Interrater Agreement of Bosniak Classification Version 2019 and Version 2005 for Cystic Renal Masses at CT and MRI.

Background The Bosniak classification system for cystic renal masses was updated in 2019 in part to improve agreement compared with the 2005 version. Purpose To compare and investigate interrater agreement of Bosniak version 2019 and Bosniak version 2005 at CT and MRI. Materials and Methods In this retrospective single-center study, a blinded eight-reader assessment was performed in which 195 renal masses prospectively considered Bosniak IIF-IV (95 at CT, 100 at MRI, from 2006 to 2019 with version 2005) were re-evaluated with Bosniak versions 2019 and 2005. Radiologists (four faculty members, four residents) who were blinded to the initial clinical reading and histopathologic findings assessed all feature components and reported the overall Bosniak class for each system independently. Agreement was assessed with Gwet agreement coefficients. Uni- and multivariable linear regression models were developed to identify predictors of dispersion in the final Bosniak class assignment that could inform system refinement. Results A total of 185 patients were included (mean age, 63 years ± 13 [standard deviation]; 118 men). Overall interrater agreement was similar between Bosniak version 2019 and version 2005 (Gwet agreement coefficient: 0.51 [95% CI: 0.45, 0.57] vs 0.46 [95% CI: 0.42, 0.51]). This was true for experts (0.54 vs 0.49) and novices (0.50 vs 0.47) and at CT (0.56 vs 0.51) and MRI (0.52 vs 0.43). Nine percent of masses prospectively considered cystic using Bosniak version 2005 criteria were considered solid using version 2019 criteria. In general, masses were more commonly classified in lower categories when radiologists used Bosniak version 2019 criteria compared with version 2005 criteria. The sole predictor of dispersion in Bosniak version 2019 class assignment was dispersion in septa or wall quality (ie, smooth vs irregular thickening vs nodule; 72% [MRI] and 60% [CT] overall model variance explained; multivariable P < .001). Conclusion Overall interrater agreement was similar between Bosniak version 2019 and version 2005; disagreements in septa or wall quality were common and strongly predictive of variation in Bosniak class assignment. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Eberhardt in this issue.

Bosniak Classification of Cystic Renal Masses Version 2019: Comparison With Version 2005 for Class Distribution, Diagnostic Performance, and Interreader Agreement Using CT and MRI.

BACKGROUND. The Bosniak classification system for cystic renal masses (CRMs) was updated in 2019, requiring further investigation. OBJECTIVE. The purpose of this study was to compare versions 2005 and 2019 of the Bosniak classification system in terms of class distribution, diagnostic performance, interreader agreement, and intermodality agreement between CT and MRI. METHODS. This retrospective study included 100 patients (mean age, 52.4 ± 11.6 years; 68 men, 32 women) with 104 CRMs (74 malignant) who underwent CT, MRI, and resection between 2010 and 2019. Two radiologists independently evaluated CRMs in separate sessions for each combination of version and modality and assigned a Bosniak class. Diagnostic performance was compared using McNemar tests. Interreader and intermodality agreement were analyzed using weighted kappa coefficients. RESULTS. Across readers and modalities, the proportion of class IIF CRMs was higher for version 2019 than version 2005 (reader 1: 28.8-30.8% vs 6.7-12.5%; reader 2: 26.0-28.8% vs 8.7-19.2%), although 95% CIs overlapped for reader 2 on CT. The proportion of class III CRMs was lower for version 2019 than version 2005 (reader 1: 33.7-35.6% vs 49.0-51.9%; reader 2: 31.7-40.4% vs 37.5-52.9%), although 95% CIs overlapped for all comparisons. Version 2019 showed lower sensitivity for malignancy than version 2005 across readers and modalities (all p < .05); for example, using CT, sensitivity was 75.7% for both readers with version 2019 versus 85.1-87.8% with version 2005. However, version 2019 showed higher specificity than version 2005, which was significant (all p < .05) for reader 1. For example, using CT, specificity was 73.3% (reader 1) and 70.0% (reader 2) with version 2019 versus 50.0% (reader 1) and 56.7% (reader 2) with version 2005. Diagnostic accuracy was not different between versions (version 2005: 76.9-85.6%; version 2019: 74.0-78.8%). Interreader and intermodality agreement were substantial for version 2005 (κ = 0.676-0.782 and 0.711-0.723, respectively) and version 2019 (κ = 0.756-0.804 and 0.704-0.781, respectively). CONCLUSION. Use of version 2019 versus version 2005 of the Bosniak classification system results in a shift in CRM assignment from class III to class IIF. Version 2019 results in lower sensitivity, higher specificity, and similar accuracy versus version 2005. Interreader and intermodality agreement are similar between versions. CLINICAL IMPACT. Version 2019 facilitates recommending imaging surveillance for more CRMs.

Multi-disciplinary team conference clarifies bosniak classification of complex renal cysts.

OBJECTIVES: The aims of this study are to determine the progression rate of Bosniak IIF cysts, the malignancy rates of complex renal cysts in patients undergoing surgery and explore the influence of multi-disciplinary team conference (MDT) on re-classification of Bosniak cysts. MATERIALS AND METHODS: All CT scans from January 2010 to 2017 were pooled into a database. Initially, 167 patients were identified with possible Bosniak IIF, III or IV cysts. Patients with follow up of less than 24 months, without progression or regression were excluded. RESULTS: Thirty-one (18.6%) cysts of the initial 167 cysts were either up or downgraded at a MDT. Twenty-six of the 31 cysts were up or downgraded at the primary MDT, 13 cysts (50%) were downgraded, five cysts (19.2%) were upgraded and eight cysts (30.8%) were re-classified as solid tumors. Of those 19/26 (73.1%) were primary interpreted by a periphery radiologist and re-classified centrally. The last five patients 5/120 cysts (4.2%) were re-classified during follow up. 116 patients with a total of 120 cysts met the inclusion criteria, 79 (65.8%) Bosniak IIF, 28 (23.3%) Bosniak III and 13 (10.8%) Bosniak IV cysts represented. Median follow up of Bosniak IIF cysts were 46 months. One Bosniak IIF cyst progressed to a solid tumor at 15 months from diagnosis, progression rate 1.3%. Histopathology was papillary renal cell carcinoma. Malignancy rates of Bosniak III and IV cysts were 50% and 78%, respectively. CONCLUSION: Multi-disciplinary team conference may have an important role in correct classification of Bosniak cysts. TRIAL REGISTRATION: None.

The Modified Bosniak Classification for Intermediate-Risk Renal Cysts in Children.

OBJECTIVES: To examine correlations of the modified Bosniak categories assigned by radiologists to histological results and inter-rater reliability, focusing on intermediate-risk lesions. MATERIALS AND METHODS: The data of pediatric patients who underwent surgery for intermediate-risk complex renal cyst at a tertiary medical center in 2006-2019 were collected retrospectively. Four pediatric radiologists from 2 different medical centers reviewed the available imaging scans, and assigned each to one of the four modified Bosniak classification categories. Binary cohorts of the Bosniak categories (I-II vs III-IV) were compared to the histological results. Diagnostic accuracy (benign- vs intermediate-risk lesion) was calculated for each radiologist and for each imaging modality. Krippendorff's α test was used to measure inter-rater reliability. RESULTS: The cohort included seven children, each with 1 complex cyst that was rated as intermediate-risk on pathological study. The median age was 1.5 years (IQR 1, 11.9). A correct classification was made in 41/56 imaging readings (sensitivity 73.2%). Applying Krippendorff's test to the binary Bosniak cohorts yielded poor inter-rater agreement (α = 0.08). CONCLUSION: Implementation of the modified Bosniak classification in children caused a disconcerting underestimation of intermediate risk. There was a low inter-rater consistency for the categories intended to guide decisions regarding surgery or conservative management. The findings suggest that clinicians should be cautious using the modified Bosniak system for children.

Bosniak Classification of Cystic Renal Masses Version 2019: Comparison of Categorization Using CT and MRI.

BACKGROUND. Bosniak classification version 2019 proposed refinements for cystic renal mass characterization and now formally incorporates MRI, which may improve concordance with CT. OBJECTIVE. The purpose of this study is to compare concordance of CT and MRI in evaluation of cystic renal masses using Bosniak classification version 2019. METHODS. Three abdominal radiologists retrospectively reviewed 68 consecutive cystic renal masses from 45 patients assessed with both CT and MRI renal mass protocols within a year between 2005 and 2019. CT and MRI were reviewed independently and in separate sessions, using both the original and 2019 versions of Bosniak classification systems. RESULTS. Using Bosniak classification version 2019, cystic renal masses were classified into 12 category I, 19 category II, 13 category IIF, four category III, and 20 category IV by CT and eight category I, 15 category II, 23 category IIF, nine category III, and 13 category IV by MRI. Among individual features, MRI showed more septa (p < 0.001, p = 0.046, p = 0.005; McNemar test) for all three radiologists, although both CT and MRI showed a similar number of protrusions (p = 0.823, p = 1.0, p = 0.302) and maximal septa and wall thickness (p = 1.0, p = 1.0, p = 0.145). Of the discordant cases with version 2019, MRI led to a higher categorization in 12 masses. The reason for upgrade was most commonly because of protrusions identified only on MRI (n = 4), an increased number of septa (n = 3), and a new category: heterogeneously T1-weighted hyperintensity (n = 3). Neither modality was more likely to lead to a categorization change for either version 2019 (p = 0.502; McNemar test) or the original (p = 0.823) Bosniak classification system. Overall interrater agreement was substantial for both CT (κ = 0.745) and MRI (κ = 0.655) using version 2019 and was slightly higher than that of the original system for CT (κ = 0.707) and MRI (κ = 0.623). CONCLUSION. CT and MRI were concordant in the majority of cases using Bosniak classification version 2019, and category changes by modality were not statistically significant. Interrater agreements were substantial for both CT and MRI. CLINICAL IMPACT. Bosniak classification version 2019 as applied to cystic renal masses has substantial interrater agreement and does not lead to systematic category upgrades with either CT or MRI.

Bosniak classification of cystic renal masses: utility of contrastenhanced ultrasound using version 2019.

AIM: To compare the latest 2019 version of Bosniak classification (BCnew) against Bosniak classification prior to 2019 (BCold) using contrast-enhanced ultrasound (CEUS) and to compare CEUS against contrast-enhanced CT (CECT) based on BCnew. MATERIAL AND METHODS: Patients who had both CEUS and CECT of the kidneys performed within three months of each other were included. CECT and CEUS images of renal cysts were retrospectively analysed by two independent readers using BCnew, extrapolating the BCnew criteria to CEUS. Where histopathology was not available, 3-year imaging follow-up was used as a reference standard. RESULTS: Forty-nine patients with a total of 54 cysts were included. Using BCnew, Bosniak category between CEUS and CECT and both readers was concordant in 18 cysts (33.3%). Bosniak category between CEUS and CT was concordant in 27 cysts (50%) in reader 1 and in 33 cysts (61%) for reader 2. Based on Cohen's weighted kappa statistic (k), inter-observer agreement was moderate for CEUS (k=0.49) and fair for CECT (k=0.36). Agreement between CEUS and CECT for both readers was fair (reader 1, k=0.24; reader 2, k=0.37). Compared to using BCold, almost half of the benign cysts were assigned to a lower Bosniak category with CEUS using BCnew (reader 1, 42.6%; reader 2, 50%). CONCLUSIONS: CEUS assessment based on BCnew more appropriately assigns benign renal cysts to a lower category than CEUS based on BCold. Readers tend to grade renal cysts to a higher Bosniak category with BCnew but with greater inter-reader agreement on CEUS than on CECT.

Bosniak classification of cystic renal masses version 2019 does not increase the interobserver agreement or the proportion of masses categorized into lower Bosniak classes for non-subspecialized readers on CT or MR.

PURPOSE: In a condition so prevalent as renal cysts, classifications should display satisfactory reproducibility not only among subspecialized readers. We aimed to compare the interobserver agreement of the Bosniak classification version 2019 (BC19) and current Bosniak classification (CBC) for non-subspecialized readers on CT and MRI and to verify whether BC19 leads to a downgrade of renal cystic masses when compared to CBC. METHODS: We evaluated 50 renal cystic masses in 47 patients on MR and CT (25 per method). Eighteen readers (nine third-year radiology residents and nine abdominal imaging fellows) assessed the images using BC19 and CBC with an eight-week interval. Kappa statistic was used to assess agreement. An average score of Bosniak categories across all raters evaluated if there was downgrading of lesions on BC19. RESULTS: The highest values of Kappa were found for fellows on CBC-MR (κ = 0.51), and the lowest values were found for residents on CBC-MR and fellows on BC19-MR (both κ = 0.36). On CBC, interobserver agreement was moderate for MR and CT (κ = 0.42 and 0.43, respectively), whereas on BC19, it was fair (κ = 0.38 and 0.40, respectively). The best agreements were in categories I (κ = 0.49-0.69) and IV (κ = 0.45-0.51). The poorest agreements occurred at IIF (κ = 0.18 on BC19-CT). There was a moderate median increase from CBC to BC19 in terms of Bosniak categories for both methods (MR [Z=-2.058, p = 0.040] and CT [Z=-2.509, p = 0.012]). CONCLUSION: BC19, when compared to CBC, did not improve interobserver agreement nor diminished the proportion of masses categorized into lower Bosniak classes among non-subspecialized readers.

MRI-based Bosniak Classification of Cystic Renal Masses, Version 2019: Interobserver Agreement, Impact of Readers' Experience, and Diagnostic Performance.

Background The 2019 Bosniak classification (version 2019) of cystic renal masses (CRMs) provides a systematic update to the currently used 2005 Bosniak classification (version 2005). Further validation is required before widespread application. Purpose To evaluate the interobserver agreement of MRI criteria, the impact of readers' experience, and the diagnostic performance between version 2019 and version 2005. Materials and Methods From January 2009 to December 2018, consecutive patients with CRM who had undergone renal MRI and surgical-pathologic examination were included in this retrospective study. On the basis of version 2019 and version 2005, all CRMs were independently classified by eight radiologists with different levels of experience. By using multirater κ statistics, interobserver agreement was evaluated with comparisons between classifications and between senior and junior radiologists. Diagnostic performance between classifications by dichotomizing classes I-IV into lower (I-IIF) and higher (III-IV) classes was compared by using the McNemar test. P < .05 was considered to indicate a statistically significant difference. Results A total of 207 patients (mean age ± standard deviation, 49 years ± 12; 139 male and 68 female patients) with CRMs were included. Overall, interobserver agreement was higher with version 2019 than version 2005 (weighted κ = 0.64 vs 0.50, respectively; P < .001). Interobserver agreement between senior and junior radiologists did not differ between version 2019 (weighted κ = 0.65 vs 0.64, respectively; P = .71) and version 2005 (weighted κ = 0.54 vs 0.46; P < .001). Diagnostic specificity for malignancy was higher with version 2019 than with version 2005 (83% [92 of 111] vs 68% [75 of 111], respectively; P < .001), without any difference in sensitivity (89% [85 of 96] vs 84% [81 of 96]; P = .34). Conclusion In the updated Bosniak classification, interobserver agreement improved and was unaffected by observers' experience. The diagnostic performance with version 2019 was superior to that with version 2005, with higher specificity. Published under a CC BY 4.0 license. Online supplemental material is available for this article. See also the editorial by Choyke in this issue.

Bosniak Classification Version 2019 of Cystic Renal Masses Assessed With MRI.

OBJECTIVE. The purpose of this study was to determine how use of Bosniak classification version 2019 affects categorization and overall accuracy of MRI evaluation of cystic renal masses with tissue pathologic analysis as the reference standard. MATERIALS AND METHODS. MR images of 50 consecutively registered patients with tissue pathologic results from 2005 to 2019 were retrospectively reviewed by two abdominal radiologists. Each radiologist independently assigned a category based on the original and Bosniak classification version 2019 systems. Interreader agreements (kappa statistic) for both were calculated, and consensus reading was performed. Tissue pathologic analysis was used as the reference standard to determine whether a lesion was benign or renal cell carcinoma. RESULTS. Fifty-nine cystic renal masses were characterized as 38 renal cell carcinomas and 21 benign lesions on the basis of the results of tissue pathologic analysis. By consensus, according to the original Bosniak criteria, the renal masses were classified into three category I, five category II, four category IIF, 25 category III, and 22 category IV lesions. By consensus, according to the version 2019 criteria, the renal masses were classified into three category I, two category II, 12 category IIF, 18 category III, and 24 category IV lesions. Overall sensitivity and specificity for identifying renal cell carcinoma were 95% and 81%, respectively, with the original classification system and 100% and 86%, respectively, with version 2019. Weighted interreader agreement was moderate for both the original system (κ = 0.57) and version 2019 (κ = 0.55). CONCLUSION. Use of Bosniak classification version 2019 system improves sensitivity and specificity for malignancy among cystic renal masses characterized with MRI. Most lesions that changed categories were reclassified as Bosniak category IIF.

Management of complex renal cysts in Canada: results of a survey study.

BACKGROUND: Bosniak III and IV cysts have a high risk of malignancy and have traditionally been managed surgically. However, growing evidence suggests that many can be managed by active surveillance. The main objective of this study was to characterize the use of surveillance in the management of complex renal cysts. METHODS: A web-based survey was sent to all registered, active members of the Canadian Urological Association (N = 583) in October 2018. RESULTS: The survey response rate was 24.7%. Management of Bosniak III cysts varied considerably. A large proportion of respondents (33.1%) offered active surveillance in > 50% of cases. Only 13.7% of respondents reported never or rarely (< 5% of cases) offering surveillance. In contrast, for Bosniak IV cysts, 60.1% of urologists never or rarely offered surveillance, while only 10.1% offer it in > 50% of cases. A significantly greater proportion of academic urologists, compared to non-academic urologists, viewed surveillance as a management option for patients with a Bosniak III or IV cyst. The most commonly reported barriers to a greater adoption of surveillance were concerns regarding its oncologic safety, the lack of data to support surveillance in this population, and the lack of triggers for discontinuation of active surveillance and intervention. CONCLUSIONS: Despite active surveillance being included as a management option in guidelines, many Canadian urologists are reluctant to offer surveillance to patients with Bosniak III or IV cysts. Practice patterns are heterogeneous among those offering surveillance. High-quality studies are required to better define the benefits and risks of cystic renal mass surveillance.

Comparison of computed tomography and magnetic resonance imaging in the assessment of complex renal cysts by using the Bosniak classification. / Comparación entre tomografía computarizada y resonancia magnética en la evaluación de quistes renales complejos empleando la clasificación de Bosniak.

INTRODUCTION AND OBJECTIVES: The Bosniak classification of cystic renal lesions was first published in 1986 based on computed tomography (CT). In the present study, we aimed to investigate the effect of magnetic resonance imaging (MRI) on Bosniak category compared with CT, and to determine how this effect changed the treatment modality in the evaluation of complex renal cysts. MATERIAL AND METHODS: Data of 144 patients were collected retrospectively. After exclusion criteria, 102 cystic renal lesions with a Bosniak category of at least IIF on CT or MRI between 2013 and 2016 were evaluated by 2abdominal radiologists. The demographic data, Bosniak category, interobserver agreement, and pathologic data of patients who underwent surgery were recorded. RESULTS: The coherence between MRI and CT was 75.5%. The Bosniak classification of 17 patients was upgraded with MRI, and the treatment modality changed in 10 patients, and they underwent surgery. The Bosniak category was downgraded from III to IIF in 6 patients out of 8 whose Bosniak category was downgraded with MRI and the treatment modality changed. Surgery was performed in one patient out of these 6 patients, and the pathology was reported as benign. Progression was detected in the follow-up at month 18 of 1 patient out of 5, and surgery was performed. The pathology was reported as renal cell carcinoma. The pathology result was reported as RCC in 35 (68.6%) patients out of 51 who underwent surgery. Progression was detected in 7 patients out of 51 who were followed up (13.7%), and the pathology results were reported as RCC. The majority of the malignant tumors were low stage and grade. CONCLUSIONS: MRI may be successfully used in the evaluation of renal cystic lesions. In particular, the challenging Bosniak IIF and all Bosniak III lesions must be evaluated using MRI before making the decision for surgery. The upgrading of Bosniak category with MRI is more possible compared with CT due to its high-contrast resolution, therefore further studies are required to identify whether it was the cause of overtreatment of Bosniak III 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.

Small (< 4 cm) Bosniak renal cysts: association of initial fluid percentage and enhancing solid volume thresholds with future lesion behavior.

PURPOSE: Evaluate the fluid percentage (FP) and enhancing solid volume (SV) of small (< 4 cm) Bosniak 2F, 3 and 4 renal lesions and the association with Bosniak category at baseline and follow-up. METHODS: Hospital database was searched from 1/1/2010 to 8/3/2018 for small (< 4 cm) Bosniak 2F, 3 and 4 lesions studied with initial and follow-up C+CT/MRI. Two radiologists blindly assigned Bosniak categories to first and last available studies. One radiologist performed volumetric analysis of each lesion, calculating the FP and SV. Association with Bosniak category was explored. RESULTS: 121 patients (84:37 M:F) were identified with 136 renal lesions (84, 37 and 15 Bosniak category 2F, 3 and 4) and followed for 1-12.3 years (mean 3.5 years). 87% (73/84) of 2F lesions were downgraded or remained stable. 48% (25/52) of 3/4 lesions were downgraded. Higher FP was associated with a lower Bosniak category (p value = 0.0042). Increase in FP was associated with the probability of being downgraded on follow-up (OR 1.03, p value = 0.0036), while increase in fluid volume of lesion was directly associated with change in overall lesion size among lesions that were downgraded (b-estimate = 0.03, p value = 0.0003). All Bosniak 3/4 lesions with initial SV less than 0.05 cc were downgraded. CONCLUSION: FP and SV are useful quantitative surrogates for Bosniak category and future behavior, respectively. Growth of small renal lesions by an increase in fluid volume and FP leads to a downgrade in Bosniak category. Initial SV less than 0.05 cc in Bosniak 3/4 lesions suggests possible future downgrade.

Bosniak Classification and other Variables in the Prediction of Renal Cystic Masses.

OBJECTIVE: To evaluate the variables of cystic renal lesions to predict the renal tumors. STUDY DESIGN: An observational study. PLACE AND DURATION OF STUDY: Urology Department, Ankara Yüksek Ihtisas, Samsun Research and Training Hospitals, Turkey, from January 2013 to June 2017. METHODOLOGY: Records of patients with renal cystic lesions were retrospectively evaluated. Preoperative CT results in terms of diameter number and enhancement; and clinical variables such as gender body mass index [(weight (kg)/ height²(m)] and smoking status were recorded. Student's t-test and ANOVA were used for determing significance, which was set at p<0.05. RESULTS: Due to pathology results, all group I patients were benign, 7.9% (3/38) of group II, 31.8% (7/22) of group II-F, 55.3% (21/38) of group III, 69% (40/58) group IV patients were found to be malignant. For clinical factors, obesity and smoking, while for radiological parameters, about 59.3 +11.7 HU enhancement were found to be predictor significant of malignancy (all p<0.05). No significant difference was observed between cystic lesion diameter number or laterality (right/left) and malignancy. CONCLUSION: Renal cysts have a high malignancy possibility in the patients with history of smoking in the past or actively, high BMI, and preoperative CT with about 59.3 +11.7 HU post-contrast enhancement.

The Histopathologic Correlation of Bosniak 3 Cyst Subclassification.

OBJECTIVE: To evaluate the histopathologic correlation of recently described subclassification of Bosniak category 3 cysts (3s and 3n). MATERIALS AND METHODS: A total of 106 patients who underwent partial/radical nephrectomy due to a complex renal cyst (≥Bosniak 3) were retrospectively reviewed. All the scans of the patients were reevaluated by 2 experienced uroradiologists. Bosniak 3 cysts were reclassified as 3n (nodularity on the cyst wall/septae) and 3s (septated cysts without nodularity) as described in a recently published paper. Group 1 consisted of patients with Bosniak 3s, Group 2 consisted of patients with Bosniak 3n, and Group 3 consisted of patients with Bosniak 4 cysts. Three groups were compared according to patients' characteristics, radiological findings, histopathologic results, and survival outcomes. RESULTS: There were 52 patients in Bosniak 3 group and 54 patients in Bosniak 4 group. Mean follow-up was 35.3 months. Among Bosniak 3 cysts, 37 lesions were classified in 3s and 15 were classified in 3n. Malignancy was higher in 3n group than 3s (86.7% vs 54.1%, P= .026). Lesion size was significantly lower for malignant cysts compared to benign ones in the patients with Bosniak 3 lesions (44.2 ± 27.5 vs 80 ± 55.9 P= .005). In the subgroups, malignant lesions were significantly smaller than benign lesions in 3s group similar to general Bosniak 3 group. Most of the Bosniak 3 lesions were organ confined and low grade. CONCLUSION: The subclassification of Bosniak 3 cysts as 3s and 3n can help to differentiate highly suspicious malignant lesions from the relatively less suspicious ones.

Development and prospective validation of a novel weighted quantitative scoring system aimed at predicting the pathological features of cystic renal masses.

OBJECTIVES: To develop and prospectively validate a novel weighted quantitative scoring system based on CT findings, namely, the renal cyst index (RCI), aimed at preoperatively predicting the pathological features of cystic renal masses (CRMs). METHODS: The RCI was based on four critical features of CRMs: the cyst wall, septal, nodule, and cyst contents. These parameters were scored with 1, 2, or 3 points. Weight coefficients for these parameters were determined by the multivariable logistic regression. The odds ratio (OR) and 95% confidence interval (95% CI) were used to summarise the results. The RCI was defined as the sum of these four weight coefficients. Malignancy risk prediction models were built based on the retrospective evaluation of 441 patients. We also compared the prediction ability of the RCI with the Bosniak classification in the 441 patients and applied these novel models to 152 masses resected in our institution to prospectively validate the efficiency of the RCI. RESULTS: The wall point (OR = 5.71 [95% CI = 1.734-18.808, p = 0.004, point = 2], OR = 12.665 [95% CI = 3.750-42.770, p < 0.001, point = 3]), septal point (OR = 3.325 [95% CI = 1.272-8.692, p = 0.014, point = 3]), nodule point (OR = 4.588 [95% CI = 1.429-14.729, p < 0.001, point = 2], OR = 17.032 [95% CI = 5.017-57.820, p = 0.010, point = 3]), content point (OR = 22.822 [95% CI = 1.041-495.995, p = 0.047, point = 2], OR = 2.723 [95% CI = 1.296-10.696, p = 0.015, point = 3]), and RCI (OR = 1.247 [95% CI = 1.197-1.299, p < 0.001]) were significantly associated with malignancy. Masses with an RCI < 6 were regarded as benign masses; masses with an RCI ≥ 10 were regarded as malignant masses. The malignancy risk of masses with an RCI > 6 but < 10 were determined by a nomogram. The prediction ability of the RCI was significantly superior to the Bosniak classification for Bosniak IIF and III masses (AUC: 0.912 vs. 0.753, p = 0.001). The RCI also accurately predicted the pathological features of 152 masses. CONCLUSION: The RCI is a reliable quantitative scoring system in predicting the malignancy risk of CRMs, and it outperformed the Bosniak classification system in some ways. KEY POINTS: • The renal cyst index (RCI) is a useful weighted quantitative classification system based on CT findings for diagnosing cystic renal masses. • The RCI outperforms the Bosniak classification system in some ways, especially for Bosniak IIF and III masses. • Masses with an RCI < 6 can be regarded as a simple cyst, while those with an RCI > 10 can be regarded as malignant masses.

[The incidence of malignant transformation of renal cysts of category 1, 2, and 2F by the BOSNIAK classification into multilocular cystic renal cell carcinoma].

RELEVANCE: Renal cysts remain the most common of benign renal lesions, but current literature is lacking large observational studies on the incidence of their malignant transformation. AIM: To assess the incidence of malignant transformation of renal cysts of category 1, 2, and 2F by the Bosniak classification into multilocular cystic renal cell carcinoma. MATERIALS AND METHODS: From January 2009 to December 2017, 177 patients with renal cysts of category 1 (n=50), 2 (n=74), and 2F (n=53) underwent laparoscopic decortication. In 10 cases, post-operative histological and immunohistochemical studies revealed foci of grade 1 (pT1a) multilocular cystic renal cell carcinoma. RESULTS: Foci of grade 1 (pT1a) multilocular cystic renal cell carcinoma were detected in 10 (5.65%) patients (five men, five women, mean age 58.9 years). The incidence of malignant transformation of renal cysts of categories 1, 2, and 2F was 0%, 2.7% (2 of 74 patients), and 15.1% (8 of 53 patients), respectively. Subsequently, all ten patients were submitted to surgical treatment: eight of them underwent a partial nephrectomy, and two received a nephrectomy. During a median of 49.3 (31-72) months follow-up, no metastasis, and recurrence of multilocular cystic RCC were observed. CONCLUSION: A more modern algorithm for managing patients with Bosniak category 1, 2 and 2F cysts need to be developed to establish early surveillance of patients starting with category 1 cysts. Given the low malignant potential of these tumors, they should be treated with organ-sparing surgery.

Contemporary assessment of the correlation between Bosniak classification and histological characteristics of surgically removed atypical renal cysts (UroCCR-12 study).

PURPOSE: To evaluate and compare pathological characteristics of renal cysts Bosniak IIF, III and IV in light of recent histological classification. PATIENTS AND METHODS: The French research network for kidney cancer UroCCR conducted a multicentre study on patients treated surgically for a renal cyst between 2007 and 2016. Independent radiological and centralized pathological reviews were performed for every patient. Pathological characteristics were compared to the Bosniak classification. RESULTS: Of a total 216 patients included, 175 (81.0%) tumours (90.9% of Bosniak IV, 69.8% of Bosniak III) were malignant or had a low malignant potential, with 60% of clear cell renal cell carcinoma (CCRCC), 24% of papillary RCC (PRCC) and 6.9% of multilocular cystic renal tumour of low malignant potential (MCRTLMP). Malignancies were mostly of low pT stage (86.4% of pT1-2), and low ISUP grade (68.0% of 1-2). Bosniak III cysts had a lower rate of CCRCC (46.7 vs. 67.3%), higher rate of PRCC (30 vs. 20.9%) and MCRTLMP (18.3 vs. 0.9%) compared to Bosniak IV (p < 0.001). Low-malignant potential lesions were less likely Bosniak IV and pT3-4 stage was more frequent in Bosniak IV vs. III (15.7 vs. 3.5%; p = 0.04). There were two recurrences (1.1%) and no cancer-related death occurred during follow-up. CONCLUSION: These results confirmed that cystic renal malignancies have excellent prognosis. Bosniak III cysts had a low malignant potential, which suggests surveillance could be an option for these lesions.

Simple and complex renal cysts in adults: Classification system for renal cystic masses.

Ultrasound and slice imaging are currently the key modalities for diagnosing simple renal cysts. Benign simple renal cysts are defined by a set of strict criteria. Any cystic lesions that do not meet these criteria should be classified as "atypical" or "complex" and considered as suspicious. For over three decades, the Bosniak classification has been the central tool for diagnosing renal cystic masses larger than 1 cm. The Bosniak classification is based upon the results of a well-established pre- and post-contrast computed tomography (CT) protocol. Lesions that are difficult to classify or that remain indeterminate after CT can benefit from a multimodal diagnostic approach combining CT, non-contrast-enhanced and contrast-enhanced ultrasound, and magnetic resonance imaging.