How are simple renal cysts differentiated from Wilms tumor on imaging?

Updated: Mar 04, 2019
  • Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Eugene C Lin, MD  more...
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The exact etiology of simple renal cysts is uncertain. These lesions may be retention cysts due to obstruction, or they may arise in embryonic rests. Simple renal cysts are uncommon in children, being found in 2-4% of pediatric postmortem examinations. However, their frequency increases with age, and they are found in 50% of adults older than 50 years.

Simple cysts are usually asymptomatic unless they are complicated by hemorrhage or infection. Their mass effect may be large. The cysts arise in a parapelvic position and compress part of the renal collecting system. On sonograms, the cysts are entirely free of echoes, with good sound transmission. They give rise to distal acoustic enhancement. The cyst has a smooth outline without a demonstrable wall. Small cysts may appear echo-free only when they are in the focal zone of the ultrasound beam because of partial-volume affects. Cysts smaller than 3 mm in diameter cannot be identified in the parenchyma.

Ultrasonography is more accurate than CT for visualizing the internal septae and for demonstrating the internal morphologic features of the cyst. If the nature of a cyst identified during sonography is in doubt, follow-up scanning or aspiration of the cyst should be performed. If the appearance is classically that of a simple cyst, no further action is needed.

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