| ObjectiveTo investigate and analyze the CT features and characteristics of hypervascular renal tumors (diameter≤4cm) by multiple phases enhancement in order to improve the accuracy of preoperative diagnosis.MethodsWe retrospectively analyzed the CT images of 114 hypervascular renal tumors (diameter≤4cm) confirmed by surgery and pathology at our institution between 2010 and 2015. All CT examinations were performed using helical CT scanners HD750 (GE Medical Systems) and Aquilion ONE 640 (TOSHIBA Medical Systems). All patients had four-phase CT imaging that included an unenhanced image and the multiphase images [corticomedullary (CMP), nephrographic (NP), and excretory phase (EP)] after injection of contrast agent. The delayed time were 35 seconds for the CMP,65～70 seconds for the NP, and 180-300 seconds for the EP.CT images were reviewed at a picture archiving and communication system workstation (AW 4.0, GE Healthcare, USA). All the CT images were analyzed and got the consistent diagnosis by two experienced radiologists who were blinded to the final histologic diagnosis. We reviewed the shape of tumor (round or oval, irregular), and location of the tumor. We analyzed the angle of tumor with the surrounding renal parenchyma when tumor was exogenous. To review the internal structure features of tumors that include cystic degeneration, central scar and calcification. The enhancement patterns were classified as homogeneous and heterogeneous. We measured the CT value of tumor on four phases and the percentage of enhancement(the CT value in enhanced phase—the CT value on unenhanced phase/the CT value on unenhanced phase).The relationship between the subtypes of the small renal masses in the gender, morphological features, and pattern of contrast enhancement were analyzed by using the chi-square test. Patients’age, tumors size and degree of contrast enhancement were compared by the analysis of variance. Diagnostic performance of CT value for differentiating the histologic subtype was calculated by using receiver operating characteristic (ROC) curve analysis. The optimal cut-off value was defined according to the value at which the sum of the sensitivity and specificity was maximized (Youden index). A P-value< 0.05 was considered to be statistically significant. All statistical analyses were performed using SPSS software (SPSS for Windows, version 19.0; Chicago, USA),ResultsOne hundred and fourteen patients were evaluated. Pathologic diagnoses included clear cell renal cell carcinoma (CCRCC) (n=74), chromophobic renal cell carcinoma (CRCC) (n=13), oncocytoma(RO) (n=10) and minimal fat angiomyolipoma (RAML) (n=17). The male-to-female ratio in four groups of tumor patients were 28:9,5:8,4:6 and 4:13, although no significant difference between CRCC and RO, there was significant difference between any two other of its comparison (P< 0.05). There was no statistical significance in age (P>0.05).In 74 CCRCC patients, the shape of 14 CCRCCs were irregular. There were 5 tumors had "angle sign" in 52 exogenous tumors. Cystic degeneration and necrosis were seen in 43 cases (58.1%). Calcification was seen in 7 cases(9.5%). The phenomenon of central scar was seen in 9 cases (12.2%). There were 26 cases (35.1%) had pseudocapsule. CT enhanced images showed that 54 cases (73%) were heterogeneously enhanced on the corticomedullary phase.In 13 CRCC patients, the shape of tumor were irregular only in 2 cases (15.4%), There were 2 tumors have "angle sign" in 9 exogenous tumors. Cystic degeneration was seen in 6 cases (46.2%). Only 1 case (7.69%) had calcification structure in the tumor. Pseudocapsule was seen in 5 cases (38.5%). In corticomedullary phase, CT enhanced image showed that 8 cases (61.5%) were homogeneously enhanced, and 5 cases (38.5%) were heterogeneously enhanced.In 10 RO patients, the shape of all the tumors were round or oval. There were not "angular sign" in 6 (60.0%) exogenous tumors. There was 1 case (10.0%) could find cystic degeneration. Calcification was seen in 3 cases (30.0%). The phenomenon of central scar was seen in 5 cases (50.0%). There was significant difference between RO and other subtypes of renal tumors (P=0.001). Pseudocapsule were seen in 2 cases (20.0%).CT enhanced image showed that 7 cases (70%) were heterogeneously enhanced on the corticomedullary phase.In 17 RAML cases, the shape of 3 cases (17.6%) were irregular.8 cases (57.1%) had "angle sign" in 14 exogenous tumors (82.4%). Tumor cystic degeneration was seen in 4 cases (23.5%). Calcification was seen in 1 case (5.88%). All the tumors had no phenomenon of central scar. There were only 2 cases (11.8%) had pseudocapsule. CT enhanced image showed 7 cases were heterogeneously enhanced on the corticomedullary phase.The "angle sign" was showed in CT images of exogenous tumors had significant difference between RAML and another three kinds of renal tumors (P<0.05). The CT images showed pseudocapsule which was no statistical significance differentiated the pathological types of renal tumors, but it could be differentiated the benign and malignant lesions (P= 0.040). The phenomenon of central scar had significant difference between RO and another three kinds of renal tumors (P<0.05).To compare the average CT value of four kinds of tumors. On the CMP, the average CT value of RO (130.31±26.31HU) were highest than CCRCC and CRCC, there was significant difference between any two subtypes of its comparison (P<0.05). On the excretory phase, the degree of contrast enhancement of the four hypervascular renal tumors from highest to lowest (diameter≤4cm) were:RO (100.82±10.36HU), RAML (85.39±10.13HU), CCRCC (81.13±15.04 HU), CRCC (70.08±7.96 HU). The mean CT value of CRCC was the lowest in four subtypes of renal tumors (P< 0.05). The mean CT value of RO was the highest in four subtypes of renal tumors (P< 0.05). The percentage of enhancement of CRCC were also the lowest in four kinds of tumors, there was significant difference between CRCC、CCRCC and RO (P< 0.05). We used the ROC curve to analyze the mean CT value of CRCC and RO. The ROC curve analysis showed that the optimal cut-off value with the highest accuracy for CRCC was 78 HU on the EP (84.6%specificity and 90% sensitivity). The optimal cut-off value for oncocytoma was 99HU on the EP (87.8% specificity and 80% sensitivity).ConclusionIn summary, on the excretory phase, this study found that the degree of contrast enhancement of the four hypervascular renal tumors from highest to lowest (diameter≤4cm) were:RO, RAML/CCRCC, CRCC. The optimal cut-off value was 78HU for chromophobic renal cell carcinoma (84.6% specificity and 90% sensitivity), that for oncocytoma was 99HU (87.8% specificity and 80% sensitivity) on the EP. Meanwhile combined with cystic degeneration was easily seen in CCRCC, the central scar can be seen in RO, and the "angle sign" with exogenous growth pattern was easily found in RAML. Those characteristics showed in CT images may provide information for differentiating hypervascular renal tumors (diameter≤4cm), which can assist and guide the clinical treatment and prognosis. |
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