Adrenal lesion frequency: A prospective, cross-sectional CT study in a defined region, including systematic re-evaluation

Purpose: To prospectively estimate and validate the prevalence of incidentally detected adrenal lesions (adrenal incidentaloma) in patients with or without malignant disease undergoing CT. Material and Methods: During 18 months all adult patients with incidentally discovered adrenal lesions detected at CT were prospectively reported from the radiology departments of all hospitals in Western Sweden (1.66 million inhabitants). Frequencies of adrenal lesions initially reported at CT and at a systematic re-evaluation were compared. The interobserver variation in blindly assessing adrenal lesions was also analyzed. Results: Adrenal lesions were reported and verified in 339 patients (193 females; mean age 69 years, range 30-94 years). Mean lesion size was 25.8 mm (range 8-94 mm). The mean frequency of originally reported adrenal lesions was 0.9% (range 0-2.4% between hospitals). The systematic re-evaluation of 3801 randomly selected cases showed a mean frequency of 4.5% (range 1.8-7.1% between hospitals). The re-evaluation revealed 177 cases with adrenal lesions, 30% of these were submitted by the local radiologist in accordance with the study design, 23% were described in the local radiology report but not submitted to the study center, while 47% were neither locally reported nor submitted. Conclusion: Adrenal lesions are under-reported in clinical practice. Prevalence figures for adrenal incidentalomas should therefore be interpreted with caution, especially in multi-center settings.