The pituitary gland, often called the “master gland,” is a small, pea-sized structure located at the base of the brain that orchestrates the function of many other glands. A pituitary tumor is an abnormal growth of cells within this gland. Although these growths are nearly always non-cancerous, they can disrupt normal bodily function. Tumors cause problems in two primary ways: by producing excess hormones that destabilize the body’s balance or by growing large enough to press on nearby nerves and brain structures. Identifying the tumor is the first step toward effective management.
When Diagnostic Testing is Necessary
Diagnostic evaluation for a pituitary tumor typically begins when a patient reports specific, persistent symptoms suggesting a hormonal imbalance or pressure on surrounding structures. Symptoms related to hormone overproduction vary depending on the specific hormone involved. For example, excess prolactin may cause milky discharge or irregular menstrual periods in women, or decreased libido and erectile dysfunction in men. Other hormonal signs include unexplained weight changes, new-onset diabetes, or changes in facial features and the size of hands and feet, indicating issues with cortisol or growth hormone.
The second scenario involves symptoms related to the tumor’s physical size, known as a mass effect. These include persistent headaches or specific vision problems, signaling the tumor is pressing on adjacent nerves. Sometimes, a pituitary tumor is discovered incidentally during an unrelated brain imaging scan, prompting immediate follow-up.
Biochemical Analysis of Hormone Levels
The initial step in diagnosis is biochemical analysis, using blood and urine tests to determine if the tumor is “functional” (producing excess hormones) or “non-functional.” Testing measures baseline levels of hormones regulated by the pituitary gland, including Prolactin, Growth Hormone, Thyroid-Stimulating Hormone (TSH), and Adrenocorticotropic Hormone (ACTH). Elevated Prolactin often suggests a prolactinoma, the most common functional pituitary tumor.
Growth Hormone Testing
For tumors suspected of secreting Growth Hormone, doctors measure Insulin-like Growth Factor-1 (IGF-1). IGF-1 is a more stable indicator than Growth Hormone itself because its levels do not fluctuate throughout the day. If results are unclear, a dynamic test like the oral glucose tolerance test may confirm a diagnosis such as acromegaly. In this test, a healthy person’s Growth Hormone level should drop after consuming glucose, but a patient with an overproducing tumor fails to suppress the level.
ACTH and Other Hormones
Diagnosing Cushing’s disease, caused by an ACTH-secreting tumor, involves specialized testing, such as a 24-hour urine collection to measure cortisol or a low-dose dexamethasone suppression test. If the source of high ACTH is unclear, Inferior Petrosal Sinus Sampling (IPSS) may be performed. IPSS involves collecting blood samples directly from the veins draining the pituitary gland to localize the source of excess ACTH secretion. Testing also includes Gonadotropins (LH and FSH) and TSH to check for other functional tumors.
Structural Confirmation Through Imaging
Structural confirmation through imaging is the next step after hormonal abnormalities or mass-effect symptoms are identified. Magnetic Resonance Imaging (MRI) is the gold standard, providing superior soft tissue resolution for detailed visualization of the pituitary gland and surrounding brain structures. A dedicated pituitary MRI protocol uses thin-sliced images in both coronal and sagittal planes to optimally capture the gland.
To enhance visibility, a contrast agent, typically Gadolinium, is administered intravenously. The tumor often takes up the contrast differently than healthy tissue, helping to delineate its size, shape, and exact location. Tumor size is a key factor: those under 1 centimeter (cm) are microadenomas, and those 1 cm or larger are macroadenomas.
A Computed Tomography (CT) scan may be used if a patient cannot undergo an MRI due to a medical implant. However, CT scans are less effective at identifying smaller tumors because they offer less soft tissue detail. CT may be utilized to assess the bony structures around the pituitary, such as the sella turcica, or to help plan surgical approaches.
Evaluating Neurological and Visual Impact
Evaluating the tumor’s neurological and visual impact is essential, particularly for macroadenomas. This assessment is necessary because the optic chiasm, where the optic nerves cross, sits directly above the pituitary gland. A growing macroadenoma can press upward on this structure, causing specific patterns of vision loss.
The primary test is formal Visual Field Testing, also known as perimetry. This automated test checks the patient’s peripheral vision. The characteristic finding in pituitary compression is bitemporal hemianopsia—a loss of peripheral vision on the outer side of both eyes. Patients often do not notice this gradual loss until it is advanced.
A comprehensive neuro-ophthalmic exam checks other cranial nerve functions, especially if the tumor has extended laterally. The cavernous sinuses, located on either side of the pituitary, house nerves controlling eye movement. Compression or invasion of these sinuses can lead to double vision (diplopia) or drooping of the eyelid, requiring immediate attention.