Plurihormonal tumors produce more than one hormone. Morphologically, they can be either monomorphous or plurimorphous. Monomorphous plurihormonal adenomas consist of one cell population that produces two or more hormones. The adenoma cells often differ from nontumorous adenohypophysial cells, and their cellular derivation may remain obscure despite extensive morphological studies. Plurimorphous plurihormonal adenomas consist of two or more distinct cell types, and each produces one hormone. Thyrotroph adenomas are often plurihormonal.
Nonfunctioning (Endocrine-Inactive) Adenomas
These tumors arise from the adenohypophysis and cause symptoms when they extend beyond the sella, which results in pressure on the surrounding structures rather than secretion of a hormonally active substance. Endocrine-inactive adenomas show positive immunostaining for one or more pituitary hormones; however, they are not associated with clinical and biochemical evidence of hormone excess. Gonadotrophic hormones, as detected by antisera to beta-FSH and beta-LH, are present in many clinically nonfunctioning adenomas. Some of these adenomas are recognized by electron microscopy to have gonadotrophic differentiation, but some have characteristics of less well-differentiated cells and resemble the null cells that were initially thought to be undifferentiated precursors of adenohypophysial cells. Endocrine-inactive pituitary adenomas comprise approximately 30% to 35% of the pituitary tumors in most series and are the most common type of macroadenoma.
Oncocytic tumors of the pituitary, also known as pituitary oncocytomas, are characterized by an abundance of mitochondria, which may fill up to 50% of the cytoplasmic area, which is normally around 8%, and obscure other organelles. These tumors are usually unassociated with clinical and biochemical evidence of hormone excess; in some cases, they may be accompanied by various degrees of hypopituitarism and/or mild hyperprolactinemia. Oncocytic change may occur in several other pituitary tumor types.
Pituitary carcinomas are usually endocrinologically functional, and ACTH-producing and PRL-producing tumors are the most frequent.[2,9] The histological and cytological characteristics of pituitary carcinomas vary from bland and monotonous to frankly malignant. Carcinomas show a variable degree of nuclear atypia and cellular pleomorphism, but they also show significantly higher mitotic rates and cell proliferation indices than adenomas. Carcinomas account for 0.1% to 0.2% of all pituitary tumors.[9,11]
Breast and lung cancer are the most common primary neoplasms metastasizing to the pituitary. Although tumors that are metastatic to the pituitary have been reported to be as high as 28% in autopsy series, the majority of metastatic tumors are clinically silent.
Other tumors that arise in the pituitary include craniopharyngiomas, meningiomas, and germ cell tumors; the rare granular cell tumors, pituicytomas, and gangliogliomas; and the even rarer gangliocytomas, lymphomas, astrocytomas, and ependymomas.
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- Ezzat S, Asa SL, Couldwell WT, et al.: The prevalence of pituitary adenomas: a systematic review. Cancer 101 (3): 613-9, 2004.
- Teramoto A, Sanno N, Tahara S, et al.: Pathological study of thyrotropin-secreting pituitary adenoma: plurihormonality and medical treatment. Acta Neuropathol (Berl) 108 (2): 147-53, 2004.
- Snyder PJ: Extensive personal experience: gonadotroph adenomas. J Clin Endocrinol Metab 80 (4): 1059-61, 1995.
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- Yeh PJ, Chen JW: Pituitary tumors: surgical and medical management. Surg Oncol 6 (2): 67-92, 1997.
- Ragel BT, Couldwell WT: Pituitary carcinoma: a review of the literature. Neurosurg Focus 16 (4): E7, 2004.
- Pernicone PJ, Scheithauer BW: Invasive pituitary adenoma and pituitary carcinoma. In: Thapar K, Kovacs K, Scheithauer BW, et al., eds.: Diagnosis and Management of Pituitary Tumors. Totowa, NJ: Humana Press, 2001, pp 369-86.
- Pernicone PJ, Scheithauer BW, Sebo TJ, et al.: Pituitary carcinoma: a clinicopathologic study of 15 cases. Cancer 79 (4): 804-12, 1997.
- Komninos J, Vlassopoulou V, Protopapa D, et al.: Tumors metastatic to the pituitary gland: case report and literature review. J Clin Endocrinol Metab 89 (2): 574-80, 2004.