Multicenter Evaluation of Multiparametric MRI Clear Cell Likelihood Scores in Solid Indeterminate Small Renal Masses

Abstract

GENITOURINARY IMAGING R enal masses are commonly encountered as incidental findings in patients undergoing cross-sectional imaging (1,2). The majority of solid small (4 cm [cT1a]) renal masses (SRMs) are malignant, but up to 20% are benign (3,4). Moreover, even when malignant, cT1a renal cell carcinoma (RCC) is frequently indolent and, when treated, rarely recurs locally or metastasizes (5). Indeed, cT1a RCC is an uncommon cause of patient mortality, particularly in older patients who may have other competing comorbidities (6). Among the various RCC subtypes, clear cell RCC (ccRCC) is the most common and is often aggressive; on the basis of this combination of characteristics, ccRCC is the most common cause of disease progression and metastasis in active surveillance populations (7).Various methods have been proposed to differentiate benign from malignant SRMs and indolent from aggressive SRMs in clinical practice. Renal mass biopsy can be used to differentiate between the various histologic subtypes of solid SRMs (8). However, a biopsy represents an additional diagnostic procedure, is invasive (median complication rate 8%) (8), is not feasible in all patients, and is nondiagnostic in up to 20% of renal masses (9). Moreover, renal mass biopsy is not widely used in clinical practice due to the perception among many urologists that its results do not alter management (10).Use of noninvasive imaging to diagnose renal mass subtype among solid SRMs with CT or MRI represents an alternative to biopsy, has been studied extensively, and has been shown, to some extent, to be accurate in the diagnosis of some renal mass histopathologic subtypes (11)(12)(13)(14)(15). However, studies on this topic have been mainly limited to single-center retrospective case-control series and therefore show selection bias (13,14,16-19). To date, unlike for cystic renal masses, where imaging assessment is performed using Background: Solid small renal masses (SRMs) (4 cm) represent benign and malignant tumors. Among SRMs, clear cell renal cell carcinoma (ccRCC) is frequently aggressive. When compared with invasive percutaneous biopsies, the objective of the proposed clear cell likelihood score (ccLS) is to classify ccRCC noninvasively by using multiparametric MRI, but it lacks external validation.Purpose: To evaluate the performance of and interobserver agreement for ccLS to diagnose ccRCC among solid SRMs. Materials and Methods:This retrospective multicenter cross-sectional study included patients with consecutive solid (25% approximate volume enhancement) SRMs undergoing multiparametric MRI between December 2012 and December 2019 at five academic medical centers with histologic confirmation of diagnosis. Masses with macroscopic fat were excluded. After a 1.5-hour training session, two abdominal radiologists per center independently rendered a ccLS for 50 masses. The diagnostic performance for ccRCC was calculated using random-effects logistic regression modeling. The distribution of ccRCC by ccLS was tabulated. Interobserver agreement for...

Systematic review and meta-analysis of multiparametric MRI clear cell likelihood scores for classification of small renal masses

“…The reported radiologists’ experience ranged from 1 to 30 years, with inter-reader agreement measured with kappa value of 0.53-0.65. Regarding cutoff values, 3 studies reported that the results were derived from the threshold of ccLS ≥4 ( 26 , 28 , 30 ), whereas the remaining 3 studies reported results from both ccLS ≥3 and ccLS≥4 ( 19 , 27 , 29 ). Concerning technique characteristics, nearly all studies reported that the images acquired from 1.5T or 3.0 T MRI; however, in one study the field strength was not reported ( 28 ).…”

“…Concerning technique characteristics, nearly all studies reported that the images acquired from 1.5T or 3.0 T MRI; however, in one study the field strength was not reported ( 28 ). As for MRI protocol, only 3 studies used all sequences of T1, T2, dynamic contrast-enhanced (DCE), and diffusion-weighted imaging (DWI) ( 27 , 29 , 30 ). Concerning the reference standard, surgical resection pathological results were used in 4 studies, in the remaining 2 studies the biopsy results also were used in case of pathological results were not available ( 26 , 27 ).…”

“…Full-text reviewing was performed among the remaining 33 potential results and 27 were excluded for insufficient data (n=5), not in the field of interest (n=22). Ultimately, a total of 6 studies involving 785 patients were included in this meta-analysis (19,(26)(27)(28)(29)(30).…”

Diagnostic Accuracy of MRI for Solid Renal Masses: A Systematic Review and Meta‐analysis

“…Table 2 and supplementary Tables S6 and S7 provide a detailed description of the MRI sequences used in each study. The following studies used ccLS to diagnoses clear cell RCC from other renal masses: Steinberg et al, 18,43 Canvasser et al, 43 and Schieda et al 47…”

“…FIGURE 5: sROC curve of the sensitivity and specificity for each clear cell likelihood score (ccLS). Steinberg et al,18 Canavsser et al,43 and Schieda et al47 used ccLS scores to diagnose ccRCC. Point estimates were calculated using the linear mixed effects model for modeling multiple threshold data, as described by Schneider et al[40][41][42] The figure was generated using R.…”