Pituitary Adenoma

What Is It?

A pituitary adenoma is a benign tumor of the anterior pituitary gland. It is the most common pituitary tumor of the gland itself. Adenoma is a general term for a benign tumor of a secreting tissue. There is no known cause in most cases of these pituitary tumors.

The pituitary gland is a small structure that lies at the base of the brain. It works closely with the brain to aid in coordination of many aspects of endocrine (hormonal) function. It is vital to the normal functioning of metabolism and other glands such as the thyroid, adrenals, mammary, testes and ovaries and even aspects of kidney function. It is comprised of an anterior pituitary (known as the adenohypophysis) as well as a posterior pituitary (called the neurohypophysis). Pituitary adenomas always arise from the anterior part.

Pituitary adenomas vary greatly from one to the next. While many are simply a mass which grows in the pituitary, several types actually secrete pituitary hormones. Rather than secreting these hormones in a normal manner, they over secrete them so that there is an over abundance of that hormone in the body. This abnormal secretion can lead to very specific clinical syndromes related to that hormone. These syndromes are described briefly below but each have a separate page to describe them in more detail.

• Prolactinoma: A pituitary tumor which secretes the hormone prolactin.
• Growth Hormone Secreting Adenoma: A pituitary adenoma which secretes growth hormone. This can lead to the syndromes of Acromegaly andGigantism.
• Cushing's Disease: A pituitary adenoma which secretes the hormone adrenocorticotropic hormone (ACTH) which stimulates the adrenal gland to secrete cortisol.
• Nonsecreting Pituitary Adenoma (Endocrine Inactive Adenoma): A pituitary tumor which does not directly secrete any hormones.
• Pituitary tumors which secrete the other anterior pituitary hormones, thyroid stimulating hormone (TSH), leutinizing hormone (LH), and follicle stimulating hormone (FSH), are all very rare. TSH secreting tumors can lead to hyperthyroidism or over secretion of thyroid hormone from the thyroid gland. Secretion of either FSH or LH can lead to loss of normal menstrual cycles and infertility in women as well as impotence and infertility in men.

In addition to the secretion of hormones, as a pituitary adenoma grows it can cause damage to the normal pituitary gland adjacent to it so that the patient may develop pituitary insufficiency of one or more hormone. Finally, with any pituitary tumor, increased secretion of prolactin (hyperprolactinemia), a hormone important for the development of breast tissue (the mammary glands), can lead to abnormal menses in women or impotence in men.

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What Types of Symptoms Are Typical?

Presenting symptoms of pituitary tumors vary depending on the type of the tumor and its size.

Headaches: Any pituitary tumor can present with headaches.

Visual Loss: Any pituitary tumor which is large enough can cause compression of a part of the visual system in the brain which runs just above the pituitary gland. This compression can lead to loss of normal visual function which usually presents initially with loss of peripheral vision in both eyes (called homonymous hemianopsia). Some loss of visual acuity can occur as well and very large tumors that go untreated or expand quickly can lead to complete blindness. Some of this visual loss can be reversible with treatment of the tumor in some cases.

Hyperprolactinemia: Any pituitary tumor that gets big enough can interfere with the normal secretion of the hormone called prolactin. This leads to an increase in secretion of the hormone, although it does not typically get as high as from a secreting prolactinoma. This elevated prolactin can be asymptomatic but it can also cause abnormal reproductive function including loss of normal menstrual cycles in women and impotence in men. It can also lead to breast development and secretion of a milk-like substance from both men and women.

Hormone Syndromes: If a pituitary tumor secretes a hormone, additional symptoms related to that hormone can occur. For a more thorough description of those clinical syndromes, see the pages for acromegaly,gigantism, prolactinoma, and Cushing's disease.

Rarely, a pituitary adenoma can bleed suddenly (called pituitary apoplexy), causing a sudden enlargement in its size. This often leads to acute pituitary dysfunction as well as sudden loss of vision. This is generally considered a surgical emergency and most often leads to an emergent operation to remove the tumor and blood.

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How Is The Diagnosis Typically Made?

Patients present in various ways, depending on the type of tumor they have. However, after a neurological evaluation, a CT scan or MRI scan are usually ordered to detect the tumor. The appearance of a pituitary adenoma is generally regular enough to make the diagnosis with a good degree of accuracy just based on the MRI alone. However, some related tumors can be mistaken for a pituitary tumor. Some examples of these areRathke's cleft cyst, craniopharyngioma, meningiomas of the tuberculum sellae and diaphragma sellae.

To confirm the diagnosis, tumor tissue needs to be assessed by a pathologist in most cases.

In addition the the imaging studies described above, patients with pituitary tumors will usually undergo blood tests to assess their hormonal function. The purpose of these tests is to both look for any oversecretion of hormones associated with the tumor as well as to determine if the patient has any impaired function of normal pituitary gland function. In the case ofCushing's disease, some patients will undergo inferior petrosal sinus sampling (a special blood test done by a radiologist) to confirm and refine the diagnosis.

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What Are Some Common Treatments?

The majority of pituitary adenomas, particularly if the patient has symptoms, are treated by surgery. In most cases this involves a procedure called the transsphenoidal approach. This approach, through the nasal passages, is the most direct route to the area of the pituitary gland and is generally better tolerated with a quicker recovery than a craniotomy (opening the skull).

In patients who have loss of some normal pituitary function, they may require hormonal replacement therapy to prevent symptoms. For example, if the patient presents with low thyroid hormone, they may require treatment with synthetic thyroid hormone.

In a few cases of tumors which secrete hormones, medical therapy to control the tumor may be attempted. The most commonly used example of this is using drugs called dopamine agonists (bromocriptine and cabergoline are the most commonly used examples) in patients with prolactinoma. In some cases, this hormone will inhibit the tumor and can even cause the tumor to shrink on its own, preventing or delaying the need for surgery.

Each tumor and patient is different, so it is hard and inappropriate to make generalizations about what treatment plan is most appropriate. Each patient should discuss their options with their own physician team.