Radiological Features of T1a Renal Cell Carcinoma on Axial Unenhanced Computed Tomography

Abstract

CT has become a commonly used diagnostic procedure in clinical practice, particularly in emergency healthcare delivery. Accordingly, the increase in CT usage has increased the likelihood of incidental detections (ID) of renal cell carcinomas (RCCs). This article discusses key points and limitations associated with the diagnosis and characterization of T1a RCC (≤4 cm in diameter) and shows how to improvise on the differentiation of T1a RCC with unenhanced CT (UE-CT). We retrospectively reviewed UE-CT findings of cases associated with the histopathologic diagnosis of T1a RCC and examined the discrimination capacity and radiological characteristics with regard to small RCCs (SRCCs). Detection and characterization of T1a RCC based on UE-CT are not easy in many cases due to limitations in CT findings, but there are notable radiological features to facilitate detection and differentiation. The growth pattern is important for the detection of SRCCs. Internal characteristic features (average attenuation, heterogeneity) are useful for the characterization of the RCC. In addition, CT image visualization techniques may help improve the detectability of RCCs on UE-CT. Radiological features are important in detecting SRCCs and facilitating further examination. In this study, we discuss some cases of T1a RCCs and evaluate the radiological characteristics of the tumors seen on UE-CT.

Keywords: renal cell carcinoma; renal mass; t1a; tumor detectability; unenhanced computed tomography.

Figure 1. CT images of a 57-year-old woman with endophytic clear cell RCC

A: unenhanced image; B: enhanced image in nephrographic phase A heterogeneous renal mass without deformation of the cortical outline is seen in the inner segment of the right kidney on UE-CT (arrows). Pathologic examination confirmed that the mass was a 2.0-cm clear cell RCC of the ENT type ENT: endophytic; RCC: renal cell carcinoma; UE-CT: unenhanced computed tomography

Figure 2. CT images of a 71-year-old man with clear cell RCC

A: unenhanced image; B: enhanced image in nephrographic phase On axial UE-CT, a 2.8-cm isodense mass with unclear margins is seen in the right kidney (arrow). The mass protrudes inside the renal cortex like a column of Bertin. Pathologic examination confirmed that the mass was a 2.8 cm clear cell RCC protruding inside the renal cortex RCC: renal cell carcinoma; UE-CT: unenhanced computed tomography

Figure 3. CT images of a 39-year-old man with clear cell RCC

A: unenhanced image; B: enhanced image in nephrographic phase On axial UE-CT, there are two hypodense masses with a diameter of 2.1 cm, one in each kidney. Both masses are homogeneous and low-density lesions. The mean attenuation of the right mass is 26 HU (arrow), which is slightly higher than that of the left mass (arrowhead, 18 HU). The right renal mass shows enhancement, which proved to be a clear cell type RCC pathologically RCC: renal cell carcinoma; UE-CT: unenhanced computed tomography

Figure 4. CT images of a 59-year-old man with clear cell RCC

A: unenhanced image; B: enhanced image in nephrographic phase On axial UE-CT, a 2.7-cm heterogeneous isodense mass with unclear margins is seen in the left kidney (arrows). The mass protrudes slightly outside the renal cortex and its mean attenuation is 31 HU. It shows heterogeneous enhancement and proved to be a clear cell type RCC pathologically RCC: renal cell carcinoma; UE-CT: unenhanced computed tomography

Figure 5. CT images of a 70-year-old man with clear cell RCC

A; UE-CT, width: 400 HU, level: 40 HU; B: UE-CT, width: 185 HU, level: 45 HU; C: enhanced image in nephrographic phase On axial UE-CT, a 1.2-cm Hgy low-density mass with unclear margins is detected in the right kidney (arrows). The mass was undetectable on unenhanced scans, but it could be detected by using the ‘‘liver window’’. Pathologic examination confirmed that the mass was a 1.2-cm clear cell RCC RCC: renal cell carcinoma; UE-CT: unenhanced computed tomography

Figure 6. CT images of a 50-year-old man with clear cell RCC

A: unenhanced image; B: enhanced image; C: unenhanced coronal image On axial UE-CT, a 1.8-cm heterogeneous isodense mass with unclear margins is seen in the left kidney (arrows). The mass protrudes slightly outside the renal cortex. When multiplanar reconstruction is used, the mass can be detected in the lower pole of the kidney by visualizing the protrusion of the mass on the coronal image RCC: renal cell carcinoma; UE-CT: unenhanced computed tomography

Figure 7. CT images of an 83-year-old man with clear cell RCC

A: unenhanced image; B: enhanced image; C: unenhanced image 4 years before A, B: On axial UE-CT, a 2.2-cm heterogeneous hypodense mass is detected in the left kidney and enhanced heterogeneously (arrows). The mass protrudes from the outer segment of the left kidney. Pathologic examination confirmed that the mass was a 2.2-cm clear cell RCC. C: The renal mass was smaller and not more protruded from the outer segment of the left kidney (arrowhead). The mass was homogeneous and of low density on UE-CT, and therefore it was very difficult to be detected as malignancy 4 years before RCC: renal cell carcinoma; UE-CT: unenhanced computed tomography

Figure 8. CT images of a 68-year-old man with clear cell RCC

A: unenhanced image; B: enhanced image in nephrographic phase On axial UE-CT, a 2.4-cm heterogeneous hypodense mass with a thick wall and a mural nodule is seen in the lower pole of the right kidney (arrow). The enhanced image demonstrates a well-enhancing mural nodule within the mass, suggestive of Bosniak category IV. Pathologic examination confirmed that the mass was a clear cell RCC RCC: renal cell carcinoma; UE-CT: unenhanced computed tomography