The pituitary gland regulates the function of numerous endocrine glands through the hormones it produces. A pituitary macroadenoma is a common, non-cancerous growth that develops within this small gland located at the base of the brain. When these tumors grow large, they can disrupt hormonal balance and compress surrounding neurological structures.
Anatomy and Definition of Macroadenomas
The pituitary gland rests in a small, bony pocket at the base of the skull called the sella turcica, which means “Turkish saddle.” Pituitary adenomas are classified by size, with a macroadenoma specifically defined as a tumor measuring greater than 10 millimeters, or one centimeter, in diameter. Tumors smaller than this threshold are categorized as microadenomas, which often remain confined within the sella turcica.
The designation of “macro” indicates a tumor’s increased size, which is significant because it is more likely to extend beyond the bony confines of the sella. These growths arise from the glandular tissue of the anterior pituitary lobe and are almost always benign, meaning they do not spread to other parts of the body.
Clinical Manifestations: Mass Effects and Hormonal Imbalances
Pituitary macroadenomas cause problems in two primary ways: mass effects and hormonal imbalances. As the tumor expands upward out of the sella turcica, it can exert pressure on the overlying optic chiasm, the structure where the optic nerves from both eyes cross. This compression frequently results in specific visual field deficits, most commonly a loss of peripheral vision known as bitemporal hemianopsia. Headaches are another common symptom associated with the increased pressure caused by the tumor mass.
Hormonal imbalance manifests as either an overproduction or an underproduction of pituitary hormones. Functional macroadenomas actively secrete excess hormones, leading to distinct clinical syndromes. Conversely, large tumors that do not secrete hormones, termed non-functional macroadenomas, are often discovered only after their mass effect causes hypopituitarism.
Functional Macroadenomas
A Prolactinoma overproduces prolactin, which can cause galactorrhea (unintended breast milk production) and hypogonadism, leading to irregular menstrual cycles in women and decreased libido in men. Excessive secretion of growth hormone (GH) causes acromegaly in adults, characterized by the enlargement of the hands, feet, and facial features. Adrenocorticotropic hormone (ACTH)-secreting tumors can lead to Cushing’s disease, involving symptoms like central weight gain, easy bruising, and muscle weakness due to high cortisol levels.
Identifying Macroadenomas: Diagnostic Procedures
The evaluation for a suspected macroadenoma combines specialized imaging and detailed laboratory analysis. Magnetic Resonance Imaging (MRI) is the preferred method for visualizing the tumor, providing precise images of its size, shape, and relationship to surrounding structures like the optic chiasm. Contrast dye is often administered during the MRI to enhance the visibility of the adenoma, helping to distinguish it from normal brain tissue.
Biochemical testing determines the tumor’s functional status and assesses the overall health of the pituitary gland. Blood tests measure the baseline levels of various pituitary hormones, including prolactin, growth hormone, ACTH, thyroid-stimulating hormone (TSH), and gonadotropins (LH and FSH). This hormonal panel identifies any excess hormone production and checks for signs of hypopituitarism.
Visual field testing is a necessary component of the diagnostic process, particularly when the macroadenoma extends above the sella turcica. This test accurately maps a patient’s field of vision to detect the subtle peripheral vision loss that often occurs with compression of the optic chiasm.
Management Strategies: Medical, Surgical, and Radiotherapy
The approach to managing a pituitary macroadenoma is highly individualized, determined by the tumor’s size, hormonal activity, and whether it is causing visual impairment.
Medical management is the first-line therapy for Prolactinomas, which are uniquely sensitive to certain medications. Dopamine agonists, such as cabergoline or bromocriptine, can effectively shrink the tumor and normalize prolactin levels, often avoiding the need for surgery.
For non-functional macroadenomas or those causing significant vision loss, surgical intervention is often the initial recommendation. The most common procedure is Transsphenoidal Surgery (TSS), where the surgeon accesses the pituitary gland through the nasal cavity and sphenoid sinus. This minimally invasive technique is designed to remove the tumor, relieve pressure on the optic chiasm, and preserve the surrounding normal pituitary tissue.
Radiotherapy, which includes techniques like stereotactic radiosurgery, is generally reserved for cases where the tumor cannot be completely removed surgically or when it continues to grow despite medical therapy. Radiation therapy delivers a focused dose of energy to the residual tumor tissue, aiming to stop its growth and decrease hormone production over time. A team of specialists, including endocrinologists and neurosurgeons, works together to tailor a treatment plan that offers the best chance for tumor control and preservation of neurological and endocrine function.