KEY FACTS
Terminology
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Benign, fluid-filled, nonneoplastic renal lesion
Imaging
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Ultrasound is ideal for characterizing simple or complex renal cysts in nonobese patients
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Unilocular, thin-walled, round/oval renal lesion
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Anechoic: No internal echoes, septations, or solid components; distinct posterior wall
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Increased sound transmission gives rise to characteristic posterior acoustic enhancement
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Variable size
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Location: Intraparenchymal, exophytic, parapelvic
Top Differential Diagnoses
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Complex renal cyst
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Peripelvic cysts
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Prominent pyramids
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Cystic disease of dialysis
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Perinephric collections
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Pyelogenic cyst/pyelocalyceal diverticulum
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Multilocular cystic nephroma
Clinical Issues
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In 20-30% of middle-aged adults and 50% > 50 years of age
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Most common renal lesion, usually detected incidentally
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No further imaging or monitoring of cyst is warranted
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May present with pain from bleeding/rupture/infection or mass effect when large
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Multiple renal cysts may indicate syndrome, such as autosomal dominant polycystic kidney disease
Diagnostic Checklist
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Well-defined, round or ovoid renal lesion with posterior acoustic enhancement, distinct echogenic posterior wall, and complete lack of internal echoes (anechoic)
Scanning Tips
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Distinguish simple renal cysts from complex cystic renal lesions; look for solid nodules and septa
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Optimize ultrasound by adjusting frequency and focal zone; use harmonics and turn off compounding for optimal detection of posterior enhancement
with complete lack of internal echoes, imperceptible walls, and posterior acoustic enhancement 
. The gallbladder 
was normal.
in addition to multiple smaller cortical cysts 
. Large cysts may produce distension, pain, or spontaneous hemorrhage.
. Color Doppler should be used to confirm that an anechoic lesion is not vascular.
. Acoustic enhancement 
is well seen despite the small size of the cyst.
