Pituitary adenoma
Description
Pituitary adenomas are benign tumors that arise from cells of the pituitary gland (hypophysis). Women are slightly more likely to be affected by this disease than men. This type of tumor is classified according to size as either macroadenoma (> 1 cm) or microadenoma (<1 cm). Adenomas are further categorized, depending on whether or not they produce hormones, into hormone-secreting (endocrine) or non-hormone-secreting (null cell). So we can distinguish, for example, between prolactinoma (prolactin hormone-secreting), somatotropin (growth hormone-secreting), corticotroph (adrenal cortex-stimulating) and gonadotropic (gonadal-stimulating) adenomas.
Symptoms and Ailments
General symptoms are headaches and restricted vision caused by disruption of the visual field (bitemporal hemianopia). Hormonally inactive pituitary adenomas (incidentalomas) may at first have no specific perceivable symptoms and so are often only discovered late. Occurrences of hormone deficiency are also typical here. Anemia, fatigue, lethargy, menstrual disorders, libido and sexual disorders, constipation or symptoms of hypothyroidism (underactive thyroid) can also occur. Endocrine pituitary adenomas have a very specific set of symptoms and side effects due to the action of the respective hormone that is over-produced. Prolactin can cause galactorrhea and menstrual disorders or loss of libido. Somattropin (growth hormone) can lead to acromegaly and gigantism. ACTH-producing adenoma may cause Cushing's disease. Pituitary adenomas can also be found as a result of multiple endocrine neoplasia type 1 (MEN-1 syndrome), a hereditary genetic disease resulting from tumors in various glands of the body. In case of failure of the posterior pituitary lobe, diabetes insipidus can occur, in which the body loses large amounts of fluid through the kidneys (polyuria and polydipsia).
Causes and Risks
The causes of the development of pituitary adenomas are largely unclear or insufficiently explored. However, studies point to a probable relationship between multiple endocrine neoplasia type 1 (MEN-1 syndrome) and the development of pituitary adenomas.
Examination and Diagnosis
In every case where pituitary adenoma is suspected, an endocrinological blood test should first be carried out. Blood tests: Examination of the basal hormone levels in the blood can assist in an initial evaluation. Blood levels of cortisol, ACTH, thyroid stimulating hormone (TSH), free T3, free T4, hGH, prolactin, the gonadal stimulating hormones LH and FSH, as well as female and male sex hormones (estradiol and testosterone) should all be determined.
Depending on the symptoms and basal levels, in each case further hormone function tests (ACTH stimulation, dexamethasone suppresion, TRH, LHRH, GHRH, CRH) are necessary to confirm the diagnosis.
Skull X-rays and tomography are no longer employed in the diagnosis of pituitary adenoma. Only through use of special magnetic resonance imaging (MRI) can a pituitary adenoma be accurately displayed, even with very small tumors. With the help of a visual field measurement (Octopus), possible compressions of the optic nerve can be examined.
Treatment
Today, prolactinoma adenomas are rarely handled surgically, but are solely treated medicinally using dopamine agonists (bromocriptine, cabergoline, quinagolide) over a period of several years,. These drugs lead to an ebbing of prolactin production and reduction in the size of the adenomas.
If they do not cause symptoms, non-hormone-secreting (null cell) microadenomas (<1 cm) need only be examined by MRI every 12 months. Unless they have a tendency to grow, they can be left alone for life without further therapy.
Whenever possible other pituitary adenomas, particularly those that over-produce hormones, should be surgically removed. In about 98 percent of cases a microsurgical procedure using a transnasal-transsphenoidal approach is used. This means a minimally-invasive surgery via the nasal cavity. The aim is the selective removal of the adenoma without impairing the function of the healthy pituitary gland. This must be carried out by highly specialized neurosurgeons using a surgical microscope. In cases of recurrence or inoperable tumors, radiation therapy can be used.
Course and Prognosis
The prognosis in a case of pituitary adenoma is very individual and depends on the point in time at which the diagnosis is made. Prolactinoma adenomas can be optimally treated over 90 percent of the time using only medication. In case of surgical removal, the average the rate of recurrence is about 10 percent after 8 years and about 30 percent after 20 years. Depending on the symptoms and size of the adenoma, hormonal defects can also arise which may require lifelong treatment by means of hormone replacement therapy. Therefore, regular monitoring of hormone levels by an endocrinologist is necessary after surgical treatment. Today, all defects in the pituitary can be optimally replaced with hormones. Depending on requirements, L-thyroxine (thyroid hormone), hydrocortisone (adrenal hormone), growth hormone, estrogen/progestin and/or testosterone, as well as vasopressin (posterior pituitary hormone) can be replaced. In principle, regular control measures (hormone levels, MRI) are necessary since there may be recurrence, after surgery as well as after successful radiotherapy. However with optimal treatment there are few restrictions on the quality of life, or life expectancy.