The adrenal glands are small, triangular-shaped organs situated atop each kidney. These glands play a vital role in the endocrine system, producing hormones that regulate metabolism, blood pressure, and the body’s stress response. An adrenal nodule is an abnormal growth or lump that develops on an adrenal gland.
What Are Adrenal Nodules?
Adrenal nodules are frequently discovered incidentally during imaging tests, such as CT or MRI scans, performed for unrelated medical reasons. These growths are often called “incidentalomas” because their detection is accidental.
A primary distinction for adrenal nodules is whether they are “functional” or “non-functional.” Functional nodules produce excess hormones, leading to various symptoms and health issues, depending on the specific hormone involved. In contrast, non-functional nodules do not secrete hormones in excessive amounts.
Another important classification is whether a nodule is “benign” (non-cancerous) or “malignant” (cancerous). The vast majority of adrenal nodules are benign and non-functional, meaning they do not produce excess hormones and are not cancerous.
Benign Adrenal Nodule Causes
Benign causes account for most adrenal nodules found. Adrenal adenomas are the most common type of non-cancerous adrenal growth. These typically slow-growing masses originate from the adrenal cortex and generally do not spread to other parts of the body.
Adrenal adenomas can be either non-functional or functional. Most adenomas are non-functional, meaning they do not produce excess hormones and often cause no symptoms, requiring only monitoring.
However, functional adenomas can lead to conditions resulting from hormone overproduction. For instance, an adenoma producing too much cortisol can cause Cushing’s syndrome, characterized by symptoms such as weight gain, high blood pressure, and muscle weakness. Similarly, an adenoma overproducing aldosterone can lead to primary aldosteronism, also known as Conn’s syndrome, which is associated with severe high blood pressure and low potassium levels.
Adrenal hyperplasia is another benign cause of adrenal nodules, involving an enlargement or overgrowth of the adrenal gland tissue. This overgrowth can appear as a distinct nodule or as a more diffuse thickening of the gland. It can affect one or both adrenal glands. Like functional adenomas, hyperplasia can sometimes result in the overproduction of hormones, leading to hormonal imbalances.
Malignant and Less Common Causes
While less frequent, some adrenal nodules are malignant or represent other serious conditions. Pheochromocytoma is a rare tumor that arises from the adrenal medulla, the inner part of the adrenal gland. These tumors produce excessive amounts of catecholamines, such as adrenaline and noradrenaline, which can cause symptoms like sudden spikes in blood pressure, headaches, rapid heartbeats, and profuse sweating. Most pheochromocytomas are benign, but their hormonal activity necessitates careful management due to the potential for severe cardiovascular complications.
Adrenocortical carcinoma (ACC) is a rare but aggressive form of cancer originating in the adrenal cortex. ACCs can be either functional, producing excess hormones, or non-functional. These cancerous nodules often present as larger masses and tend to grow more rapidly than benign lesions.
Nodules on the adrenal glands can also signify metastatic disease, meaning cancer cells have spread from a primary tumor located elsewhere in the body. Cancers from sites such as the lungs, kidneys, breast, colon, and melanoma are known to metastasize to the adrenal glands.