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Medullary nephrocalcinosis refers to diffuse calcium deposition within the renal medulla (renal pyramids). It represents parenchymal calcification rather than calculi in the collecting system.
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The condition occurs due to disorders that produce hypercalcemia, hypercalciuria, hyperphosphaturia, or hyperoxaluria, leading to precipitation of calcium salts in the renal medullary interstitium or tubules.
| Etiology | Causes |
|---|---|
| Hypercalcemic states | Causes associated with increased serum calcium: |
| • Primary hyperparathyroidism | |
| • Vitamin D intoxication | |
| • Sarcoidosis | |
| • Milk-alkali syndrome | |
| • Malignancy-associated hypercalcemia | |
| Hypercalciuria without hypercalcemia | Serum calcium may be normal but urinary calcium is elevated. Common causes include: |
| • Distal renal tubular acidosis (Type 1) – most common cause in adults | |
| • Medullary sponge kidney | |
| • Loop diuretics (e.g., furosemide) | |
| • Idiopathic hypercalciuria | |
| Hyperoxaluric conditions | • Primary hyperoxaluria |
| • Enteric hyperoxaluria | |
| • Ethylene glycol toxicity | |
| Other causes | • Papillary necrosis |
| • Hyperphosphatemia | |
| • Neonatal nephrocalcinosis | |
| • Chronic glomerulonephritis |
Calcium deposition occurs in:
Two major mechanisms:
The deposits are usually calcium phosphate or calcium oxalate.
| Modality | Imaging features | Notes |
|---|---|---|
| XR (KUB) | Classic finding: Symmetric pyramidal calcifications | • Multiple fine stippled calcifications |
| • Triangular/pyramidal pattern following renal medulla | ||
| • May appear as dense renal pyramids | ||
| US | • Hyperechoic renal pyramids | |
| • Posterior acoustic shadowing (when calcification is dense) | Patterns: | |
| • Diffuse medullary echogenicity | ||
| • Discrete echogenic pyramids | ||
| CT | • High attenuation within renal pyramids | |
| • Medullary distribution | ||
| • May show striated or punctate calcifications | CT can also identify underlying etiologies such as: | |
| • Medullary sponge kidney | ||
| • Papillary necrosis | ||
| • Obstructive uropathy |
Imaging appearances of medullary nephrocalcinosis: Coronal maximum intensity projection (MIP) image from non-contrast CT (a) and longitudinal image from sonogram (b) in a 35-year-old woman show hyperdensity (arrows) and hyperechogenicity (arrowheads) with shadowing (asterisks), consistent with medullary nephrocalcinosis. Axial T1-weighted (c) and T2-weighted (d) MR images in a 47-year-old women with known medullary nephrocalcinosis show hypointensity (black arrows) of the medullary pyramids due to susceptibility-related signal loss from dense calcification
Thomas, J., Ludwig, D.R., Ballard, D.H. et al. Spilling the beans: an inside scoop on the imaging of renal parenchymal disease. Abdom Radiol 47, 2420–2441 (2022). https://doi.org/10.1007/s00261-022-03540-2
Other causes of medullary nephrocalcinosis. Coronal (a) and axial (b, c) CECT images in a 61-year-old man with MEN 2A syndrome show medullary nephrocalcinosis (arrows) related to a hypercalcemia from a prior parathyroid adenoma. Surgical clips from prior left adrenalectomy (circle) and thyroidectomy (open arrow) relate to prior resections of pheochromocytoma and medullary thyroid carcinoma, respectively. Calcified hepatic lesions (arrowheads) represented medullary thyroid carcinoma metastases. Coronal CECT images (d) in a 43-year-old woman with type 1 renal tubular acidosis show symmetric bilateral medullary nephrocalcinosis (black arrows)
Thomas, J., Ludwig, D.R., Ballard, D.H. et al. Spilling the beans: an inside scoop on the imaging of renal parenchymal disease. Abdom Radiol 47, 2420–2441 (2022). https://doi.org/10.1007/s00261-022-03540-2