Diagnostic Ultrasound - Abdomen and Pelvis

Nephrocalcinosis
TERMINOLOGY
Abbreviations
• Nephrocalcinosis (NC)
Synonyms
• Medullary nephrocalcinosis, cortical nephrocalcinosis
Definitions
• Calcification of renal parenchyma
IMAGING
General Features
• Best diagnostic clue
○ Calcification within renal parenchyma
• Location
○ Medullary NC (95%): Calcification in medullary pyramids
○ Cortical NC (5%): Cortical calcification and along central
septa of Bertin
○ Both cortical and medullary: Rare
• Size
○ Kidneys often have normal size and contour
Ultrasonographic Findings
• Grayscale ultrasound
○ Medullary nephrocalcinosis
– Generalized increased echogenicity of renal pyramids
±acoustic shadowing
– Reversal of normal corticomedullary differentiation
– Medullary rings: Hyperechoic rim outlining medullary
pyramids
– Medullary sponge kidney: Echogenic medullary
pyramids regardless of whether or not medullary
nephrocalcinosis is present
– Papillary necrosis → sloughed papilla seen as
echogenic nonshadowing structure at pyramids
□ Calcified sloughed papilla with distal acoustic
shadowing
□ Clubbing of adjacent calyces
□ Cystic collections within medullary pyramids
○ Cortical nephrocalcinosis
– Increased cortical echogenicity ±acoustic shadowing
○ Comparison of US and CT in induced nephrocalcinosis in
rabbits showed higher sensitivity for US (96% vs. 64%)
but better specificity for CT (96% vs. 85%)
Radiographic Findings
• Radiography
○ Medullary NC: Stippled, coarse, or confluent calcification
in pyramids
○ Cortical NC
– Diffusely dense renal shadows
– Thin, peripheral band of calcification, often with
extension into septal cortex
– 2 thin, parallel calcified tracks (tram lines)
– Punctate calcifications representing necrotic cortical
tubules (least common)
• IVP
○ Medullary sponge kidney (MSK)
– Mild → "paintbrush" appearance of linear striations in
pyramids from contrast in ectatic tubules
– Moderate to severe → "bouquet of flowers" and
"bunch of grapes" appearances of contrast pooling in
cystic dilations of collecting tubules
– Pros: Highly sensitive for collecting tubule dilation
– Cons: Contrast and radiation exposure; low sensitivity
for small stones and nephrocalcinosis; not routinely
used
CT Findings
• NECT
○ Medullary NC: Stippled, coarse, or confluent
calcifications in medulla
– Hyperparathyroidism and renal tubular acidosis (RTA)
type 1 → usually diffuse, uniform calcification
□ Dense, confluent medullary calcification: Common
in renal tubular acidosis
– Medullary sponge kidney → often asymmetrical,
segmental, or unilateral calcifications
□ Cluster of calcifications in papillae is characteristic
□ Highly sensitive for stones but low sensitivity for
tubular ectasia
□ Medullary NC is often present but not mandatory
for diagnosis of MSK
– Papillary necrosis → coarsely calcified necrotic papillae
(commonly in analgesic nephropathy)
○ Cortical NC: Thin band or tram line cortical calcification
with small perpendicular extensions in Bertin columns
• CECT
○ MSK on CT intravenous pyelogram (IVP) = "paintbrush"
appearance in mild cases; "bouquet of flowers" or
"bunch of grapes" appearances in more severe cases
– CT IVP: Highly sensitive for stones, medullary cysts,
and collecting tubule dilation; contrast and radiation
exposure
– Advanced→ deformed papillae and distorted calyces
Imaging Recommendations
• Best imaging tool
○ US is 1st diagnostic imaging option in infants and
children with suspected nephrocalcinosis
○ Noncontrast CT in adults except for MSK where CT IVP
may be best (sensitive for stones and collecting tubule
dilation)
• Protocol advice
○ US is sensitive for screening of early nephrocalcinosis in
children with known predisposing metabolic conditions,
such as RTA and hyperoxaluria
○ Detection of nephrocalcinosis on plain films is improved
by low kV technique
DIFFERENTIAL DIAGNOSIS
Renal Calculus
• Discrete echogenic focus with sharp posterior acoustic
shadowing
Emphysematous Pyelonephritis
• Gas within renal parenchyma associated with "dirty
shadowing"
Other Causes of Hyperechoic Medulla
• Autosomal recessive polycystic kidney disease
Diagnoses: Urinary Tract
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