Adrenal cortical adenoma with the maximal diameter greater than 5 cm: can they be differentiated from adrenal cortical carcinoma by CT?

To study the computed tomographic findings of adrenal adenoma with the maximal diameter greater than 5 cm and to discuss whether such tumor can be differentiated from adrenal carcinoma by CT examination. Fourteen consecutive patients with adrenal adenoma with the maximal diameter larger than 5 cm, proven pathologically, were enrolled. All patients underwent non-enhanced and contrast-enhanced CT examination. The CT findings, including size, shape, edge, density on non-enhanced CT and schedule of reinforcement after contrast administration for each lesion were retrospectively analyzed. CT data of 13 patients with adrenocortical carcinoma were also evaluated to determine whether differentiating characteristics existed. The maximal diameter of the 14 masses of adenoma ranged from 5.5 cm to 20 cm (mean, 10 cm). One mass showed lobulated, the rest 13 masses showed rounded or ovoid. Eleven and 3 masses appeared well-circumscribed and ill-circumscribed, respectively. All of 14 masses presented heterogeneous density on non-enhanced CT images with patchy low-attenuation foci or stippled calcification. All of 14 masses revealed moderately to markedly heterogeneous enhancement after contrast administration. None of 14 masses developed local invasion and distant metastasis. Except for recurrence, metastasis and venous tumor emboli which only occurred in the cases of adrenal carcinoma, no definite computed tomographic features could be found that enabled the identification of adenomas with the maximal diameter greater than 5 cm with adrenal carcinomas. The characteristic CT findings of adrenal adenoma with the maximal diameter greater than 5 cm include bulky, well-circumscribed, rounded or ovoid masses, heterogeneous attenuation with low-attenuation foci on non-enhanced CT images and heterogeneous enhancement after contrast administration. The differential diagnosis between such tumor and adrenal cortical carcinoma by CT examination is relatively difficult, such findings as recurrence, metastasis and venous tumor emboli may be of some significance.