An aldosteronoma is a benign tumor that forms within an endocrine gland and leads to a condition known as primary hyperaldosteronism. This tumor causes the gland to produce and release an inappropriate, excessive amount of a hormone into the bloodstream. The resulting hormonal imbalance classifies the condition as primary hyperaldosteronism, often historically referred to as Conn’s syndrome. This overproduction is autonomous, meaning it occurs independently of the body’s normal regulatory signals.
The Affected Gland: Location and Structure
The gland affected by an aldosteronoma is the adrenal gland, a small, triangular-shaped organ located directly on top of each kidney. Each adrenal gland is composed of an outer layer, the cortex, and an inner core, the medulla. The cortex is responsible for producing steroid hormones and is further divided into three zones. The tumor originates in the outermost layer, which is called the zona glomerulosa. This specific zone is the main site for the synthesis and secretion of mineralocorticoid hormones, primarily aldosterone.
Understanding Aldosterone Overproduction
Aldosterone’s normal role is maintaining the body’s balance of electrolytes and fluid volume. It acts on the distal nephron in the kidneys, prompting the reabsorption of sodium back into the blood while simultaneously promoting the excretion of potassium into the urine. This sodium retention also causes water retention, which helps regulate blood volume and, consequently, blood pressure. When an aldosteronoma forms, it secretes aldosterone at a high, unregulated rate, overriding the body’s feedback mechanisms. This chronic, unsuppressed overproduction results in a high level of aldosterone in the blood, disrupting the delicate balance of sodium and potassium.
Common Physical Effects of Hyperaldosteronism
The most common and clinically significant effect of this hormonal excess is refractory hypertension, which is high blood pressure that is difficult to control even with the use of multiple medications. The increased fluid volume resulting from chronic sodium and water retention places a persistent strain on the cardiovascular system, raising systemic blood pressure. Patients with primary hyperaldosteronism are also at a heightened risk for serious health issues, including stroke, heart attack, and kidney damage, compared to those with other forms of hypertension.
Another significant manifestation is hypokalemia, or abnormally low potassium levels in the blood, resulting from the excessive urinary excretion driven by the hormone overload. While not all patients experience hypokalemia, those who do often suffer from symptoms like profound fatigue, muscle weakness, and cramping. Severe potassium depletion can also cause increased urination, excessive thirst, and temporary muscle paralysis. The chronic mineralocorticoid excess can also lead to metabolic alkalosis.
Diagnostic Confirmation and Treatment Options
Diagnosis of primary hyperaldosteronism typically begins by measuring the ratio of aldosterone to renin in the blood. A high aldosterone-to-renin ratio suggests that the excess aldosterone is being produced autonomously by the adrenal gland, rather than being a response to a signal from the kidneys. If the screening test is positive, confirmatory tests are performed, such as a saline infusion test, followed by imaging like a CT or MRI scan to visualize the adrenal glands and localize the adenoma. To definitively determine if the tumor is the sole source of the hormone excess, a specialized procedure called adrenal venous sampling (AVS) may be performed to compare aldosterone levels in the veins draining each adrenal gland.
Treatment options are determined by whether the overproduction is unilateral, caused by a single aldosteronoma, or bilateral, affecting both glands. For a unilateral aldosteronoma, the preferred treatment is a laparoscopic adrenalectomy, which is the surgical removal of the affected adrenal gland. This procedure can normalize potassium levels and potentially cure the hypertension in about one-third of patients, while significantly improving blood pressure control for others. If the condition affects both adrenal glands, or if a patient is not a candidate for surgery, medical management is the standard approach. This involves the use of mineralocorticoid receptor antagonists, such as spironolactone or eplerenone, which directly block the action of aldosterone on the kidneys.