A pituitary neuroendocrine tumor is a growth that develops in the pituitary gland, a pea-sized organ at the base of the brain. Often called the body’s “master gland,” it produces hormones that direct many processes, from growth and metabolism to reproductive function. These tumors account for about 15% of all growths within the skull.
Most of these tumors are benign, meaning they are not cancerous and tend to grow slowly. However, a benign tumor can still cause health issues depending on its size or whether it produces excess hormones. The change in name from “pituitary adenoma” to “pituitary neuroendocrine tumor” (PNET) reflects a more detailed understanding of their cellular origins.
Understanding Functional and Non-Functional Tumors
Pituitary neuroendocrine tumors are classified into two main categories: functional and non-functional. This classification is based on the tumor’s ability to secrete hormones, not its size. A functional tumor actively produces and releases excess hormones into the bloodstream, leading to hormonal imbalances throughout the body. The symptoms are directly related to the specific hormone being overproduced.
In contrast, non-functional tumors do not secrete hormones and cause problems by growing large enough to press on surrounding structures, a phenomenon known as the “mass effect.” These tumors are often discovered incidentally during brain imaging for unrelated issues.
Symptoms Caused by Hormone Imbalances
The symptoms of a functional pituitary tumor depend on which hormone it secretes in excessive amounts. Prolactin-secreting tumors, or prolactinomas, are the most prevalent type, accounting for about four out of ten pituitary tumors. In women, high prolactin levels disrupt the menstrual cycle, leading to irregular periods and a milky nipple discharge called galactorrhea. In men, it often leads to reduced libido and erectile dysfunction.
Tumors that secrete Adrenocorticotropic Hormone (ACTH) lead to Cushing’s disease. ACTH stimulates the adrenal glands to produce cortisol, and its overproduction results in weight gain in the face (“moon face”) and around the abdomen, while the arms and legs may thin. Other signs include high blood pressure, skin that bruises easily, and purplish stretch marks.
Another type of functional tumor produces excess growth hormone (GH). In adults, this condition is called acromegaly, causing a gradual enlargement of the hands, feet, and facial features. In children whose growth plates have not closed, a GH-secreting tumor can lead to gigantism.
Symptoms Caused by Tumor Pressure
When a pituitary tumor grows to a significant size, it can exert pressure on adjacent brain structures. This “mass effect” is responsible for symptoms unrelated to hormone production. A primary symptom is vision loss, which occurs as the tumor presses on the optic chiasm, where the optic nerves from both eyes cross.
This pressure causes a loss of peripheral vision, a condition known as bitemporal hemianopsia, which may cause patients to bump into objects. Headaches are another frequent symptom, often described as a persistent pain located behind the eyes or across the forehead.
A large tumor can also compress the healthy portion of the pituitary gland. This can disrupt normal hormone production and lead to a condition called hypopituitarism, causing symptoms like chronic fatigue, weakness, and weight loss.
The Diagnostic Process
Diagnosing a pituitary neuroendocrine tumor involves both hormonal analysis and brain imaging. The first step is measuring hormone levels to determine if a tumor is functional and which hormone it is overproducing. This is done with blood and urine tests that can detect abnormal levels of hormones like prolactin, ACTH, or growth hormone.
For instance, high prolactin levels are a strong indicator of a prolactinoma. Hormone testing can also reveal deficiencies caused by a large tumor compressing the gland.
The second part of diagnosis is imaging. A Magnetic Resonance Imaging (MRI) scan is the preferred method for visualizing the pituitary gland and any tumor. An MRI provides detailed images that confirm the tumor’s presence and show its precise size, shape, and location, which helps guide treatment decisions.
Primary Treatment Options
The treatment for a PNET is tailored to its type, size, and the symptoms it causes. For many functional tumors, medication is the first line of defense. Prolactinomas, for example, often respond well to dopamine agonist drugs, which lower prolactin levels and can shrink the tumor, often eliminating the need for surgery. Medications are also available to block the hormone production associated with Cushing’s disease and acromegaly.
When medication is not effective or for non-functional tumors causing pressure symptoms, surgery is recommended. The most common procedure is transsphenoidal surgery, where a surgeon accesses the pituitary gland through the nasal cavity and sphenoid sinus. This minimally invasive approach allows them to remove the tumor without an external incision on the face.
Radiation therapy is reserved for situations where surgery cannot remove the entire tumor or if it grows back. Techniques like stereotactic radiosurgery deliver a focused beam of radiation to the tumor while minimizing damage to surrounding healthy brain tissue. This can also be a primary treatment for patients who are not suitable for surgery.