A microadenoma is a small, typically non-cancerous growth that develops in the pituitary gland. These tumors are defined by their size, measuring less than 10 millimeters (or 1 centimeter) in diameter. Microadenomas are quite common and are often discovered incidentally during imaging tests performed for other health concerns. They are a type of pituitary adenoma.
Understanding the Pituitary Gland
The pituitary gland, often called the “master gland,” is a small, pea-sized organ located at the base of the brain. This gland plays a central role in the endocrine system, producing and regulating hormones that control various bodily functions. It controls processes such as growth, metabolism, blood pressure regulation, and reproduction. The pituitary sends signals to other glands, including the thyroid, adrenal glands, and reproductive organs, to produce their own hormones.
How Microadenomas Cause Symptoms
Microadenomas can lead to symptoms primarily through two mechanisms: by overproducing hormones or, less commonly due to their small size, by pressing on nearby structures. Many microadenomas are “functioning” tumors, meaning they secrete excessive amounts of specific hormones. Symptoms depend on which hormone is being overproduced.
One common type is a prolactin-producing microadenoma, known as a prolactinoma. In women, this can cause irregular menstrual periods or their absence, infertility, and milky discharge from the breasts not related to pregnancy. Men might experience decreased libido, erectile dysfunction, and sometimes enlarged breast tissue.
Growth hormone-producing microadenomas can lead to acromegaly in adults, characterized by the enlargement of hands and feet, changes in facial features, and joint pain. In children, excessive growth hormone causes gigantism, resulting in rapid growth and unusual height.
Another type, an ACTH-producing microadenoma, causes Cushing’s disease. Symptoms include unexplained weight gain, particularly in the face and torso, high blood pressure, muscle weakness, and easy bruising. Purple stretch marks are also common.
Thyroid-stimulating hormone (TSH)-producing microadenomas are rare but can lead to hyperthyroidism. Symptoms include rapid heart rate, unintentional weight loss, nervousness, and increased sweating.
While uncommon for microadenomas due to their small size, a tumor could grow large enough to exert pressure on adjacent brain structures. If a microadenoma presses on the optic nerves, it might lead to vision problems, blurred vision or peripheral vision loss. This mass effect is more characteristic of larger pituitary tumors (macroadenomas).
Identifying and Treating Microadenomas
Diagnosis typically involves assessing symptoms and a physical examination. Blood tests measure hormone levels, indicating if a functioning microadenoma is present. For instance, elevated prolactin levels suggest a prolactinoma.
Imaging techniques, particularly Magnetic Resonance Imaging (MRI), are essential for visualizing the pituitary gland and detecting small tumors. An MRI can pinpoint the microadenoma’s exact size and location.
Treatment options for microadenomas vary by tumor size, hormone production, and symptom severity. For asymptomatic, non-functioning microadenomas, a “watchful waiting” approach with regular monitoring may be recommended, involving periodic MRI scans to track tumor growth.
Medication is often the first-line treatment for certain functioning microadenomas, especially prolactinomas. Dopamine agonists, such as cabergoline, can effectively shrink these tumors and normalize prolactin levels, managing hormone overproduction and reducing symptoms.
Surgery is a common and effective treatment for symptomatic microadenomas, particularly those producing growth hormone or ACTH, or if medication is ineffective. Transsphenoidal surgery, a minimally invasive procedure performed through the nasal passages, allows surgeons to access the pituitary gland without opening the skull, minimizing recovery time and complications.
Radiation therapy is a secondary treatment option, reserved for cases where surgery is not feasible, unsuccessful, or if the tumor recurs. This therapy uses targeted radiation beams to destroy tumor cells. While effective, full hormonal effects may take time, and it is less common for microadenomas compared to larger tumors.