Differences in Growth Rate on CT of Adrenal Adenomas and Malignant Adrenal Nodules.

Abstract

<b>OBJECTIVE.</b> The purpose of this study is to determine the differences in growth rate of adrenal adenomas and malignant adrenal nodules. <b>MATERIALS AND METHODS.</b> This was a retrospective review of adults with an adrenal nodule seen at two different abdominal or chest CT examinations or PET/CT examinations. Patients in the adenoma group were included if they had a CT, MRI, or pathologic diagnosis of an adrenal adenoma. Patients in the malignant group were included if they had a pathologically proven malignant adrenal nodule. Nodule growth was defined as a change in the largest axial diameter greater than or equal to 3 mm. Growth rate was calculated by dividing the change in the longest axial diameter by the time between the first and last imaging examination. <b>RESULTS.</b> There were 105 adenomas and 26 malignant nodules. Of the 105 adenomas, 34 (32.4%; 95% CI, 23.6-42.2%) grew, three (2.9%; 95% CI, 0.6-8.1%) became smaller, and 68 (64.8%; 95% CI, 54.8-73.8%), were unchanged in size. All 26 (100%; 95% CI, 89.1-100%) malignant nodules grew. The mean (± SD) growth rate of adenomas was 1.0 ± 0.67 mm/year (range, 0.3-2.8 mm/year), compared with 58.4 ± 78.5 mm/year (range, 5.8-395.4 mm/year) for malignant nodules (<i>p</i> < 0.001). A growth rate of 3 mm/year distinguished adenomas from malignant nodules with a sensitivity of 100% (95% CI, 86.8-100%) and a specificity of 100% (95% CI, 96.6-100%). <b>CONCLUSION.</b> Approximately one-third of radiologically proven adrenal adenomas grew, all of which grew at a rate less than 3 mm/year. All malignant adrenal nodules grew, and all at a rate greater than 5 mm/year.