Adrenal Masses

Adrenal Adenoma

Adrenal cortical adenomas are common benign tumors arising from the cortex of the adrenal gland. The majority of adrenal adenomas are nonfunctional incidentalomas. A small percentage of adenomas that produce excessive steroid hormones will cause symptoms manifesting as Cushing's syndrome or Conn's syndrome or with excess acne and hair growth. Therefore, all incidentally detected adenomas or adrenal masses on imaging should be correlated with the clinical presentation and, if necessary, serum and urine biochemical analysis for the presence of a functional adenoma. The overall prevalence of adrenal adenomas increases with advancing age.

Computed Tomography

Computed tomography (CT) is the primary imaging modality used in establishing a diagnosis of adenoma. Histologically, two types of adrenal cortical adenomas are identified: those that contain a high percentage of intracytoplasmic lipid (lipid rich), which represent approximately 70% of all adrenal cortical adenomas, and those that are lipid poor, which represent the remaining approximately 30%. Calcifications, necrosis, and hemorrhage are atypical but can occur, especially in larger lesions. The vast majority of lipid-rich adenomas can be accurately identified by CT density. Typically, adenomas demonstrate a density of less than 10 Hounsfield units (HU) on unenhanced images ( Figure 71-1, A ). Approximately 10% to 40% of all adenomas demonstrate CT density greater than 10 HU and are considered lipid-poor adenomas. Some of the lipid-poor adenomas can be characterized on washout characteristics on delayed-phase contrast-enhanced images. On analysis of washout characteristics, adenomas have relative percentage washout (RPW) and absolute percentage washout (APW) values of more than 38% and 52%, respectively, after a 10-minute delay or 40% and 60%, respectively, after a 15-minute delay. These washout patterns are diagnostic for adenoma. Both lipid-rich and lipid-poor adenomas have a similar washout pattern.