Cortisol Secreting Adenoma – Subclinical Cushing’s Syndrome (SCS). These lesions are characterized by autonomous glucocorticoid production without specific signs and symptoms of Cushing’s syndrome (CS), a condition termed subclinical hypercortisolism (SCS). This syndrome is the most frequent endocrine dysfunction detected in patients with adrenal incidentalomas, accounting from 5 to 20 % of all cases. Clinical signs and symptoms range from small increment of diurnal cortisol rhythm to occurrence of complications. This syndrome is reported to be closely associated with cardiologic and metabolic diseases such as hypertension, insulin resistance, glucose and lipid metabolic disorders, obesity (cluster metabolic syndrome), and osteoporosis [8].

Aldosteronoma . Aldosterone secreting adenoma manifests as Conn’s disease. The possible clinical manifestation that may be found in AI Conn’s disease is mild hypertension, even if hypokalemia, nocturia, polyuria, muscle cramps, palpitations may occur. In some cases patients with Conn’s disease on adrenal incidentaloma are totally asymptomatic even when hormonal tests are positive [4].

Sex hormone secreting cortical adrenal tumor . Sex hormone secreting tumors are rare. In the vast majority of cases, mainly in female patients, symptoms may include light and atypical hyperandrogenism: deepening of the voice, acne, hirsutism.

Primary adrenocortical carcinoma . Primary adrenocortical carcinoma (ACC) is rare and extremely malignant tumor. Among patients with AI, its prevalence is estimated to be about 4 %: with increasing risk in case of large tumors. As an example, ACC represents 2 % of all AIs ≤ 4 cm in size, 6 % of those 4–6 cm and up to 25 % of tumors > 6 cm [3, 8]. Primary adrenocortical carcinoma can be functional (about two/third of the cases) or non-functional. The clinical manifestation involves light symptoms related to adrenal hypersecretion, such as hypercortisolism (more common), as well as high sex hormones or aldosterone hypersecretion. Hormonally inactive masses (usually the larger ones) may present with abdominal discomfort or back pain.

Pheochromocytoma . Classically, clinicians report that only a quarter of pheochromocytomas are detected ante mortem, the remnant are found on post mortem as most patients die due to cardiovascular complication even before pheochromocytoma was diagnosed. Clinically, symptoms include history of hypertension with pathognomonic pheochromocytoma triad, including headache, perspiration, and palpitation, which make it possible to be detected. On the other side, such triad symptoms rarely noticed and it is missed by the clinicians due to its paroxysmal quality and considered as a common discomfort. Approximately 10–40 % of pheochromocytoma on adrenal incidentaloma is asymptomatic and it is called sub clinical pheochromocytoma. Whilst the vast majority of them are sporadic (about 86 %), the remainder are associated with familial syndromes, such as neurofibromatosis type 1, von Hippel-Lindau syndrome, multiple endocrine neoplasia type 1 (MEN1) and 2 (MEN2) and the pheo/paraganglioma syndromes. This should be kept in mind when a relative of a patient with one of these syndromes is evaluated for an adrenal mass. Finally, the risk to have a malignant pheo is not trivial (10 %) and distant metastases can be found during radiological evaluations [6, 8].

Other adrenal masses . These include myelolipoma, cyst and ganglioneuroma; however, they are rare and no typical or characteristic symptom is found. Adrenal is a common site of metastases, mainly due to breast, lung and kidney cancer, melanoma and lymphoma. These lesions, when incidentally found, are generally asymptomatic.

Ultrasonography . The reliability of ultrasonography (US) depends largely on operator skill, patient habitus and adrenal lesion size: obesity and overlying gas are frequent obstacles for visualization of the adrenal glands, moreover lesions < 3 cm are not visible with US. Ultrasonography is not able to differentiate benignant and malignant lesions but has a good reliability in evaluating mass size and its growth during follow up [8, 9].

CT . Most abdominal and chest CT scans leading to the unexpected discovery of an adrenal mass are obtained without the use of current technical recommendations for an optimal CT study of the adrenal glands, i.e. analysis on contiguous 3–5 mm-thick CT slices, preferentially on multiple sections using multidetector row protocols. In those cases, it may be helpful to perform an additional CT scan specifically aimed for the study of the adrenal glands. The size and radiological features of an adrenal mass on unenhanced CT may lead to a differentiation between benign and malignant lesions. Four cm cut off seems to be the most reliable one to diagnose malignancy but it has a very low specificity (Fig. 9.1). Inhomogeneous lesion with irregular border and presence of necrotic area generally illustrate a malignancy whilst infiltration of the neighbour tissues clearly indicates a malignant lesion. Density of the lesion may distinguish benign from malignant lesion as mass with density < 10 HU are more likely benignant, tumor with density >10 HU on unenhanced CT are considered indeterminate and required further for characterization. Enhanced CT may further help in characterization of adrenal mass. The percentage washout on delayed images contributes to the differentiation between adenomas and malignant adrenal masses. The ‘washout’– decreases more quickly in adenomas than malignant masses. A 10–15 min delay after administration of contrast medium was shared by several authors. Loss of 50 % or more of the attenuation value on delayed CT is specific for adenoma, whereas less than 50 % washout is indicative of malignant lesions or atypical adenoma. Others suggest a threshold washout of 60 % [1, 3, 8].

MRI . The differentiation between benign and malignant masses was based both on the findings from chemical shift both on the signal intensities of conventional techniques. Chemical shift imaging relies on the different resonance frequencies of protons in water and triglyceride molecules and, therefore, may permit a more specific diagnosis of adrenal adenomas that contain abundant lipids (Fig. 9.2) [3, 8]. Today there is no evidence about the superiority of MRI on CT in the characterization of the adrenal masses, and in the clinical practice MRI studies are indicated after a CT study only in very selected cases.