Adrenal adenomas are the most common adrenal masses. They are benign and most commonly found on CT as an incidental finding, or one that was not expected. Adrenal adenomas increase in frequency as one gets older. A small percentage of adrenal adenomas can be associated with hyper function, or excess hormone secretion which can cause symptoms.
Adrenal adenomas classically are round, smooth masses with low density on CT done without contrast administered through the vein. The low density is because of internal fat. They often can not be characterized on only post contrast imaging CT and require a dedicated CT exam with washout. Adrenal adenomas can look unusual with blood, calcification or lack of fat. Some can be larger then 4-6 cm and mimic other neoplasms.
Adrenal adenomas can look similar to more dangerous neoplasms and metastasis in cancer patients. When large or having unusual features, they can mimic adrenal cortical carcinomas which are deadly and in some cases pheochromocytomas which can classically elevate blood pressure and cause other neurologic symptoms. In cancer patients, differentiating benign adenomas from spread to the adrenal gland can be crucial for treatment.
When it is not clear what an adrenal mass is, a washout CT or adrenal MR may be done. A washout CT is done to see how the contrast in the adrenal mass changes over time. A higher percentage of contrast washout on the last phase imaged is more suggestive of adenoma. An adrenal MR utilizes a special technique called in and out of phase imaging which is very sensitive for detecting intracellular fat. Idea being that a mass that has intracellular fat is an adenoma, although other masses can show this in rare cases.
Despite these techniques, it is sometimes not possible to say what exactly an adrenal mass is. A biopsy may be warranted in some cases. Adrenal adenomas which secrete excess hormones or masses which are large will often be removed. Even in cancer patients, many adrenal nodules will turn out to be adenomas. Some guidelines for follow up of adrenal masses of varying sizes has been proposed in difficult cases.