Is it uncommon to have kidney stones in the parenchymal mid inferior kidney?

Kidney Stones in the Renal Parenchyma

Yes, it is uncommon to have kidney stones located within the renal parenchyma itself—most kidney stones form in the renal calyces and pelvis, not embedded within the kidney tissue. 1, 2

Typical Stone Locations vs. Parenchymal Stones

Normal Stone Distribution

• Kidney stones typically form in the collecting system: renal calyces (upper, middle, or lower) and the renal pelvis, where urine collects and minerals can crystallize 3, 1
• Lower pole calyceal stones are particularly common due to gravitational effects and impaired drainage from anatomical factors 1
• Stones form at Randall's plaques on the renal papillary surfaces, which are located at the interface between the collecting system and kidney tissue, not within the parenchyma itself 2

Parenchymal Stones Are Distinct Entities

• True parenchymal stones represent calcified renal scars rather than typical urinary stones, often resulting from old granulomatous disease, renal abscess, or organized hematoma 4
• These appear as densely calcified solitary masses in peripheral kidney locations, often with exophytic projection, and are considered benign without malignant potential 4
• Parenchymal calcifications are stable over time and represent organized, calcified tissue rather than mobile crystalline deposits in the collecting system 4

Clinical Implications

Diagnostic Considerations

• Ultrasound can identify parenchymal calcifications but has only 45% sensitivity for detecting stones in the collecting system 5, 1
• Non-contrast CT is the gold standard for distinguishing between true collecting system stones and parenchymal calcifications, with 93-96% sensitivity 5, 1
• Parenchymal calcifications typically show complete stability on long-term follow-up without evidence of growth or soft-tissue mass extension 4

Management Differences

• Collecting system stones may require intervention based on size, location, and symptoms, with options including shock wave lithotripsy, ureteroscopy, or percutaneous nephrolithotomy 1
• Parenchymal calcifications generally require no treatment, as they represent benign scarring rather than active stone disease 4
• The distinction is critical because parenchymal calcifications should not be mistaken for stones requiring lithotripsy or surgical removal 4

Common Pitfalls

Do not confuse medullary pyramids or renal sinus fat with stones—these normal anatomical structures can mimic pathology on ultrasound, especially in young patients 3

Recognize that small stones (<3 mm) are usually not identified by ultrasound and are detected primarily by the acoustic shadowing they produce 3

Be aware that parenchymal calcifications may be mistaken for collecting system stones if imaging is not carefully interpreted in the context of stone location relative to the renal parenchyma versus the collecting system 4