MDCT-based scoring system for differentiating angiomyolipoma with minimal fat from renal cell carcinoma.

BACKGROUND: Subtype-related various computed tomography (CT) features of renal cell carcinoma (RCC) are a confusing factor in differentiating angiomyolipoma with minimal fat (AMLmf) from RCC. To overcome RCC heterogeneity, a scoring system, which integrates multiple discrimitive parameters can be helpful for differentiating AMLmf from RCC.

PURPOSE: To develop a MDCT-based scoring system for differentiating AMLmf from RCC.

MATERIAL AND METHODS: In 407 patients with pathologically confirmed 48 AMLmfs and 359 RCCs (247 clear cell RCCs, 67 papillary RCCs, and 45 chromophobe RCCs), MDCT features (ratio of long-to-short diameter, enhancement characteristics, tumor attenuation on unenhanced scan, tumor margin, calcification), age, and sex were compared between AMLmf and RCCs. Based on logistic regression, a scoring system for diagnosing AMLmf over RCC was built, and its diagnostic accuracy was evaluated.

RESULTS: Scores suggesting AMLmf, i.e. the logit function as used in logistic regression analysis, were calculated as follows: $$\hbox{ Score }=\frac{{e}^{6.16.\hbox{ A }-0.003.\hbox{ B }+1.20.\hbox{ C }+0.97.\hbox{ D }+2.13.\hbox{ E }-0.05.\hbox{ F }}}{1+{e}^{6.16.\hbox{ A }-0.003.\hbox{ B }+1.20.\hbox{ C }+0.97.\hbox{ D }+2.13.\hbox{ E }-0.05.\hbox{ F }}}$$ , where A = ratio of long-to-short diameter, B = enhancement amount in early excretory phase, C = homogeneous enhancement, D = tumor attenuation on unenhanced scan, E = sex, and F = age. Area under receiver-operating characteristics curve of scoring system was 0.919. With a score of 0.204 or higher, the scoring system yielded greatest accuracy (90%, 368/407) for diagnosing AMLmf over RCC, which was greater than that of any single MDCT or clinical parameter (53-85%) (P < 0.05). With a score of 0.317 or higher, sensitivity and specificity were 68% (32/48) and 95% (340/359).

CONCLUSION: MDCT-based scoring system can improve diagnostic performance of MDCT in differentiating AMLmf from RCC and help patients with AMLmf to avoid unnecessary surgery with high specificity.