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Sonographically, renal cysts exhibit no echos within the cyst fluid (anechoic), show increased echos deep to the cyst (acoustic enhancement) and also demonstrate a well defined posterior wall. Most cysts are spherical in shape and unilocular but can have septations. Cysts with internal echos, septations and/or nodularity are considered complex in nature. This complexity is usually related to previous hemorrhage. As renal cell carcinomas can present in this fashion, complex cysts are typically followed or treated more aggressively.
Computed tomography also demonstrates cysts as a well circumscribed, spherical intra-renal mass. The internal aspect of the cyst should exhibit fluid attenuation (density similar to water). Simple cysts do not enhance with the administration of intravenous contrast.
The intravenous urogram is poor at evaluating cysts as they are typically seen as an indeterminate mass on this examination. If a mass is seen on IVU, then an ultrasound can be performed to determine whether not the perceived mass is solid or cystic.
The accompanying ultrasound demonstrates a well defined cyst in the lower pole of the left kidney. Note the anechoic fluid, clear margins, acoustic enhancement and well defined posterior wall. This is clearly a benign cyst sonographically. No further follow-up of this cyst is warranted.
The CT scan, of a different patient, demonstrates a well defined cortical cyst which is smaller than the one seen sonographically. This again demonstrates benign characteristics in that it exhibits fluid attenuation and it does not enhance. Incidentally noted on the CT scan is periaortic adenopathy in this patient with lymphoma.
(Prepared by Michael P. Buetow, M.D.)
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