Primary Study Of The Value Of Spectral CT Imaging For Distinguishing Renal Cell Carcinoma And Minimal Fat Renal Angiomyolipoma

Background and ObjectiveRenal cell carcinoma(RCC) is the most common primary malignant tumors of kidney, accounting for about85%～90%of all malignant tumors of kidney,and the clear cell renal cell carcinoma(CCRCC) is the most common subtype.The incidence of RCC is increasing with the proportion of2%～4%annually in recent years.Renal angiomyolipoma(RAML) can be short for hamartoma, it is the most common benign tumors of kidney,typical renal angiomyolipoma is easy to diagnosis for their characteristic fat low density on CT images.It is difficult to distinguish minimal fat renal angiomyolipoma from RCC,which is accounting for4%～5%of all RAMLs.The imaging differentiation diagnosis of them can guide for the accurate clinical treatment, so it is particularly important to make the correct diagnosis before operations.It is very necessary and critical for using the imaging means for accurate identification of the two renal lesions.CT examination is the most common and functional imaging examination,conditional CT was single parameter and mixed-energy imaging,and Gemstone Spectral CT is mlti-parameter and monochromatic imaging,with the function of sbstances based quantitative analysis and spectrum analysis.The purpose of this study is to summarize the enhanced CT characteristics of CCRCC and minimal fat RAML,and investigate the preliminary application of spectral CT imaging in differentiating CCRCC and minimal fat RAML.Materials and methods28patients with CCRCC,detected a total of33lesions and10patients minimal fat RMAL,detected a total of11lesions,all cases were proved by surgical and pathological findings.All the patients underwent plain CT scan and two phases of enhanced spectral CT imaging by Discovery CT750HD,obtained the plain CT images and quality check images,the40-140keV monochromatic images and iodine-based material decomposition images.They were reconstructed of cortical phase and corticomedullary phase.The analysis of contents were:1、Analyzed the common CT features of the lesions, measured the CT value of the regions of interest (ROI) of the lesions. The evaluation were as follows:The boundary、density and calcification of the renal lesions on plain CT scan, the renal lesions were homogeneous or inhomogeneous enhancement,the pattern of the enhancement,the lesions had pseudocapsule or not, including the patient’s age and gender, the results were statistically analyzed.2、Analyzed the spectral imaging CT features of the lesions:①ROIs were placed on the renal lesions (ICrena, iodine content of renal) on the iodine images, and the aorta(ICaa,iodine content of abdominal aorta)as a reference. Normalized iodine concentrations for the renal lesions were obtained as NIC=ICrenal/ICaa.②Calculated slope K of the spectral HU curve from the monochromatic image using the GSI viewer.The K was the slope of the straight line:40keV on the spectral HU curve was a stationary point, XkeV was another point,and X was from70keV to140keV,10keV interval,drew a straight line between two points,we can got8straight lines and8groups of K.K=(HU(at40keV)-HU(at XkeV))/(X-30).Comparison the slope K between group CCRCC and minimal fat RAML,analyzed the difference of each index in the area under each ROC,and got the optimal K for differentiating the two tumors.Results4(36.4%) lesions in minimal fat RAML group were homogeneous enhancement, and only1(3.03%) in CCRCC group was homogeneous enhancement in corticomedullary phase,there was significant difference between the two groups (P<0.05).Enhancement pattern was a valuable predictor for differentiating minimal fat RAML from CCRCC(P<0.001), a prolonged enhancement pattern was observed in9lesions (81.8%) of the all patients with minimal fat RAML, whereas an early wash-out pattern was observed in most30(90.9%)of the patients with CCRCC. In the cortical phase, both of the mean ICrenal and mean NIC of CCRCC group were higher than these of minimal fat RAML group.(P<0.05) In the corticomedullary phase, the mean NIC of CCRCC group was higher than that of minimal fat RAML group(P<0.05).There was significant difference between the each mean slope K of8groups between CCRCC group and minimal fat RAML group(P≤0.001) in the cortical phase,there was slightly difference between the each mean slope K of8groups between CCRCC group and minimal fat RAML group(P≤0.05) in the corticomedullary phase.The each group mean slope k of8CCRCC group was higher than minimal fat RAML group. When K>6.925in cortical phase,its sensitivity was82.5%, specificity was80.0%.ConclusionDual-phase enhanced scan of spectral CT was useful in differentiating minimal fat RAML from CCRCC,with homogeneous enhancement and enhancement pattern being the most valuable CT findings. Both the iodine concentration of the iodine density images and the spectral curve of monochromatic images of spectral CT imaging demonstrated the potential in differentiating CCRCC and minimal fat RAML.