Imaging techniques in the characterization of adrenal lesions.

Abstract

Radiol Bras. 2014 Nov/Dez;47(6):V–VI Currently, with the increasing utilization of sectional imaging methods, most adrenal masses are incidentally found during imaging investigation performed for other indications. Non-functional adenomas constitute the majority of incidentally found adrenal masses. However, the suprarenal gland is also a common site of metastasis and less frequently primary tumors including myelolipoma, pheochromocytoma, and adrenocortical carcinoma. The characterization of an adrenal lesion is critical for an appropriate management of the patient, and is fundamentally based either on the functional or non functional behavior of the lesion, in addition to its benign or malignant nature. Functional adrenal lesions may be symptomatic, with typical clinical and laboratory features, like in many cases of cortical adenomas and pheochromocytomas, which makes their characterization easier. The characterization of non functional adrenal lesions represents a major diagnostic challenge. Extensive lesions may cause symptoms, while smaller lesions are in general incidentally identified or found during staging procedures in cancer patients. In both situations, the characterization of the lesion is strongly based on imaging diagnosis techniques. Fortunately, the advances achieved in the last years allow for a definition of the nature of most adrenal lesions. Computed tomography (CT), magnetic resonance imaging (MRI) and nuclear medicine techniques, including positron emission tomography (PET), may be employed, and all of such techniques are clinically useful in the differentiation of such lesions. Stability is the simplest characteristic to be observed at imaging in order to define the nature of adrenal masses. The absence of growth determined by a simple analysis of previous images represents a consistent characteristic of benignity. The nature of an adrenal lesion is also related to its dimensions; lesions with < 4 cm in diameter tend to be benign, and those above 4 cm in diameter present higher risk for malignancy. CT and MRI techniques can also make the specific diagnosis of adenoma by taking advantage of the abundant amount of intracellular fat that is present in the majority of such lesions. In a pioneering study published in 1991, Lee et al. reported that the radiological attenuation at CT might effectively differentiate adrenal adenomas from non-adenomatous lesions. In a meta analysis, Boland et al. have demonstrated that, with a threshold of 10 Hounsfield units (HU), the test sensitivity for the diagnosis of adenoma would be 71%, and the specificity, 98%. In such a case,