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Background
Incidental adrenal masses are not uncommon in the adult population, occurring in 3 - 7% of adults. By comparison, however, incidental adrenal lesions in the pediatric population are rare. The rate of detection of incidental adrenal lesions is increasing due to a combination of increasing frequency of diagnostic radiology examinations as well as improving spatial resolution on imaging. Even in patients with a known history of malignancy, an incidentally detected adrenal mass in an adult is statistically most likely to be benign. Having a step-wise approach to the interpretation of adrenal lesions as well as knowing the next most appropriate imaging modality is important for practice. Over-investigation of adrenal masses can lead to heightened anxiety for patients and can at times be wasteful of resources.

Educational Goals / Teaching Points
Adrenal lesions, when detected incidentally, may be difficult to diagnose on the index study. Multi-modality imaging may be needed in their work-up. This exhibit aims to provide a review of typical imaging features. It also outlines important caveats to be aware of when interpreting multiphasic imaging. Further imaging and interpretation should take the patient’s history into account, including any history of malignancy and current clinical features. Some adrenal lesions including functional adenomas and pheochromocytomas may be clinically quiescent at the time of imaging and therefore imaging and clinical features may be discordant. Biochemical correlation may contribute.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Features reassuring of benignity include the presence of macroscopic fat, attenuation value of less than/equal to 10 HU and signal loss on opposed phase MR sequences. A growing lesion and the size of the lesion, among other features, are important discriminators for malignant potential. Lesions more than 4 cm should generally be considered suspicious for malignancy. Caution is needed when interpreting multiphase CT adrenal studies. A not insignificant proportion of pheochromocytomas (approximately 30%) may demonstrate absolute percentage washout (APW) of more than 60% (2). If a lesion has HU more than 120 on either portal venous or delayed phase imaging, regardless of washout values, pheochromocytoma remains in the differential. Some hypervascular adrenal metastases, including from renal cell carcinoma (RCC) or hepatocellular carcinoma (HCC) primary, can demonstrate an APW of more than 60%. Conventional imaging cannot distinguish between functioning and non-functioning adenomas. Therefore, reporting terminology is important and lesions should not be dismissed as they may be clinically relevant. Nuclear medicine studies, for example metaiodobenzylguanidine labelled to iodine-123 (MIBG I-123) are important for diagnosing neural crest tumors such as neuroblastoma or pheochromocytoma and can also identify sites of metastatic disease.

Conclusion
Incidental adrenal lesions are not uncommon in adult patients, although are less frequent in pediatrics. Recognition of "don’t touch"’ lesions and knowing when and how to further investigate adrenal lesions is important in day-to-day practice.