the pituitary gland's anterior lobe (adenohypophysis) is a true gland which produces and secretes six different hormones: thyroid-stimulating hormone (tsh), adrenocorticotropic hormone (acth), follicle-stimulating hormone (fsh), luteinizing hormone (lh), growth hormone (gh), and prolactin (prl). diagnosis diagnosis of pituitary adenoma can be made, or at least suspected, by a constellation of related symptoms presented above. the differential diagnosis includes pituitary tuberculoma, especially in developing countries and in immumocompromised patients. the diagnosis is confirmed by testing hormone levels, and by radiographic imaging of the pituitary (for example, by ct scan or mri). classification unlike tumors of the posterior pituitary, pituitary adenomas are classified as endocrine tumors (not brain tumors). pituitary adenomas are classified based upon anatomical, histological and functional criteria. anatomically pituitary tumors are classified by their size based on radiological findings; either microadenomas (less than <10 mm) or macroadenomas (equal or greater than ≥10 mm). classification based on radioanatomical findings places adenomas into 1 of 4 grades (i–iv): stage i: microadenomas (<1 cm) without sella expansion. stage ii: macroadenomas (≥1 cm) and may extend above the sella. stage iii: macroadenomas with enlargement and invasion of the floor or suprasellar extension. stage iv: destruction of the sella. histological classification utilizes an immunohistological characterization of the tumors in terms of their hormone production. historically they were classed as either basophilic, acidophilic, or chromophobic on the basis of whether or not they took up the tinctorial stains hematoxylin and eosin. this classification has fallen into disuse, in favor of a classification based on what type of hormone is secreted by the tumor. approximately 20–25% of adenomas do not secrete any readily identifiable active hormones ('non-functioning tumors') yet they are still sometimes referred to as 'chromophobic'. functional classification is based upon the tumors endocrine activity as determined by serum hormone levels and pituitary tissue cellular hormone secretion detected via immunohistochemical staining. the "percentage of hormone production cases" values are the fractions of adenomas producing each related hormone of each tumor type as compared to all cases of pituitary tumors, and does not directly correlate to the percentages of each tumor type because of smaller or greater incidences of absence of secretion of the expected hormone. thus, non secretive adenomas may be either null cell adenomas or a more specific adenoma that, however, remains non-secretive. any type of pituitary adenocarcinoma listed in the table below may cause compressive symptoms due to local expansion in addition to the systemic effects of secreted hormones listed in the pathology column. null cell adenomas by definition do not secrete hormones, but they commonly cause compressive effects on the pituitary stalk (stalk effect). this leads to decreased levels of dopamine from the hypothalamus reaching the anterior pituitary gland. dopamine exerts an inhibitory effect on prolactin secretion. with the absence of this inhibitory effect, prolactin levels increase and are often increased in null cell adenomas. this leads to symptoms of hypogonadism. type of adenomasecretionstainingpathologypercentage of hormone production casespercentage of silent cases lactotrophic adenomas (prolactinomas)secrete prolactinacidophilicgalactorrhea, hypogonadism, amenorrhea, infertility, and impotence30%<9% somatotrophic adenomassecrete growth hormone (gh)acidophilicacromegaly in adults; gigantism in children15%<9% corticotrophic adenomassecrete adenocorticotropic hormone (acth)basophiliccushing's disease2–6%10% gonadotrophic adenomassecrete luteinizing hormone (lh), follicle-stimulating hormone (fsh) and their subunitsbasophilicusually do not cause symptoms, occasionally hypergonadism 10%73% thyrotrophic adenomas (rare)secrete thyroid-stimulating hormone (tsh)basophilic to chromophobicoccasionally hyperthyroidism, usually do not cause symptomsless than 1%<9% null cell adenomasdo not secrete hormonesmay stain positive for synaptophysinasymptomatic or hypogonadism25% of pituitary adenomas are nonsecretive1% somatotroph pituitary adenoma, showing acidophilic cytoplasm a silent gonadotroph pituitary adenoma which is, in this case, eosinophilic (contrary to normal, basophilic, gonadotroph cells) true null cell adenomas are typically composed of uniform, mildly atypical cells with chromophobic cytoplasm. this case has papillary architecture similar to gonadotroph adenomas. pituitary incidentalomas pituitary incidentalomas are pituitary tumors that are characterized as an incidental finding. they are often discovered by computed tomography (ct) or magnetic resonance imaging (mri), performed in the evaluation of unrelated medical conditions such as suspected head trauma, in cancer staging or in the evaluation of nonspecific symptoms such as dizziness and headache. it is not uncommon for them to be discovered at autopsy. in a meta-analysis, adenomas were found in an average of 16.7% in postmortem studies, with most being microadenomas (<10mm); macrodenomas accounted for only 0.16% to 0.2% of the decedents. while non-secreting, noninvasive pituitary microadenomas are generally considered to be literally as well as clinically benign, there are to date scant studies of low quality to support this assertion. it has been recommended in the current clinical practice guidelines (2011) by the endocrine society – a professional, international medical organization in the field of endocrinology and metabolism – that all patients with pituitary incidentalomas undergo a complete medical history and physical examination, laboratory evaluations to screen for hormone hypersecretion and for hypopituitarism. if the lesion is in close proximity to the optic nerves or optic chiasm, a visual field examination should be performed. for those with incidentalomas which do not require surgical removal, follow up clinical assessments and neuroimaging should be performed as well follow-up visual field examinations for incidentalomas that abut or compress the optic nerve and chiasm and follow-up endocrine testing for macroincidentalomas. ectopic pituitary adenoma an ectopic (occurring in an abnormal place) pituitary adenoma is a rare type of tumor which occurs outside of the sella turcica, most often in the sphenoid sinus, suprasellar region, nasopharynx and the cavernous sinuses. metastases to the pituitary gland carcinomas that metastasize into the pituitary gland are uncommon and typically seen in the elderly, with lung and breast cancers being the most prevalent, in breast cancer patients, metastases to the pituitary gland occur in approximately 6–8% of cases. symptomatic pituitary metastases account for only 7% of reported cases. in those who are symptomatic diabetes insipidus often occurs, with rates approximately 29–71%. other commonly reported symptoms include anterior pituitary dysfunction, visual field defects, headache/pain, and ophthalmoplegia. treatment treatment options depend on the type of tumor and on its size: prolactinomas are most often treated with cabergoline or bromocriptine (both dopamine agonists), which decrease tumor size as well as alleviates symptoms, followed by serial imaging to detect any increase in size. treatment, where the tumor is large, can be with radiation therapy, proton therapy or surgery, and patients generally respond well. unlike prolactinomas, thyrotrophic adenomas characteristically respond poorly to dopamine agonist treatment. somatotrophic adenomas respond to octreotide or lanreotide, which are long-acting somatostatin analogs. these somatostatin receptor analogs inhibit secretion of growth hormone. they were found to be about 50–55% effective in reducing tumor mass and reducing growth hormone and insulin like growth factor 1 (igf-1) levels in studies. the growth hormone receptor antagonist pegvisomant is also used in the treatment of somatotrophic adenomas. pegvisomant blocks the action of growth hormone. it can either be used as monotherapy or combined with a somatostatin analog. surgery is a common treatment for pituitary tumors. the normal approach is trans-sphenoidal adenectomy, which usually can remove the tumor without affecting the brain or optic nerves. radiation is also used to treat pituitary adenomas. examples include external beam or proton beam radiation therapy or stereotactic radiosurgery. external radiation of pituitary adenomas can arrest tumor growth for several years but pituitary failure develops within 10 years in most patients necessitating lifelong hormone replacement. radiation therapy for pituitary adenomas is associated with a four-fold increase in mortality due to cerebrovascular disease.