KEY FACTS
Terminology
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Hypertrophic band of normal cortical tissue that separates pyramids of renal medulla
Imaging
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Band of tissue isoechoic to cortex and continuous with renal cortex, extending between renal pyramids
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Echogenicity may be increased because of anisotropy
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At junction of upper and middle 1/3 of kidney
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Left side > right side
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Unilateral > bilateral (18% of cases)
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Measures < 3 cm
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Indents renal sinus laterally
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Normal external renal contour
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No vascular distortion with preserved arcuate arteries surrounding pyramids
Top Differential Diagnoses
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Renal tumor
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Renal scarring with pseudotumor
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Renal duplication
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Dromedary hump
Pathology
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Embryology: Incomplete resorption of polar parenchyma of subkidneys that fuse to form normal kidney
Clinical Issues
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Normal variant, asymptomatic
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Found on imaging
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Most likely to simulate mass on sonography
Scanning Tips
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Optimize ultrasound by focusing on lesion and placing it in center of field of view
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Use color Doppler to differentiate from tumor
