A novel CT-based normalization strategy using lesion-to-spleen density ratios for renal mass characterization

Accurate preoperative characterization of renal masses remains a major clinical challenge, as a substantial proportion of surgically resected lesions ultimately prove to be benign. Absolute Hounsfield unit (HU) measurements on contrast-enhanced computed tomography (CT) are widely used but are vulnerable to technical and patient-related variability. This study aimed to introduce and evaluate a novel CT-based normalization strategy using lesion-to-organ HU ratios to improve differentiation between benign and malignant renal masses and to explore its performance across renal cell carcinoma (RCC) subtypes.

This retrospective single-center study included 248 patients with histopathologically confirmed renal tumors who underwent multiphasic CT. Attenuation values were measured from the lesion, contralateral renal cortex, and spleen on both non-contrast and contrast-enhanced images. Lesion-to-kidney (LK) and lesion-to-spleen (LS) HU ratios were calculated. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis, and predictors of malignancy were assessed with univariate and multivariate logistic regression. Subgroup analysis was performed across RCC subtypes.

Both contrast-enhanced lesion-to-kidney (CE-LK) and lesion-to-spleen (CE-LS) HU ratios differed significantly between benign and malignant lesions (p < 0.01). The CE-LK HU ratio demonstrated excellent diagnostic performance (AUC = 0.914), achieving 83.8% sensitivity and 100% specificity at a cut-off of ≤ 0.76. The CE-LS HU ratio showed similarly high accuracy (AUC = 0.883), with 87.4% sensitivity and 87.5% specificity at a cut-off of ≤ 0.89. In multivariate analysis adjusting for lesion size and absolute enhancement, only the CE-LS HU ratio remained an independent predictor of malignancy (OR = 36.9, p = 0.004). Subtype analysis revealed that papillary RCC exhibited significantly lower CE-LS HU ratios compared with clear cell RCC (p = 0.020), while no significant differences were observed between chromophobe RCC and other subtypes.

Lesion-to-spleen HU normalization is a simple, reproducible, and broadly applicable CT-based approach that enhances renal mass characterization and may aid in reducing unnecessary surgical interventions.