groups and reduce benign cyst resections. The aim of the present study was to compare the diagnostic accuracy and inter-observer agreement rate of the original (v2005) and updated classifications (v2019).

METHOD

Resected/biopsied cysts were categorised according to Bosniak classifications (v2005 and v2019) and the diagnostic accuracy was assessed with reference to histopathological analysis. The inter-observer agreement of v2005 and v2019 was determined.

RESULTS

The malignancy rate of the cohort was 83.6% (51/61). Using v2019, a higher proportion of malignant cysts were categorised as Bosniak ≥ III (88.2% vs 84.3%) and a significantly higher percentage were categorised as Bosniak IV (68.9% vs 47.1%; p = 0.049) in comparison to v2005. v2019 would have resulted in less benign cyst resections (13.5% vs 15.7%). Calcified versus non-calcified cysts had lower rates of malignancy (57.1% vs 91.5%; RR,0.62; p = 0.002). The inter-observer agreement of v2005 was higher than that of v2019 (kappa, 0.70 vs kappa, 0.43).

DISCUSSION

The updated classification improves the categorisation of malignant cysts and reduces benign cyst resection. The low inter-observer agreement remains a challenge to the updated classification system.

CEUS Bosniak Classification-Time for Differentiation and Change in Renal Cyst Surveillance

It is time for a change. CEUS is an established method that should be much more actively included in renal cyst monitoring strategies. This review compares the accuracies, strengths, and weaknesses of CEUS, CECT, and MRI in the classification of renal cysts. In order to avoid overstaging by CEUS, a further differentiation of classes IIF, III, and IV is required. A further development in the refinement of the CEUS-Bosniak classification aims to integrate CEUS more closely into the monitoring of renal cysts and to develop new and complex monitoring algorithms.

Effect of Ultra-High-Resolution CT on Pseudoenhancement in Renal Cysts: A Phantom Experiment and Clinical Study

BACKGROUND. Ultra-high-resolution CT (UHRCT) allows acquisition using a small detector element size, in turn allowing very high spatial resolutions. The high resolution may reduce partial-volume averaging and thereby renal cyst pseudoenhancement. OBJECTIVE. The purpose of this article was to assess the impact of UHRCT on renal cyst pseudoenhancement. METHODS. A phantom was constructed that contained 7-, 15-, and 25-mm simulated cysts within compartments simulating unenhanced and nephrographic phase renal parenchyma. The phantom underwent two UHRCT acquisitions using 0.25- and 0.5-mm detector elements, with reconstruction at varying matrices and slice thicknesses. A retrospective study was performed of 36 patients (24 men, 12 women; mean age, 75.7 ± 9.4 [SD] years) with 118 renal cysts who underwent renal-mass protocol CT using UHRCT and the 0.25-mm detector element, with reconstruction at varying matrices and slice thicknesses; detector element size could not be retrospectively adjusted. ROIs were placed to measure cysts' attenuation increase from unenhanced to nephrographic phases (to reflect pseudoenhancement) and SD of unenhanced phase attenuation (to reflect image noise). RESULTS. In the phantom, attenuation increase was lower for the 0.25- than 0.5-mm detector element for the 15-mm cyst (4.6 ± 2.7 HU vs 6.8 ± 2.9 HU, p = .03) and 25-mm cyst (2.3 ± 1.4 HU vs 3.8 ± 1.2 HU, p = .02), but not the 7-mm cyst (p = .72). Attenuation increase was not different between 512 × 512 and 1024 × 1024 matrices for any cyst size in the phantom or patients (p > .05). Attenuation increase was not associated with slice thickness for any cyst size in the phantom or in patients for cysts that were between 5 mm and less than 10 mm and those that were 10 mm and larger (p > .05). For cysts smaller than 5 mm in patients, attenuation increase showed decreases with thinner slices, though there was no significant difference between 0.5-mm and 0.25-mm (3-mm slice: 23.7 ± 22.5 HU; 2-mm slice: 20.2 ± 22.7 HU; 0.5-mm slice: 11.6 ± 17.5 HU; 0.25-mm slice: 12.6 ± 19.7 HU; p < .001). Smaller detector element size, increased matrix size, and thinner slices all increased image noise for cysts of all sizes in the phantom and patients (p < .05). CONCLUSION. UHRCT may reduce renal cyst pseudoenhancement through a smaller detector element size and, for cysts smaller than 5 mm, very thin slices; however, these adjustments result in increased noise. CLINICAL IMPACT. Although requiring further clinical evaluation, UHRCT may facilitate characterization of small cystic renal lesions, thereby reducing equivocal interpretations and follow-up recommendations.

Ultrasound, CT, and MR Imaging for Evaluation of Cystic Renal Masses

Cystic renal masses are often encountered during abdominal imaging. Although most of them are benign simple cysts, some cystic masses have malignant characteristics. The Bosniak classification system provides a useful way to classify cystic masses. The Bosniak classification is based on the results of a well-established computed tomography protocol. Over the past 30 years, the classification system has been refined and improved. This paper reviews the literature on this topic and compares the advantages and disadvantages of different screening and classification methods. Patients will benefit from multimodal diagnosis for lesions that are difficult to classify after a single examination.

A Comprehensive Commentary on the Multilocular Cystic Renal Neoplasm of Low Malignant Potential: A Urologist’s Perspective

Multilocular cystic renal neoplasm of low malignant potential (MCRNLMP) is a cystic renal tumor with indolent clinical behavior. In most of cases, it is an incidental finding during the examination of other health issues. The true incidence rate is estimated to be between 1.5% and 4% of all RCCs. These lesions are classified according to the Bosniak classification as Bosniak category III. There is a wide spectrum of diagnostic tools that can be utilized in the identification of this tumor, such as computed tomography (CT), magnetic resonance (MRI) or contrast-enhanced ultrasonography (CEUS). Management choices of these lesions range from conservative approaches, such as clinical follow-up, to surgery. Minimally invasive techniques (i.e., robotic surgery and laparoscopy) are preferred, with an emphasis on nephron sparing surgery, if clinically feasible.

Value of Quantitative CTTA in Differentiating Malignant From Benign Bosniak III Renal Lesions on CT Images

OBJECTIVE

The aim of this study was to investigate whether computed tomography texture analysis can differentiate malignant from benign Bosniak III renal lesions on computed tomography (CT) images.

METHODS

This retrospective case-control study included 45 patients/lesions (22 benign and 23 malignant lesions) with Bosniak III renal lesions who underwent CT examination. Axial image slices in the unenhanced phase, corticomedullary phase, and nephrographic phase were selected and delineated manually. Computed tomography texture analysis was performed on each lesion during these 3 phases. Histogram-based, gray-level co-occurrence matrix, and gray-level run-length matrix features were extracted using open-source software and analyzed. In addition, receiver operating characteristic curve was constructed, and the area under the receiver operating characteristic curve (AUC) of each feature was constructed.

RESULTS

Of the 33 extracted features, 16 features showed significant differences (P < 0.05). Eight features were significantly different between the 2 groups after Holm-Bonferroni correction, including 3 histogram-based, 4 gray-level co-occurrence matrix, and 1 gray-level run-length matrix features (P < 0.01). The texture features resulted in the highest AUC of 0.769 ± 0.074. Renal cell carcinomas were labeled with a higher degree of lesion gray-level disorder and lower lesion homogeneity, and a model incorporating the 3 most discriminative features resulted in an AUC of 0.846 ± 0.058.

CONCLUSIONS

The results of this study showed that CT texture features were related to malignancy in Bosniak III renal lesions. Computed tomography texture analysis might help in differentiating malignant from benign Bosniak III renal lesions on CT images.

Prevalence of Cystic Lesions in Parenchymal Abdominal Organs

Introduction: Abdominal cystic lesions can be localized either in parenchymal or non-parenchymal organs and can be acquired or congenital. Knowing the characteristic imaging features as well as demographic data and the prevalence of cystic lesions can help radiologists in establishing the correct diagnosis. In this article, we conducted a statistical study of congenital and acquired cystic lesions of the abdomen, diagnosed by CT scan in patients hospitalized in Emergency Clinical County Hospital of Constanţa in years 2019 - 2020.

Material and methods: The retrospective study included 285 patients admitted to the hospital. In the case of each patient, we recorded the following variables: Age, Sex, Localization of the lesion, Types of cysts for each localization.

Results: The average age of the patients is 61.53 years. Most of the cystic lesions were localized in the liver (182 cases) and they were represented by: hydatid cysts, simple hepatic cysts, hepatic abscess, hepato-renal polycystic disease and hepatic adenocarcinoma. Cystic lesions of the kidney (56 cases) were represented by: autosomal dominant polycystic kidney disease, renal carcinoma, simple renal cysts, acquired polycystic renal disease, tuberous sclerosis, clear cell renal carcinoma and von Hippel Lindau syndrome. Cystic lesions of pancreas (47 cases) were represented by: pancreatic cysts, pancreatic pseudocysts and pancreatic adenocarcinoma.

Conclusions: CT examination is extremely useful in establishing the location, type, imaging characteristics of cystic lesions, echo over surrounding organs, possibility of malignant transformation. The prevalence of certain types of localizations and morphologies depending on the age and organ involved always helps to obtain a correct and rapid diagnosis.

Structured Reporting in the Characterization of Renal Cysts by Contrast-Enhanced Ultrasound (CEUS) Using the Bosniak Classification System-Improvement of Report Quality and Interdisciplinary Communication

BACKGROUND

This study aims to evaluate the potential benefits of structured reporting (SR) compared to conventional free-text reporting (FTR) in contrast-enhanced ultrasound (CEUS) of cystic renal lesions, based on the Bosniak classification.

METHODS

Fifty patients with cystic renal lesions who underwent CEUS were included in this single-center study. FTR created in clinical routine were compared to SR retrospectively generated by using a structured reporting template. Two experienced urologists evaluated the reports regarding integrity, effort for information extraction, linguistic quality, and overall quality.

RESULTS

The required information could easily be extracted by the reviewers in 100% of SR vs. 82% of FTR (p < 0.001). The reviewers trusted the information given by SR significantly more with a mean of 5.99 vs. 5.52 for FTR (p < 0.001). SR significantly improved the linguistic quality (6.0 for SR vs. 5.68 for FTR (p < 0.001)) and the overall report quality (5.98 for SR vs. 5.58 for FTR (p < 0.001)).

CONCLUSIONS

SR significantly increases the quality of radiologic reports in CEUS examinations of cystic renal lesions compared to conventional FTR and represents a promising approach to facilitate interdisciplinary communication in the future.

Contrast-Enhanced Ultrasound (CEUS) for the Evaluation of Bosniak III Complex Renal Cystic Lesions-A 10-Year Specialized European Single-Center Experience with Histopathological Validation

Background and objectives: The aim of the present retrospective single-center study is to evaluate the diagnostic performance of contrast-enhanced ultrasound (CEUS) for assessing Bosniak III complex renal cystic lesions with histopathological validation. Materials and Methods: 49 patients with CEUS-categorized Bosniak III renal cystic lesions were included in this retrospective study. All patients underwent native B-mode, Color Doppler, contrast-enhanced ultrasound (CEUS) between 2010-2020. Eight and five patients underwent computed tomography (CT) and magnetic resonance imaging (MRI), respectively. Twenty-nine underwent (partial) nephrectomy allowing for histopathological analysis. The applied contrast agent for CEUS was a second-generation blood pool agent. Ultrasonography examinations were performed and interpreted by a single experienced radiologist with more than 15 years of experience (EFSUMB Level 3). Results: CEUS examinations were successfully performed in all included patients without registering any adverse effects. The malignancy rate of CEUS-categorized Bosniak III renal lesions accounted for 66%. Initially, cystic complexity was visualized in native B-mode. In none of the renal lesions hypervascularization was detected in Color Doppler. CEUS allowed for detection of contrast enhancement patterns in all included Bosniak III renal lesions. Delayed wash-out could be detected in 6/29 renal lesions. In two cases of histopathologically confirmed clear-cell RCC, appropriate up-grading from Bosniak IIF to III was achieved by CEUS. Conclusions: CEUS depicts a promising imaging modality for the precise diagnostic workup and stratification of renal cystic lesions according to the Bosniak classification system, thereby helping guidance of adequate clinical management in the future.

Complex Renal Cysts (Bosniak ≥ IIF): Outcomes in a Population-Based Cohort Study

Simple Summary

Researchers from the University of Dundee have found that not all kidney cancers will need urgent surgery. In a published research in the Cancers, Dr Lucocq et al have carefully established database record of patients with kidney cancer looking like water filled sacs on CT scan and reported that these cancers are low grade and perhaps less harmful on long-term follow-up. In fact, behaviour of these cancer cells is much slower compared to other diseases such as heart failure and high blood pressure. Most people die from chronic disease much before cancer spread or progression. The researchers in this group have shown that surgical removal of these cancers, particularly in elderly people and those with other health conditions such as heart failure may not be necessary. Patients in Tayside Urological Cancers (TUCAN) database were carefully assessed using CT scans and discussed in multidisciplinary meetings and were followed up for more than 6 years. This kind of population-based study adds new knowledge to the understanding behaviour of a subset kidney cancers which otherwise have very poor outcome. The researchers and paper highlight careful documentation of cohort to understand natural history of disease.

Abstract

There is emerging evidence to suggest that con-current medical conditions influence the outcome of cancers, irrespective of therapy offered. The prevalence and impact of co-morbidities on the survival outcome of complex renal cystic masses in not known. The objective was to study complex renal cysts (Bosniak ≥IIF ) and assess the overall and renal cancer-specific survival in a population-based database including impact of con-current morbidities. The Tayside Urological Cancer Network (TUCAN) database covering a stable population of more than 416,090 inhabitants in a defined geographical area identified 452 complex renal cysts in 415 patients between 2009 and 2019. Each patient was tracked and followed up using a unique identifier and deterministic linkage methodology. The last date of follow-up including cause of death was determined. Co-morbidities were recorded from primary care referrals. Renal cancer-specific mortality was 1.7% at a median follow-up of 76.0 months; however, overall survival was poor, particularly in patients ≥ 70 years of age and with ≥ 2 significant co-morbid conditions (p < 0.0001). A total of 38.3% of the cohort showed con-current morbidities. Age and co-morbidities were significant risk factors for overall survival in patients with complex renal cystic disease and a careful assessment should be made to recommend surgical intervention in the elderly population, in particular in those with other health-related conditions.

Complex renal cysts (Bosniak ≥IIF): interobserver agreement, progression and malignancy rates

Objective

The objective was to assess the interobserver agreement rate, progression rates and malignancy rates in the assessment of complex renal cysts (≥ Bosniak IIF) using a population-based database.

Methods

A regional database identified 452 complex renal cysts in 415 patients between 2009 and 2019. Each patient was tracked and followed up using a unique identifier and deterministic linkage methodology. The interobserver agreement rate between radiologists was calculated using a weighted kappa statistic. Progression and malignancy rates of cysts (Bosniak ≥IIF) over the 11-year period were calculated.

Results

The linear-weighted kappa value was 0.69 for all complex cysts. The rate of progression and regression of Bosniak IIF cysts was 4.6% (7/151) and 3.3% (5/151), respectively. All malignant IIF cysts progressed within 16 months of diagnosis. The malignancy rate of surgically resected Bosniak III and IV cysts was 79.3% (23/29) and 84.5% (39/46), respectively. Of all malignant tumours, 73.8% and 93.7% were of low ISUP grade and low stage, respectively.

Conclusions

This study further confirms that there is a good degree of agreement between radiologists in classifying complex renal masses using the Bosniak classification. The progression rate of Bosniak IIF cysts is low, but the malignancy rates of surgically resected Bosniak IIF, III and IV cysts are high. Benign cysts are frequently resected, and a very high proportion of histopathologically confirmed cancers in complex renal cysts are of low grade and stage.

Key Points

•There is a good degree of agreement between radiologists in classifying complex renal masses using the Bosniak classification.

•The rate of progression of Bosniak IIF cysts is low, and malignant cysts progress early during surveillance. Although the malignancy rates of resected Bosniak IIF, III and IV cysts are high, the rate of benign cyst resection is significant.

Electronic supplementary material

The online version of this article (10.1007/s00330-020-07186-w) contains supplementary material, which is available to authorized users.

Contrast-Enhanced Ultrasound (CEUS) for Follow-Up of Bosniak 2F Complex Renal Cystic Lesions-A 12-Year Retrospective Study in a Specialized European Center

Bosniak 2F renal cystic lesions feature morphologic characteristics between Bosniak I and III categories, the majority of which remain benign. However, a minor part of Bosniak 2F lesions may progress to malignancy. The purpose of this study was to assess Bosniak 2F cystic lesions during follow-up examinations by CEUS. One-hundred-and-twelve out of 364 patients with Bosniak 2F lesions underwent follow-up CEUS examinations between February 2008 and February 2020. Twelve out of 364 patients underwent renal surgery without follow-up CEUS. The progression rate of Bosniak 2F renal lesions detected by CEUS accounted for 7.1% (8/112 patients) after a mean of 12.9 months. The first follow-up CEUS revealed 75% of progressions (6/8), the remaining 25% (2/8) of progressions were detected during second follow-up CEUS. Underlying clear-cell renal cell carcinoma was histopathologically validated in 5/8 progressive complex cystic renal lesions. Stable sonomorphologic features were observed in 92.1% (104/112 patients). CEUS depicts a promising diagnostic imaging modality in the diagnostic work-up and follow-up of complex renal cystic lesions at higher spatial and temporal resolutions than CT or MRI. Its excellent safety profile, its easy and repeatable accessibility, and low financial costs render CEUS an attractive and powerful alternative imaging tool for monitoring complex renal cystic lesions.

How does contrast-enhanced ultrasonography influence Bosniak classification for complex cystic renal mass compared with conventional ultrasonography?

To analyze the degree and pattern of influence of contrast-enhanced ultrasonography (CEUS) on the Bosniak classification system for complex renal cystic mass as compared with conventional ultrasonography (US). One hundred two consecutive patients with complex renal cystic masses were retrospectively analyzed. The diagnostic performance of the Conventional US and CEUS were evaluated separately for malignant and benign lesions. The diagnostic concordance rates were calculated according to pathologic diagnoses. ROC curve analysis determined the confidence in the diagnostic accuracy by calculating the area under each ROC curve. Compared to the Conventional US, septae number, wall and/or septae thickness, solid component and the Bosniak classification changed in 17 (16.7%), 39 (38.2%), 31 (30.4%), and 67 (65.7%) patients as compared with 0 (0.0%), 21 (20.6%), 31 (30.4%), and 37 (36.3%) of the treatment strategy that changed after CEUS respectively. The diagnostic performance of CEUS showed overall higher in terms of sensitivity (100.0 vs 97.2%); specificity (90.9 vs 62.1%); positive predictive value (PPV) (85.7 vs 58.3%); negative predictive value (NPV) (100.0 vs 97.6%); and the concordance with pathology (kappa = 0.876 vs 0.515). CEUS had a higher diagnostic confidence (P < .05) according to the area under the ROC curve (AUC = 0.968 vs 0.799).CEUS performed better than the Conventional US in the diagnosis of complex renal cystic mass, and it might be considered as the first tool to evaluate a complex cystic renal mass, especially for these Bosniak III masses displaying the presence of hemorrhage or infection.

Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment

Cystic renal cell carcinoma (RCC) is almost certainly overdiagnosed and overtreated. Efforts to diagnose and treat RCC at a curable stage result in many benign neoplasms and indolent cancers being resected without clear benefit. This is especially true for cystic masses, which compared with solid masses are more likely to be benign and, when malignant, less aggressive. For more than 30 years, the Bosniak classification has been used to stratify the risk of malignancy in cystic renal masses. Although it is widely used and still effective, the classification does not formally incorporate masses identified at MRI or US or masses that are incompletely characterized but are highly likely to be benign, and it is affected by interreader variability and variable reported malignancy rates. The Bosniak classification system cannot fully differentiate aggressive from indolent cancers and results in many benign masses being resected. This proposed update to the Bosniak classification addresses some of these shortcomings. The primary modifications incorporate MRI, establish definitions for previously vague imaging terms, and enable a greater proportion of masses to enter lower-risk classes. Although the update will require validation, it aims to expand the number of cystic masses to which the Bosniak classification can be applied while improving its precision and accuracy for the likelihood of cancer in each class.

Active Surveillance of Small (< 4 cm) Bosniak Category 2F, 3, and 4 Renal Lesions: What Happens on Imaging Follow-Up?

OBJECTIVE. The purpose of this study was to determine the percentage of small (< 4 cm) Bosniak category 2F, 3, and 4 lesions that regress during active surveillance. MATERIALS AND METHODS. In this retrospective study, a hospital database was searched from January 1, 2005, through September 9, 2017, for small (< 4 cm) Bosniak category 2F, 3, and 4 lesions studied with initial and follow-up unenhanced and contrast-enhanced CT or MRI. Prospective Bosniak categories were recorded. Two blinded radiologists retrospectively reassigned Bosniak categories to the initial and last follow-up studies. Interreader variability was analyzed. Rates of stability, regression, and progression were calculated and stratified by size. Logistic regression was used to assess the effects of lesion size, lesion growth, and duration of follow-up on the change in Bosniak categories. RESULTS. The search identified 123 patients (85 men, 38 women) with 138 renal lesions (according to the blinded readings, 83 Bosniak category 2F, 37 category 3, and 18 category 4) and followed for 1-12.3 years (median, 2.7 years). Fifty-one percent (70/138) of the lesions were smaller than 2 cm. Eighty-eight percent (73/83) of category 2F lesions were downgraded or remained stable. Forty-five percent (25/55) of category 3 or 4 lesions were downgraded to 2F or lower. Kappa values were 0.94 between the two readers and 0.72-0.76 between the readers and the prospective Bosniak categories. There was no association between initial size, change in size, or duration of follow-up and change in Bosniak category. CONCLUSION. Approximately one-half of small (< 4 cm) Bosniak category 3 and 4 cystic renal lesions were downgraded, and the majority (88%) of small Bosniak category 2F lesions regressed or remained stable during active surveillance. Therefore, small size should be a consideration for conservative management.

Active Surveillance Versus Nephron-Sparing Surgery for a Bosniak IIF or III Renal Cyst: A Cost-Effectiveness Analysis

OBJECTIVE

The objective of our study was to evaluate the cost-effectiveness of active surveillance (AS) versus nephron-sparing surgery (NSS) in patients with a Bosniak IIF or III renal cyst.

MATERIALS AND METHODS

Markov models were developed to estimate life expectancy and lifetime costs for 60-year-old patients with a Bosniak IIF or III renal cyst (the reference cases) managed by AS versus NSS. The models incorporated the malignancy rates, reclassification rates during follow-up, treatment effectiveness, complications and costs, and short- and long-term outcomes. An incremental cost-effectiveness analysis was performed to identify management preference under an assumed $75,000 per quality-adjusted life-year (QALY) societal willingness-to-pay threshold, using data from studies in the literature and the 2015 Medicare Physician Fee Schedule. The effects of key parameters were addressed in a multiway sensitivity analysis.

RESULTS

The prevalence of malignancy for Bosniak IIF and III renal cysts was 26% (25/96) and 52% (542/1046). Under base case assumptions for Bosniak IIF cysts, the incremental cost-effectiveness ratio of NSS relative to AS was $731,309 per QALY for women, exceeding the assumed societal willingness-to-pay threshold, and AS outperformed NSS for both life expectancy and cost for men. For Bosniak III cysts, AS yielded greater life expectancy (24.8 and 19.4 more days) and lower lifetime costs (cost difference of $12,128 and $11,901) than NSS for men and women, indicating dominance of AS over NSS. Superiority of AS held true in sensitivity analyses for men 46 years old or older and women 57 years old or older even when all parameters were set to favor NSS.

CONCLUSION

AS is more cost-effective than NSS for patients with a Bosniak IIF or III renal cyst.

Multislice computed tomography/contrast-enhanced ultrasound image fusion as a tool for evaluating unclear renal cysts

Ultrasonography is a generally accepted imaging technique for diagnosing and monitoring cystic renal lesions. The widely used Bosniak classification (I-IV) categorizes renal cystic lesions into five distinctive groups according to ultrasonography and computed tomography (CT) image criteria. For solid renal lesions, determination of vascularity is discriminatory for malignancy in most instances. In indeterminate cases, contrast-enhanced ultrasound (CEUS) and magnetic resonance imaging/CT-ultrasound image fusion are able to detect and characterize difficult pathologies, with superior performance to either technique alone. In contrast to multislice CT (MS-CT), ultrasound image fusion is a real-time imaging technique that can be used in combination with other cross-sectional imaging modalities. This technical note describes state-of-the-art image fusion of CEUS and MS-CT to detect and characterize unclear renal pathologies.

Image-Guided Renal Interventions

Image-guided renal biopsies have an increasing role in clinical practice. Renal mass and renal parenchymal biopsy indications, techniques, and other clinical considerations are reviewed in this article. Image-guided renal mass ablation shows significant promise and increasing clinical usefulness as more studies demonstrate its safety and efficacy. Renal mass ablation indications, techniques, and other considerations are also reviewed.

Magnetic resonance imaging as an adjunct diagnostic tool in computed tomography defined Bosniak IIF-III renal cysts: a multicenter study

INTRODUCTION

CT imaging is the standard examination for renal cystic lesions and defines the Bosniak category, which dictates further management. Given that Bosniak II/IIF/III renal cystic lesions can potentially harbor renal cell carcinoma (RCC), additional diagnostic modalities may be required in management decision making.

AIM

To determine the value of additional magnetic resonance imaging in CT-defined Bosniak IIF-III renal cystic lesions.

MATERIALS AND METHODS

This a multicenter retrospective study of 46 consecutive patients, diagnosed with cystic renal lesions between 2009 and 2016. The inclusion criteria were: (1) cystic renal lesion classified as Bosniak IIF-III on CT, (2) a subsequent MRI examination, and (3) documented outcome via surgery for cystic renal mass or follow-up.

RESULTS

46 patients (35 males, 11 females) were included. The mean size of the cystic lesion was 3.92 cm (0.7-10 cm). According to the CT findings, Bosniak IIF and III were found in 12 (26.1%) and 34 (73.9%) cases. Reclassification of Bosniak category was done after MRI examination in 31 cases (67.4%). An upgrade rate of 58.7% (27 cases) to a higher category was made, while the downgrade rate to a lower category was achieved in 4 cases (8.7%). As a result, significant therapeutic management change was made in 12/31 patients (38.7%), of whom 8 underwent subsequent surgery.

CONCLUSION

MRI study may reduce the use of Bosniak IIF category (in comparison with CT), which has a direct impact on therapeutic management (surgery vs. surveillance) in a significant proportion of patients.

Contrast-enhanced ultrasound of the kidney: a single-institution experience

BACKGROUND

Focal renal masses are typically evaluated by means of triphasic contrast-enhanced CT or MRI scan but use of iodinated contrast or gadolinium is unsuitable for some patients. Contrast-enhanced ultrasound (CEUS) is an imaging alternative in this scenario but has limited availability in Ireland.

AIM

The aim of the study was to retrospectively evaluate experience with selective use of CEUS for non-invasive characterization of focal renal masses in a tertiary referral institution in Ireland, with a particular focus on cystic renal lesions and the influence of CEUS on final Bosniak classification and treatment outcomes.

METHODS

All cases of renal CEUS between 2009 and 2017 were identified. Imaging history, patient records, histopathology reports, urology conference notes, clinical follow-up details, details of lesion progression or stability on surveillance, biopsy and/or resection details and pre- and post-CEUS Bosniak scores were recorded.

RESULTS

Thirty-one patients underwent renal CEUS (7 solid renal lesions, 21 cystic renal lesions and 3 'indeterminate' renal lesions). After CEUS, the CEUS-modified Bosniak score was upgraded in nine patients and downgraded in two patients. All three lesions upgraded from Bosniak III to IV were renal cell carcinomas. One of two lesions downgraded from Bosniak IV to III was resected (cystic nephroma) and the other showed no progression after 19 months of surveillance.

CONCLUSION

CEUS is a valuable alternative to CT in assessing complex cystic or solid renal lesions where iodinated CT contrast or gadolinium is inappropriate. CEUS can also refine the Bosniak category of atypical cystic renal lesions and help facilitate treatment decisions.

Renal cyst masses (Bosniak category II-III) may be over evaluated by the Bosniak criteria based on MR findings

A classification system of renal cysts developed by Bosniak is based on computed tomography (CT) findings and has been applied to deal with the complex cystic renal masses. Magnetic resonance (MR) has excellent soft-tissue resolution, it has been used to further evaluate some complex renal lesions, especially those suspected of containing soft tissue components and hyperattenuating cystic lesions seen on CT. Compared with CT, MR images may find additional information, which may lead to inconsistent classification. However, at present, there is no consensus on the treatment of these inconsistent lesions. This study aimed to investigate the value of MR in the evaluation of renal cystic masses by using the Bosniak classification system and improve understanding of the MR features of renal cyst masses.The present study retrospectively analyzed 35 renal cyst masses in 34 patients (10 men and 24 women with age from 20 to 65 years old, with an average of 49 ± 12.08), who underwent both MR and computed tomography (CT) examinations within 6 months (range from 1 to 135 days with an average of 11 ± 24.16 days). Twenty-four lesions (9 category III and 15 category IV on CT) received surgical treatment, 4 category IIF lesions on CT were upgraded to category III on MR, which were finally accepted operative resection. The remaining 7 lesions (category II-IIF on both CT and MR) were followed up for at least 3 years. For each lesion, size of both cyst and solid component, presence of calcification, number of septa, thickness of wall and septa, and appearance of enhancement were analyzed. Each lesion was categorized by using Bosniak criteria on CT and MR, respectively. The MR findings were compared with CT and pathology or follow-up results.On MR, categories of the lesions were as follows: category IIF (n = 7), III (n = 12), IV (n = 16). On CT, categories of the lesions were as follows: II (n = 3), IIF (n = 8), III (n = 9), and IV (n = 15). Findings on MR and CT images were inconsistent in 8 (23%) lesions. Among them, 3 category II lesions on CT were classified as category IIF on MR images, 4 category IIF lesions on CT were upgraded to category III on MR, and 1 category III lesions to category IV. In these lesions, MR detected more increased wall/septa thickness (n = 8) and septa number (n = 3) than CT, resulting in an upgrade in classification. Based on the pathological results, 5 of category III (5/9, 56%) and all category IV (15/15, 100%) lesions on CT images were malignant. On MR, 4 of category III (4/12, 33%) and all category IV (16/16, 100%) lesions were malignant.The renal cyst masses in some cases, especially category II to III lesions, may be over evaluated by the Bosniak criteria based on MR findings. It is necessary to combine MR features with CT findings in evaluation and management of these cases with renal cystic masses.

Imaging and Screening of Kidney Cancer

Renal cell carcinoma (RCC) exhibits a diverse and heterogeneous disease spectrum, but insight into its molecular biology has provided an improved understanding of potential risk factors, oncologic behavior, and imaging features. Computed tomography (CT) and MR imaging may allow the identification and preoperative subtyping of RCC and assessment of a response to various therapies. Active surveillance is a viable management option in some patients and has provided further insight into the natural history of RCC, including the favorable prognosis of cystic neoplasms. This article reviews CT and MR imaging in RCC and the role of screening in selected high-risk populations.

Minimally Complex Renal Cysts: Outcomes and Ultrasound Evaluation Compared with Contrast-Enhanced Cross-Sectional Imaging Bosniak Classification

We correlated contrast-enhanced cross-sectional imaging and outcomes to assess the reproducibility of ultrasonographic criteria for renal minimally complex (MC) cysts. From 2003 to 2015, 143 cysts were described as complex or MC by ultrasound (US). After exclusions, 98 US studies were retrospectively evaluated and compared with computed tomography (CT)/magnetic resonance imaging (MRI). At sonography, 51 were MC cysts and 47 were complexes according to two independent observers. Inter-observer agreement for US was 0.704 and 0.745 for CT/MRI. Of 51 cysts classified as MC by US, 38 were Bosniak I/II and 6 were Bosniak IIF by CT/MRI. In 7, there were no cross-sectional images; however, they were stable for at least 2 y. Of 47 complex cysts, 9 were Bosniak II, 22 Bosniak IIF, 8 Bosniak III and 8 Bosniak IV. No Bosniak III/IV cysts by CT/MRI were classified as MC by US. Our results indicate that US offers reproducible criteria for MC cysts and may be used alone for these lesions.

MRI and contrast enhanced ultrasound (CEUS) image fusion of renal lesions

Ultrasound is a common and established imaging method for the initial characterization of renal lesions. The widespread used Bosniak classification (I-IV) classifies renal lesions in five individual groups using contrast-enhanced computer tomography (CE-CT), magnetic resonance imaging (MRI) and/or contrast-enhanced ultrasound (CEUS) imaging criteria. For complex pathologies, CEUS/MRI image fusion is a novel imaging technique for the differentiation of benign and malignant renal lesions. Compared to CE-CT and MRI alone, ultrasound image fusion offers the additional possibility of being a real-time imaging technique that can be used together with other cross-sectional imaging techniques.This article describes the newest possibilities of image fusion with CEUS and MRI in detection and characterization of unclear renal lesions.

Crizotinib Associated Renal Cysts [CARCs]: incidence and patterns of evolution

Background

Novel therapeutic agents recently introduced for the treatment of cancer have several unusual side effects. An increased incidence of renal cystic lesions, often with features concerning for malignancy or infection, has been reported in patients with anaplastic lymphoma kinase (ALK) - rearranged advanced non-small cell lung cancer (NSCLC) treated with Crizotinib. Many of these lesions undergo spontaneous resolution despite developing complex features on imaging. We assess the incidence and patterns of evolution of Crizotinib Associated Renal Cysts [CARCs] at our institute and provide histopathology correlation of their benign nature.

Methods

A retrospective analysis of renal lesions in computerised tomography (CT) scans of 35 patients with advanced ALK-rearranged NSCLC who had been prescribed crizotinib at our institution was performed by three radiologists, who analysed the evolution of these lesions, particularly for pre-defined significant and complex changes.

Results

Of 26 patients eligible for this analysis, 4 (15%) had cysts at baseline that remained stable on crizotinib treatment while 11(42%) developed significant change in 28 renal cysts. Commonest pattern of cyst evolution was enlargement from baseline followed by spontaneous regression (17/28 lesions) while other patterns noted were stable lesions, regression from baseline and ongoing enlargement. The median maximum size reached was 23 mm (range 9 – 67 mm) after a median of 178 days (160 to 1342) on crizotinib. Complex change occurred in 12 cysts, in 7/26 (27%) patients and within 60 days of starting Crizotinib in 10 cysts. Imaging features were falsely concerning for malignancy or abscess in 4/26 patients.

Conclusion

Most CARCs resolve spontaneously, or have a benign evolution despite enlargement and other features concerning for malignancy or infection on imaging. This unusual manifestation of chemotherapy should be recognised, particularly by radiologists, so that inappropriate treatment decisions are avoided.

Malignancy rates and diagnostic performance of the Bosniak classification for the diagnosis of cystic renal lesions in computed tomography - a systematic review and meta-analysis

Objective

To systematically review the literature on the Bosniak classification system in CT to determine its diagnostic performance to diagnose malignant cystic lesions and the prevalence of malignancy in Bosniak categories.

Methods

A predefined database search was performed from 1 January 1986 to 18 January 2016. Two independent reviewers extracted data on malignancy rates in Bosniak categories and several covariates using predefined criteria. Study quality was assessed using QUADAS-2. Meta-analysis included data pooling, subgroup analyses, meta-regression and investigation of publication bias.

Results

A total of 35 studies, which included 2,578 lesions, were investigated. Data on observer experience, inter-observer variation and technical CT standards were insufficiently reported. The pooled rate of malignancy increased from Bosniak I (3.2 %, 95 % CI 0–6.8, I² = 5 %) to Bosniak II (6 %, 95 % CI 2.7–9.3, I² = 32 %), IIF (6.7 %, 95 % CI 5–8.4, I² = 0 %), III (55.1 %, 95 % CI 45.7–64.5, I² = 89 %) and IV (91 %, 95 % CI 87.7–94.2, I² = 36). Several study design-related influences on malignancy rates and subsequent diagnostic performance indices were identified.

Conclusion

The Bosniak classification is an accurate tool with which to stratify the risk of malignancy in renal cystic lesions.

Key points

• The Bosniak classification can accurately rule out malignancy.

• Specificity remains moderate at 74 % (95 % CI 64–82).

• Follow-up examinations should be considered in Bosniak IIF and Bosniak II cysts.

• Data on the influence of reader experience and inter-reader variability are insufficient.

• Technical CT standards and publication year did not influence diagnostic performance.

Electronic supplementary material

The online version of this article (doi:10.1007/s00330-016-4631-9) contains supplementary material, which is available to authorized users.

A Practical Approach to Indeterminate and Cystic Renal Masses

Cystic renal masses are a common entity with a wide differential diagnosis encountered by the radiologist in daily practice. Their characterization relies on the Bosniak classification system that has been widely accepted by radiologists and urologists as a pertinent diagnostic and communication tool. It has been designed to separate cystic lesions requiring surgery (categories III and IV) from those that can be ignored and left alone (categories I and II) or followed (category IIF). Utilization of the Bosniak classification requires, first, previous identification of the cystic nature of a renal mass with the exception of very small lesions.

The role of contrast-enhanced ultrasound in the classification of CT-indeterminate renal lesions

OBJECTIVE

Focal renal lesions are common incidental findings on computed tomography (CT). For lesions with a cystic appearance, the Bosniak classification system has enabled an important separation of benign and (potentially) malignant cysts, giving a practical guide for management. The purpose of this study was to evaluate contrast-enhanced ultrasound (CEUS) as a problem-solving modality for classification of indeterminate renal lesions detected with CT.

MATERIALS AND METHODS

In total, 140 consecutive patients with 148 indeterminate renal lesions were examined with ultrasound combined with CEUS (81 men and 59 women with mean age 63.8 years).

RESULTS

Altogether, 146 lesions were classified by CEUS in categories according to the Bosniak classification system, or as solid lesions. Mean lesion diameter was 30 mm (range 5-166 mm). Nine lesions were classified as category I, 32 as category II and 59 as category IIF ("non-surgical lesions"). 48 IIF cysts were followed for a minimum of 2 years (mean 4 years and 8 months): three lesions were upgraded to category III (6%) and 45 were stable category. 19 lesions had a more complex cystic appearance: 12 were classified as category III and seven as category IV cysts. 27 lesions were diagnosed as solid, enhancing tumors. In total, 25 patients with lesions of category III, IV and solid ("surgical lesions") underwent renal surgery, with malignancy diagnosed in 18.

CONCLUSION

In the common setting of indeterminate renal lesions incidentally detected with a CT exam, CEUS has the potential to classify lesions into "non-surgical" and "surgical" categories, providing a platform for urological decision making, while avoiding radiation exposure.

The renal effects of ALK inhibitors

Anaplastic lymphoma kinase 1 (ALK-1) is a member of the insulin receptor tyrosine kinase family. In clinical practice, three small molecule inhibitors of ALK-1 are used, namely crizotinib, ceritinib and alectinib. Several more agents are in active pre-clinical and clinical studies. Crizotinib is approved for the treatment of advanced ALK-positive non-small cell lung cancer (NSCLC). According to the package insert and published literature, treatment with crizotinib appears to be associated with kidney failure as well as an increased risk for the development and progression of renal cysts. In addition, this agent is associated with development of peripheral edema and rare electrolyte disorders. This review focuses on the adverse renal effects of Crizotinib in clinical practice.

Diagnostic modalities

The incidental detection of small renal masses on imaging undertaken to evaluate unrelated symptoms or conditions is an increasingly common occurrence. Accurate imaging characterisation is fundamental to determining optimum patient management. The goals of imaging small renal masses include determining whether a lesion is solid or cystic, if there are signs of biological aggressiveness and whether the lesion is likely benign or malignant. The current imaging practices and the evidence supporting the use of different imaging modalities for the characterisation of small renal masses are discussed. CT remains the primary imaging modality and is able to classify most masses into surgical or non-surgical lesions. MRI and contrast enhanced ultrasound are most often employed to problem solve in lesions deemed indeterminate on contrast enhanced CT or for patients in which CECT is contraindicated. Percutaneous biopsy should be considered in lesions that remain indeterminate after initial imaging investigations. Given the central role of imaging in the management of small renal masses, all multidisciplinary team members involved in renal cancer care should have an understanding of the performance of the different imaging modalities.

Cystic renal masses

PURPOSE

The purpose of the study is to provide an update on the imaging evaluation of cystic renal masses, to review benign and malignant etiologies of cystic renal masses, and to review current controversies and future directions in the management of these lesions.

CONCLUSIONS

Cystic renal masses are relatively common in daily practice. The Bosniak classification is a time-proven method for the imaging classification and management of these lesions. Knowledge of the pathognomonic features of certain benign Bosniak 2F/3 lesions is important to avoid surgery on these lesions (e.g., localized cystic disease, renal abscess). For traditionally surgical Bosniak lesions (Classes 3 and 4), there are evolving data that risk stratification based on patient demographics, imaging size, and appearance may allow for expanded management options including tailored surveillance or ablation, along with the traditional surgical approach.

The role of Bosniak classification in malignant tumor diagnosis: A single institution experience

PURPOSE

To evaluate the clinical reliability of the Bosniak classification in Korea, and to identify independent predictors of malignancy in complicated renal cysts.

MATERIALS AND METHODS

We reviewed the records of 368 patients with renal cysts between January 2001 and December 2014; 14 patients were excluded, due to interobserver variability in Bosniak classification between the radiologist and urologist. Clinical characteristics and radiologic findings of malignant cystic masses were analyzed, retrospectively.

RESULTS

In 324 surgically excised lesions from patients (n=312) with renal cysts, the percentages of malignancy in the different Bosniak classifications were as follows: category I, 1.0% (1 of 103); II, 3.8% (2 of 53); IIF, 17.1% (7 of 41); III, 38.0% (27 of 71); and IV, 82.1% (46 of 56). Mean age and lesion size were 59.88±11.9 years (180 men, 144 women) and 5.47±3.51 cm, respectively. Univariate analysis identified hypertension (p=0.011), a history of smoking (p=0.038), and obesity (p=0.015) as the strongest risk factors of malignancy. In a study of Bosniak category III patients, hypertension (p=0.018), lesion size (p<0.001), and difference of Hounsfield Unit (HU) (p=0.027) were the strongest risk factors of malignancy. Multivariate analysis identified lesion size as the strongest potential predictor of malignancy, followed by hypertension and difference of HU.

CONCLUSIONS

Risk factors of malignancy in complicated renal cyst patients were not different from those published previously. In Bosniak category III lesions, hypertension and lesion size were the strongest predictors of malignancy. Characteristically, the lesion size was smaller than in benign complicated renal cysts, in contrast with other categories.

Development of renal cysts after crizotinib treatment in advanced ALK-positive non-small-cell lung cancer

INTRODUCTION

The development of complex renal cysts after crizotinib treatment for non-small-cell lung cancer (NSCLC) is a reported side effect. However, its occurrence and characteristics have not been reported.

METHODS

Medical records and computed tomography images of crizotinib-treated patients in three prospective clinical trials were reviewed. The size and Bosniak category of the renal cysts before and after crizotinib treatment were determined. Patients' clinical characteristics, tumor stage, treatment response, renal function, and outcomes were analyzed.

RESULTS

During December 2010 to March 2013, we enrolled 32 patients who received crizotinib. There were 23 patients who had renal cysts before crizotinib. The median follow-up time was 493 days. Seven patients (22%, six with baseline renal cyst and one without baseline renal cyst) had significant renal cyst change. Four (13% of all) had new complex renal cysts. The median time from crizotinib treatment to first recognization of significant renal cyst change was 77 days. After stopping crizotinib, complex renal cysts regressed significantly. Patients with significant renal cyst change received more previous anticancer therapy (median, 5 lines versus 3 lines, p = 0.04) and received crizotinib for longer duration (median, 956 days versus 248 days, p = 0.007) compared with those without significant renal cyst change.

CONCLUSIONS

Change of renal cysts after crizotinib treatment is not uncommon. Development of complex renal cysts reverses after stopping crizotinib.

Contrast-enhanced ultrasonography for evaluation of cystic renal mass: in comparison to contrast-enhanced CT and conventional ultrasound

PURPOSE

To assess the value of contrast-enhanced ultrasonography (CEUS) in evaluating cystic renal lesions compared with conventional ultrasound (US) and contrast-enhanced computed tomography (CECT).

METHODS

One hundred and three patients with complex cystic renal masses underwent preoperative US and CEUS, among which 70 conducted CECT at our institution. The images were analyzed with the number of septa, septa and wall thickness and the presence of solid component, and final diagnosis was made.

RESULTS

In malignancies, CEUS demonstrated more septa, thicker wall or septa, and more solid components than US and CECT. CEUS permitted categorization of 51.7% (30/58) and 28.6% (10/35) of malignant tumors in higher grade than by US and CECT, respectively. In benign lesions, CEUS detected more septa than CECT and correctly diagnosed benign cysts which appeared as solid lesions in US. CEUS permitted downgrading of 71.1% (32/45) and 17.1% (6/35) of benign lesions compared to US and CECT. The diagnostic performance of CEUS was better than US for benign cystic lesions. The phenomenon that solid-like component by US did not enhance by CEUS was a strong predictor of benign disease, with a positive predictive value (PPV) of 100%. Enhancement of solid, soft tissue by CEUS was highly predictive of malignancy, with a PPV of 100%.

CONCLUSIONS

CEUS was superior to US and CECT in visualizing the number of septa septa and wall thickness, and the presence of solid component of cystic renal lesions. CEUS may play a similar role to CECT in the diagnosis of renal cystic lesions, and better than US.

Widespread renal polycystosis induced by crizotinib

With the widespread availability of biological antitumor drugs, the current scene of chemotherapies is changing. New chemotherapy agents, such as crizotinib, an inhibitor of anaplastic lymphoma kinase (ALK) and ROS1, usually used in pretreated advanced ALK-positive non-small-cell lung carcinoma, are more often used, and a description of the onset of side effects with suggestions for their management could be of interest for physicians. We describe a case of diffuse and aggressive renal polycystosis induced by crizotinib, which regressed after therapy, which could be of interest considering its wide extension and disappearance after the end of treatment. We also suggest some considerations from the literature and from the case reported that could be helpful in the management of this condition, which is known to be caused by crizotinib treatment.

Renal Masses With Equivocal Enhancement at CT: Characterization With Contrast-Enhanced Ultrasound

OBJECTIVE

The purpose of this article is to retrospectively investigate in two radiology centers the role of contrast-enhanced ultrasound in the characterization of renal masses with equivocal enhancement at CT (i.e., with a density increase of 10-20 HU between unenhanced and contrast-enhanced scans) not characterized with conventional ultrasound modes.

MATERIALS AND METHODS

Forty-seven renal lesions (range, 0.8-7.7 cm; average, 2.6 cm) with equivocal enhancement at CT underwent contrast-enhanced ultrasound using sulfur hexafluoride-filled microbubbles. Examinations were digitally recorded for retrospective blinded evaluation by two radiologists with 20 and 10 years' experience in urologic imaging. Histologic results were available for 30 of 47 (64%) lesions (25 primary malignant tumors, two metastases, and three primary benign lesions). Two lesions increased in size and complexity during the follow-up and were considered malignant. One Bosniak category III and 14 category IIF cysts were stable after a follow-up of at least 3 years and were considered benign. ROC curve analysis was used to assess the capability of contrast-enhanced ultrasound to differentiate benign from malignant lesions.

RESULTS

Twelve likely complex cystic lesions at gray-scale ultrasound were cystic also on contrast-enhanced ultrasound and reference procedures. Eleven of 34 lesions that appeared solid at gray-scale ultrasound were cystic on contrast-enhanced ultrasound and reference procedures. One lesion considered likely solid by one radiologist and possibly cystic by the other was a solid tumor at contrast-enhanced ultrasound and histologic analysis. The diagnostic performance of contrast-enhanced ultrasound to characterize the lesions as benign or malignant was high for both readers (AUC, 0.958 and 0.966, respectively).

CONCLUSION

Contrast-enhanced ultrasound is effective for characterizing renal lesions presenting with equivocal enhancement at CT.

Ultrasound classification of solitary renal cysts in children

INTRODUCTION

Solitary renal cysts are typically incidentally found in children who have undergone renal ultrasound (US). The main concern is a cystic tumor. There is no US-based grading system for children to guide management.

OBJECTIVE

To evaluate a US-based, modified Bosniak grading system in order to differentiate between simple (grade I or II) and complex (grade II or IV) renal cysts and guide management in children.

STUDY DESIGN

This was a retrospective (2003-2011) study of 212 children (114 females), age range one day to 17 years (mean 8.4 years), with solitary renal cysts diagnosed by US. Two radiologists, who were independent and blinded to clinical information, graded the cysts using the modified Bosniak classification system. In children with more than one year of follow-up US, the change (>10%) in cyst diameter was evaluated. Inter-observer variability (Kappa) was calculated.

RESULTS

Radiologists one and two saw simple renal cysts in 96.2-96.6% (204-205/212) of the children. Ten children had complex renal cysts, as rated by either of the radiologists. There was good inter-observer agreement (kappa = 0.65) for simple versus complex cysts. In 20.2% (18/89) of the children, the cysts increased in size. A definitive diagnosis was obtained in 8.5% (18/212) of the children. A cystic tumor (multilocular cystic nephroma) was found in one child (Figure) with a complex cyst (graded III by both radiologists).

DISCUSSION

The use of a modified Bosniak classification system to grade renal cysts was found to have good inter-observer variability (kappa = 0.65) in differentiating between simple and complex renal cysts. Using this classification, few (<4%) renal cysts were classified as complex. Cystic tumors are rare and the only cystic tumor (multilocular cystic nephroma) was classified as complex renal cysts by the two radiologists. Growth of simple, solitary renal cyst is common (20.2%) and, therefore, if not associated with other imaging findings, is not an indication for a cystic tumor. There were limitations inherent in the retrospective nature of the study and because only one child had a cystic tumor.

CONCLUSION

The modified Bosniak classification system demonstrated good inter-observer agreement, and identified the single tumor as a complex cyst. The vast majority of solitary renal cysts in children are simple and if asymptomatic, they require no other imaging evaluation. Complex renal cysts are uncommon and should be evaluated with a pre-intravenous and postintravenous contrast CT scan to exclude a tumor.