Persistent fetal lobulation
Normal anatomical variant where fetal renal lobulations persist into adulthood, causing shallow external cortical clefts between renal pyramids without cortical loss or parenchymal scarring.
Key imaging features
- External scalloped/indented renal outline.
- Clefts lie between medullary pyramids, aligned with interlobar arteries.
- Cortical thickness preserved between clefts and calyces.
- No associated:
- Cortical thinning
- Deformity of calyces
- Focal volume loss or contour flattening.
Main differential (vs renal scarring)
| Feature | Persistent fetal lobulation | Renal scarring (e.g. reflux / chronic pyelo) |
|---|---|---|
| Location of indentation | Between pyramids (interlobar region) | Over a pyramid |
| Cortical thickness | Preserved, normal thickness | Thinned cortex at site of scar |
| Calyces | Normal shape and orientation | Clubbing, distortion, retraction of adjacent calyx |
| Parenchymal volume | No focal volume loss | Focal volume loss, kidney may be small if advanced |
| Overall impression | Normal variant, symmetrical, smooth internal anatomy | Acquired damage, often asymmetric, associated with CKD |
Exam nuggets
- Common normal variant in adults; often bilateral.
- Classic Q: “How to distinguish from scarring?” → look for cortical thinning + calyceal deformity (present in scar, absent in fetal lobulation).
