The unexpected discovery of an adrenal nodule, often termed an adrenal incidentaloma, on a computed tomography (CT) or magnetic resonance imaging (MRI) scan can cause significant anxiety. This finding occurs because modern, highly sensitive imaging techniques are frequently used for reasons unrelated to the adrenal glands. Managing this concern involves assessing two primary factors: whether the nodule is overproducing hormones and whether it shows characteristics suspicious for cancer.
What Are Adrenal Glands and Nodules
The adrenal glands are small, triangular organs situated atop each kidney, playing a profound role in regulating various bodily functions. They are composed of two distinct parts: the outer cortex and the inner medulla. The cortex produces steroid hormones like cortisol and aldosterone, which manage metabolism, blood pressure, and the stress response. The medulla generates catecholamines such as adrenaline and noradrenaline.
An adrenal nodule, or incidentaloma, is an adrenal mass greater than one centimeter in diameter found during an imaging study performed for a different medical reason. Prevalence increases with age, detected in up to 4% of abdominal CT scans and 7% of individuals over 70. The vast majority of these nodules are benign, non-functional growths called adenomas, but their presence warrants evaluation to rule out the small percentage that can be problematic.
Determining if the Nodule is Hormonally Active
The first major clinical concern is determining if the nodule is producing hormones in excess, even without obvious symptoms. A hormonally active mass can lead to health issues, including high blood pressure, diabetes, and bone loss, and requires treatment regardless of its size or appearance. Standard screening involves laboratory tests to check for overproduction of the three main adrenal hormones: cortisol, aldosterone, and catecholamines.
Cortisol excess, even at a mild or subclinical level, is screened for using a low-dose dexamethasone suppression test. This test involves taking dexamethasone late in the evening, followed by a blood test the next morning to check for suppressed cortisol production. Failure to suppress suggests autonomous cortisol secretion, a condition that can have negative long-term health effects.
To check for a nodule producing excess catecholamines, which indicates a pheochromocytoma, a 24-hour urine collection or a plasma test for fractionated metanephrines is performed. Pheochromocytomas, though rare, can cause severe and episodic hypertension, headaches, sweating, and heart palpitations, and must be identified before surgery. Patients with hypertension or low potassium levels are screened for aldosterone overproduction, which causes Conn’s syndrome, using the aldosterone-to-renin ratio (ARR).
Assessing the Likelihood of Cancer
The second concern is the possibility of cancer, such as adrenocortical carcinoma or a metastasis. Although the risk is low, as most incidentalomas are benign adenomas, a detailed analysis of the nodule’s structural characteristics on imaging is necessary. Radiologists use specific CT measurements to differentiate benign lesions from suspicious ones.
The most informative measurement is the nodule’s density on a non-contrast CT scan, expressed in Hounsfield units (HU). Benign adenomas contain high intracellular fat, causing them to appear dark, or hypodense, with a measurement of 10 HU or less. A reading below this threshold strongly indicates a benign lesion and usually requires no further imaging.
Nodules greater than 10 HU are classified as lipid-poor and require additional evaluation because their density overlaps with malignant lesions. For these indeterminate masses, a contrast-enhanced CT scan with “wash-out” protocols is often used. Benign adenomas rapidly lose the contrast dye, showing an absolute wash-out of 60% or more, while malignant tumors tend to retain the contrast longer.
Another factor in cancer assessment is the nodule’s size, with 4 centimeters (cm) being a key threshold. Nodules less than 4 cm carry a low risk of cancer. Masses larger than 6 cm have a significantly higher probability of malignancy. These size and density criteria, combined with the patient’s medical history, determine the overall risk profile.
Monitoring and Management Protocols
Once the initial hormonal and structural assessments are complete, the management plan follows one of two main pathways: surveillance or intervention. For small nodules (less than 4 cm) that are non-functional and demonstrate benign imaging characteristics, active surveillance is recommended. This involves repeating hormonal screening and a follow-up imaging study, such as a CT or MRI, at 6 to 12 months after discovery.
If the nodule shows no significant growth and remains non-functional at the one-year mark, the risk of it becoming problematic is extremely low, and follow-up frequency can be reduced. Long-term surveillance detects delayed hormonal activity or unexpected size increases. The other pathway is surgical intervention, or adrenalectomy.
Surgery is recommended for any mass that is hormonally active, regardless of size, to prevent complications associated with hormone excess. Intervention is also indicated for nodules suspicious for cancer, including those larger than 4 cm with indeterminate imaging features or any mass showing rapid growth during surveillance. A multidisciplinary team of endocrinologists and surgeons uses these specific criteria to create a personalized management strategy.