Bosniak classification for complex renal cysts: history and critical analysis

Scientific Status Quo of Small Renal Lesions: Diagnostic Assessment and Radiomics

Background: Small renal masses (SRMs) are defined as contrast-enhanced renal lesions less than or equal to 4 cm in maximal diameter, which can be compatible with stage T1a renal cell carcinomas (RCCs). Currently, 50-61% of all renal tumors are found incidentally. Methods: The characteristics of the lesion influence the choice of the type of management, which include several methods SRM of management, including nephrectomy, partial nephrectomy, ablation, observation, and also stereotactic body radiotherapy. Typical imaging methods available for differentiating benign from malignant renal lesions include ultrasound (US), contrast-enhanced ultrasound (CEUS), computed tomography (CT), and magnetic resonance imaging (MRI). Results: Although ultrasound is the first imaging technique used to detect small renal lesions, it has several limitations. CT is the main and most widely used imaging technique for SRM characterization. The main advantages of MRI compared to CT are the better contrast resolution and tissue characterization, the use of functional imaging sequences, the possibility of performing the examination in patients allergic to iodine-containing contrast medium, and the absence of exposure to ionizing radiation. For a correct evaluation during imaging follow-up, it is necessary to use a reliable method for the assessment of renal lesions, represented by the Bosniak classification system. This classification was initially developed based on contrast-enhanced CT imaging findings, and the 2019 revision proposed the inclusion of MRI features; however, the latest classification has not yet received widespread validation. Conclusions: The use of radiomics in the evaluation of renal masses is an emerging and increasingly central field with several applications such as characterizing renal masses, distinguishing RCC subtypes, monitoring response to targeted therapeutic agents, and prognosis in a metastatic context.

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.

Burden of Renal Cysts Imaging: A Survey of Patients among the Greater Plains Collaborative

PURPOSE

Renal cysts are a frequent incidental finding on cross-sectional radiographic imaging. While most cysts are indolent, individuals with such cysts are frequently monitored for interval growth and potential malignant transformation, which is ultimately rare. In this study, we aimed to assess patients' values and preferences (believes and attitudes) about renal cysts.

METHODS

We deployed a cross-sectional survey to a random sample of patients with a diagnosis of renal cysts who were identified by billing code and self-identification. We collected data about demographics, insurance status, family history and overall health, and characteristics of patients with renal cysts. We performed a binary regression analysis (adjusted for age, gender, family history of cancer and kidney disease, and treatment plan for renal cysts) to determine anxiety predictors in patients with renal cysts.

RESULTS

We included 301 respondents in whom billing code and self-identification corresponded; of these, 138 had renal cysts and 163 did not. In an adjusted regression analysis, there was a suggestion that a clear management plan (OR = 0.49, 95% CI [0.22-1.11]) (p value 0.08) may be associated with less anxiety and a family history of renal disease may be associated with more anxiety (OR = 1.94 [0.76-4.94]) (p value 0.17). Family history of cancer also did not significantly predict anxiety (OR = 0.54 [0.24-1.19]) (p value 0.13). All these results were not statistically significant and had wide confidence intervals of the effect estimates make the results imprecise.

CONCLUSION

Findings of this pilot study suggest a clear management plan for the renal cyst(s) management may be associated with a lower level of anxiety, thereby by emphasizing the importance of good communication, patient engagement and evidence-based guidance. More definitive, adequately powered studies are needed to evaluate this finding further. In addition, further studies exploring differences in imaging practices, patient symptomatology and patient engagement by different provider types would be insightful. Ultimately, tools to improve shared decision-making are needed to provide more patient-centered care.

Comparison of computed tomography and magnetic resonance imaging in the assessment of complex renal cysts by using the Bosniak classification

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.

Clinical Correlation Between Computerized Tomography Findings and Pathologic Diagnosis in Patients Surgically Treated for Complex Renal Cysts in a Colombian Tertiary Center

Introduction Recent data have reexamined the historical rates of malignancy observed in Bosniak IIF and III cystic lesions, and this has led to an endorsement of the use of active surveillance as the standard of care for Bosniak III renal cysts by affirming that overtreatment rates for this subgroup are close to 50%. In light of this, the present study describes the correlation between imaging studies and pathologic diagnosis in patients surgically treated for complex renal cysts in Colombia. Materials and methods This is a retrospective, descriptive, and observational study. We analyzed the medical histories of patients who had been surgically treated for complex renal cysts between 2010 and 2018 in the urology department of a tertiary center in Bogota, Colombia. The exclusion criteria were incomplete clinical histories and absent diagnostic images or their official interpretation. Results Out of the 235 urological procedures performed, nine were excluded. And 6.19% (n = 14) were cases of surgically treated complex renal cysts; 38.46% were compatible with Bosniak IIF, 46.15% were Bosniak III, and 15.38% were Bosniak IV. The percentage of renal cancer as revealed by the histopathological study was 60, 66.7 and 100 for renal cysts Bosniak IIF, III, and IV, respectively; 77.7% of these confirmed oncological cases had received a diagnosis of clear cell renal carcinoma. Conclusions In our study, the percentage of malignancy in patients with renal cysts Bosniak IIF and III was found to be greater compared to the findings in the recent medical literature. We believe that the management offered to the population with complex renal cysts in Colombia should be tailored to the individual risk characteristics of each patient.

Paraneoplastic cerebellar degeneration as initial presentation of renal cell carcinoma

Background

Paraneoplastic cerebellar degeneration is usually associated with gynecological and breast cancer, lung cancer, and Hodgkin’s lymphoma. Renal cell carcinoma has rarely been described as an underlying malignancy in these cases.

Case presentation

We report the case of a 75 year-old woman who develop cerebellar ataxia following a respiratory viral infection. During investigation, around 1 year afterward, she noticed constitutional symptoms suggestive of malignancy. Renal carcinoma was found and the hypothesis of paraneoplastic cerebellar degeneration was considered.

Conclusions

As no specific antineuronal antibodies have been described in the setting of renal cell carcinoma, paraneoplastic cerebellar degeneration should be considered when the tumor is detected and other causes are excluded. Immunotherapy should be prescribed as soon as possible.

Point of care renal ultrasonography for the busy nephrologist: A pictorial review

The application of bedside ultrasonography in routine clinical practice has dramatically evolved over the last few decades and will likely continue to grow as technological advances lead to enhanced portability and affordability of the equipment. Despite mounting interest, most nephrology fellowship training programs do not offer formal training in renal ultrasonography and there is inertia among practicing nephrologists to adopt this skill as a practice-changing advancement. Lack of familiarity with the topic is considered a key reason for this inertia. Understanding of basic ultrasound physics, instrumentation, principles of optimal image acquisition and interpretation is critical for enhanced efficiency and patient safety while using this tool. Herein, we provide a brief overview of the basic principles of diagnostic renal ultrasonography as well as introduction to common sonographic pathologies encountered in day-to-day nephrology practice with illustrative images.

Progression rate in Bosniak category IIF complex renal cysts

Objective

To evaluate progression rate of Bosniak category IIF complex renal cysts and the malignancy rate among surgically resected cysts.

Materials and Methods

We performed a database search for complex renal cysts classified as Bosniak category IIF on computed tomography or magnetic resonance imaging between January 2008 and April 2016. Follow-up examinations (computed tomography or magnetic resonance imaging) were used in order to evaluate progression (Bosniak category reclassification) and stability, the latter being defined as remaining stable for a minimum of six months. Pathology reports were used as the reference to assess the malignancy rate of surgically resected cysts.

Results

A total of 152 cysts in 143 patients were included in the final analysis. Seven cysts (4.6%) were reclassified on follow-up studies, and mean time to progression was 20 months (range, 1 month to 4 years). Three cysts were surgically resected. All three were diagnosed as low-grade malignant renal cell carcinomas (RCCs): one clear cell RCC and two papillary RCCs. The remaining 145 cysts remained unchanged after a mean follow-up period of 28 months (range, 6 to 118 months).

Conclusion

The progression rate in Bosniak category IIF cysts was low. Even lesions that were upgraded on follow-up remained stable, indicating an indolent behavior. Our data support the idea of conservative management of Bosniak IIF renal cyst.

Simple renal cysts are associated with increased arterial stiffness in a Taiwanese population

Arterial stiffness has been found to be a predictive risk factor for cardiovascular disease. Simple renal cysts are associated with prehypertension, hypertension, diabetes, and increased serum creatinine, which are risk factors of cardiovascular events. The aim of this work was to clarify the association between simple renal cysts and arterial stiffness defined by the brachial and ankle pulse wave velocity (baPWV). Subjects with and without simple renal cysts had right baPWV values of 1522.8 ± 357.5 cm/s and 1344.2 ± 268.8 cm/s, respectively (p < 0.001). Based on multiple linear regression analysis, the presence of simple renal cysts was associated with increased baPWV values (p < 0.001). Both the size and the number of simple renal cysts were positively associated with an increased baPWV value. Subjects with a cyst size ≥2 cm (p < 0.001) and a cyst number ≥2 (p < 0.01) had higher baPWV values than those without SRCs. Simple renal cysts are associated with increased arterial stiffness.

Magnetic resonance imaging (MRI) of the renal sinus

This article presents methods to improve MR imaging approach of disorders of the renal sinus which are relatively uncommon and can be technically challenging. Multi-planar Single-shot T2-weighted (T2W) Fast Spin-Echo sequences are recommended to optimally assess anatomic relations of disease. Multi-planar 3D-T1W Gradient Recalled Echo imaging before and after Gadolinium administration depicts the presence and type of enhancement and relation to arterial, venous, and collecting system structures. To improve urographic phase MRI, concentrated Gadolinium in the collecting systems should be diluted. Diffusion-Weighted Imaging (DWI) should be performed before Gadolinium administration to minimize T2* effects. Renal sinus cysts are common but can occasionally be confused for dilated collecting system or calyceal diverticula, with the latter communicating with the collecting system and filling on urographic phase imaging. Vascular lesions (e.g., aneurysm, fistulas) may mimic cystic (or solid) lesions on non-enhanced MRI but can be suspected by noting similar signal intensity to the blood pool and diagnosis can be confirmed with MR angiogram/venogram. Multilocular cystic nephroma commonly extends to the renal sinus, however, to date are indistinguishable from cystic renal cell carcinoma (RCC). Solid hilar tumors are most commonly RCC and urothelial cell carcinoma (UCC). Hilar RCC are heterogeneous, hypervascular with epicenter in the renal cortex compared to UCC which are centered in the collecting system, homogeneously hypovascular, and show profound restricted diffusion. Diagnosis of renal sinus invasion in RCC is critically important as it is the most common imaging cause of pre-operative under-staging of disease. Fat is a normal component of the renal sinus; however, amount of sinus fat correlates with cardiovascular disease and is also seen in lipomatosis. Fat-containing hilar lesions include lipomas, angiomyolipomas, and less commonly other tumors which engulf sinus fat. Mesenchymal hilar tumors are rare. MR imaging diagnosis is generally not possible, although anatomic relations should be described to guide diagnosis by percutaneous biopsy or surgery.

Urologic Diseases Germane to the Medical Renal Biopsy: Review of a Large Diagnostic Experience in the Context of the Renal Architecture and Its Environs

The kidney is one of the most complicated organs in development and is susceptible to more types of diseases than other organs. The disease spectrum includes developmental and cystic diseases, involvement by systemic diseases, iatrogenic complications, ascending infections and urinary tract obstruction, and neoplastic diseases. The diagnosis of kidney disease is unique involving 2 subspecialties, urologic pathology and renal pathology. Both renal and urologic pathologists employ the renal biopsy as a diagnostic modality. However, urologic pathologists commonly have a generous specimen in the form of a nephrectomy or partial nephrectomy while a renal pathologist requires ancillary modalities of immunofluorescence and electron microscopy. The 2 subspecialties differ in the disease spectrum they diagnose. This separation is not absolute as diseases of one subspecialty not infrequently appear in the diagnostic materials of the other. The presence of medical renal diseases in a nephrectomy specimen is well described and recommendations for reporting these findings have been formalized. However, urologic diseases appearing in a medical renal biopsy have received less attention. This review attempts to fill that gap by first reviewing the perirenal anatomy to illustrate why inadvertent biopsy of adjacent organs occurs and determine its incidence in renal biopsies followed by a discussion of gross anatomic features relevant to the microscopic domain of the medical renal biopsy. Unsuspected neoplasms and renal cysts and cystic kidney diseases will then be discussed as they create a diagnostic challenge for the renal pathologist who often has limited training and experience in these diseases.

Transcatheter Arterial Embolization Therapy for Huge Renal Cysts: Two Case Reports

We encountered 2 patients with symptomatic huge simple renal cysts. In case 1, 4,000 mL of cyst fluid was drained via a catheter, but intracystic bleeding occurred immediately afterwards. Transcatheter arterial embolization (TAE) was performed, after which the bleeding stopped, and cyst drainage was repeated successfully. After 2 years, the total cyst volume was reduced from 11,775 mL to 75.4 mL. In case 2, TAE was performed prophylactically before drainage. Subsequently, 9,400 mL of fluid was removed from multiple cysts. After 1 year, the total cyst volume was reduced from 9,215 mL to 633 mL without bleeding. Based on these 2 cases, prophylactic TAE before drainage may be useful in patients with huge renal cysts.

Bilaterally enlarged adrenal glands without obvious cause: need for a multidisciplinary diagnostic work-up

Bilateral enlarged adrenal glands are rare, and as diagnostic delay may have serious consequences for the patient, we recommend a multidisciplinary approach of specialists in the field of endocrinology, oncology, radiology, and clinical chemistry prior to the start of the diagnostic work‐up.

Radiologic Pearls for Internists: A Case-Based Review

Modern technologic advances in medical imaging and the increasing use of imaging across all disciplines in medicine have led to a striking rise in incidental findings unrelated to the original study indication. Often, these findings have no clinical relevance and will not impact the current or future health status of the patient. It is incumbent on radiologists to report these findings in a definitive and unambiguous manner. Similarly, it is essential for clinicians to restrain from further diagnostic investigation of incidental findings that are conclusive by imaging. A classic and common example is the finding of a cyst. This article presents several cases of incidentally found cysts for which a confident diagnosis can be made without any need for follow-up.

Diffusion-weighted magnetic resonance imaging in cystic renal masses

INTRODUCTION

We aimed to introduce the diagnostic value of diffusion-weighted (DWI) magnetic resonance imaging (MRI) for distinguishing benign and malignant renal cystic masses.

METHODS

Abdominal DWI-MRIs of patients with Bosniak categories 2F, 3, and 4 cystic renal masses were evaluated retrospectively. Cystic masses were assigned as benign or malignant according to histopathological or followup MRI findings and compared with apparent diffusion coefficient (ADC) values.

RESULTS

There were 30 patients (18 males and 12 females, mean age was 59.23 ± 12.08 years [range 38-83 years]) with cystic renal masses (eight Bosniak category 2F, 12 Bosniak category 3, 10 Bosniak category 4). Among them, 14 cysts were diagnosed as benign and 16 as malignant by followup imaging or histopathological findings. For the malignant lesions, the mean ADC values were lower than for benign lesions (p=0.001). An ADC value of ≤2.28 ×10^-6 mm²/s or less had a sensitivity of 75% and a specificity of 92.86% for detecting malignancy.

CONCLUSIONS

ADC can improve the diagnostic performance of MRI in the evaluation of complex renal cysts when used together with conventional MRI sequences.

Surveillance of Bosniak IIF renal cysts: Rationalising follow-up policy

Objectives:

To assess the clinical outcomes of patients diagnosed with Bosniak IIF renal cysts, in order to rationalise our surveillance policy.

Patients and methods:

We identified all patients diagnosed with a Bosniak IIF cyst between September 2011 and September 2014. Patient demographics, duration, frequency and modality of surveillance were recorded. Changes in the size, appearance or characteristics of the cyst(s) were recorded, as well as any subsequent surgery and histology. We also estimated the overall cost of imaging and follow up.

Results:

We identified 198 patients. The majority of IIF cysts were incidental findings (86.5%), with 56% of cysts > 3 cm at diagnosis. Median follow-up time was 27 months. We found that 98% of cysts were unchanged in their Bosniak score and 66% did not change in size. We followed up on 86 patients (43%) beyond two years: None had radiological progression. Four patients (2%) underwent partial nephrectomy secondary to radiological progression: One (0.5%) had histological malignancy. Features of malignancy were noticed in the first 24 months of the follow-up period.

Conclusions:

Radiological progression of Bosniak IIF cysts is low and progression to malignancy lower still, typically occurring within 24 months of diagnosis. Our data suggested that ceasing radiological follow-up surveillance after a minimum of two years of stable surveillance could be considered. Rational follow-up protocols for Bosniak IIF cysts would have significant cost-saving implications for the National Health Service (NHS) and alleviate pressure on radiology and urology services.

MRI evaluation of complex renal cysts using the Bosniak classification: a comparison to CT

PURPOSE

The purpose of this study was to compare the ability of magnetic resonance imaging (MRI) and computed tomography (CT) to discriminate between benign and malignant cystic renal lesions utilizing the Bosniak classification.

MATERIALS AND METHODS

We retrospectively searched our Radiological Information System using renal/kidney cysts as entries. The search retrieved 2929 patients and 525 complex renal cysts. After exclusions, 42 complex cysts, from 37 patients, with CT and MRI, up to six months apart, were included. Surgery and pathology report and follow-up of at least 24 months were used as a standard of reference.

RESULTS

The mean age of patients was 51.4 years, ranging from 11 to 82 years old. Twenty-nine lesions were classified as Bosniak I, II or II-F by CT and/or MRI and 13 as Bosniak III or IV, by one of the methods. The interobserver agreement for Bosniak classification for CT was 0.87 and 0.93 for MRI. Fifteen lesions had higher Bosniak categories on MRI, included six with change in management. Only two lesions had a higher category on CT, one with change in management. The frequency of malignancy for Bosniak III was 50 % (2/4) for CT and 20% for MRI (1/5), as Bosniak upgrades by MRI resulted in surgery for benign lesions. Both methods had 100 % frequency of malignancy for category 4.

CONCLUSION

MRI led to category migration and management change of complex renal cysts in a significant proportion of cases, likely due to its superior soft tissue and contrast resolution. The impact of MRI on detection and outcomes of malignant complex renal cysts still requires further investigation.

Unusual renal tumour: multilocular cystic renal cell carcinoma

Multilocular cystic renal cell carcinoma (MCRCC) is a rare presentation of renal cell carcinoma. Most patients are asymptomatic and frequently MCRCCs are detected incidentally. MCRCCs have good prognosis because of their low malignant potential. We report a case of a 39-year-old woman who presented with mild right flank pain and normal laboratory data. On imaging examinations, a Bosniak III cystic lesion was detected in the lower third of the right kidney. She underwent right partial nephrectomy and histopathology showed a multilocular cystic renal cell carcinoma Fuhrman grade 1. In this article, we also present a review of the literature on MCRCC, highlight the correlation of the pathological and imaging characteristics of these low aggressive renal lesions, and underscore the importance of their recognition to prevent unnecessary radical surgery.