A pituitary tumor is a growth that develops in the pituitary gland, a small gland located at the base of the brain that governs the body’s hormone production. These growths are almost always noncancerous, or benign, and are formally known as pituitary adenomas. The rate of growth varies significantly, depending primarily on the tumor’s cellular makeup and its ability to secrete hormones. Predicting the tumor’s behavior and determining the appropriate management strategy requires understanding its specific characteristics.
Understanding Growth Variability by Tumor Type
The growth rate is largely determined by whether the cells produce excess hormones, classifying the tumor as a functional or non-functional adenoma. Most pituitary tumors are slow-growing; one study showed an average annual volume increase of approximately 0.33 milliliters per year for untreated adenomas. This slow rate means many growths remain stable for years, with about three-quarters of conservatively managed tumors showing no measurable growth.
Size also distinguishes tumor behavior: microadenomas are less than one centimeter, while macroadenomas are one centimeter or larger. Macroadenomas are more likely to experience future growth than their smaller counterparts, enlarging more frequently at a rate of 12.5 per 100 patient-years compared to 3.3 per 100 patient-years for microadenomas. Non-functional adenomas do not secrete measurable hormones and are typically monitored until they cause symptoms due to their mass.
Functional tumors are often detected early because excess hormone production causes distinct symptoms, even when the tumor is small. Prolactinomas, the most common functional type, are typically slow-growing and highly responsive to medication. These growths often shrink quickly and significantly with medical therapy. In contrast, a small fraction of tumors, such as the rare pituitary carcinomas, can be aggressive and grow rapidly, sometimes defined as a size increase of more than 20% over six months.
Methods for Tracking Tumor Progression
Clinicians monitor tumor progression using diagnostic tools to assess both size and function over time. Magnetic Resonance Imaging (MRI) is the primary method for tracking physical changes and measuring the growth rate of the tumor. Providers perform serial imaging, often every six months to a year, to measure the tumor’s volume and diameter. Comparing these measurements over time provides the objective data necessary to calculate the growth velocity.
For tumors that produce hormones, blood tests are an important component of monitoring. Hormonal levels are measured periodically to determine if the tumor’s secretory activity is increasing, which may signal a need for intervention. For example, tracking prolactin levels monitors prolactinomas, indicating tumor activity even before a significant size change is visible on a scan.
Clinical symptoms, particularly changes in vision, serve as a key indicator of growth, especially for macroadenomas. These larger tumors may compress the optic chiasm, potentially causing a loss of peripheral vision. Worsening visual field tests or new symptoms like severe headaches prompt an urgent reassessment of the tumor’s stability.
Treatment Decisions Based on Growth Rate
The determined growth rate is a primary factor directing the management strategy. For tumors that are small, non-functional, and show a stable or very slow growth rate, a strategy of watchful waiting is often employed. This approach involves rigorous, regular monitoring with periodic imaging and clinical assessments instead of immediate active treatment.
Medical Management
If a tumor is functional, such as a prolactinoma, the decision is guided less by physical growth and more by hormonal control. These tumors are highly susceptible to dopamine agonist medications, which lower hormone levels and often cause the tumor to shrink substantially. This effectively controls growth without the need for surgery. For other secreting tumors, like those causing acromegaly, medication may suppress hormone production, sometimes used before surgery or to manage residual disease.
Radiation Therapy
A moderate but steady growth rate, or growth causing persistent, non-urgent symptoms, may lead to the consideration of radiation therapy. Radiation is highly effective at controlling tumor growth over the long term, often achieving control rates exceeding 90% in many clinical series. This option is typically reserved for residual tumors after surgery or for those that do not respond to medical therapy.
Surgical Intervention
Rapid growth, or any growth causing urgent symptoms such as acute visual impairment, typically necessitates immediate surgical intervention. The goal of surgery, often performed through the nose, is to remove as much of the growth as possible. This relieves pressure on nearby structures and prevents permanent damage. The growth rate thus shifts management from a conservative, observational approach to an urgent, interventional one.