CT of the hyperdense renal cyst: sonographic correlation

The computed tomographic (CT) appearances of 19 hyperdense renal cysts in nine patients are reported. Sixteen of these cysts were found over a period of only 1 year with state-of-the-art CT equipment. Hyperdense renal cysts are probably more common than suggested by case reports. Their rate of detection can be expected to increase with the wider availability of fast CT scanners using thin collimation. A CT diagnosis of benign hyperdense renal cyst can be made if a lesion meets all of the following criteria: (1) smoothly outlined imperceptible wall with sharp demarcation from the kidney; (2) before intravenous contrast injection, homogeneous internal content with CT numbers 40%-240% higher (70%-240% higher for lesions 10 mm or more in diameter) than renal parenchyma; and (3) after intravenous contrast injection, persistent internal homogeneity and insignificant enhancement (less than 6%) relative to normal renal cortex. For masses exceeding 15 mm in diameter, sonography can be a valuable confirmatory test.