E5023. The Indeterminate Incidental Adrenal Nodule: Watch Out for Washout
  1. David Casper; Creighton University College of Medicine Phoenix
  2. Andrew Liguori; Creighton University College of Medicine Phoenix
A significant portion of medical imaging is to further characterize incidental findings, so-called “incidentalomas.” Adrenal nodules are a common culprit found on up to 5% of patients. The American College of Radiology white paper algorithm helps stratify risk and appropriate follow-up recommendations, with a large portion of follow-up imaging centering on the indeterminant 1.0–3.9 cm nodule. Dedicated multiphase adrenal CTs are one of the workhorses to evaluate the indeterminate nodule, with a goal of distinguishing a benign mass or adenoma from nonadenoma. Benign adenomas are estimated to comprise 75% of adrenal nodules, and thus make up the bulk of these imaging follow ups. While washout characteristics confirm a benign diagnosis, understanding enhancement and washout elucidates unique patterns across numerous adrenal pathologies. Through tactful stratification, unnecessary follow-up imaging can often be avoided or at least minimized. Over-imaging, although just a single component of health care expenditures, is increasingly adding to the overall burden of excess healthcare spending, estimating 200–250 billion dollars per year. The majority of dedicated adrenal CTs turn out to be benign adenomas, but these often have unique washout characteristics that can be diagnosed on earlier delays, commonly found on examinations such as CT urograms, CT renal/liver mass, and occasional trauma or bleed studies. Beyond adenomas, appropriate application of enhancement patterns serves as a valuable review of a common diagnostic dilemma.

Educational Goals / Teaching Points
Review the components of the ACR whitepaper and extrapolate enhancement and washout characteristics to further stratify adrenal incidentalomas. An additional goal is to understand our role to combat over-imaging, and how small steps, such as adrenal imaging, can help curb health care costs.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Adrenal nodules encompass numerous pathologies with differing enhancement and washout patterns. Adrenal adenomas demonstrate rapid enhancement with robust washout on 15-minute delayed images. Varying techniques trialing shorter delay times show decreased specificity and sensitivity; however, early delays shine with a high PPV to rule in a benign adenoma when relative washout is present. Pheochromocytomas demonstrate similar avid washout but have a unique tell: marked enhancement on portal venous phase imaging > 110–120 Hounsfield units. Brisk enhancement is seen with metastases, which often lack subsequent threshold washout. Numerous rare pathologies exist, including but not limited to ganglioneuroma, collision tumors, hemangiomas, and adrenal cortical carcinomas, which also yield unique enhancement patterns.

Adrenal incidentalomas are common, the majority of which are benign adenomas. An incidental adrenal nodule on a nondedicated CT with early delayed imaging and relative washout can confidently be called a benign adenoma. Applying the ACR whitepaper and understanding enhancement and washout characteristics afford the ability to accurately stratify incidentalomas.