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The incidental adrenal mass on CT: prevalence of adrenal disease in 1,049 consecutive adrenal masses in patients with no known malignancy
Song JH, Chaudhry FS, Mayo-Smith WW
Department of Diagnostic Imaging, Rhode Island Hospital and Warren Alpert Medical School of Brown University, Providence, RI, USA
AJR, Am J Roentgenol 2008; 190: 1163-1168

• Purpose: The purpose of our study was to determine the nature and prevalence of adrenal lesions identified on CT in patients with no known malignancy.
• Materials and Methods: A computer search of abdominal CT reports using the term “adrenal” was performed in 65,231 consecutive patients with examinations performed from January 2000 to December 2003. An adrenal mass was identified in 3,307 (5%) patients. Patients with no known malignancy and no suspicion for a hyperfunctioning adrenal mass were further isolated. Nine hundred seventy-three patients with 1,049 adrenal masses fulfilled the study criteria. The nature of each lesion was determined by histopathology; imaging characterization with CT, MRI, or washout; a minimum of 1 year of stability on follow-up imaging; or clinical follow-up of at least 2 years.
• Results: One thousand forty-nine adrenal masses were characterized with the following methods: histopathology (n = 12), imaging characterization (n = 909), imaging follow-up (n = 87), and clinical follow-up (n = 41). There were 788 adenomas constituting 75% of all lesions. There were 68 myelolipomas (6%), 47 hematomas (4%), and 13 cysts (1%). Three pheochromocytomas (0.3%) and one cortisol-producing adenoma (0.1%) were found incidentally. One hundred twenty-eight lesions (12%) were presumed to be benign by imaging or clinical stability. No malignant adrenal masses were found, even among the 14 patients who later developed malignancy elsewhere.
• Conclusions: In 973 consecutive patients with an incidental adrenal mass and no history of cancer, no malignant lesions were identified. Adenomas (75%) and myelolipomas (6%) were the most common lesions.
  
  
• Editorial Comment
  The authors report very large retrospective study regarding the prevalence of adrenal incidentalomas on CT studies performed in patients without cancer. Actually this publication encompasses a larger number of patients when compared with previous study published by the same authors where all of the incidentally detected adrenal masses with a CT attenuation of equal or less than 10 HU were benign (1). Adrenal incidentalomas were classified almost exclusively by classical and well known imaging criteria (unenhanced and enhanced CT studies and chemical-shift MR imaging). Although the authors reports that only 1% of the adrenal masses of this large series was histological evaluated , their criteria has been proved to be effective by other large series where histological confirmation were obtained(2,3). As radiologic experience accumulates, the tendency to accept strict and specific imaging features for adequate characterization of adrenal adenomas continues to grow. Large series with histological confirmation, large number of patients without histological confirmation but with prolonged clinical and radiological follow-up continues to strength the role of imaging features in the evaluation of adrenal adenomas. In many centers, radiologic characterization of adrenal adenomas is accepted similarly to the radiologic characterization of other adrenal incidentalomas such as cysts, pseudocysts, hematomas and mielolipomas .Small, < 3 cm in diameter, homogeneous and well defined adrenal mass with CT attenuation of equal or less than 10 HU or showing more than 20% of loss of signal intensity on chemical-shit MR imaging should be considered as an adrenal adenoma.

References
1. Song JH et al. The incidental indeterminate adrenal mass on CT (> 10 H) in patients without cancer: is further imaging necessary? Follow-up of 321 consecutive indeterminate adrenal masses. AJR Am J Roentgenol. 2007; 189: 1119-23.
2. Kloos RT, et al. Incidentaly discovered adrenal masses. Endocr Rev. 1995; 16: 460-84.
3. Boland GW, et al. Characterization of adrenal masses using unenhanced CT: an analysis of the CT literature. AJR Am J Roentgenol. 1998; 171: 201-4.

Dr. Adilson Prando
Chief, Department of Radiology and
Diagnostic Imaging
Vera Cruz Hospital
Campinas, São Paulo, Brazil
E-mail: aprando@mpc.com.br