| Pituitary adenoma | |
|---|---|
| Classification and external resources | |
| ICD-10 | D35.2 |
| ICD-9 | 237.0 |
| ICD-O: | M8140/0 |
| MedlinePlus | 000704 |
| eMedicine | neuro/312 |
| MeSH | D010911 |
Pituitary adenomas are tumors that occur in the pituitary gland, and account for about 15% of intracranial neoplasms. Tumors which exceed 10 mm in size are defined as macroadenomas, and those smaller than 10 mm are referred to as microadenomas. Most pituitary adenomas are microadenomas, which often remain undiagnosed, and have an estimated prevalence of 16.7% (14.4% in autopsy studies and 22.5% in radiologic studies).[1][2]
It was previously believed that clinically active pituitary adenomas were rare, however recent studies have suggested that clinically active pituitary adenomas affect approximately one in 1000 of the general population.[3]
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Pituitary tumors were, historically, classed as basophilic, acidophilic, or chromophobic on the basis of whether or not they took up the 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 (though tumors which do not secrete any active hormone ("non-functioning tumors") are still sometimes called "chromophobic").
At present, classification of pituitary tumors is based on plasma hormone levels or immunohistochemical staining, as given in table below. 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, nonsecretive adenomas may be either null cell adenomas or a more specific adenoma that, however, remains nonsecretive.
| Type of adenoma | Secretion | Staining | Pathology | Percentage of hormone production cases |
| lactotrophic adenomas (prolactinomas) | secrete prolactin | acidophilic | galactorrhea, hypogonadism, amenorrhea, infertility, and impotence | 30%[4] |
| somatotrophic adenomas | secrete growth hormone (GH) | acidophilic | acromegaly (gigantism) | 15%[4] |
| corticotrophic adenomas | secrete adenocorticotropic hormone (ACTH) | basophilic | Cushing's disease | |
| gonadotrophic adenomas | secrete luteinizing hormone (LH), follicle-stimulating hormone (FSH) and their subunits | basophilic | usually doesn't cause symptoms | 10%[4] |
| thyrotrophic adenomas (rare) | secrete thyroid-stimulating hormone (TSH) | basophilic to chromophobic | occasionally hyperthyroidism,[5] usually doesn't cause symptoms | Less than 1%[4] |
| null cell adenomas | do not secrete hormones | may stain positive for synaptophysin | 25% of pituitary adenomas are nonsecretive[4] |
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.[9]While pituitary microadenomas are generally considered benign, there are to date scant studies of low quality to support this assertion.[10]The presence of a microadenoma has been positively identified as a risk factor for suicide in a postmortem study of suicide victims.[11][12]
It has been recommended in the current Clinical Practice Guidelines (2011) by the the Endocrine Society -a professional, international medical organization in the field of endocrinology and metabolism-, that all patients with a 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 requre surgical removal, follow up clinical assesments and neuroimaging should be performed as well a follow-up visual field examinations for incidentalomas that abut or compress the optic nerve and chiasm and follow-up endocrine testing for macroincidentalomas.[13]
Adenomas of the anterior pituitary gland are a major clinical feature of multiple endocrine neoplasia type 1 (MEN1), a rare inherited endocrine syndrome that affects 1 person in every 30,000. MEN causes various combinations of benign or malignant tumors in various glands in the endocrine system or may cause the glands to become enlarged without forming tumors. It often affects the parathyroid glands, pancreatic islet cells, and anterior pituitary gland. MEN1 may also cause non-endocrine tumors such as facial angiofibromas, collagenomas, lipomas, meningiomas, ependymomas, and leiomyomas. Approximately 25 percent of patients with MEN1 develop pituitary adenomas.[14][15]
Carney complex (CNC), also known as LAMB syndrome[16] and NAME syndrome[16] is an autosomal dominant condition comprising myxomas of the heart and skin, hyperpigmentation of the skin (lentiginosis), and endocrine overactivity and is distinct from Carney's triad.[17][18]Approximately 7% of all cardiac myxomas are associated with Carney complex.[19] Patients with CNC develop growth hormone (GH)-producing pituitary tumors and in some instances these same tumors also secrete prolactin. There are however no isolated prolactinomas or any other type of pituitary tumor. In some patients with CNC, the pituitary gland is characterized by hyperplastic areas with the hyperplasia most likely preceding the formation of GH-producing adenomas.[20]
Familial isolated pituitary adenoma (FIPA) is a term that used to identify a condition that displays an autosomal dominant inheritance and is charaterised by the presence of two or more related patients affected by adenomas of the pituitary gland only, with no other no other associated symptoms that occur in Multiple endocrine neoplasia Type 1 or Carney complex.[21][22]
Hormone secreting pituitary adenomas cause one of several forms of hyperpituitarism. The specifics depend on the type of hormone. Some tumors secrete more than one hormone, the most common combination being GH and prolactin.
In addition, a pituitary adenoma may present with visual field defects, classically bitemporal hemianopia. It arises from the compression of the optic nerve by the tumor. The specific area of the visual pathway at which compression by these tumours occurs is at the optic chiasma.
The anatomy of this structure causes pressure on it to produce a defect in the temporal visual field on both sides, a condition called bitemporal hemianopia. If originating superior to the optic chiasm, more commonly in a craniopharyngioma of the pituitary stalk, the visual field defect will first appear as bitemporal inferior quadrantanopia, if originating inferior to the optic chiasm the visual field defect will first appear as bitemporal superior quadrantanopia. Lateral expansion of a pituitary adenoma can also compress the abducens nerve, causing a lateral rectus palsy.
Also, a pituitary adenoma can cause symptoms of increased intracranial pressure.
Prolactinomas often start to give symptoms especially during pregnancy, when the hormone progesterone increases the tumor's growth rate.
Headaches may be present.
Various psychiatric manifestations have been associated with pituitary disorders including pitutary adenomas. Psychiatric symptoms such as depression, apathy, emotional instability, easy irritability and hostility have been noted.[23]
Acromegaly is a syndrome that results when the anterior pituitary gland produces excess growth hormone (GH). Approximately 90-95% of acromegaly cases are caused by a pituitary adenoma and it most commonly affects middle aged adults,[24] Acromegly can result in severe disfigurement, serious complicating conditions, and premature death if unchecked. The disease which is often also associated with gigantism, is difficult to diagnose in the early stages and is frequently missed for many years, until changes in external features, especially of the face, become noticeable with the median time from the development of initial symptoms to diagnosis being twelve years.[25]
Pituitary apoplexy is a condition that occurs when pituitary adenomas suddenly hemmorhage internally, causing a rapid increase in size or when the tumor outgrows its' blood supply which causes tissue necrosis and subsequent swelling of the dead tissue. Pituitary apoplexy often presents with visual loss and sudden onset headache and requires timely treatment often with corticosteroids and if necessary surgical intervention.[26]
Central diabetes insipidus is caused by diminished production of the antidiuretic hormone vasopressin that causes severe thirst and excessive production of very dilute urine (polyuria) which can lead to dehydration. Vasopressin is produced in the hypothalamus and is then transported down the pituitary stalk and stored in the posterior lobe of the pituitary gland which then secretes it into the bloodstream.[27]
The diagnosis of CDI is based on the reults of urine and blood tests, and a water deprivation test which tests the body's ability to concentrate urine. CDI is often treated with desmopressin acetate a synthetic vasopressin known as DDAVP administered via nasal spray.
Diagnosis of pituitary adenoma can be made, or at least suspected, by a constellation of related symptoms presented above.
Tumors which cause visual difficulty are likely to be a macroadenoma greater than 10 mm in diameter; tumors less than 10 mm are microadenoma.
The differential diagnosis includes pituitary tuberculoma, especially in developing countries and in immumocompromised patients. [28] The diagnosis is confirmed by testing hormone levels, and by radiographic imaging of the pituitary (for example, by CT scan or MRI).
Treatment options depend on the type of tumor and on its size:
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