Adrenal Mass Characterization in the Era of Quantitative Imaging: State of the Art

Abstract

Detection and characterization of adrenal lesions have evolved during the past two decades. Although the role of imaging in adrenal lesions associated with hormonal secretion is usually straightforward, characterization of non-functioning adrenal lesions may be challenging to confidently identify those that need to be resected. Although many adrenal lesions can be readily diagnosed when they display typical imaging features, the diagnosis may be challenging for atypical lesions. Computed tomography (CT) remains the cornerstone of adrenal imaging, but other morphological or functional modalities can be used in combination to reach a diagnosis and avoid useless biopsy or surgery. Early- and delayed-phase contrast-enhanced CT images are essential for diagnosing lipid-poor adenoma. Ongoing studies are evaluating the capabilities of dual-energy CT to provide valid virtual non-contrast attenuation and iodine density measurements from contrast-enhanced examinations. Adrenal lesions with attenuation values between 10 and 30 Hounsfield units (HU) on unenhanced CT can be characterized by MRI when iodinated contrast material injection cannot be performed. 18F-FDG PET/CT helps differentiate between atypical benign and malignant adrenal lesions, with the adrenal-to-liver maximum standardized uptake value ratio being the most discriminative variable. Recent studies evaluating the capabilities of radiomics and artificial intelligence have shown encouraging results.

Machine Learning-Based Texture Analysis in the Characterization of Cortisol Secreting vs. Non-Secreting Adrenocortical Incidentalomas in CT Scan

“…In fact, through the HU measurement in the basal and post-contrast sequences, CT is capable of discriminating a lesion. Similarly, the chemical shift method in MR allows to obtain precise information on the adrenal masses (15,16). However, both of these methods lack sufficient diagnostic specificity and sensitivity in more than 30% of AIs.…”

Subtyping of Cushing’s Syndrome: A Step Ahead

“…glands show an attenuation close to the liver on CT and have homogeneous enhancement after contrast injection [87]. On unenhanced CT scan, adrenal adenomas are characterized by attenuation values lower than 10 Hounsfield Units (HU), secondary to a high lipid content [88].…”

Adrenal nodules for the non-specialist: What to look out for and when to refer

“…Adenomas typically exhibit rapid contrast washout, whereas non-adenomas have delayed contrast washout. 14,15 In patient without known extra-adrenal malignancy, an adrenal mass with a non-contrast density of <10 HU is unlikely to be malignant. 16 The maximum diameter of the adrenal nodule is predictive of malignancy, with the risks increasing in adrenal nodules measuring >4 cm.…”