The embryonic remnant of the fusion site between the upper and lower poles of the kidney is called what?

• A. Junctional parenchymal defect
• B. Papilla
• C. Fetal lobulation
• D. Hypertrophied column of Bertin

Answer: (A)

During kidney development, the fetal lobes fuse to form a single organ. Sometimes a small embryologic remnant persists along the fusion line between the upper and lower poles, appearing as a distinct intraparenchymal defect. This is called a junctional parenchymal defect. It’s considered a benign variant and is typically seen on ultrasound or CT as a triangular wedge-shaped area within the renal parenchyma at the pole fusion site, not a true lesion.

This differs from papilla, which is the apex of a renal pyramid; from fetal lobulation, which refers to surface indentations from incomplete lobar fusion and thus the external contour rather than an internal defect; and from a hypertrophied column of Bertin, which is thickened renal cortical column that can mimic a mass.