Diagnostic Accuracy of MRI for Detecting Inferior Vena Cava Wall Invasion in Renal Cell Carcinoma Tumor Thrombus Using Quantitative and Subjective Analysis

OBJECTIVE. The purpose of this study is to evaluate MRI in inferior vena cava (IVC) renal cell carcinoma (RCC) tumor thrombus for the diagnosis of caval wall invasion. MATERIALS AND METHODS. This retrospective case-control study evaluated 24 consecutive patients who underwent thrombectomy for RCC IVC tumor thrombus (11 [45.8%] with invasion) seen at preoperative MRI. A blinded radiologist segmented tumor thrombus on apparent diffusion coefficient (ADC) maps and T2-weighted images for texture analysis, measured the diameter of the renal vein and IVC at the level of the renal vein ostium, and measured the craniocaudal extent and volume of the tumor thrombus. Two blinded radiologists independently evaluated the margin of the tumor thrombus (smooth vs irregular), thinning or thickening and abnormal T2-weighted signal or enhancement of the IVC wall, and overall impression of invasion. Comparisons were performed using logistic regression models and chi-square with accuracy calculated using ROC. RESULTS. Subjective features were associated with invasion (p = 0.001-0.045) with moderate-to-substantial agreement (kappa = 0.49-0.66). The overall impression of invasion had a sensitivity of 63.6% (95% CI, 30.8-89.1%) and a specificity of 92.3% (95% CI, 64.0-99.8%) with perfect agreement (kappa = 1.0). Tumor thrombus with invasion had larger diameters of renal vein (28 +/- 8 vs 15 +/- 6 mm; p = 0.031) and IVC (41 +/- 9 vs 19 +/- 6 mm; p = 0.003), greater craniocaudal extent (87 +/- 34 vs 51 +/- 31 mm; p = 0.0239), and greater volume (77.4 +/- 57.6 vs 17.7 +/- 17.4 cm(3); p = 0.003) than did thrombi without invasion. The ROC AUC ranged from 0.78 to 0.83. ADC and texture parameters were not significantly different between groups (p = 0.208-0.503); however, larger entropy in invasive tumor thrombus trended toward significance (p = 0.061). A model combining volume, entropy, and overall impression achieved an AUC of 0.91 (95% CI, 0.77-1.0). CONCLUSION. T he combination of t umor t hrombus volume with entropy a nd subjective overall impression of IVC wall invasion achieved the highest accuracy for diagnosis.