Differential diagnosis of complex cystic renal mass using multiphase computerized tomography

The efficacy of the new Bosniak classification v.2019 in benign lesions prediction within the higher Bosniak cysts classes

INTRODUCTION

Identification of benign lesions among higher classes of renal Bosniak cysts who are vulnerable to active surveillance instead of surgical approach is still questionable. We aimed in this study to delineate the efficacy of the new Bosniak v2019 classification in benign lesions identification among those cases with higher Bosniak classes in comparison with the final histopathology.

MATERIALS

In a retrospective review between 2010 and 2021 for patients diagnosed as higher classes Bosniak renal masses was done. Patients' demographics and radiological data i.e.,: age, gender, and final Bosniak v2019 categorization for class III: (1) Enhancing thick wall/septa >4 mm (III-WS) and (2) Enhancing irregular wall/septa or convex protrusion with obtuse margins <3 mm (III-OP) and for class IV as: (1) Enhancing nodule or convex protrusion with obtuse margins >4 mm (IV-OP) and (2) Enhancing nodule or convex protrusion with acute margins of any size (IV-AP).

RESULTS

A total of 137 patients were included. Bosniak III was identified in 56 patients. Malignancy was detected in 74.5% of resected masses. Among resected Bosniak III cyst, 46.4% were benign histopathologically. Male gender and Bosniak III-OP were independent risks for malignancy among the resected Bosniak III cysts. Conversely, in resected Bosniak IV renal cysts, only 9 of resected masses were benign. In univariate analysis, male gender, absence of multilocular cyst and endophytic masses were predictors for malignancy in resected Bosniak IV cyst. None of the previous predictors was significant in multivariate analysis.

CONCLUSION

The Bosniak subclassification v.2019 can define benign lesions. Bosniak III-OP was an independent risk for malignancy detection among the resected Bosniak III cysts.

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.

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.

CT and MRI findings of cystic renal cell carcinoma: comparison with cystic collecting duct carcinoma

BACKGROUND

Cystic renal cell carcinoma (CRCC) and cystic collecting duct carcinoma (CCDC) share similar oncogeni and some imaging findings. The aim of this study was to characterize the clinical and CT imagings features of CRCC and CCDC.

METHODS

Thirty-three patients with CRCC and thirteen patients with CCDC with pathologically proven were retrospectively studied. Tumor characteristics were assessed.

RESULTS

On CT imaging, 33 patients(100 %) with CRCC and 13 patients(100 %) with CCDC, tumors calcifications (8 vs. 9, P < 0.0001), had a clear boundary (capsule sign, 30 vs. 2, P < 0.0001), infiltrative appearance (1 vs. 13, P < 0.0001), exogenous appearance (29 vs. 3, P < 0.0001), invaded the renal pelvis or ureter (1 vs. 10, P < 0.0001), hemorrhage (1 vs. 10, P < 0.0001), had retroperitoneal lymph node or distant metastasis (2 vs. 10, P < 0.0001), thickened enhancing internal septations (31 vs. 2, P < 0.0001), and mural soft-tissue nodules (21 vs. 1, P < 0.0001). On MR imaging,13 patients(39 %) with CRCC and 4 patients(31 %) with CCDC, all CRCCs appeared hypointense on T1-weighted images and hyperintense on T2-weighted images, however, all CCDCs appeared hypointense on T1-weighted images and hypointense on T2-weighted images(P < 0.0001). 33 patients with CRCC, they were all alive from3 years to 10 years follow-up, however, 13 patients with CCDC, of which 11 patients were able to be followed up, and 9 patients expired within 5 years of the initial diagnosis and the others are currently still alive.

CONCLUSIONS

Distinguishing features of CRCC and CCDC included calcifications, capsule signs, infiltrative appearance, metastasis, internal septations, mural nodules and signal on CT or MR images. These imaging features may help in differentiating the two renal tumor types.

Predictive Value of Additional Clinical and Radiological Parameters for Discrimination of Malignancy in Bosniak 3 Cysts

INTRODUCTION

Almost half of the cystic renal lesions are still overdiagnosed and overtreated. New clinical and radiological parameters are needed to distinguish the malignant Bosniak 3 lesions from the benign ones. We aimed to evaluate the clinical and radiological parameters that may be related to malignancy risk for Bosniak category 3 renal cysts.

MATERIALS AND METHODS

Patients who underwent surgical resection of a histopathologically confirmed Bosniak 3 renal cyst between March 2007 and September 2019 were evaluated. Two experienced uro-radiologists have reevaluated the last preoperative computed tomography and/or MRI images of the patients and reclassified the lesions according to the Bosniak classification. They also reported cystic features such as nodularity, septation, focal thickening, enhancement, and calcification. Clinical, pathological, and oncological outcomes were recorded. Then patients were divided into 2 groups as Group 1 (benign pathology) and Group 2 (malignant pathology) according to final histopathological report.

RESULTS

A total of 79 patients were included in this study. Mean follow-up time was 47 ± 34 months. There were 30 patients in Group 1 and 49 patients in Group 2. Hypertension (p = 0.001) and smoking history (p = 0.008) were more common in malignant group. Among the radiological findings, lower tumor diameter (p = 0.024), presence of cyst wall enhancement (p = 0.025), presence of nodularity (p = 0.002), and presence of focal thickening (p = 0.031) were found to be statistically significant for malignancy. Most of the tumors were at pathological T1 stage and Fuhrmann Grade 1-2. Only nodularity was found to be independent predictive factor for malignancy in multivariate analysis.

CONCLUSION

Clinical factors including hypertension and smoking, radiological factors including lower lesion size, cyst wall enhancement, nodularity, and focal thickening were predictors for malignancy of Bosniak 3 cysts.

Comparison of enhancement quantification from virtual unenhanced images to true unenhanced images in multiphase renal Dual-Energy computed tomography: A phantom study

Multiphase computed tomography (CT) exams are a commonly used imaging technique for the diagnosis of renal lesions and involve the acquisition of a true unenhanced (TUE) series followed by one or more postcontrast series. The difference in CT number of the mass in pre- and postcontrast images is used to quantify enhancement, which is an important criterion used for diagnosis. This study sought to assess the feasibility of replacing TUE images with virtual unenhanced (VUE) images derived from Dual-Energy CT datasets in renal CT exams. Eliminating TUE image acquisition could reduce patient dose and improve clinical efficiency. A rapid kVp-switching CT scanner was used to assess enhancement accuracy when using VUE compared to TUE images as the baseline for enhancement calculations across a wide range of clinical scenarios simulated in a phantom study. Three phantoms were constructed to simulate small, medium, and large patients, each with varying lesion size and location. Nonenhancing cystic lesions were simulated using distilled water. Intermediate (10-20 HU [Hounsfield units]) and positively enhancing masses (≥20 HU) were simulated by filling the spherical inserts in each phantom with varied levels of iodinated contrast mixed with a blood surrogate. The results were analyzed using Bayesian hierarchical models. Posterior probabilities were used to classify enhancement measured using VUE compared to TUE images as significantly less, not significantly different, or significantly higher. Enhancement measured using TUE images was considered the ground truth in this study. For simulation of nonenhancing renal lesions, enhancement values were not significantly different when using VUE versus TUE images, with posterior probabilities ranging from 0.23-0.56 across all phantom sizes and an associated specificity of 100%. However, for simulation of intermediate and positively enhancing lesions significant differences were observed, with posterior probabilities < 0.05, indicating significantly lower measured enhancement when using VUE versus TUE images. Positively enhancing masses were categorized accurately, with a sensitivity of 91.2%, when using VUE images as the baseline. For all scenarios where iodine was present, VUE-based enhancement measurements classified lesions with a sensitivity of 43.2%, a specificity of 100%, and an accuracy of 78.1%. Enhancement calculated using VUE images proved to be feasible for classifying nonenhancing and highly enhancing lesions. However, differences in measured enhancement for simulation of intermediately enhancing lesions demonstrated that replacement of TUE with VUE images may not be advisable for renal CT exams.

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.

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.

Declining incidence of benign lesions among small renal masses treated with surgery: Effect of diagnostic tests for characterization

PURPOSE

We evaluated the changes in the incidence of benign lesions in surgically removed small renal masses (SRMs) and the effect of diagnostic tests for characterizing SRMs.

METHODS

We included 2,707 patients receiving surgery for SRMs (<4cm). Trends in the incidence of benign histology were evaluated according to the surgery year (period 1: 2001-2005, 2: 2006-2010, and 3: 2011-2015). Multivariable logistic regression analysis was performed to identify factors associated with benign lesions. Additionally, the number of surgeries prevented due to benign histological findings on renal mass biopsies (RMB) done on 206 patients with SRM during study period was evaluated.

RESULTS

Benign histology was identified in 192 (7.1%) patients. Incidence of benign histology was 9.7%, 7.0%, and 6.3% for period 1, 2 and 3, respectively. The uses of multiphase computed tomography and magnetic resonance imaging were more common in periods 2 and 3 than in period 1 (P<0.001). The use of RMB in period 3 was higher than in periods 1 and 2 (0.8 vs. 0.9 vs. 9.0%, P<0.001). In multivariable analysis, older age, male sex, larger tumor size, and recent surgery year (period 3 vs. 1, odds ratio = 0.62, P = 0.028) were independently associated with decreased odds of benign lesions. The number of prevented surgeries by performing RMB was 0, 10, and 39 in periods 1, 2, and 3, respectively.

CONCLUSIONS

Incidence of benign histology after surgery for SRMs declined during recent years, which might be associated with the recent increased use of RMB.

Bosniak category III renal lesions: likelihood of malignancy based on computed tomography findings

Introduction

Bosniak introduced a classification of renal cysts based on imaging characteristics. Cystic renal changes are categorized determining their risk of malignancy and further management. However, defining the malignancy of category III lesions still remains a challenge and our aim was to evaluate the features of malignancy in computed tomography within this category.

Material and methods

The Vilnius University Hospital Santariškių Klinikos information system was retrospectively searched for computed tomography examinations in which Bosniak category III lesions were reported. Data of genetic disorders and history of malignancy were collected. Longest diameter, location, shape, amount and location of calcification, contrast enhancement of Bosniak category III lesions were evaluated. The relation between collected data and malignancy was estimated.

RESULTS

There were 73 patients with Bosniak category III lesions included and 43 cysts were surgically removed and histologically analyzed. Mean tumor size was significantly lower in malignant lesions. Mean enhancement in arterial and portovenous phase, change of mean enhancement in portovenous and native phases were significantly different between benign and malignant lesions. Significant differences in the contrast enhancement pattern was found: septa and capsular enhancement was detected in 28.6% (n = 12) of cases in malignant lesions, while only 4.8% (n = 2) benign lesions show the same enhancement pattern. Some other features showed tendencies to be more prevalent in malignant lesions, however, no significant differences were found.

Conclusions

The collected data and selected features do not allow us to reliably differentiate Bosniak category III cystic lesions as benign or malignant. Some of the criteria showed some tendencies, however, further studies are required to confirm these findings' potential.

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.

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.

Bosniak classification for complex renal cysts: history and critical analysis

The Bosniak classification for renal cysts was developed in the late 1980s in an attempt to standardize the description and management of complex cystic renal lesions. Alterations were made to such a classification in the 1990s and, the last one, in 2005. Currently, five categories of cystic renal lesions are defined - namely, I, II, II-F, III and IV –, according to their degree of complexity and likelihood of malignancy. Despite being initially described for computed tomography, this classification has been also utilized with some advantages also for magnetic resonance imaging. The present article reviews the different phases of this classification, its diagnostic efficacy and the most controversial features of its use.

New modalities for evaluation and surveillance of complex renal cysts

PURPOSE

The increased use of abdominal imaging has led to more frequent detection of incidental renal cysts. Since the inception of the Bosniak classification system, management of Bosniak I, III and IV cysts has been clearly defined, while evaluation and management of Bosniak II and IIF cysts have remained a clinical dilemma. Discussions of new imaging modalities are becoming increasingly prevalent in the radiological literature. In this context we performed a comprehensive review of the recent literature on complex renal cysts focusing on new imaging modalities, surveillance strategies and biopsy.

MATERIALS AND METHODS

We performed a comprehensive literature review of articles published from January 1, 1998 through December 31, 2013 via MEDLINE(®), EMBASE and the Cochrane Collection using a predetermined search strategy. All studies included were performed in humans older than 18 years, were written in English and had an abstract available for review. We grouped studies into 1 of 5 categories, ie computerized tomography, magnetic resonance imaging, ultrasound, biopsy and surveillance.

RESULTS

While computerized tomography and magnetic resonance imaging with and without contrast enhancement remain the gold standard to evaluate cystic lesions of the kidney, diffusion-weighted magnetic resonance imaging and contrast enhanced ultrasound have surfaced as new tools for assessment of complex cysts. Comparative effectiveness studies on these new imaging modalities are limited. Image guided biopsy has increasingly been shown to be useful for evaluation of intermediate (Bosniak II and IIF) complex cysts. We found few studies providing guidance on the duration and/or intensity of surveillance required for intermediate complex renal cysts.

CONCLUSIONS

Although new and enhanced techniques are in development and may be useful in the future management of complex renal cysts, there is a paucity of data regarding the value of these new techniques. Future research should focus on surveillance of intermediate complex renal cysts, particularly on the ideal frequency and type of imaging required.

Pathological characteristics and radiographic correlates of complex renal cysts

OBJECTIVES

To characterize pathological and cancer-specific outcomes of surgically resected cystic renal tumors and to identify clinical or radiographic features associated with these outcomes.

METHODS AND MATERIALS

All patients at our institution who underwent radical or partial nephrectomy for complex renal cystic masses between 2004 and 2011 with available computed tomographic imaging were included. The Bosniak score was determined, as were 10 specific radiographic characteristics of renal cysts in patients with preoperative imaging available for review. These characteristics were correlated with cystic mass histopathology. Recurrence-free survival after surgery was determined.

RESULTS

Overall, 133 patients underwent renal surgery for complex cystic lesions, 89 (67%) of whom had malignant lesions. Malignancy risk increased with Bosniak score (P≤0.01) and presence of mural nodules (P = 0.01). Most (63%) malignancies demonstrated clear cell histology. The papillary renal cell carcinomas (25%) exhibited lower enhancement levels (P = 0.04) and were less often septated (P<0.01). Of the malignancies, 79% were low stage (pT1), and 73% were Fuhrman grade 1 or 2. Large cyst size was associated with advanced tumor stage (P = 0.05). Neither Bosniak score nor any other radiographic parameter was associated with Fuhrman grade. In 70 patients with a median follow-up of 43 months, only 1 (1.4%) developed disease recurrence.

CONCLUSIONS

Most cystic renal malignancies are low-stage, low-grade lesions. Papillary renal cell carcinomas account for nearly a quarter of cystic renal malignancies and have unique radiographic characteristics. Disease recurrence after surgical resection is rare. These findings suggest an indolent behavior for cystic renal tumors, and these lesions may be amenable to active surveillance.

Three-phase, contrast-enhanced, multidetector CT in the evaluation of complicated renal cysts: comparison of the postcontrast phase combination

BACKGROUND

Multiphasic multidetector computed tomography (MDCT) is widely used for the assessment and diagnosis of complicated renal cysts.

PURPOSE

To determine the optimal combination of postcontrast phases of MDCT for the evaluation of complicated renal cysts.

MATERIAL AND METHODS

In 164 renal cysts with pathology confirmation or follow-up >2 years, the Bosniak category was recorded by two radiologists in consensus. They reviewed the MDCT images during three interpretation sessions. In the first session, the radiologists evaluated two phases of images (unenhanced and corticomedullary phases), while during the second session, they evaluated two phases of images (unenhanced and parenchymal phases), and in the third session, they evaluated all three phases of images (unenhanced, corticomedullary, and parenchymal phases). The diagnostic accuracy for evaluating renal cysts was compared in each session using receiver-operating characteristics (ROC) analysis.

RESULTS

There were 106 benign renal cysts and 58 malignant renal cysts. The areas under the ROC curves (AUCs) of the second and third sessions were greater than that of the first session (P < 0.05). The sensitivity, specificity, positive predictive value, and negative predictive value of the first session were 74%, 88%, 77%, and 86%, respectively, and those of the second session were 90%, 85%, 77%, and 94%, respectively. The values of the third session were identical to those of the second session.

CONCLUSION

Unenhanced and parenchymal phase CT scans are sufficient for differentiating malignant from benign renal cysts and there was no additional value by adding the corticomedullary phase to the combination of unenhanced and parenchymal phase CT.

Chromophobe renal cell carcinoma: multiphase MDCT enhancement patterns and morphologic features

OBJECTIVE

The purpose of this investigation is to retrospectively describe morphologic features, enhancement characteristics, and clinical outcomes in a series of pathologically proven chromophobe renal cell carcinomas (RCCs).

MATERIALS AND METHODS

Thirty-five patients who were imaged at a single institution between 2005 and 2012 with pathologically proven chromophobe RCC were identified, all of whom underwent preoperative renal protocol CT (unenhanced, arterial, venous, and delayed images). The morphologic characteristics of each tumor (e.g., necrosis, tumor composition, and calcification), as well as attenuation values (in Hounsfield units) of the tumor, aorta, inferior vena cava, and kidney were evaluated by a board-certified radiologist. In addition, information regarding patient demographics and survival was obtained by a separate radiologist from the electronic medical record.

RESULTS

Sixty percent of the patients were men, with a mean age of 60.2 years. Forty-six percent of cases were incidentally identified, without patient symptoms. None of the patients had evidence of distant metastatic disease, either on initial staging CT or over the course of follow-up (mean, 2.0 years). Mean maximal tumor diameter was 5.24 cm. Forty-six percent of tumors were homogeneous, 85% of lesions were either completely solid or mostly solid, 14% showed calcifications, and 34% showed a central scar or necrosis. Mean maximum attenuation values were 87.9 HU (arterial phase), 83.9 HU (venous phase), and 60.6 HU (delayed phase), with an average delayed washout of 31%. Tumor-to-cortex ratios for the three enhanced phases were 0.59, 0.48, and 0.50, respectively.

CONCLUSION

Chromophobe RCCs were found to have a wider variability of CT features than previously reported, although they do have a greater propensity for homogeneity and the presence of a central scar or necrosis. Their enhancement characteristics fall in between those of clear cell and papillary RCC, although there is considerable overlap.

Evaluation of Bosniak category IIF complex renal cysts

PURPOSE

To evaluate moderately complex renal cysts of Bosniak category IIF.

MATERIALS AND METHODS

The regional ethics committee approved the study. In the period 2003-2009, radiological CT reports of 8,402 CT examinations of the kidneys were analysed retrospectively by one radiologist. All complex cystic lesions in the kidney (n = 550 in the same number of patients) were reclassified according to the Bosniak classification by two radiologists in consensus. If a patient had more than one lesion, only the highest Bosniak category was recorded. All Bosniak IIF lesions with ≥2-year follow-up were included in the study.

RESULTS

Thirty-two Bosniak IIF lesions were found. Five lesions (16 %) were upgraded during follow-up and the patients were offered surgery. Pathology of three lesions showed papillary carcinoma, clear cell renal carcinoma and chronic inflammation, respectively. Due to comorbidity the remaining two patients were followed with CT without intervention. Ten lesions (31 %) with follow-up periods >5 years had no further radiological changes and clinical follow-up was stopped.

CONCLUSION

The use of Bosniak category IIF is clinically applicable, resulting in an overall surgical nephron-sparing approach to complex renal cysts.

TEACHING POINTS

• The Bosniak classification is used to categorise complex renal cystic masses • BIIF cysts behave mostly as benign lesions • Radiological progression in complexity occurs in only 16 % of cases • BIIF category seems promising for clinical application, potentially avoiding unnecessary surgery.

Renal cell carcinoma: attenuation values on unenhanced CT

OBJECTIVE

The purpose of this study is to analyze the attenuation values of pathologically proven renal cell carcinomas (RCCs) on unenhanced CT and to determine the range of values wherein malignancy should be considered.

MATERIALS AND METHODS

A retrospective review was performed of 189 consecutive patients with 193 pathologically proven RCCs 1 cm or larger on unenhanced CT. For each RCC, attenuation values were assessed throughout the tumor by continuous sampling with a 25-100-mm(2) region of interest (ROI), avoiding foci of calcification and peritumoral volume averaging. The lowest and highest ROI attenuation values per lesion were recorded. Each tumor was categorized as either homogeneous or heterogeneous on the basis of visual inspection with soft-tissue window settings.

RESULTS

The 193 malignant tumors ranged in size from 1.1 to 20.1 cm (mean [± SD], 5.1 ± 3.4 cm). Eighteen RCCs (9.3%) were homogeneous in appearance on unenhanced CT. The minimum and maximum ROI attenuation values obtained by sampling throughout each tumor were 27.5 ± 10.4 HU (range, 4-67 HU) and 39.7 ± 10.6 HU (range, 21-80 HU), respectively. Regional areas of minimum attenuation less than 20 HU and maximum attenuation greater than 70 HU were seen in 24.9% (48/193) and 2.1% (4/193) of RCCs, respectively. However, all 193 RCCs (100%) were predominantly composed of noncalcific regions within 20-70 HU; 72.5% (140/193) fell entirely within this 20-70 HU "danger zone," including all 18 homogeneous lesions.

CONCLUSION

All proven RCCs in this series contained substantial noncalcified regions that measured 20-70 HU in ROI attenuation on unenhanced CT. Indeterminate renal lesions on unenhanced CT measuring within this 20-70-HU danger zone warrant further workup, whereas lesions that fall entirely outside this range may be considered benign.

Incidental finding of renal masses at unenhanced CT: prevalence and analysis of features for guiding management

OBJECTIVE

The purposes of this study were to investigate the frequency and clinical relevance of the incidental finding of renal masses at low-dose unenhanced CT and to analyze the results for features that can be used to guide evaluation.

MATERIALS AND METHODS

Images from unenhanced CT colonographic examinations of 3001 consecutively registered adults without symptoms (1667 women, 1334 men; mean age, 57 years) were retrospectively reviewed for the presence of cystic and solid renal masses 1 cm in diameter or larger. An index mass, that is, the most complex or concerning, in each patient was assessed for size, mean attenuation, and morphologic features. Masses containing fat or with attenuation less than 20 HU or greater than 70 HU were considered benign if they did not contain thickened walls or septations, three or more septations, mural nodules, or thick calcifications. Masses with attenuation between 20 and 70 HU or any of these features were considered indeterminate. The performance of CT colonography in the detection of renal cell carcinoma was calculated for masses with 2 or more years of follow-up.

RESULTS

At least one renal mass was identified in 433 (14.4%) patients. The mean size of the index masses was 25 ± 16 mm; 376 (86.8%) masses were classified as benign and 57 (13.2%) as indeterminate. The 20- to 70-HU attenuation criterion alone was used for classification of 53 indeterminate lesions. Follow-up data (mean follow-up period, 4.4 years; range, 2-6.3 years) were available for 353 (81.5%) patients with masses (41 indeterminate, 312 benign). Four of the 41 indeterminate masses were diagnosed as renal cell carcinoma. The sensitivity and specificity for renal cell carcinoma on the basis of the indeterminate criteria were 100% and 89.4%. The positive and negative predictive values were 9.8% and 100%.

CONCLUSION

The incidental finding of a renal mass is relatively common at unenhanced CT, but imaging criteria can be used for reliable identification of most of these lesions as benign without further workup. Mean attenuation alone appears reliable for determining which renal masses need further evaluation.

Multilocular cystic renal cell carcinoma: clinicopathological features and preoperative prediction using multiphase computed tomography

OBJECTIVE

• To analyse the clinicopathological and radiological features of multilocular cystic renal cell carcinoma (MCRCC) and to determine the preoperative factors differentiating MCRCC from other cystic RCC (CRCC).

PATIENTS AND METHODS

• The medical records of 53 patients with complex cystic renal masses evaluated by multiphase computed tomography (CT), surgically removed and confirmed as sporadic RCC were reviewed. • Of these 53 patients, 23 were classified as having MCRCC and 30 as other CRCCs, defined as RCCs with extensive cystic change or cystic necrosis. • Another 22 patients were treated for complex cystic renal masses presumed to be RCC and diagnosed as having benign cyst.

RESULTS

• Benign cysts and MCRCCs were significantly more likely to be of Bosniak classification III than other CRCCs (77% vs 61% vs 27%, P= 0.001). • The mean Hounsfield unit (HU) during the corticomedullary phase (CMP) was significantly higher in other CRCCs, with HU ≥38 having 83% sensitivity and 80% specificity for predicting other CRCCs. • In a multiple regression model, Bosniak classification and mean HU during CMP were independent factors predictive of other CRCCs. • In the 41 patients with masses >4 cm in diameter, the combination of Bosniak classification IV and HU ≥38 during CMP showed 63% sensitivity, 96% specificity, 91% positive predictive value and 80% negative predictive value, yielding 2% false-positive and 15% false-negative rates.

CONCLUSIONS

• The mean HU during CMP and Bosniak classification can differentiate MCRCC from other CRCCs. • This could help in selecting an appropriate surgical method, such as nephron-sparing surgery, for complex cystic renal masses >4 cm.

Interpersonal variability and present diagnostic dilemmas in Bosniak classification system

OBJECTIVE

The purpose of the study was to evaluate the management and interpersonal variability of Bosniak classification and demonstrate the present diagnostic dilemmas.

MATERIAL AND METHODS

One-hundred and four patients with 113 complex renal cystic masses (26 Bosniak II,15 IIF,28 III and 44 IV) were included and analysed between April 1996 and May 2009.In total, 71 cystic masses were characterized by two radiologists in consensus initially as the first diagnosis (group 1), and then by a radiologist (group 2) and a urologist (group 3) independently in a blinded fashion.

RESULTS

Only 11 patients (10.6%) were symptomatic (one Bosniak IIF, six III and four IV). Only one had renal cell carcinoma (RCC) on final histology, whereas the others (n = 10) had benign lesions. An overall pathological result was obtained in 71 masses (62.8%) (two Bosniak II, three IIF, 27 III and 39 IV). The overall incidence of RCC in surgically treated patients was 0%, 20%, 55.6% and 76.9% for each category, respectively. The interpersonal variability was significant among the three groups (especially in Bosniak II, IIF), and the overall category was changed in 54%, 20% and 41%, respectively (p < 0.001). After correlation with final histology and presumed benign character of Bosniak II/IIF lesions (all patients having reached 5-year follow-up) the differences were not significant.

CONCLUSION

It is challenging to minimize unnecessary surgical procedures in Bosniak category III. According to these results, it may make practical sense to group Bosniak II and IIF masses in one category.

Characterization of complex renal cysts: a critical evaluation of the Bosniak classification

OBJECTIVE

Complex renal cysts represent a major clinical problem, since it is often difficult to exclude malignancy. The Bosniak classification system, based on computed tomography (CT), is widely used to categorize cystic renal lesions. The aim of this study was to evaluate critically available data on the Bosniak classification.

MATERIAL AND METHODS

All publications from an Entrez Pubmed search were reviewed, focusing on clinical applicability and the use of imaging modalities other than CT to categorize complex renal cysts.

RESULTS

Fifteen retrospective studies were found. Most series were small, with only six studies comprising more than 30 patients. When the results of these six studies were pooled the percentage of malignancy was: category I, 0%; category II, 15.6%; category IIF, 0%; category III, 65.3%; and category IV, 91.7%. Category IIF was included in only three studies. Both magnetic resonance imaging and contrast-enhanced ultrasonography (US) seemed to have reasonable agreement with CT, although both modalities had a tendency to upgrade lesions.

CONCLUSIONS

The main problem with the Bosniak classification is in separating category II and III lesions, which is of major importance, since decisions on intervention are based on this separation. The use of category IIF seems promising to detect those category II lesions that eventually will develop into malignancy and reduce overtreatment of lesions originally classified as category III. The scientific basis of this "new" classification strategy is, however, still missing. Data on other imaging modalities are too limited for conclusions to be drawn.

CA9 as a molecular marker for differential diagnosis of cystic renal tumors

OBJECTIVE

CA9 is proven to be a powerful marker for clear cell renal cell carcinoma. The studies on CA9 have been limited to solid renal cell carcinomas (RCC). We have conducted a study of CA9 expression in renal cystic tumors. The purpose of the present study was to extend the utility of CA9 for cystic renal tumors.

MATERIALS AND METHODS

Immunohistochemistry and enzyme-linked immunosorbent assay (ELISA) were used to detect CA9 expression in cystic renal tumors. Forty-three cystic renal tumors (22 benign and 21 malignant) were included for the immunohistochemical staining. Thirty-six patients with a cystic renal mass (20 malignant and 16 benign cystic tumors) were studied to measure CA9 level in the fluid by ELISA. Sixteen cysts (9 malignant and 7 benign cysts) were subjected both to immunohistochemistry and CA9 measurement in the fluid.

RESULTS

Using immunohistochemical staining, all the benign cystic renal tumors including the 18 simple cyst and 4 benign multilocular cystic nephromas did not express CA9. All 13 cystic clear cell RCC were scored as strong staining for CA9. For 8 multilocular clear cell RCC, 7 were scored as strong staining for CA9 and the other one was negative. There was a significant difference in positive percentage (P < 0.001) between the 2 groups of malignant and benign cysts. For the 16 benign cysts, the mean concentration of CA9 in the fluid of cyst was 162 ± 133 pg/ml (median: 0 pg/ml; range: 0-2140 pg/ml). For the 20 malignant renal cystic tumors, the mean concentration of CA9 in the fluid of cyst was 2043 ± 62 pg/ml (median: 2,140 pg/ml; range: 1,112-2,140 pg/ml). There was a significant difference in mean concentration of CA9 between the two groups of malignant and benign cysts (P < 0.001). The presence or absence of CA9 expression measured by immunohistochemistry and ELISA test was concordant in 14 out of 16 cases (88%).

CONCLUSIONS

Malignant cystic renal tumors expressed strongly CA9 while the benign renal cysts did not express CA9. CA9 can be detected in the fluid of malignant cystic renal tumors. CA9 is a promising molecular marker to differentiate the malignant cystic renal tumors from the benign cysts.

Imaging renal cell carcinoma with ultrasonography, CT and MRI

The increased use of abdominal imaging techniques for a variety of indications has contributed to more-frequent detection of renal cell carcinoma (RCC). Ultrasonography has been used to characterize the solid versus cystic nature of renal masses. This modality has limitations, however, in further characterization of solid tumors and in staging of malignancy, although contrast-enhanced ultrasonography has shown promise. Cross-sectional imaging with multiplanar reconstruction capability via CT or MRI has become the standard-bearer in the diagnosis, staging and surveillance of renal cancers. The use of specific protocols and the exploitation of different imaging characteristics of RCC subtypes, including variations in contrast agent timing, MRI weighting and digital subtraction, have contributed to this diagnostic capability. Cystic renal masses are a special case, evaluation of which can require multiple imaging modalities. Rigorous evaluation of these lesions can provide information that is crucial to prediction of the likelihood of malignancy. Such imaging is not without risk, however, as radiation from frequent CT imaging has been implicated in the development of secondary malignancies, and contrast agents for CT and MRI can pose risks, particularly in patients with compromised renal function.