The adrenal glands are small, triangular-shaped organs situated atop each kidney, forming part of the endocrine system. They produce hormones like cortisol, aldosterone, and adrenaline, which regulate metabolism, blood pressure, and the body’s stress response. An adrenal nodule, or adrenal mass, is an abnormal lump or growth of tissue that develops within the gland. Most masses are discovered unintentionally during imaging scans (CT or MRI) performed for unrelated reasons, a finding medically termed an adrenal “incidentaloma.” Adrenal nodules become more common as people age, with an estimated prevalence of up to 4% in the adult population.
The Most Common Cause: Benign Non-Functional Nodules
The overwhelming majority of adrenal nodules are benign and are primarily classified as adrenocortical adenomas. These adenomas arise from the outer layer of the gland, the cortex. They are considered “non-functional” because they do not produce enough excess hormones to disrupt the body’s balance or cause symptoms, making them the most frequent finding among incidentalomas.
Adrenocortical adenomas often contain high amounts of intracellular fat, allowing physicians to identify them as benign using specialized imaging techniques. Because these nodules are typically harmless, they usually do not require surgical removal. The standard medical approach involves periodic surveillance with follow-up imaging and biochemical testing to monitor for significant growth or the development of hormone overproduction.
Nodules That Cause Symptoms: Hormone Overproduction
A smaller percentage of adrenal nodules are classified as “functional” because they secrete excessive amounts of hormones, leading to recognizable health syndromes. The specific hormone being overproduced dictates the patient’s symptoms and the resulting medical condition. Although often benign, these functional nodules can cause significant health issues due to the hormonal imbalances they create.
One common functional nodule causes Cushing’s Syndrome, resulting from the overproduction of cortisol. This excess cortisol leads to symptoms including central weight gain, a rounded face, easy bruising, and purple stretch marks. Another condition is Conn’s Syndrome (primary aldosteronism), where a nodule secretes too much aldosterone. This excess hormone causes the body to retain sodium and lose potassium, resulting in difficult-to-control high blood pressure and muscle weakness.
Nodules originating in the inner part of the gland, the adrenal medulla, can cause a condition called pheochromocytoma. These tumors secrete excessive catecholamines, such as adrenaline and noradrenaline. Symptoms are often episodic, including severe headache, profuse sweating, and a rapid heartbeat, frequently accompanied by dangerously high blood pressure. Although most are benign, pheochromocytomas require specialized medical management before surgical removal due to the risk of a life-threatening hypertensive crisis.
Structural and Non-Tumor Origins
Not all adrenal masses are traditional adenomas or carcinomas; some are distinct structural lesions. Myelolipomas are one example, consisting of a benign mixture of mature fat cells and blood-forming (hematopoietic) tissue. These tumors generally do not produce hormones, but they can grow quite large, sometimes exceeding ten centimeters, causing symptoms like abdominal pain or pressure.
Adrenal cysts are another type of non-tumor mass, characterized as fluid-filled sacs that are almost always benign. They can be simple fluid collections or complex pseudocysts that form following hemorrhage or inflammation.
Nodular hyperplasia is a different cause, involving an abnormal enlargement of the entire adrenal gland, sometimes appearing as multiple small nodules. Hyperplasia can affect one or both glands and may be a non-tumor cause of hormone excess, such as primary aldosteronism.
When Adrenal Nodules Are Malignant
The primary concern when an adrenal nodule is discovered is the possibility of malignancy, although this is rare, especially for incidentalomas. Malignant adrenal masses fall into two main categories: primary tumors that originate in the gland, and secondary tumors that have spread from elsewhere.
The most common primary adrenal cancer is adrenocortical carcinoma (ACC), an aggressive and rare malignancy. ACC arises from the adrenal cortex and can be either functional (causing rapid onset of Cushing’s syndrome symptoms) or non-functional. Because of its aggressive nature, a nodule is viewed with higher suspicion if it is large (typically over four to six centimeters) or displays irregular features on imaging.
Secondary cancers, or metastases, are significantly more common in the adrenal glands than primary ACC, especially in patients with a known history of cancer. The adrenal glands are a common site for the spread of tumors originating in other organs, frequently including the lung, breast, kidney, and melanoma. For a patient with a known malignancy, an adrenal nodule is highly likely to be a metastatic lesion and is managed based on the primary cancer’s type and stage.