EP145 - ECE_2148 - Histopathological diagnosis of surgically treated indeterminate adrenal masses

Abstract

Adrenal incidentalomas are increasingly detected due to widespread use of advanced imaging modalities. Imaging evaluation plays a central role in assessing the risk of malignancy, with homogeneous, lipid-rich lesions (<10 Hounsfield units [HU] on unenhanced CT) considered benign. However, a substantial proportion of adrenal masses do not meet these criteria and are classified as indeterminate. Indeterminate adrenal masses are incidentally discovered lesions lacking definitive imaging or biochemical features of benignity or malignancy. While many are ultimately benign—most commonly lipid-poor adrenocortical adenomas—the differential diagnosis includes adrenocortical carcinoma and other rare malignant entities, posing a significant diagnostic challenge. To report histopathological diagnoses of surgically treated indeterminate adrenal masses and assess their relationship with preoperative imaging characteristics, including CT in all patients and MRI and/or FDG-PET, where available. We retrospectively identified patients who underwent adrenalectomy for indeterminate masses between 2022 and 2025. Patients with lesions showing clear features of malignancy (metastases, compatible biochemical findings, or known extra-adrenal primary malignancy) or diagnostic biochemical evidence of pheochromocytoma were excluded. Collected data included demographics, hormonal activity, imaging features and histopathological diagnosis. 32 patients were included (mean age 60.5 ± 12.4 years). Mean tumor size was 5.9 ± 3.2 cm (range 2.4-17 cm), with a mean unenhanced CT attenuation of 26.5 ± 9.7 HU. FDG-PET was available in 19 patients, with a mean SUVmax of 4.6 ± 2.0. Twenty patients (63%) had benign lesions: 16 lipid-poor adrenocortical adenomas, one black adenoma, one adrenal oncocytoma, two ganglioneuromas. Three patients had adrenocortical oncocytic neoplasms of uncertain malignant potential. Nine patients (28%) had malignant lesions: five adrenocortical carcinomas and four non-adrenocortical malignancies (metastasis, angiosarcoma, lymphoma, liposarcoma). Regarding hormonal activity, 12 patients exhibited mild autonomous cortisol secretion. Tumor size (5.4 vs 5.9 cm), unenhanced CT attenuation (26.4 vs 29.5 HU), and SUVmax (4.7 vs 6.7) did not differ significantly between benign and malignant lesions. Notably, no malignant lesion had unenhanced CT attenuation <20 HU, whereas five benign lesions and one of uncertain malignant potential did. Indeterminate adrenal masses represent a diagnostic challenge, encompassing a broad spectrum of benign and malignant conditions. Although additional imaging modalities may aid risk stratification, no single technique reliably establishes a definitive diagnosis, and significant overlap exists between benign and malignant lesions, including FDG-PET uptake. Consequently, final diagnosis often remains dependent on histopathological evaluation following surgery, underscoring the need for individualized, multidisciplinary diagnostic approach.