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Incidentalomas, unsuspected adrenal tumors that are encountered during radiographic testing done for unrelated causes, are among the most common solid organ tumors in humans. This classification carries a very broad differential diagnosis (Table 12-1) and spans the spectrum of aggressiveness in tumors. Although most incidentalomas are benign and require no intervention, adrenocortical cancer (ACC) is among the most aggressive cancers in humans. Moreover, a significant subset of incidentalomas is hormonally functional, and although these tumors are histologically benign, failure to diagnose and treat patients with these tumors results in increased morbidity and may risk mortality.

Table 12-1. The Most Common Incidentally Found Adrenal Tumors and Their Relative Frequencies in the Literature

With the increasing use of cross-sectional, sonographic, and other imaging technologies, incidentalomas are likely to be diagnosed even more frequently in the future. After they have been identified, these tumors must be characterized as benign or malignant (and if malignant, as primary vs. metastatic) and as hypersecretory or nonhypersecretory. Because the majority of incidentalomas are ultimately managed nonsurgically, their increasing incidence and their follow-up are likely to become an even more important diagnostic, logistic, financial, and therapeutic challenge for individual practitioners and for our health care system. This chapter discusses the prevalence, differential diagnosis, and diagnostic and therapeutic strategies of these fascinating tumors.

First described in the early 1980s,1 the term incidentaloma refers to all clinically unapparent adrenal tumors that are incidentally discovered during imaging studies that are done for other causes. Tumors that are discovered during the initial assessment or follow-up of patients with nonadrenal malignancies are excluded from this definition. Similarly, large adrenal tumors that are symptomatic because of mass effect are also excluded. The reported prevalence of these tumors ranges from 0.35% to 5%2 and is affected by the sensitivity of the radiologic examination that is being used and the inclusion criteria of patients. Thin-cut helical computed tomography (CT) scanning and high-resolution magnetic resonance imaging (MRI) can now identify subcentimeter adrenal lesions that were previously undetectable. Moreover, studies that include many elderly patients or patients with symptoms that can retrospectively be attributed to their adrenal masses report a higher frequency of incidentalomas and have a higher frequency of malignant or metastatic tumors in the adrenal gland.

Similar to the variation seen in the prevalence reported by radiologic tests, autopsy data are also inconsistent. Depending on inclusion criteria, the reported prevalence of adrenal tumors is between 1.05%3 and 32%.4 Autopsies of hypertensive patients reveal an ...

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