Using Aorta-Lesion-Attenuation Difference on Preoperative Contrast-enhanced Computed Tomography Scan to Differentiate Between Malignant and Benign Renal Tumors.

OBJECTIVE: To evaluate the ability of Aorta-Lesion-Attenuation Difference (ALAD) to differentiate malignant renal tumors from renal oncocytomas.
METHODS: A retrospective review of preoperative computed tomography (CT) scans and surgical pathology was performed on patients undergoing partial nephrectomy for small, solid renal masses. ALAD was calculated by measuring the difference in Hounsfield units (HU) between the aorta and the lesion of interest on the same image slice on preoperative CT scan. The discriminative ability of ALAD to differentiate malignant pathology from oncocytoma was evaluated by sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under curve (AUC) using receiver operating characteristic analysis.
RESULTS: A total of 227 preoperative CT scans and corresponding pathology reports were reviewed. ALAD values were calculated during the excretory and nephrographic phases. Nephrographic ALAD was able to differentiate malignant pathology from oncocytoma using a HU threshold of 24 with a sensitivity of 84%, specificity of 86%, PPV of 98%, and NPV of 33%. The AUC for malignant pathology vs oncocytoma was 0.86 (95% confidence intervals 0.77-0.96). Nephrographic ALAD was able to differentiate chromophobe renal cell carcinoma (RCC) from oncocytoma using a HU threshold of 24 with a sensitivity of 100%, specificity of 86%, PPV of 75%, and NPV of 100%. The AUC for chromophobe RCC vs oncocytoma was 0.98 (95% confidence intervals 0.91-1.00).
CONCLUSION: ALAD discriminates well between chromophobe RCC and oncocytoma, which may aid in the management of patients with indeterminate diagnoses of oncocytic neoplasm on diagnostic needle biopsy. Further validation of ALAD will be necessary prior to routine use in clinical practice.