Characterization of Adrenal Masses with Contrast enhanced CT – Washout Study.

Aim of the study: To prospectively characterize adrenal masses as adenomas or non adenomas with Contrast enhanced CT and correlate with histopathological results Materials & Methods: Fifty four adrenal masses were evaluated. CT attenuation values were measured using a circular region of interest on images of the lesion, covering at least one half of the mass. Adrenal masses that had attenuation values greater than 10 HU at unenhanced imaging underwent enhanced CT imaging 60 seconds after intravenous administration of contrast material and then underwent delayed enhanced CT imaging at 15 minutes. Enhancement washout percentages were calculated with the following equations: Absolute percentage of enhancement washout: ([Attenuation value at enhanced CT - Attenuation value at delayed enhanced CT]/ [Attenuation value at enhanced CT - Attenuation value at unenhanced CT]) * 100. Relative percentage of enhancement washout: ([Attenuation value at enhanced CT - Attenuation value at delayed enhanced CT]/ Attenuation value at enhanced CT) * 100. An adenoma was diagnosed if a mass had an absolute percentage enhancement washout value of 60% or higher or relative percentage enhancement washout value of 40% or higher. Results: The pathological diagnosis was 25 adenomas and 29 non adenomas. Absolute percent washout diagnosed 24 of 25 adenomas and 27 of 29 non adenomas. It had a Sensitivity of 96.00%, Specificity of 93.10%, Positive Predictive Value of 92.31% and Negative Predictive Value of 96.43%. Relative percent washout diagnosed 23 of 25 adenomas and 26 of 29 non adenomas. It had a sensitivity of 92%, specificity of 89.66%, Positive Predictive value of 88.46% and Negative Predictive Value of 92.86%. Both were found to be statistically significant. Conclusion: CT contrast washout study is helpful in categorising adenomas and non adenomas in adrenal masses with high degree of accuracy, sensitivity and specificity and helps guide clinical management