The pituitary gland, often called the “master gland,” is a small, pea-sized organ located at the base of the brain. It regulates numerous bodily functions by producing and releasing hormones that control other glands, including the thyroid and adrenals. These hormones govern processes such as growth, metabolism, reproduction, and the body’s response to stress. Like other tissues, the pituitary gland can develop abnormal growths, broadly classified as pituitary tumors. Their significance depends on their biological nature and location within the skull base.
The Classification: Adenoma vs. Carcinoma
Pituitary tumors are classified into two primary categories: adenoma and carcinoma. The vast majority are non-cancerous pituitary adenomas. These benign tumors do not spread to other parts of the body. Pituitary carcinoma, the malignant form, is exceedingly rare, estimated to be between 0.1% and 0.4% of all pituitary tumors. A tumor is definitively diagnosed as a carcinoma only when there is proof of metastasis to other areas of the brain or distant organs like the bone or liver. Most patients are diagnosed with the benign adenoma type. While typically slow-growing, some adenomas may demonstrate aggressive behavior, recurring or growing rapidly. These aggressive tumors, though not cancerous, present a significant management challenge due to their persistent growth despite treatment.
Impact of Non-Cancerous Pituitary Tumors
Even though most pituitary tumors are benign adenomas, they are medically significant because they cause substantial health problems. These issues stem from two main factors: hormonal disruption and the physical pressure they exert on surrounding structures. The pituitary gland is enclosed in a bony cavity, meaning that any growth in this confined space can quickly cause symptoms.
Functional Tumors
Tumors that produce an excess of hormones are known as functional or secretory tumors. Symptoms depend on the specific hormone being overproduced. For example, a prolactin-secreting tumor (prolactinoma) can cause unexpected milk production and menstrual irregularities in women, or reduced testosterone levels in men. Other functional tumors secrete growth hormone, leading to acromegaly in adults, characterized by the abnormal growth of hands, feet, and facial features. Tumors secreting adrenocorticotropic hormone (ACTH) cause Cushing’s disease, resulting in weight gain, high blood pressure, and muscle weakness. These hormone imbalances require careful management to prevent long-term complications.
Non-Functional Tumors
Tumors that do not produce excess hormones are called non-functioning or non-secretory adenomas. These tumors cause problems primarily through a “mass effect” as they grow larger, often exceeding 10 millimeters in size (macroadenomas). The most serious consequence of this growth is pressure on the optic chiasm, where the optic nerves cross. Compression of this structure results in visual impairment, typically affecting peripheral or side vision. Large tumors can also cause persistent headaches or damage the normal pituitary tissue, leading to a deficiency in other necessary hormones.
Detection and Management Strategies
Diagnosing a pituitary tumor involves a combination of imaging and laboratory workup. Magnetic resonance imaging (MRI) of the brain is the preferred method for visualizing the tumor, detailing its size, location, and proximity to surrounding structures. Computed tomography (CT) scans may be used if MRI is contraindicated, but they offer less soft tissue detail. Blood tests measure hormone levels to determine if the tumor is functional and which hormone is being overproduced. For tumors pressing on the optic chiasm, visual field testing checks for peripheral vision loss. This comprehensive evaluation provides the necessary information for specialists to plan treatment.
Management strategies are tailored to the tumor type, size, and patient effects. For prolactinomas, initial treatment is often medication, such as cabergoline, which can shrink the tumor and normalize hormone levels, often allowing patients to avoid surgery. For most other symptomatic pituitary adenomas, surgical removal is the primary treatment. The most common procedure is transsphenoidal surgery, where the surgeon accesses the pituitary gland through the nasal passages and the sphenoid sinus. This technique is minimally invasive, avoids cutting into the skull, and results in a faster recovery. If the tumor cannot be entirely removed or regrows after surgery, radiation therapy may be used to stop the remaining cells from multiplying.