What does it mean to have lobulated kidneys?

Lobulated Kidneys: Clinical Significance and Interpretation

Lobulated kidneys refer to a normal anatomical variant called persistent fetal lobulation, where the kidney surface shows multiple rounded contours or lobes, representing a benign developmental finding that typically requires no intervention. 1

Normal Anatomical Variant

• Persistent fetal lobulation is a structural anomaly of renal form where the kidney retains its fetal appearance with visible surface lobulations, which normally disappear during childhood development 2
• This represents incomplete fusion of the renal lobes during embryologic development and is considered a benign variant with no clinical significance in most cases 2
• The lobulated appearance reflects the underlying organization of renal lobes, each containing a medullary pyramid and its associated cortical tissue 1

Distinguishing from Pathologic Conditions

When Lobulation is Benign

• Smooth, regular lobulations with preserved cortical thickness and normal renal size indicate persistent fetal lobulation, which requires no treatment 2
• The kidney maintains normal function, and the lobulated contour is purely a morphologic finding without associated complications 2

When Lobulation Suggests Disease

• In ADPKD (Autosomal Dominant Polycystic Kidney Disease), lobular accentuation of glomerular tufts may be present on microscopy, but this refers to glomerular architecture rather than external kidney contour 1
• Pancake kidney, a rare fusion anomaly, presents as a lobulated pelvic renal mass with two fused lateral lobes, but this is distinctly different from simple persistent fetal lobulation 3, 4, 5
• Pathologic lobulation in glomerular disease refers to mesangial expansion creating a lobular appearance on microscopy, not external kidney morphology 1, 6

Imaging Characteristics

• Ultrasound is the first-line imaging modality and will show smooth, regular indentations on the kidney surface without associated masses, cortical thinning, or collecting system abnormalities 3, 2
• The lobulations should be symmetric and regular without focal masses or disruption of normal renal architecture 2
• CT or MRI may provide additional anatomic detail if there is concern for underlying pathology, but is typically unnecessary for simple persistent fetal lobulation 2

Clinical Management

• No intervention is required for persistent fetal lobulation, as this is a normal variant 2
• Routine follow-up is unnecessary unless there are other clinical concerns such as hematuria, proteinuria, or elevated creatinine that would warrant investigation independent of the lobulated appearance 1
• The finding should be documented as a normal variant to prevent unnecessary future investigations 3, 2

Key Pitfall to Avoid

• Do not confuse persistent fetal lobulation with renal scarring from chronic pyelonephritis or reflux nephropathy, which shows irregular, asymmetric cortical thinning overlying dilated calyces rather than smooth, regular lobulations 2
• Ensure the lobulations are bilateral and symmetric; unilateral or focal lobulation warrants further investigation to exclude mass lesions or focal scarring 2