Differentiating renal cell carcinoma clear cell subtype from other subtypes on multiphasic multidetector computed tomography

Abstract

Background : Renal cell carcinomas (RCC) represent about 1 - 3% of all visceral cancers and 85% of renal cancers in adults. The tumors occur most often in old age, usually in sixth and seventh decades of life, and more predominantly in males. There are different prognosis between each subtype of RCC and different targeted therapy of choice for clear cell and non-clear cell subtypes of RCC. Subtype differentiation of RCC is quite important for guided treatments and predicted prognosis. (according to the NCCN’s Clinical Practice Guideline for Renal Cancer 2009).

Objective : This study aims to differentiate clear cell subtype of RCC from other subtypes on multiphase MDCT scans.

Setting : The Department of Radiology and Department of Pathology, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand.

Research design : Retrospective-Descriptive study

Material and Methods : We reviewed CT scans of all RCC subtypes covering 33 clearcell RCC, 12 papillary RCC and 4 chromophobe RCC. Nineteen CT scans, which consist of unenhanced, corticomedullary phase (CMP) and nephrographic phase (NP) scans and 28 CT scans (unenhanced, angiographic phase, CMP, NP and excretory phase scans) are included in the study. We compared tumor size, enhancement patterns, degree of tumor enhancement in these subtypes.

Results : Enhancement ratio in CMP and NP and absolute tumor enhancement in CMP are significantly different between clear - cell RCC and other RCCs (P < 0.05). We did not find any significance of absolute tumor enhancement in NP between clear- cell RCC and other RCCs. The sensitivity and specificity for differentiating clear- cell RCC from other RCCs were 75.8% and 75% when enhancement ratio of 0.45 was used as the cutoff value in the CMP and 75.8% and 62.5% when enhancement ratio of 0.43 was the cutoff value in the NP. The sensitivity and specificity for differentiating clear- cell RCC from other RCCs were 75.8% and 75% when absolute tumor enhancement of 48.8 HU was used as the cutoff value in CMP.

Conclusions : The enhancement ratio in CMP can be used for differentiating clear- cell RCC from other RCCs with equal sensitivity and specificity to absolute tumor enhancement in CMP. However, the area under the ROC curves of enhancement ratio is more than that of tumor absolute enhancement. Hence, the enhancement ratio could be superior to absolute tumor enhancement value for differentiating clear -cell RCC from other subtypes.