3601_e08_p208-236 2/15/02 4:35 PM Page 208 8 Pituitary Tumors IAN E. MCCUTCHEON Pituitary tumors are the most commonly occurring rologic damage by provoking cranial neuropathies or intracranial neoplasms. They are found in 8% to 24% optic nerve dysfunction; engulfing the carotid arter- of autopsied people, most of whom in life harbored ies and their tributaries; or impinging on the brain. small asymptomatic tumors that did not cause hor- Such aggressive variants behave as malignant tumors monal disturbance (Kovacs et al., 1980; Parent et al., of the skull base. Even small, benign tumors may pro- 1981; Teramoto et al., 1994; Tomita and Gates, duce a chronic, uncontrolled hypersecretion of pitu- 1999). Pituitary tumors can, however, produce pro- itary hormone that causes profound physiologic found physiologic upset by secreting supraphysiologic changes over time. By any of these means, pituitary amounts of hormones or, when large, by compress- adenomas continue to pose an oncologic threat that ing critical neural structures adjacent to their typical warrants their inclusion in any list of clinically sig- location in the sella turcica. nificant tumors of the central nervous system (CNS). The treatment of pituitary tumors has undergone a renaissance since the revival of transsphenoidal techniques by Guiot and Hardy 35 years ago. This pro- PATHOLOGY cess has been aided by the development of hormonal assaying techniques and radiographic imaging during Most pituitary gland tumors arise from the anterior the last three decades. Today, small pituitary tumors portion of the gland known as the adenohypophysis. can be detected more easily and their hormonal ac- They are adenomas, tumors of the secretory elements, tivity can be assessed more accurately than has pre- which in many cases produce and release one or viously been possible. Medical therapy, particularly more of the pituitary hormones produced by the an- for prolactin-secreting adenomas, but also for terior lobe. A pseudocapsule, sharply demarcating acromegaly, has developed sufficiently so that surgery them from the adjacent normal gland, which may be can be avoided in some patients who can be man- compressed by tumor, usually encloses these lesions. aged with drugs alone. Although preferred locations for each of the different In general, pituitary tumors are diagnosed earlier secretory types have been described within the ante- and treated more effectively now than at any previous rior lobe, in actual fact any of the different subtypes time. Nevertheless, a significant number of pituitary can arise anywhere within the anterior lobe. Rare tumors deviate from the typical pattern of benign his- cases have been reported of adenomas arising in the tology and slow growth. pars tuberalis, a small extension of the anterior lobe Pituitary adenomas can be invasive and penetrate along the distal anterior portion of the stalk (Roth- adjacent dura to enter the sphenoid sinus, cavernous man et al., 1976), or of tumors arising within the sinuses, or other parts of the skull base. These tu- sphenoid sinus, nasopharynx, or clivus from embry- mors can grow to a significant size and cause neu- onic rests of the pharyngeal pituitary (Hori et al., 208 3601_e08_p208-236 2/15/02 4:35 PM Page 209 Pituitary Tumors 209 1999). When less than 10 mm in diameter, these tu- lently to produce a bioactive molecule. Some tumors mors are called microadenomas; when larger, they produce hormone that is detectable through conven- are called macroadenomas. A typical adenoma his- tional techniques but is biologically inactive (Katznel- tologically shows loss of the normal acinar pattern son et al., 1992; Trouillas et al., 1991) or hyperac- and its intervening reticulin network. The cells are tive (Gesundheit et al., 1989). In most patients, fairly uniform in appearance, with small nuclei and however, a reasonable correlation exists between the a small amount of cytoplasm (Fig. 8–1). clinical endocrine status of the patient, serum hor- Older schemes of classification, which have relied mone levels, and the hormones demonstrated within on standard hematoxylin and eosin staining to pro- the tumor through immunohistochemistry. duce an appearance of basophilic, acidophilic, or The spectrum of tumors that are truly inactive has chromophobe staining, have little functional signifi- narrowed greatly with the development of more sen- cance and are now obsolete. Current pathologic anal- sitive hormone detection techniques. Such tumors are ysis of pituitary adenomas relies heavily on immuno- called null-cell adenomas (Kovacs et al., 1980). histochemistry (Asa, 1998). The six major hormones These tumors stain negatively for all hormones and of the anterior lobe (prolactin, growth hormone, thy- contain none of the granules detected by electron mi- rotropin [TSH], luteinizing hormone [LH], follicle- croscopy in typical secretory tumors. It has been sug- stimulating hormone [FSH], and adrenocorticotropin gested that they arise from cells of gonadotrophic lin- [ACTH]) can be detected by applying a polyclonal or eage, although their origin remains controversial. A monoclonal antiserum to tumor sections and then ex- subset of these tumors contains large numbers of mi- posing the sections to a secondary antibody linked to tochondria visible by electron microscopy, which are reagents that give a colorizing reaction. The demon- called onocytomas (Bauserman et al., 1978). Onco- stration of hormonal production does not necessar- cytomas are typically large when diagnosed and af- ily correlate with hormone secretion, and a number fect males more frequently than females (Silbergeld of clinically nonfunctional tumors, which produce no et al., 1993). detectable rise in serum hormone levels, have been It is now apparent that many of the tumors tradi- found to contain hormone, usually FSH or LH, that tionally called nonsecreting actually do secrete hor- has been synthesized in small amounts but not se- mone in amounts too small to be of clinical signifi- creted or secreted inefficiently (Black et al., 1987; cance (Asa et al., 1992; Greenman et al., 1998), or Daneshdoost et al., 1993; Sano and Yamada, 1994). they may produce the ␣-subunit or chromogranin In addition, pituitary tumors in many cases produce (Nobels et al., 1993). These two secreted products, hormones in a disorderly fashion, with an imbalance neither of which has hormonal activity, can be de- in the production of the ␣- and ␤-subunits, which tected in the blood of some patients with clinically (in the case of TSH, LH, and FSH) must link cova- nonfunctional adenomas. The ␣-subunit is one of the Figure 8–1. Hematotoxylin and eosin stained (A) prolactinoma demonstrating monomorphic population of cells with spherical nuclei and delicate rims of cytoplasm. The same tumor stained with prolactin (B) shows immunoreactivity in the paranuclear lo- cation corresponding to the Golgi apparatus. 3601_e08_p208-236 2/15/02 4:35 PM Page 210 210 PRIMARY CENTRAL NERVOUS SYSTEM TUMORS two subunits necessary for hormonal activity in gly- that present hormone levels predict future hormone coprotein hormones; alone, however, the ␣-sub- levels in the untreated state. unit has no hormonal function. Chromogranin is produced by a variety of neuroendocrine tumors, including most pituitary tumors. These two prod- CLINICAL PRESENTATION ucts may be the only molecular species available for surveillance after surgery or other types of ther- Pituitary tumors cause a panoply of signs and symp- apy in patients with hormonally inactive adenomas. toms that can be grouped into four categories: The most common nonfunctional adenomas in pa- (1) compression of adjacent normal gland, (2) hor- tients under 40 years of age are silent corticotropic monal hypersecretion, (3) visual disturbance, and and gonadotropic adenomas, and their oncocytic (4) headache. variants typically occur in patients over age 40 years. Compression of Adjacent Normal Gland Patients may present with hypopituitarism, that is, NATURAL HISTORY impairment of the normal function of the various hormonal axes subserved by the anterior pituitary. Although pituitary adenomas are rare in children and Particularly vulnerable is the pituitary-gonadal axis, fairly common in elderly patients at autopsy, the true in which minor disturbances of the cycling of FSH prevalence of pituitary tumors in the different decades or LH can affect libido and fertility in both sexes and of life is not known. One preliminary study found fo- the menstrual cycle of women. Also vulnerable to cal abnormality of the pituitary suggestive of tumor in local pressure effects are the pituitary-thyroid and 10% of asymptomatic adults undergoing high-resolu- pituitary-adrenal axes. Patients may therefore pres- tion scans (Hall et al., 1994). The expected rate of ent with secondary hypothyroidism or a relative change in small or large adenomas is also not known. hypocortisolism predisposing them to addisonian Although one study of patients with prolactin-secret- crisis. ing microadenomas found that many do not change In adults, low levels of prolactin are not thought in size over time (March et al., 1981), its authors to be significant. Traditionally, the same assumption used now-outdated techniques for radiologic surveil- has been held regarding growth hormone. During the lance. Another survey that examined untreated hy- past decade, however, the clinical effects of growth perprolactinemia found a gradual increase in tumor hormone deficiency on body composition and bone size in only 20%