Pseudoenhancement is an artifact in postcontrast CT evaluation of renal cysts.
The distinction between cystic and solid lesions visualised in CT is primarily made on the basis of whether the lesion enhances with contrast administration. A renal cystic lesion is considered "enhancing" when there is at least a 20 HU increase in attenuation from the precontrast series to the postcontrast series. An increase in attenuation of 10-20 HU is considered indeterminate.
While this has been shown to be a robust method, it has been shown that, especially for small lesions and where there is a high level of enhancement in the renal parenchyma, that due to beam hardening and partial voluming the HU in the lesion artificially increases 3.
Caution must be exercised, however, when using this criteria in small (<1 cm) intraparenchymal renal cystic lesions. These small lesions may actually be water attenuation (<10 HU), but because of the intense enhancement of the surrounding renal parenchyma, the Hounsfield unit reconstruction algorithm may artificially increase the attenuation in the benign cyst, making it appear as a possibly malignant enhancing cystic lesion.
Dual energy CT provides a novel approach in minimising pseudoenhancement by the use of virtual monoenergetic images at a KeV range of 80 Kev to 90 KeV. At these KeV ranges beam hardening and partial voluming is minimised and there is no increase in radiation dose delivered to the patient 3,4.