Differentiation of adrenal tumors in patients with hepatocellular carcinoma: adrenal adenoma versus metastasis.

OBJECTIVE: To investigate whether computed tomography (CT) attenuation test for differential diagnosis of adrenal nodule is applicable in patients with hepatocellular carcinoma (HCC) which shows similar image characteristics to adrenal adenoma.

MATERIALS AND METHODS: This retrospective study was approved by our institutional review board, and the requirement for informed consent from study patients was waived. Searching picture archiving and communication system, we identified 3678 patients with HCC who underwent upper abdominal unenhanced CT scans between April 2002 and March 2010, and 114 adrenal nodules (39 adenomas and 75 metastases) were included for analysis. Ten nodules were confirmed pathologically while 104 had imaging diagnosis (enlarged or emerged during the study period). Size, CT number, and the internal characteristics of the lesions were recorded.

RESULTS: Mean CT numbers of adrenal adenomas were significantly lower than those of metastases (P<0.0001, t-test) on unenhanced CT. Thresholds of 17 and 33 Hounsfield units (HU) provided the following sensitivity, specificity, and accuracy: 46.2%, 100%, and 81.6% at 17HU, and 94.9%, 89.3%, and 91.2% at 33HU, respectively. The area under receiver operating characteristic curve for the CT number test was 0.96. Metastases were significantly larger than adrenal adenoma (P=0.009, t-test). However, the accuracy of testing using mass size was 64.0% at most. All adenomas and metastases were depicted as homogeneous masses with the exception of two metastases that presented as heterogeneous masses (necrotic or lipomatous).

CONCLUSION: Adrenal adenomas can be differentiated from HCC metastases using CT number on unenhanced CT.