A 42-year-old man presents with decreased libido, erectile dysfunction, and headaches. He reports no weight change, gynecomastia, fatigue, or other symptoms. He takes no medications. Testicular size is decreased on examination. His prolactin level is 648 µg per liter (normal value, <15). Magnetic resonance imaging (MRI) reveals a sellar mass (2.5 by 1.5 by 2.0 cm) that is 5 mm below the optic chiasm and that extends bilaterally into the cavernous sinuses. What are the diagnostic and therapeutic considerations? The Clinical Problem Prolactinomas are the most common type of secretory pituitary tumor. Typically benign, they are classified according to size; microadenomas are less than 10 mm and macroadenomas 10 mm or more. Serum levels of prolactin in patients with prolactinomas are usually proportional to the tumor mass, and prolactin levels above 250 µg per liter are common in patients with macroprolactinomas; levels can exceed 10,000 µg per liter. Pituitary microadenomas are found in 10.9% of autopsies, and 44% of these microadenomas are prolactinomas.1 Although they are rarely hereditary, prolactinomas can occur as part of the multiple endocrine neoplasia type 1 syndrome. No risk factors have been identified for sporadicprolactinomas. Although it has been hypothesized that oral contraceptives might increase the risk, their use has not been associated with an increased likelihood of prolactinoma development.2 Clinical symptoms and signs of hyperprolactinemia in women include oligoamenorrhea, infertility, and galactorrhea. Restoration of ovulatory menstrual periods when pulsatile gonadotropin-releasing hormone (GnRH) is administered in women with hyperprolactinemia confirms the presence of abnormalities in GnRH secretion in these patients.3 In women with hyperprolactinemia who continue to have menses, luteal-phase abnormalities can lead to infertility. Estrogen deficiency in amenorrheic women with untreated prolactinomas causes low bone mass and is associated with an increased risk of fracture, whereas bone density is preserved in women with hyperprolactinemia who have regular menses.4,5 Large prolactinomas can also cause gonadotropin insufficiency because of mass effect(compression of normal gonadotrophs). In men, hyperprolactinemia may lead to hypogonadism, decreased libido, erectile dysfunction, infertility, gynecomastia, and, in rare instances, galactorrhea. Decreased bone mass6 and anemia can result from testosterone deficiency. In contrast with women, who usually present with microadenomas, most men present with macroadenomas, often with headache, visual symptoms, or both, in addition to hypogonadism.7 The larger tumor size in men presumably reflects diagnostic delay, although there may be sex-specific differences in biologic features of the tumors. Although rare, prolactinomas may occur in children, typically with mass effect, pubertal delay, or both.8 Continue Reading - See Attached Article Klibanski A. Prolactinomas. N Engl J Med;362(13):1219-26.