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Excerpt from ProlactinomaSynonyms, Key Words, and Related Terms: prolactin-secreting adenoma, hormone-secreting pituitary tumor, hyperprolactinemia, prolactin, PRL, pituitary adenoma, growth hormone tumor, microprolactinoma, macroprolactinoma Please click here to view the full topic text: ProlactinomaBackgroundProlactinomas are the most common hormone-secreting pituitary tumors. Based on its size, a prolactinoma can be classified as a microprolactinoma (<10 mm diameter) or a macroprolactinoma (>10 mm diameter). PathophysiologyTumor formation is due to neoplastic transformation of anterior pituitary lactotrophs, resulting in excess synthesis and secretion of prolactin (PRL). Physiologically, PRL, a polypeptide hormone consisting of 199 amino acids, is regulated by hypothalamic factors. These include prolactin-releasing factors (PRFs) and prolactin-inhibitory factors (PIFs). Dopamine (DA) is the principal PIF, and thyrotropin-releasing hormone (TRH), vasoactive intestinal peptide, and peptide histidine methionine are the putative PRFs. The physiologic role of these PRFs is not established. A delicate balance between the PRFs and PIFs normally keeps the serum PRL level within a physiologic range. Moreover, the interplay of various neurohormonal factors results in a pulsatile secretion of PRL from the pituitary. Prolactinoma is one of the several causes of pathologic hyperprolactinemia (see Other Problems to Be Considered).1, 2, 3, 4, 5 FrequencyUnited StatesThe exact frequency with which prolactinomas occur in the general population is not clearly established. In nonselected surgical series, this tumor accounts for approximately 25-30% of all pituitary adenomas. Some growth hormone (GH)–producing tumors also cosecrete PRL. Microprolactinomas are much more common than macroprolactinomas. SexAmong patients with prolactinomas, as many as 60% of the males present with macroprolactinomas, while 90% of the females present with microprolactinomas. This may partially be due to the fact that the male patients often present much later (for clinical evaluation of hypogonadism) than do the female patients (for clinical evaluation of amenorrhea).6 Please click here to view the full topic text: Prolactinoma |
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