Radiological anatomy of the kidney revisited.

In recent years some structures or features such as the "inter-renuncular septum", the "echogenic triangle" and the "echogenic line" have been described to support the concept of a kidney resulting from the fusion of two masses or renunculi. To clarify this concept and to understand the meaning of the above echographic features better, the authors have examined prospectively by sonography the kidneys of 50 children, 200 adults with a single collecting system, 25 adults with a duplicated collecting system and 32 cadavers. Furthermore, to help explain the sonographic features, we have examined 32 cadaver kidneys with sonography and 10 cadaver kidneys with magnetic resonance imaging (MRI). The sonographic, MRI and anatomical correlations have shown that the "echogenic triangle" and the "echogenic line" are not renuncular residuals, but simply an extension of the hilar fat visible when the renal sinus is rather deep. The intermediate cortical mass is not a septum dividing the kidney into an upper and lower renunculus, but a column of parenchymal tissue crossing the renal sinus, which, from an anatomical point of view, is an accessory renal lobe. The presence of two renunculi, suggested in a previous study with cortical nephrotomography, has not been confirmed.