The incidence of clinically inapparent and incidentally discovered adrenal masses, called adrenal incidentalomas, has increased dramatically over the last two decades as a result of the widespread use of abdominal imaging devices including ultrasound, computed tomography (CT), and magnetic resonance imaging. The clinical characteristics of adrenal incidentalomas are rarely reported in Taiwan. The aim of the current study was to assess the morphological characteristics and subclinical endocrine hyperfunction of adrenal incidentalomas in a regional teaching hospital in Taiwan.

This retrospective study included patients with a diagnosis of incidentally detected adrenal tumors in medical records from 2019 to 2023. Patients with a diagnosis of malignancy were excluded. Clinical data and morphological characteristics of imaging studies were assessed.

Eighty patients (41 men and 39 women) were included in the study. The mean age was 63.6 ± 9.5 years (range 37.3 -78.6 years). The mean size of the adrenal incidentalomas on CT at diagnosis was 2.0 ± 1.3 cm (range 0.8 – 9.4 cm) and incidentalomas of size > 4 cm were detected in five patients (6.3%).The Hounsfield units (HU) of the unenhanced CT was < 10 in 50 % of incidentalomas, and > 20 in 28.8% of incidentalomas. Among 26 patients with observation time greater than three years, six (23.1%) had an increase in incidentaloma size of > 0.2 cm. Five of these six adrenal tumors has an unenhanced HU > 10 (Figure 1). Forty-five patients received 1mg dexamethasone suppression test, while sixteen patients (35.6%) were non-suppressible and considered to have mild autonomous cortisol secretion. Four patients received operations, and histological diagnosis revealed adrenocortical adenoma in 2 patients, endothelial cyst in 1 patient, and ganglioneuroma in 1 patient.

In patients without underlying malignancy,the malignant potential is low in adrenal incidentalomas even with large tumor size. Adrenal adenomas with HU > 10 appeared more likely to increase in tumor size. Studies with longer observation period are warranted to investigate the natural course of adrenal incidentalomas.