Pituitary Gland Microadenoma
A pituitary microadenoma is a small, benign tumor of the pituitary gland measuring less than 10 millimeters in diameter. The pituitary gland, often called the “master gland,” sits at the base of the brain and controls many hormonal functions throughout the body. While microadenomas are common—found in approximately 10-15% of the population—most cause no symptoms and are discovered incidentally on brain imaging. Some microadenomas, however, produce excess hormones, leading to various endocrine disorders that require treatment.
What is it?
The pituitary gland is a pea-sized endocrine gland located in a small bony cavity called the sella turcica at the base of the skull, just behind the bridge of the nose. Despite its small size, this gland produces and secretes numerous hormones that regulate critical body functions including growth, metabolism, reproduction, stress response, and lactation. A microadenoma develops when cells within the pituitary gland undergo abnormal growth, forming a small tumor. By definition, microadenomas are less than 10 mm in diameter (tumors 10 mm or larger are called macroadenomas).
Pituitary microadenomas are classified based on their hormone production: functioning (secretory) adenomas produce excess amounts of specific hormones, while non-functioning (non-secretory) adenomas do not produce hormones or produce clinically insignificant amounts. Functioning microadenomas include prolactinomas (most common, producing prolactin), growth hormone-secreting adenomas (causing acromegaly or gigantism), ACTH-secreting adenomas (causing Cushing’s disease), TSH-secreting adenomas (very rare), and gonadotroph adenomas. The cause of pituitary adenomas is not fully understood, but most occur sporadically without a clear genetic component, though some rare genetic syndromes such as multiple endocrine neoplasia type 1 (MEN1) increase risk. Microadenomas are more commonly diagnosed in women and typically present in middle age, though they can occur at any age.
Important to Know
Non-functioning microadenomas typically cause no symptoms and are discovered incidentally on brain MRI performed for other reasons such as headaches or head trauma. These incidental findings, called “pituitary incidentalomas,” are very common and usually require only observation. Functioning microadenomas cause symptoms related to hormone overproduction: prolactinomas cause irregular or absent menstrual periods in women, infertility in both sexes, decreased libido, erectile dysfunction in men, and inappropriate breast milk production; growth hormone-secreting tumors cause gradual enlargement of hands, feet, and facial features in adults (acromegaly) or excessive growth in children (gigantism); ACTH-secreting tumors cause Cushing’s disease with weight gain (especially in the face and trunk), easy bruising, high blood pressure, diabetes, and mood changes. Diagnosis requires both imaging and hormonal evaluation. MRI with gadolinium contrast (specifically pituitary protocol MRI) is the gold standard for visualizing microadenomas, though small tumors can be challenging to detect. Blood tests measure pituitary hormone levels to identify functioning tumors. Treatment depends on tumor type and symptoms. Prolactinomas respond well to medication (dopamine agonists like cabergoline or bromocriptine), which shrinks the tumor and normalizes prolactin levels. Growth hormone and ACTH-secreting microadenomas typically require transsphenoidal surgery—a minimally invasive procedure performed through the nose to remove the tumor. Non-functioning microadenomas usually require only periodic MRI surveillance to ensure they’re not growing. The prognosis for pituitary microadenomas is generally excellent, with high cure rates for functioning tumors treated with surgery or medication, and most non-functioning tumors remaining stable indefinitely.