The adrenal glands are situated over the top of each kidney. Adrenal adenomas are benign (non-cancerous) tumours of the adrenal gland. They arise from the outer layer of the gland, called the adrenal cortex. The adrenal cortex normally makes hormones that belong to the steroid family. If an adrenal adenoma produces hormones, it is called 'functioning', though this term makes them sound healthy when in fact such adenomas often produce excessive amounts of steroid hormones. If an adenoma does not produce a hormone it is termed 'non-functioning'. Adrenal adenomas are often found by chance during a scan of the body for an unrelated condition. However, all adrenal masses (lumps) need careful evaluation to ascertain their nature, especially to see whether they are producing hormones.
The majority of adrenal adenomas are "nonfunctioning", which means they do not produce hormones and usually do not cause any symptoms. They are often found incidentally during imaging studies of the abdomen, in which case they are referred to as adrenal incidentalomas. However, some can become "functioning" or "active" and secrete excess hormones. Depending on the type of hormone released, adrenal tumors can cause a variety of conditions, including Cushing's syndrome, primary aldosteronism, or much less commonly, virilization.
Cushing's syndrome, also called hypercortisolism (having abnormally high levels of cortisol), is caused by adrenal adenomas that release excess levels of the hormone cortisol. Common symptoms of Cushing's syndrome can include upper body obesity; severe fatigue and muscle weakness; high blood pressure; backache; high blood sugar; easy bruising; and bluish-red stretch marks on the skin. Affected women may have increased growth of facial and body hair, and menstrual periods may become irregular or stop completely. Mild hypercortisolism without any obvious symptoms, called subclinical Cushing's syndrome, is common in people with an adrenal incidentaloma, although glucose intolerance and hypertension may be present in these cases.
Primary aldosteronism (also called Conn syndrome) is a condition in which the adrenal gland produces too much of the hormone aldosterone. This hormone is responsible for balancing the levels of sodium and potassium in the blood. Symptoms of this condition may include high blood pressure, fatigue, headache, muscle weakness, numbness and paralysis that comes and goes.
Benign cortisol-secreting adenomas can also produce small amounts of androgens (steroid hormones, such as testosterone), although androgen levels in the blood are usually not elevated. Excess amounts of androgens can cause an increase in masculine characteristics (virilization) such as increased facial and body hair (hirsutism); deepening of the voice; increased muscularity; and other characteristics.
The cause of adrenal adenomas is unknown, but the current accepted theory is that they arise because of mutations (changes) in certain genes (which are not yet identified). Adrenal adenomas are more common in some inherited diseases, including multiple endocrine neoplasia type I, Beckwith-Wiedemann syndrome and the Carney complex. Also, patients with genetic defects of the body systems that manufacture steroid hormones (eg congenital adrenal hyperplasia), especially those whose condition is poorly controlled, may have a higher risk of adrenal adenomas. However, most adrenal adenomas are not linked with an inherited disease. The likelihood of developing an adenoma increases with age. Benign adrenal adenomas are found in 1 to 32 per cent of people at autopsy, with most studies showing a detection rate of about 5 per cent. About 6 per cent of patients over 60 years of age harbour an adrenal adenoma. No other predisposing factors have been defined, and prevention is not possible.
Most adrenal adenomas are not inherited. They usually occur sporadically in people with no family history of tumors. However, in rare cases, they can occur in people with certain genetic syndromes such as multiple endocrine neoplasia, type 1 (MEN1) and familial adenomatous polyposis (FAP). Both of these conditions are inherited in an autosomal dominant manner.
Most adrenal adenomas are discovered by chance when an abdominal computed-tomography (CT) or magnetic-resonance imaging (MRI) scan is done for unrelated symptoms. Studies have found that CT scanning identifies a so-called incidental adrenal lump in about 0.3 to 11 per cent of people. As many as 80 per cent of people with such masses will have a benign non-functioning adenoma. Some people may also need a biopsy of the tumor to confirm the diagnosis. Laboratory tests that evaluate the levels of certain hormones in the blood or urine can be used to determine if the adrenal adenoma is functional or nonfunctional.
The long-term outlook for people with adenomas of the adrenal gland is usually excellent. Although adrenal adenomas that are functional (releasing hormones) can cause other medical problems such as primary aldosteronism and Cushing's syndrome, these conditions usually respond well to treatment with medications and/or surgery. Nonfunctional adrenal adenomas typically do not cause any problems and rarely require treatment.
The treatment of a functioning adenoma is to remove the affected adrenal gland surgically (adrenalectomy). In some hospitals, a laparoscopic (keyhole) adrenalectomy may be offered to the patient, but it has not been established whether this surgical method is better than standard surgery. Any adrenal lump with characteristics on the MRI scan that make its nature uncertain (eg larger than 3cm, or with evidence of bleeding or degeneration) should be removed to exclude adrenal cancer. Adrenal lumps that are not producing hormones and that have the scan appearance of a benign cortical adenoma (including size less than 3cm) can be monitored by scanning at yearly intervals to ensure nothing is changing. The risks of having an adrenalectomy are similar to those of other abdominal surgery, including the risks of having a general anaesthetic. Sometimes the spleen, situated in the abdomen under the left lung, has to be removed during the operation. Since the spleen is needed for fighting certain bacterial infections, doctors routinely vaccinate patients against the more dangerous bacteria - the pneumococci (which cause lobar pneumonia) and meningococci (which cause bacterial meningitis) - if they are going to have the left adrenal gland removed.