Cortical nephrocalcinosis

Concept

• Pathologic calcium deposition confined to the renal cortex, in contrast to medullary nephrocalcinosis (pyramids/medulla).
• Radiologic sign, not a diagnosis → usually reflects ischaemia / necrosis / advanced CKD.

Major causes

1. Acute renal cortical necrosis

   • Severe shock / sepsis
   • Obstetric catastrophes: abruptio placentae, eclampsia, septic abortion, PPH
   • Thrombotic microangiopathy: HUS, DIC
     → Global cortical ischaemia → necrosis → dystrophic calcification.

2. Chronic cortical scarring / end-stage kidneys

   • Long-standing glomerulonephritis or other causes of ESRD
   • Chronic renal transplant rejection / chronic allograft nephropathy
     → Small, shrunken kidneys with irregular cortical calcification.

3. Infectious / congenital

   • Renal TB with cortical destruction
   • Congenital / perinatal insults: intra-uterine infections (e.g. CMV, toxoplasmosis), severe perinatal asphyxia.

Imaging features

• Ultrasound

  • Echogenic renal cortex with or without acoustic shadowing.
  • Medulla may be relatively spared → helps distinguish from medullary nephrocalcinosis.

• CT

  • Thin peripheral “rim” or “tram-line” cortical calcification in cortical necrosis.
  • Alternatively patchy / plaque-like cortical calcifications in chronic scarring or TB.
  • Kidneys often small and atrophic in chronic disease.

• Plain film (KUB)

  • If extensive: faint peripheral rim or irregular cortical calcification over renal outlines.

Differentials (pattern-based)

• Medullary nephrocalcinosis → calcified pyramids, sparing cortex.
• Multiple renal calculi → usually follow collecting system rather than uniform cortical outline.
• Calcified renal scars / infarcts → more focal than the global cortical pattern of classic cortical necrosis.