Role of MRI in indeterminate renal mass: diagnostic accuracy and impact on clinical decision making

Peak early-phase enhancement ratio on contrast-enhanced MRI to differentiate chromophobe renal cell carcinoma from oncocytoma

Objectives

To evaluate the feasibility of using the peak early-phase enhancement ratio (PEER) of tumour to renal cortex measured on contrast-enhanced magnetic resonance imaging (MRI) to distinguish between chromophobe renal cell carcinoma (chRCC) and oncocytoma, which are difficult to differentiate on renal mass biopsy.

Patients and Methods

A consecutive case-control study was conducted of patients with chRCC or oncocytoma based on surgical pathology (2006-2020). Two radiologists blinded to pathology results independently measured PEER values on MRI for each tumour. PEER values were compared with surgical pathology results.

Results

For the 18 renal tumours evaluated, PEER values were higher for the 7 oncocytomas than for the 11 chRCCs (median 1.33 versus 0.55, p < 0.001). Agreement between the image interpreters was high (Pearson's: 0.90). PEER cutoff values ranging from 0.98 to 1.05 provided high performance in identifying chRCC. A PEER cutoff value of ≤1.05 had sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 100% for the averaged PEER measurements between the two radiologists. High accuracy in identifying chRCC was also achieved for each individual image interpreter using the cutoff value of ≤1.05, with sensitivity of 100%, specificity of 85.7%, PPV of 91.7% and NPV of 100% for radiologist #1 and sensitivity of 90.9%, specificity of 85.7%, PPV of 90.9% and NPV of 85.7% for radiologist #2.

Conclusion

Differentiating chRCCs from oncocytomas using PEER measurements obtained from contrast-enhanced MRI is feasible and reproducible between radiologists. We identified an accurate range for PEER cutoff values (0.98 to 1.05) requiring validation and adjustment in additional cohorts to maintain high sensitivity for detecting chRCC and negative predictive value. Using MRI PEER to evaluate oncocytic tumours with a differential diagnosis of chRCC versus oncocytoma based on biopsy pathology may help avoid unnecessary intervention for oncocytomas.

Iodine Density Threshold to Distinguish Between Enhancing and Nonenhancing Renal Lesions With Dual-Layer Dual-Energy CT

PURPOSE

This study aimed to determine the optimal threshold iodine density to distinguish enhancing and nonenhancing renal masses with dual-layer dual-energy CT (dlDECT).

METHODS

In this retrospective, HIPAA-compliant, institutional review board-approved study, 383 consecutive renal mass dlDECT studies from September 5, 2018, through December 15, 2022, were reviewed for enhancing solid renal masses with ≥∆20 HU. Studies with simple cysts in the same interval served as controls. Lesion ROI HU measurements on unenhanced and nephrographic phases and ROI iodine density measurements of each lesion and the abdominal aorta for normalization were recorded. The mean lesion HU values and absolute and normalized iodine densities were compared with enhancing and nonenhancing renal lesions using a two-sample t test. The diagnostic accuracy of iodine thresholds was assessed by calculating sensitivity and specificity, with receiver operating characteristic curve and AUC analysis.

RESULTS

There were 38 enhancing and 39 nonenhancing renal lesions. The mean (standard deviation [SD]) ∆HU was 73.5 (38.7) and 3.9 (5.1) HU for enhancing and nonenhancing lesions, respectively. The mean absolute iodine density was significantly different for enhancing and nonenhancing lesions (3.2 [1.7] mg/mL and 0.20 [0.22] mg/mL, respectively; P < 0.0001). Normalized mean iodine density was significantly different for enhancing and nonenhancing lesions (0.62 [0.33] mg/mL and 0.04 [0.04] mg/mL, respectively; P < 0.0001). The optimal absolute iodine density threshold of 0.70 mg/mL (AUC, 0.999) and normalized iodine density threshold of 0.11 mg/mL (AUC, 0.999) were 100% sensitive and 97.4% specific for discriminating enhancing and nonenhancing renal lesions.

CONCLUSIONS

This study provides absolute and normalized iodine density thresholds to distinguish enhancing and nonenhancing renal lesions with high sensitivity and specificity using dlDECT.

Deep-learning-based ensemble method for fully automated detection of renal masses on magnetic resonance images

Purpose

Accurate detection of small renal masses (SRM) is a fundamental step for automated classification of benign and malignant or indolent and aggressive renal tumors. Magnetic resonance image (MRI) may outperform computed tomography (CT) for SRM subtype differentiation due to improved tissue characterization, but is less explored compared to CT. The objective of this study is to autonomously detect SRM on contrast-enhanced magnetic resonance images (CE-MRI).

Approach

In this paper, we described a novel, fully automated methodology for accurate detection and localization of SRM on CE-MRI. We first determine the kidney boundaries using a U-Net convolutional neural network. We then search for SRM within the localized kidney regions using a mixture-of-experts ensemble model based on the U-Net architecture. Our dataset contained CE-MRI scans of 118 patients with different solid kidney tumor subtypes including renal cell carcinomas, oncocytomas, and fat-poor renal angiomyolipoma. We evaluated the proposed model on the entire CE-MRI dataset using 5-fold cross validation.

Results

The developed algorithm reported a Dice similarity coefficient of 91.20 ± 5.41 % (mean ± standard deviation) for kidney segmentation from 118 volumes consisting of 25,025 slices. Our proposed ensemble model for SRM detection yielded a recall and precision of 86.2% and 83.3% on the entire CE-MRI dataset, respectively.

Conclusions

We described a deep-learning-based method for fully automated SRM detection using CE-MR images, which has not been studied previously. The results are clinically important as SRM localization is a pre-step for fully automated diagnosis of SRM subtypes.

Superiority of magnetic resonance imaging in small renal mass diagnosis where image reports mismatches between computed tomography and magnetic resonance imaging

PURPOSE

To analyze malignancy of computed tomography (CT) and magnetic resonance imaging (MRI) results in the same renal mass.

MATERIALS AND METHODS

We retrospectively reviewed 1,216 patients who underwent partial nephrectomy from January 2017 to December 2021 in our institute. Patients who had both CT and MRI reports prior to surgery were included. We compared the diagnostic accuracy between the CT and the MRI. The patients were divided into two groups according to the consistency of reports: the 'Consistent group' and the 'Inconsistent group'. The Inconsistent group was further divided into two subgroups. Group 1 is the case that showed benign findings on CT but malignancy on MRI. Group 2 is the cases of malignancy on CT but benign on MRI.

RESULTS

410 patients were identified. Benign lesion was identified in 68 cases (16.6%). The sensitivity, specificity and diagnostic accuracy of MRI was 91.2%, 36.8%, and 82.2% respectively, whereas that of CT was 84.8%, 41.2%, and 77.6% respectively. Consistent group were 335 cases (81.7%) and inconsistent group were 75 cases (18.3%). The mean mass size was significantly smaller in the inconsistent group compared to the consistent group (consistent group vs. inconsistent group: 2.31±0.84 cm vs.1.84±0.75 cm, p<0.001). Also, the Group 1 had higher odds of malignancy compared to Group 2 in the renal mass size 2-4 cm (odds ratio, 5.62 [1.02-30.90]).

CONCLUSIONS

Smaller mass size affects the discrepancy of CT and MRI reports. In addition, MRI showed better diagnostic performance in mismatch cases in the small renal masses.

Renal lesion characterization: clinical utility of single-phase dual-energy CT compared to MRI and dual-phase single-energy CT

OBJECTIVES

To assess the impact of dual-energy CT (DECT) utilization in practice by measuring the readers' confidence, the need for additional image requests, and diagnostic performance in renal lesion assessment, compared to single-energy CT (SECT) using contrast-enhanced MRI to establish the reference standard.

MATERIALS AND METHODS

Sixty-nine patients (M/F = 47/22) who underwent a dual-phase renal SECT (n = 34) or DECT (n = 35) and had a contrast-enhanced MRI within 180 days were retrospectively collected. Three radiologists assessed images on different sessions (SECT, DECT, and MRI) for (1) likely diagnosis (enhancing/non-enhancing); (2) diagnostic confidence (5-point Likert scale); (3) need for additional imaging test (yes/no); and (4) need for follow-up imaging (yes/no). Diagnostic accuracy was compared using AUC; p value < 0.05 was considered significant.

RESULTS

One hundred fifty-six lesions consisting of 18% enhancing (n = 28/156, mean size: 30.37 mm, range: 9.9-94 mm) and 82% non-enhancing (n = 128/156, mean size: 23.91 mm, range: 5.0-94.2 mm) were included. The confidence level was significantly lower for SECT than their MRI (4.50 vs. 4.80, p value < 0.05) but not significantly different for DECT and the corresponding MRI (4.78 vs. 4.78, p > 0.05). There were significantly more requests for additional imaging in the SECT session than the corresponding MRI (20% vs. 4%), which was not significantly different between DECT and their MRI counterpart session (5.7% vs. 4.9%). Inter-reader agreement was almost perfect for DECT and MRI (kappa: 0.8-1) and substantial in SECT sessions (kappa: 0.6-0.8) with comparable diagnostic accuracy between SECT, DECT, and MRI (p value > 0.05).

CONCLUSION

Single-phase DECT allows confident and reproducible characterization of renal masses with fewer recommendation for additional and follow-up imaging tests than dual-phase SECT and a performance similar to MRI.

KEY POINTS

• DECT utilization leads to similar additional image requests to MRI (5.7% vs. 4.9%, p value > 0.05), whereas single-energy CT utilization leads to significantly higher image requests (20% vs. 4%, p value < 0.05). • DECT and MRI utilization bring highly reproducible results with almost perfect inter-reader agreement (kappa: 0.8-1), better than the inter-reader agreement in SECT utilization (kappa: 0.6-0.8). • Readers' confidence was not significantly altered between DECT and their MRI readout session (p value > 0.05). In contrast, confidence in the diagnosis was significantly lower in the SECT session than their MRI readout (p value < 0.05).

Pre-operative Serum Albumin as a Potential Predictor of Benign Lesions in Renal Masses

BACKGROUND/AIM

We investigated pre-operative factors for predicting whether renal masses are benign in order to facilitate the selection of optimal candidates for pre-operative biopsy.

PATIENTS AND METHODS

We evaluated 278 patients with renal masses suspected to be clinically T1 or T2 renal cell carcinoma. All patients had undergone a partial or radical nephrectomy. Pre-operative parameters, including patient characteristics, tumor size, and blood tests, were utilized to predict which lesions were benign.

RESULTS

Twenty-five lesions (9.0%) were benign. Multivariate analysis showed that female sex [odds ratio (OR)=2.92, p=0.016], serum albumin ≥4.3 g/dl (OR=3.50, p=0.013), and tumor size <23 mm (OR=3.96, p=0.002) were significant independent factors for benign renal masses. The incidence of benign lesions in cases with all three factors (female sex, higher serum albumin, and smaller tumor size) was 4 of 16 (25.0%), which was significantly higher (p=0.037) than that in all cases (25/278; 9.0%).

CONCLUSION

Relatively high pre-operative serum albumin levels may be a predictor of benign lesions when associated with female sex and smaller tumor size.

Cross-sectional imaging assessment of renal masses with emphasis on MRI

Magnetic resonance imaging (MRI) is a useful complementary imaging tool for the diagnosis and characterization of renal masses, as it provides both morphologic and functional information. A core MRI protocol for renal imaging should include a T1-weighted sequence with in- and opposed-phase images (or, alternatively with DIXON technique), T2-weighted and diffusion-weighted images as well as a dynamic contrast-enhanced sequence with subtraction images, followed by a delayed post-contrast T1-weighted sequence. The main advantages of MRI over computed tomography include increased sensitivity for contrast enhancement, less sensitivity for detection of calcifications, absence of pseudoenhancement, and lack of radiation exposure. MRI may be applied for renal cystic lesion characterization, differentiation of renal cell carcinoma (RCC) from benign solid renal tumors, RCC histologic grading, staging, post-treatment follow-up, and active surveillance of patients with treated or untreated RCC.

The role of imaging in the management of renal masses

The wide availability of cross-sectional imaging is responsible for the increased detection of small, usually asymptomatic renal masses. More than 50 % of renal cell carcinomas (RCCs) represent incidental findings on noninvasive imaging. Multimodality imaging, including conventional US, contrast-enhanced US (CEUS), CT and multiparametric MRI (mpMRI) is pivotal in diagnosing and characterizing a renal mass, but also provides information regarding its prognosis, therapeutic management, and follow-up. In this review, imaging data for renal masses that urologists need for accurate treatment planning will be discussed. The role of US, CEUS, CT and mpMRI in the detection and characterization of renal masses, RCC staging and follow-up of surgically treated or untreated localized RCC will be presented. The role of percutaneous image-guided ablation in the management of RCC will be also reviewed.

Infiltrative Renal Malignancies: Imaging Features, Prognostic Implications, and Mimics

Infiltrative renal malignancies are a subset of renal masses that are morphologically characterized by a poorly defined interface with the renal parenchyma. Infiltrative renal malignancies are less common but more aggressive than more typical renal malignancies and carry an overall worse prognosis. Although an infiltrative renal process often represents a malignant neoplasm, infiltrative masses include a wide spectrum of diseases including primary renal cortical, medullary, and pelvic tumors; lymphoproliferative processes; metastases; and various infectious, inflammatory, immune-mediated, and vascular mimics. The imaging features of these masses are often nonspecific, but with the appropriate history, laboratory results, and clinical context, the radiologist can help narrow the diagnosis and guide further treatment. An invited commentary by Lee is available online.Online supplemental material is available for this article. ^©RSNA, 2021.

ACR Appropriateness Criteria® Indeterminate Renal Mass

Renal masses are increasingly detected in asymptomatic individuals as incidental findings. CT and MRI with intravenous contrast and a dedicated multiphase protocol are the mainstays of evaluation for indeterminate renal masses. A single-phase postcontrast dual-energy CT can be useful when a dedicated multiphase renal protocol CT is not available. Contrast-enhanced ultrasound with microbubble agents is a useful alternative for characterizing renal masses, especially for patients in whom iodinated CT contrast or gadolinium-based MRI contrast is contraindicated. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Dual energy CT for evaluation of polycystic kidneys: a multi reader study of interpretation time and diagnostic confidence

PURPOSE

To compare dual-energy CT (DECT) iodine overlay images with renal mass protocol CT in the evaluation of polycystic kidneys with respect to reading time, diagnostic confidence, and detection of renal lesions that are not definitively benign.

METHODS

Following IRB approval, portal venous phase dual-source DECT scans performed between September 2013 and February 2016 from 55 patients (mean age 67 ± 15 years, 31 male, 24 female) with polycystic kidneys (4 or more cysts) were included. For each patient, two image sets were created: (1) DECT post-processed iodine overlay images and (2) simulated renal mass protocol CT images (virtual noncontrast and mixed images). Two radiologists independently retrospectively reviewed both sets at separate time points, evaluating for the presence of lesions that were not definitively benign (enhancing lesions or Bosniak IIF cysts), as well as reading times and Likert scale diagnostic confidence ratings (scaled 1-5) for the presence of non-benign lesions. Reading times were compared with a t test, diagnostic confidence with a McNemar test, and lesion number detection with Cohen's kappa test.

RESULTS

Iodine overlay images were read faster (mean 55 ± 26 s) than renal mass protocol (mean 105 ± 51 s) (p < 0.001). Readers assigned the highest diagnostic confidence rating in 64% using iodine overlay series, compared to 17% using renal mass protocol (p < 0.0001). The proportion of patients with recorded lesions was not significantly different between methods (p = 0.62).

CONCLUSIONS

DECT improves lesion assessment in polycystic kidneys by decreasing reading times and increasing diagnostic confidence, without affecting lesion detection rates.

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.

Automated Modular Magnetic Resonance Imaging Clinical Decision Support System (MIROR): An Application in Pediatric Cancer Diagnosis

BACKGROUND

Advances in magnetic resonance imaging and the introduction of clinical decision support systems has underlined the need for an analysis tool to extract and analyze relevant information from magnetic resonance imaging data to aid decision making, prevent errors, and enhance health care.

OBJECTIVE

The aim of this study was to design and develop a modular medical image region of interest analysis tool and repository (MIROR) for automatic processing, classification, evaluation, and representation of advanced magnetic resonance imaging data.

METHODS

The clinical decision support system was developed and evaluated for diffusion-weighted imaging of body tumors in children (cohort of 48 children, with 37 malignant and 11 benign tumors). Mevislab software and Python have been used for the development of MIROR. Regions of interests were drawn around benign and malignant body tumors on different diffusion parametric maps, and extracted information was used to discriminate the malignant tumors from benign tumors.

RESULTS

Using MIROR, the various histogram parameters derived for each tumor case when compared with the information in the repository provided additional information for tumor characterization and facilitated the discrimination between benign and malignant tumors. Clinical decision support system cross-validation showed high sensitivity and specificity in discriminating between these tumor groups using histogram parameters.

CONCLUSIONS

MIROR, as a diagnostic tool and repository, allowed the interpretation and analysis of magnetic resonance imaging images to be more accessible and comprehensive for clinicians. It aims to increase clinicians' skillset by introducing newer techniques and up-to-date findings to their repertoire and make information from previous cases available to aid decision making. The modular-based format of the tool allows integration of analyses that are not readily available clinically and streamlines the future developments.

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.

Renal Cell Carcinomas: Sonographic Appearance Depending on Size and Histologic Type

OBJECTIVES

Prior studies have demonstrated that approximately 10% of malignant renal cell carcinomas are as echogenic as angiomyolipomas on sonography. However, a recent presentation suggested that small (<1-cm) echogenic renal masses are always angiomyolipomas or other benign entities. We therefore examined our own cases of renal cell carcinoma, with corresponding sonography, to confirm that some renal cell carcinomas may also be detected as hyperechoic masses on sonography.

METHODS

Institutional Review Board approval and Health Insurance Portability and Accountability Act compliance were maintained for this retrospective review of 91 pathologically proven cases of renal cell carcinoma, with corresponding sonography. Tumors were first differentiated by histologic cell type (clear cell, papillary, and chromophobe). Tumors were then stratified according to 2 size group parameters, falling into those that were 3 cm or larger and those that were smaller than 3 cm in diameter, with the less than 3-cm group further subdivided into 2 cm or smaller and greater than 2 cm. Tumor echogenicity was graded on a 5-point scale with respect to the renal parenchyma.

RESULTS

Forty-six tumors (51%) were 3 cm in diameter or smaller, and most were found to be either isoechoic (35%) or mildly hyperechoic (26%) to the surrounding renal parenchyma. Of tumors smaller than 2 cm, most were either mildly hyperechoic (29%) or as hyperechoic as renal sinus fat (very hyperechoic; 29%). Tumors larger than 3 cm were found most often to be either isoechoic (49%) or mildly hyperechoic (33%), with only 4% found to be very hyperechoic.

CONCLUSIONS

The sonographic appearances of renal cell carcinomas include a small population that are very hyperechoic on sonography and thus could potentially be misdiagnosed as angiomyolipomas.