What is nephrocalcinosis?

What is Nephrocalcinosis

Nephrocalcinosis is the deposition of calcium salts (primarily calcium oxalate or calcium phosphate) within the renal parenchyma and tubules, distinct from kidney stones, which can lead to progressive kidney damage and chronic kidney disease. 1, 2

Definition and Pathophysiology

Nephrocalcinosis represents a generalized increase in calcium content within kidney tissue that occurs at molecular, microscopic, or macroscopic levels. 1 The calcium deposition can occur:

• Intratubularly within the renal tubules 1
• Interstitially within the renal parenchyma 1
• Along glomerular and tubular basement membranes in rare cases 3

The condition differs fundamentally from nephrolithiasis (kidney stones), though this distinction is often blurred in radiologic reporting. 4 Direct endoscopic visualization is now considered the definitive method to distinguish true tissue calcification from urinary calculi. 4

Anatomic Classification

Medullary Nephrocalcinosis

• Most common form, involving calcium deposits in the renal medulla 2
• Associated with conditions causing hypercalciuria, hyperoxaluria, or hyperphosphatemia 1

Cortical Nephrocalcinosis

• Less common, involving the renal cortex 2
• Often indicates more severe metabolic derangements 5

Mixed Nephrocalcinosis

• Involves both cortex and medulla simultaneously 6
• Suggests systemic metabolic disease with familial/genetic components 6

Clinical Significance

Nephrocalcinosis is more sinister than simple kidney stones and often implies a serious underlying metabolic defect. 1 The condition leads to:

• Progressive renal damage through chronic tubulointerstitial inflammation 7
• Chronic kidney disease in the majority of affected patients 7, 6
• End-stage kidney disease when combined with obstruction and ongoing calcium deposition 7

Common Etiologies

The major causes include conditions that increase urinary concentrations of calcium, oxalate, or phosphate: 1

• Primary hyperoxaluria - leads to recurrent stones, nephrocalcinosis, and eventual kidney failure in >70% of patients 7
• Primary hyperparathyroidism - causes hypercalcemia and hypercalciuria 6
• Distal renal tubular acidosis - impairs urinary acidification 4
• Bartter syndrome - salt-losing tubulopathy with hypercalciuria and nephrocalcinosis in the majority of patients 7
• Medullary sponge kidney 6, 4
• X-linked hypophosphataemia - requires screening with renal ultrasonography 7
• Certain medications that alter calcium-phosphate metabolism 6

Diagnostic Approach

Renal ultrasound is the first-line imaging modality for detecting nephrocalcinosis, as it is radiation-free, widely available, and specifically recommended in clinical guidelines. 7, 5, 8

CT scans provide superior accuracy for assessing renal calcifications but should be reserved for equivocal ultrasound findings or when precise localization will directly change therapeutic management. 5, 8

Once nephrocalcinosis is identified, establishing the underlying cause is essential through: 5

• Serum calcium, phosphate, and calcium-phosphate product 5
• Serum electrolytes (potassium, chloride) 5
• Arterial blood gas for metabolic alkalosis or acidosis 5
• Parathyroid hormone levels 7
• 24-hour urine studies for calcium, oxalate, and phosphate 7

Clinical Pitfall

Nephrocalcinosis can be underdiagnosed due to lack of knowledge about different presentation patterns and confusion with nephrolithiasis on imaging. 2 In the era of non-contrast CT for stone diagnosis, calcifications near renal papillae are common, but distinguishing true tissue calcification from stones requires direct endoscopic visualization. 4