Neoplastic and nonneoplasric lesions in the region of the hypothalamus and pituitary can directly or indirectly affect gonadotrope function. Lesions involving the hypothalamus may arise in the hypothalamus, suprasellar structures, or within the sella itself and extend upwards.
Pituitary Tumors / Prolactinomas
Prolactinomas present differently in men and women. In women, prolactinomas are common and usually small (microadenomas) when detected because of the symptoms of amenorrhea and galactorrhea. In men, however, these tumors are usually large, being greater than 1 cm in diameter (macroadenomas) at the time of detection. It is unclear whether the large tumor size in the male presentation is due to a late diagnosis caused by the failure of patients and physicians to appreciate the early signs of this disorder or if men experience more rapid growth of these tumors. The patients usually present with hypogonadism, erectile dysfunction, and manifestations of supersellar mass lesions (Table Presenting Symptoms in Men with Prolactinomas). Visual field cuts are common due to compression of the optic chiasm by the rumor. Hyperprolactinemia is present, with levels above 350 ng / mL being highly diagnostic for a prolactin-secreting tumor. Serum testosterone levels are usually low, with low or inappropriately normal serum luteinizing hormone and follicle-stimulating hormone concentrations, and follicle-stimulating hormone levels are decreased either because of prolacrin suppression of gonadotropin-releasing hormone secretion or because of pressure effects on the normal gonadotroph cells. A functional disorder is more common, as evidenced, in many cases, by luteinizing hormone responsiveness to administered gonadotropin-releasing hormone and reversal of both the hypogonadorropic state and Leydig cell dysfunction after the reduction of prolacrin with dopamine agonists. Patients presenting with large tumors resulting in multiple pituitary hormone deficiencies are more likely to require testosterone or gonadorropin therapy to correct the low testosterone levels. Surgery is not often considered to be a treatment option for this problem.
Table Presenting Symptoms in Men with Prolactinomas
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Tumors that secrete growth hormone (GH) present with excess growth hormone levels (acromegaly). GH- and nonsecreting pituitary adenomas are usually large tumors (macroadenomas) with symptoms and signs due to mass effects and acquired hypogonadotropic hypogonadism. Adrenocorricorrophin (ACTH) secretory tumors are usually small, and abnormalities of reproductive function may be associated with corrisol-induced dysfunction of the hypothalamic-pituitary axis.
Glycopeptide secretory adenomas were not appreciated until recently because they tend to be inefficient secretors of hormonal products (TSH, luteinizing hormone, follicle-stimulating hormone, and their subunits) or because elevated gonadotropins tend not to produce recognizable clinical syndromes. Consequently, these types of adenomas tend to present late as large mass lesions, with visual and other neurologic manifestations. Gonadotroph adenomas often produce increased basal concentrations of follicle-stimulating hormone but rarely of luteinizing hormone. As with other large pituitary tumors, the mass effects can lead to compression of the normal gonadotrophs, decreased luteinizing hormone, and testosterone levels. Occasionally, an elevation of serum luteinizing hormone and Leydig cell dysfunction [lowered testosterone level(s)] may be seen; this is believed to be due to the secretion of a less bioactive form of luteinizing hormone or free α-subunit that is detected in the assay. Elevated luteinizing hormone levels and over-stimulation of the Leydig cells with increased testosterone concentrations may also occur. In some cases, the diagnosis of a gonadotroph adenoma can be made by demonstrating paradoxical stimulation of follicle-stimulating hormone or the luteinizing hormone beta-subunit by thyrotropin-releasing hormone (TRH).