Fetal lobation. An anatomo-ultrasonographic correlation

Remnants of the fusion of fetal renunculi have been mistaken for renal scars or tumors. We compared anatomic cuts of 24 cadaveric kidneys with fetal lobation (ages ranged from 16 weeks gestation to 49 years) to identical ultrasonographic sections performed in a water bath and to sonograms of healthy persons of similar ages as the cadavers. Fetal lobation was characterized as follows: there were fine, linear demarcations indenting the renal surface, separating normal lobes, consisting of a central pyramid and surrounding cortex. Separate renunculi seen in early fetal life progressively fuse throughout gestation, leaving interlobar grooves. During the third trimester, the renal surface becomes smoother and the interlobar grooves become invisible. One prominent indentation of the renal surface, the interrenuncular junction, incorporates perirenal fat and invaginates the anterior surface of the upper third of the kidney to the hilum and is the most easily visible remnant of fetal lobation. The sharply defined linear remnants of interlobar grooves should not be mistaken for scars, which are wider, less well defined and always associated with loss of renal cortex.