The Lateralizing Asymmetry of Adrenal Adenomas.

CONTEXT: It is presumed that the incidence of adrenal adenomas is symmetric between the left and right adrenal gland; however, anecdotal observations suggest a potential lateralizing asymmetry. OBJECTIVE: To investigate the symmetry in detection of adrenal adenomas and relevance to patient care. DESIGN: Cross-sectional and longitudinal studies. POPULATION AND SETTING: One thousand three hundred seventy-six patients with abdominal computed tomography or magnetic resonance imaging demonstrating benign-appearing adrenal adenomas. MAIN OUTCOME: Location and size of adrenal adenomas. RESULTS: Left-sided adenomas were discovered in 65% of patients, right-sided in 21%, and bilateral adenomas in 14%. Among unilateral adenomas, 75% were left-sided. Left-sided adenomas were more prevalent than right-sided adenomas in each size category except the largest: <10 mm, 87%; 10 to 19 mm, 74%; 20 to 29 mm, 72%; ≥30 mm, 56% (P < 0.0001 for each category, except P = 0.19 when ≥30 mm). Among those with bilateral adenomas, the left-sided adenoma was significantly larger than the right one in 61% of patients (P < 0.001). There were no significant differences in the baseline prevalence or incidence of cardiometabolic diseases between patients with left-sided vs right-sided adenomas during 5.10 (4.2) years of follow-up. CONCLUSIONS: Adrenal adenomas are substantially more likely to be identified on the left adrenal than the right. This observation may be due to detection bias attributed to the location of the right adrenal, which may preclude identification of right-sided adenomas until they are substantially larger. These findings suggest the potential for an underrecognition of right-sided adenomas that may also impair the accurate detection of bilateral adrenal diseases.