Pituitary Tumors

     In most instances, tumors of the pituitary gland are not like other tumors. Tumors of the the breast and lung, for example, spread to many parts of the body  (metastasize) and kill many thousands of people each year. Pituitary tumors, on the other hand, are almost always benign tumors.

     This distinction being made, pituitary tumors (or pituitary adenomas) can cause serious health problems. These problems can be understood if one recognizes that for the most part pituitary adenomas cause problems by  three mechanisms:

                                    1)    where they are

                                    2)   what they produce

                                    3)   what endocrine functions are disturbed

Where they are:    too much tumor and not enough space

     The pituitary gland is normally contained within a  defined space, but there is only a limited amount of room on all sides of the gland.  Pituitary tumors can cause symptoms when the tumor grows to a point where it presses on one or more important structures that surround it. If it grows upward (toward the top of the head), it can damage portions of the optic nerves, causing a loss of vision that limits lateral peripheral vision. 

     Figure 1   This diagram shows one of the principal problems caused by an expanding mass within the pituitary foss (sella): pressure on the optic nerves and/or optic chiasm. This pressure causes degeneration of the nerves and loss of vision. When the pressure occurs on the optic chiasm, vision deteriorates first in the areas of lateral gaze. Untreated (that is, with continued tumor growth), the vision loss is usually progressive. If treated successfully the progressive loss of vision can be halted, and some of the visual field defects may resolve.

What they produce:   syndromes caused by excessive hormone production 

         Normally, the pituitary produces six different  hormones. These hormones are secreted by five distinct cell types.

                      Cell type                                    Hormone

                     Mammotrope                                 Prolactin

                     Somatotrope                                  Growth hormone

                     Thyrotrope                                    Thyroid stimulating hormone

                     Gonadotrope                                 Follicle stimulating hormone

                     Gonadotrope                                 Leutinizing hormone

                     Corticotrope                                 Adrenocorticotropic hormone

       Three major clinical syndromes can be caused by the production of excess hormones by a pituitary tumor, as shown below.

               Cell type                   Hormone                                           Disease

           Mammotrope                  Prolactin                                             Amenorrhea/Galactorrhea

            Somatotrope                 Growth hormone                                 Acromegaly

            Corticotrope                 Adrenocorticotropic hormone              Cushing's Disease 

          In approximately 20% of tumors, there is no apparent excess hormone production and the tumor is referred to as a 'non-secretory' pituitary adenoma. The management of these tumors is dictated by the mass effects caused by the size of the tumor (predominantly those related to vision or overall pituitary function).

What endocrine functions are disturbed

        The pressure exerted by the tumor upon the normal pituitary can cause a gradual decline in the production of the hormones that are normally secreted by the pituitary gland to maintain health. If such deficiencies are clinically apparent, affected patients may present with significant degrees of hypogonadism, adrenal insufficiency, or hypothyroidism. Some degree of pituitary function may be regained following treatment of the tumor by surgery or by medical therapy, but such deficiencies may need to be treated with hormone replacement long-term.

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