Use of specific contrast-enhanced CT regions of interest to differentiate renal oncocytomas from small clear cell and chromophobe renal cell carcinomas

PURPOSEWe aimed to examine the usefulness of utilizing a specific contrast-enhanced computed tomography (CT) region of interest (ROI) to differentiate renal oncocytoma (RO) from small clear cell renal cell carcinoma (ccRCC) and chromophobe renal cell carcinoma (chRCC).METHODSA retrospective analysis of pre-contrast phase (PCP), corticomedullary phase (CMP), and nephro­graphic phase (NP) contrast-enhanced CT images of the histopathologically confirmed initial cohort (27 ROs, 74 ccRCCs, and 36 chRCCs) was conducted. Small, medium, large, and whole ROIs (S-ROI, M-ROI, L-ROI, and W-ROI, respectively) were utilized for CT attenuation value of tumor (AVT), lesion-to-cortex attenuation (L/C), and heterogeneous degree of tumor (HDT) calculations. Differences in these parameters were then compared between RO and ccRCC/chRCC, with receiver operating characteristic (ROC) curves being utilized to gauge the diagnostic utility of the statistically significant parameters. Logistic regression analyses were employed to identify key factors capable of differentiating RO and ccRCC/chRCC, with predictive models further being established. A validation cohort (6 ROs, 30 ccRCCs, and 12 chRCCs) was then employed to validate the performance of the predictive models.RESULTSOf the parameters evaluated using different ROIs, L/C-CMP (S-ROI) (0.88 ± 0.15 vs. 1.13 ± 0.25, P < .001) and HDT-CMP (W-ROI) (23.02 (12.00-51.21) vs. 37.81 (16.09-89.45), P < .001) were best suited to differentiating RO and ccRCC, yielding respective area under the curve (AUC) values of 0.803 and 0.834. AVT-NP (S-ROI) (122.85 ± 18.87 vs. 86.50 ± 18.65, P < .001) and AVT-NP (M-ROI) (119 (86-167) vs. 81.5 (53-142), P < .001) were better able to differentiate RO and chRCC, yielding respective AUC values of 0.918 and 0.906. Logistic regression analyses revealed that L/C-CMP (S-ROI) and HDT-PCP, as well as AVT-NP (S-ROI) and HDT-CMP, were the primary factors capable of differentiating RO from ccRCC and chRCC, respectively. The predictive model developed to differentiate between RO and ccRCC exhibited a sensitivity of 66.67% and 55.14% in the initial and validation cohorts, respectively, with corresponding specificity of 94.59% and 93.55%, accuracy of 87.13% and 86.84%, and AUC of 0.908 and 0.876. The predictive model developed to differentiate between RO and chRCC exhibited a sensitivity of 85.19% and 100.00% in the initial and validation cohorts, respectively, with corresponding specificity of 94.59% and 92.86%, accuracy of 87.30% and 95.24%, and AUC of 0.944 and 0.959.CONCLUSIONThese data demonstrate that a combination of quantitative parameters measured with particular ROIs can enable the efficient and reliable differentiation of RO from ccRCC and chRCC for use in routine patient differential diagnosis.

Main points

• Quantitative computed tomography (CT) parameters measured using different regions of interest (ROIs) exhibit varying levels of diagnostic efficacy when differentiating renal oncocytoma (ROs) from small clear cell renal cell carcinomas (ccRCCs) and chromophobe renal cell carcinomas (chRCCs).
• Lesion-to-cortex attenuation- corticomedullary phase (CMP) (small ROI (S-ROI)) and attenuation value of the tumor-nephrographic phase (S-ROI) were identified as the most reliable enhancement degree-related quantitative parameters when distinguishing ROs from ccRCCs and chRCCs, respectively.
• Heterogeneous degree of tumor (HDT), which was defined based upon the standard deviation for CT values, can serve as a quantitative measure of heterogeneity when differentiating ROs from ccRCCs and chRCCs, with HDT-CMP exhibiting the highest degree of differential diagnostic efficacy.
• Predictive models combining the above S-ROI-based enhancement degree parameters and whole ROI-based HDT values exhibit excellent diagnostic efficacy when differentiating ROs from ccRCCs and chRCCs.

An estimated 20%-30% of solid masses < 4 cm in size are benign, with renal oncocytomas (ROs) accounting for over half of these cases while the remaining 70%-80% are renal cell carcinomas (RCCs), among which clear cell RCCs (ccRCCs) are the most prevalent, followed by papillary RCCs (pRCCs) and chromophobe RCCs (chRCCs).^1,2 Given that ROs exhibit a benign disease course and affected patients have an excellent prognosis, accurately differentiating between RO and RCC is critical to guide appropriate patient treatment.³Computed tomography (CT) is the most common approach used for the diagnosis and evaluation of renal masses. Several reports have described the differentiation between ROs and RCCs based upon both qualitative and quantitative CT findings, with the enhancement degree and heterogeneity being 2 key indicators.^4-8 Owing to a lack of reference standard uniformity, however, these studies utilized different approaches to define the regions of interest (ROIs) to obtain CT parameter values, potentially contributing to inconsistencies or opposing findings among studies. Also, tumor heterogeneity is also considered to be a largely subjective determination of limited clinical utility.^7-8 Rosenkrantz et al.⁹ found the use of a small ROI (S-ROI) to be more accurate than a large ROI (L-ROI) when differentiating between RCCs and cysts, with this approach being most effective when comparing pRCCs and cysts. Wang et al.¹⁰ also reported that S-ROI-based enhancement degree and whole ROI (W-ROI)-based enhancement heterogeneity were superior to medium ROI (M-ROI) when differentiating between small ccRCC and fat-poor angiomyolipoma (AML).To date, no studies have explored the use of different ROIs to differentiate between ROs and RCCs on contrast-enhanced CT images. Given that pRCCs are typically hypovascular, efforts to distinguish between ROs and RCCs are generally focused on the chRCCs and ccRCCs.^11-12 This study was thus developed to explore the effect of ROI size in differentiating ROs from ccRCCs and chRCCs in an effort to define the most effective quantitative parameters for routine differential diagnosis.