Neuroendocrine Function

Many organs and organ systems in our body perform functions which are very important for our overall state of health. These organs are regulated by glands, which in turn, are controlled by hormones. Together, this whole process makes up what we refer to as the endocrine system. Neuroendocrinology refers to that part which has to do directly with the brain.

The pituitary gland is a pea-sized organ nested in a bony cavity below the base of the brain and above the nasal passages. This gland produces and stores many hormones which are essential to us. We only need a small amount of the hormones circulating in our bloodstream at any given time. Therefore, the pituitary gland, along with the hypothalamus, receive signals from our body to release a hormone and in this manner, a feedback system of communication occurs between the brain and certain organs, allowing normal body functioning. The functions of the hormones include control over growth and development, regulation of tissue activity and reproduction.

The hormones and their main function are listed below:

Hormone Name              | Function
__________________________|___________________________________________________
Growth Hormone (GH)       | · Stimulates body tissues regulating an
                          |   appropriate rate and amount of growth.
                          |
Adrenocorticotrophic      | · Acts on the adrenal glands which stimulate
Hormone (ACTH)            |   the production of steroids which are naturally
                          |   occurring and control metabolism.
                          |
Thyrotrophic Hormone (TH) | · Acts on the thyroid gland which regulates rate
                          |   of metabolism.
                          |
Prolactin                 | · Acts on the breasts' mammary glands to
                          |   produce milk.
                          |
Follicle-stimulating      | · Both act on reproductive organs.
Hormone (FSH)             |
Luteinizing Hormone (LH)  |
                          |
Melanocyte-Stimulating    | · Acts to control the skin's pigment.
Hormone (MSH)             |
                          |
Antidiuretic Hormone (ADH)| · Also called vasopressin; acts to regulate
                          |   the amount of urine we produce.
                          |
Oxytocin Hormone          | · Acts to stimulate contractions of the uterus
                          |   and assists in the production of milk.

Tumors may arise from the pituitary gland itself or they may grow close to the gland and cause pressure on it thereby altering its ability to work properly. In addition, radiation therapy may cause some damage to this sensitive gland. In both instances, careful monitoring of the pituitary gland's function will be an important part of your child's care. In most centres, there is a team of endocrine specialists (doctor, nurse and social worker) to follow your child, intervene as necessary, provide teaching and offer ongoing support. Not all of the hormones will be affected equally, and some not at all.

Depending on the nature of the problem, treatment will vary. If a tumor is causing pressure on the gland itself, simple removal may be all that is required. A tumor arising from the gland itself may require surgery and / or radiation. Drug therapy to replace or supplement hormones may be necessary, or alternatively, drug therapy may be required to suppress overproduction of hormones in certain instances.

Disorders of Growth

Some children with brain tumors will grow normally for a period of years with later failure of skeletal growth.

Small Stature

Short stature with a decreasing rate of growth is a common presenting symptom of some tumors such as craniopharyngiomas and other tumors that may damage the ability of the hypothalamus to regulate growth, or the ability of the pituitary gland to release growth hormone. A decreasing rate of growth is also common in young children who have received whole brain irradiation with or without chemotherapy. A pediatric endocrinologist is essential in the monitoring of your child's growth. Routine assessment of growth rates and growth hormone levels are appropriate in all children who have had a tumor involving the hypothalamus or pituitary gland area and who have had cranial radiation. Treatment with growth hormone may be appropriate for some children with short stature secondary to growth hormone deficiency.

You may want to discuss this with someone with expertise in the growth of children, such as a pediatric endocrinologist.

Gigantism

Rare pituitary tumors that secrete large amounts of growth hormone result in excessive growth and the development of gigantism. Treatment usually involves removal of the pituitary tumor and occasionally radiation therapy is used. Medical therapy which decreases the body's response to excessive growth hormone may also be instituted.

Occasionally, tumors which involve the hypothalamus may result in excessive growth.

Disorders of Sexual Development

Precocious Puberty

Certain hormones released from the pituitary gland control our reproductive systems and the onset of puberty. If an imbalance occurs, puberty may start earlier than one would expect or want and this is referred to as precocious puberty. In addition to the obvious stresses it will place on your child, puberty and overall growth need to be carefully watched. If a child goes through all of puberty too early, he/she may not grow to the height expected of a member of your family. You may wish to discuss treatment options with your physician.

Precocious puberty is suspected when there are signs of sexual development (body hair, breast development, menstruation and enlargement of scrotum) at an unusually early age. The process can be stopped until an appropriate time by the administration of medication.

Precocious puberty may develop for a number of reasons. It may be associated with tumors on or in the pituitary gland as well as with other brain tumors, hydrocephalus and children who have received radiation therapy.

Girls reach puberty at approximately 11 - 14 years while boys do so between 12 and 15.

Delayed Adolescence

Many tumors involving the nervous system are associated with delays in sexual development. These tumors usually involve the region of the pineal gland, hypothalamus and/or pituitary gland. There may be a delay in the onset of sexual development and/or the rate at which it progresses. (For example, delayed menstruation in females and lack of pubic hair in both sexes).

Careful monitoring of sexual development in children who have had brain tumors in the hypothalamic area appears prudent. The influence of whole brain radiation and chemotherapy on sexual development may vary, however, young children seem to be most at risk.

Weight Loss and Obesity

Weight Loss

It is not uncommon for patients with brain tumors presenting with nausea and vomiting to lose weight and appear emaciated. Weight loss and anorexia are also commonly associated with radiation therapy and chemotherapy. Some tumors involving the hypothalamus and the third ventricle may result in what is termed the diencephalic syndrome. The most obvious feature of this syndrome is the complete absence of fat beneath the skin, whether the child has a normal or increased appetite, cachexia (lack of appetite) or impaired growth. Treatment of this condition will depend on the control of the hypothalamic tumor.

Obesity

Steroids are commonly associated with increased appetite and significant weight gain which can usually be controlled by a decrease in steroid dosage. When an ACTH (adrenocorticotrophic hormone) secreting pituitary tumor is present, excessive steroid is produced and the patient may appear "Cushingoid" (excessive facial and abdominal obesity associated with excessive fat in the neck area). Treatment of the pituitary tumor usually deals with the problem. If certain areas of the hypothalamus which regulate appetite are damaged, the child may develop excessive appetite (hyperphagia) and severe obesity.

Other patients who have hypothalamic tumors develop an unequal distribution of body fat and obesity not associated with excessive appetite. The reasons for this are somewhat unclear and treatment is often unsatisfactory for both these types of obesity.

Summary

It is clear that lesions in the area of the hypothalamus and pituitary gland can result in a wide variety of conditions.

Medical interpretation of these conditions depends on a careful assessment of the hormones affected and the specific control area of the hypothalamus involved.

Further information is available from:

Pituitary Tumor Network Association,
38 S. Wendy Drive,
Newbury Park, CA 91320