Fig. 2

A schema of segmental enhancement inversion and a case of a 76-year-old woman with right renal oncocytoma demonstrating segmental enhancement inversion. a Schema of segmental enhancement inversion. 1. A tumour shows two distinct areas of hyper-enhancement (white) and hypo-enhancement (dark grey) on the corticomedullary phase (30–40 s). Hyper- and hypo-enhancing areas consist of higher and lower cellularity components, respectively. 2. On the early excretory phase (120–180 s), the higher cellularity component becomes relatively low attenuation due to contrast washout. The lower cellularity component becomes relatively high attenuation due to gradual enhancement of oedematous stroma. Therefore, contrast enhancement of these two distinct areas reverse between the corticomedullary (1) and the early excretory (2) phases. The peak enhancement of the oedematous stroma and the optimal timing of segmental enhancement inversion may be variable in each tumour. b The corticomedullary phase of the axial contrast-enhanced (CE) computed tomography (CT) demonstrates an intensely enhancing mass with a small central portion of low attenuation (arrow). c The low attenuation central portion in the nephrographic phase is relatively hyperattenuating in the corticomedullary phase (arrow); the relative enhancement is reversed. d The delayed phase shows the mass to be nearly homogeneous (arrow). e (Low magnification) Oncocytoma, in addition to the tightly packed nests of tumour cells (T), less densely arranged nests are located in an oedematous stroma (arrows)