Atypical Imaging Findings in a Cortisol-producing Adrenal Adenoma Predominantly Composed of Lipid-poor Compact Cells

Cortisol-producing adrenal adenomas consist of a mixture of lipid-rich clear and lipid-poor compact cells in varying proportions. Most adenomas are mainly composed of lipid-rich clear cells and typically exhibit low computed tomography (CT) attenuation values, high uptake on ¹³¹I-adosterol scintigraphy, and mild accumulation on ¹⁸F-fluorodeoxyglucose positron emission tomography/CT. However, adenomas predominantly composed of lipid-poor compact cells are rare, with limited evidence regarding their imaging characteristics. A 27-year-old woman with weight gain and a moon face was referred to our hospital. She presented with hypertension, dyslipidemia, low plasma ACTH levels, and autonomous cortisol secretion. We diagnosed this patient with ACTH-independent Cushing syndrome with a left adrenal tumor. The adrenal tumor exhibited imaging findings atypical for an adenoma, including high CT attenuation values, negative uptake on ¹³¹I-adosterol scintigraphy, and strong accumulation on ¹⁸F-fluorodeoxyglucose positron emission tomography/CT. Histopathological analysis indicated that the tumor was a rare type of adenoma, predominantly composed of lipid-poor compact cells. These findings and recent reports suggest that the proportion of compact cells can influence the imaging findings. Therefore, in the differential diagnosis, it is important to recognize that cortisol-producing adrenal adenomas predominantly composed of compact cells can present with atypical imaging findings.