Medullary nephrocalcinosis

Non-specific radiologic pattern of calcium deposition in the renal medulla/pyramids, usually bilateral, from various metabolic or structural causes. Think “medullary calcium = systemic or tubule problem”, not a single disease.

Aetiology

1. Hypercalcaemic / metabolic causes

• Primary hyperparathyroidism
• Vitamin D excess, milk–alkali syndrome
• Sarcoidosis and other granulomatous disease
• Prolonged immobilisation
• Other causes of chronic hypercalcaemia / hypercalciuria

2. Normal-calcium hypercalciuria / tubular causes

• Distal (type 1) renal tubular acidosis ← very high yield
• Medullary sponge kidney
• Inherited tubulopathies
  • Bartter syndrome
  • Gitelman (less classic but often listed)
• Loop diuretics aka furosemide (especially in neonates/infants)
• Primary hyperoxaluria, enteric hyperoxaluria

3. Papillary / medullary damage

Chronic insults that injure the papillae → papillary necrosis + dystrophic calcification:

• Analgesic nephropathy (NSAIDs, phenacetin)
• Sickle cell disease/trait
• Diabetic nephropathy
• Obstructive uropathy (stones, reflux, chronic obstruction)
• Chronic pyelonephritis
• Renal TB

Clinical features

• Often asymptomatic – found on imaging for stones or renal workup.
• Symptoms derive from the underlying cause and associated stones:
  • Nephrolithiasis, renal colic
  • Polyuria/polydipsia (tubulopathy, RTA, hypercalcaemia)
  • Microscopic or gross haematuria
  • Recurrent UTIs
  • Gradual renal dysfunction in long-standing or severe disease

Imaging

Ultrasound

• Hyperechoic medullary pyramids due to calcium deposition.
• May or may not have posterior acoustic shadowing (depends on amount/compactness of calcium).
• Cortex often relatively spared (helps distinguish from cortical nephrocalcinosis).

CT

• Punctate, linear, or coarse calcifications in the medulla/pyramids.
• Often bilateral and symmetric.
• Frequently coexists with:
  • Nephrolithiasis
  • Features of underlying condition (e.g. MSK pattern, papillary necrosis, obstruction).