A pituitary adenoma is a slow-growing, noncancerous growth that develops on the pituitary gland, a small structure situated at the base of the brain. This gland produces and regulates many of the body’s hormones, controlling functions like growth, metabolism, and reproduction. Nonfunctioning pituitary adenomas (NFPAs) do not over-secrete hormones in a way that causes a specific hormone-excess syndrome, such as Cushing’s disease or acromegaly. This lack of hormonal overproduction distinguishes them from “functioning” counterparts. NFPAs create issues primarily through their physical size and presence, rather than chemical imbalance.
Understanding Nonfunctioning Pituitary Adenomas
These tumors originate from the cells of the anterior pituitary gland but do not release biologically active hormones in excess. Although immunohistochemistry may reveal specific cell types, this rarely translates into clinical hormonal hypersecretion. Because they do not cause symptoms of hormone excess, NFPAs often grow quite large before discovery.
Adenomas are categorized by size: microadenomas measure less than one centimeter, and macroadenomas measure more than one centimeter in diameter. Macroadenomas are most frequently diagnosed in the nonfunctioning category because their size eventually causes symptoms. The problems associated with an NFPA arise from the mass effect, where the growing tumor compresses nearby structures within the skull.
Recognizing Symptoms Caused by Tumor Growth
The most common complaints leading to an NFPA diagnosis are directly related to the tumor’s physical growth. As a macroadenoma expands upward out of the sella turcica—the bony socket housing the pituitary gland—it frequently presses on the optic chiasm. Compression of the optic chiasm, where the optic nerves from both eyes cross, typically leads to a specific form of vision loss.
This visual impairment often manifests as bitemporal hemianopsia, a gradual loss of peripheral vision in the outer half of both visual fields. Patients may not notice this loss until it is advanced because the brain adapts to the deficit, making early changes difficult to detect. Headaches are another common mass effect symptom, sometimes resulting from the tumor stretching the surrounding membrane or increasing pressure within the skull.
A growing adenoma can also compress the normal, hormone-producing tissue of the pituitary gland, leading to hypopituitarism. This results in deficiencies in one or more pituitary hormones, causing nonspecific symptoms like fatigue, weight changes, cold intolerance, and decreased sex drive. In men, this may cause low testosterone, leading to erectile dysfunction or loss of body hair. In premenopausal women, it can cause irregular or absent menstrual periods.
The Diagnostic Process
Investigation typically begins when a patient reports vision loss or persistent headaches. The primary tool for confirming the tumor’s presence, size, and location is Magnetic Resonance Imaging (MRI) of the brain and pituitary region. MRI provides detailed pictures that help clinicians determine the adenoma’s extent and its proximity to critical structures like the optic chiasm.
To evaluate the impact on vision, a formal ophthalmological assessment, including visual field testing, is performed. This test accurately maps the patient’s field of vision to check for the characteristic peripheral vision loss caused by optic chiasm compression. A comprehensive endocrine evaluation is also performed to confirm the nonfunctioning status and check for hormone deficiencies.
Blood tests measure the levels of various pituitary hormones, such as thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and sex hormones (luteinizing hormone and follicle-stimulating hormone). These tests check for hypopituitarism and confirm the tumor is not causing clinical hypersecretion of a hormone, justifying the nonfunctioning classification. The combined results from imaging, visual testing, and laboratory work establish the diagnosis and inform the treatment plan.
Primary Treatment Strategies
Treatment is determined by the tumor’s size, growth rate, and whether it is causing symptoms, particularly vision loss. For small, asymptomatic adenomas (microadenomas), a strategy of observation, or watchful waiting, is often employed. This involves regular follow-up with MRI scans and visual field tests to monitor the tumor for enlargement or changes to vision.
When the tumor causes visual impairment, significant mass effect symptoms, or is growing rapidly, surgical removal is the standard first-line treatment. The most common procedure is transsphenoidal surgery, which accesses the pituitary gland through the nasal cavity and the sphenoid sinus. This minimally invasive approach allows for adenoma removal while avoiding the need to open the skull.
The goal of surgery is to decompress the optic chiasm and relieve mass effect symptoms, often leading to improved vision and headaches. If the tumor cannot be completely removed due to its size or proximity to surrounding structures, or if it regrows after surgery, radiation therapy may be recommended. Stereotactic radiosurgery delivers focused, high-dose radiation to the remaining tumor tissue over one or several sessions to halt growth.
Long-Term Monitoring and Outlook
Following initial treatment, patients require long-term surveillance to monitor for tumor recurrence or regrowth. This involves regular follow-up MRI scans, typically performed annually for several years and then spaced out if the tumor remains stable. The risk of recurrence is significant, with regrowth occurring in a considerable percentage of patients over many years, making lifelong monitoring necessary.
Managing hormone deficiencies present before treatment or developed afterward is a major part of post-treatment care. Hypopituitarism requires hormone replacement therapy to restore normal body function. Patients may need medication to replace deficient thyroid, adrenal, or sex hormones, ensuring a good quality of life despite changes caused by the adenoma or its treatment.