Incidental adrenal lesions detected on enhanced abdominal dual-energy CT: can the diagnostic workup be shortened by the implementation of virtual unenhanced images?

OBJECTIVE: To determine whether post-processing of the data from portal-phase enhanced dual-energy CT (DECT), with or without the addition of a late enhanced phase acquisition, may enable characterization of adrenal lesions without the need for acquisition of pre-contrast images.

MATERIALS AND METHODS: Twenty-two patients with 24 adrenal lesions underwent unenhanced, venous and delayed phase DECT. Of these lesions, 20 were found to be adrenal adenomas, on the basis of histopathology, unenhanced attenuation values between 0 and -10 HU, or stability over at least 6 months. For all 24 lesions, true and virtual unenhanced attenuation values were measured based on the data of the portal (VNCp) and the delayed (VNCd) DECT acquisition. The absolute washout values based on the true non-contrast (TNC) and the VNCp and VNCd image series were also measured. The washout was also calculated based on the iodine concentration measured from both contrast-enhanced acquisitions.

RESULTS: Mean virtual unenhanced attenuation values of all lesions calculated from the portal phase images was 12.6 HU, and was 4.02 HU higher than the values based on true unenhanced images (p=0.020). Washout values calculated from virtual unenhanced attenuation based on the VNCp were also significantly different (p=0.0304) while those calculated from VNCd and from iodine concentration correlated with the corresponding values based on the true unenhanced values (p>0.999).

CONCLUSIONS: Our data indicate that attenuation values of adrenal adenomas based on virtual unenhanced images are significantly higher than those obtained with true unenhanced images. An incidental adrenal lesion with a virtual unenhanced attenuation lower than 10 HU can thus be safely characterized as an adenoma.