Hyperattenuating Renal Cyst

A hyperattenuating (hyperdense, in radiology slang) renal mass that does not contain fat can be considered a hemorrhagic or proteinaceous cyst (Bosniak II) if the following CT criteria are met:

• Shape: Round
• Margin: Smooth and sharply marginated
• Size: Diameter ≤ 3 cm
• Attenuation: 40–90 HU and homogeneous in attenuation, when examined using narrow window settings.
• Enhancement: None, when examined using narrow window settings. Masses that increase in attenuation by 10 HU or less are considered non-enhancing.
• Extent: Must extend outside of the kidney at least approximately one-fourth of its circumference so that the smoothness of some of the wall can be evaluated.

Note: There is at least one case of a cystic renal cell carcinoma that fulfilled all of the above CT criteria for a benign hyperattenuating cyst, so we can't rule out renal cell carcinoma completely.

References

• Bosniak MA. The small (less than or equal to 3.0 cm) renal parenchymal tumor: detection, diagnosis, and controversies. Radiology. 1991 May;179(2):307-17.
• Hartman DS, Weatherby E 3rd, Laskin WB, Brody JM, Corse W, Baluch JD. Cystic renal cell carcinoma: CT findings simulating a benign hyperdense cyst. AJR Am J Roentgenol. 1992 Dec;159(6):1235-7.