This was a bit tougher than the previous cases.

Findings: an isoechoic mass-like lesion extending from the cortex into the medulla, separating the pyramids, without deforming the renal contour (and I said it had normal Doppler).

Answer: Hypertrophied Column of Bertin

- remember the kidney forms from several lobules, so if those lobules don’t fuse normally, there may be some residual cortical tissue extending into the renal medulla. So it should look and act the same as cortical tissue

brief review: http://radiopaedia.org/articles/hypertrophied-column-of-bertin

Older but nice article (nice pics) : http://www.ajronline.org/doi/pdf/10.2214/ajr.146.1.53