Pituitary adenomas may be classified either according to their size or their functional status (Table 1). Those tumors that measure 10 mm or less in diameter are considered microadenomas; macroadenomas are those larger than 10 mm. Macroadenomas may also be sub-categorized as "giant" if their extent reaches far beyond the normal confines of the pituitary region or their greatest diameter exceeds 4 centimeters. Pituitary adenomas may also be categorized as either hypersecretory or non-functioning. The hypersecretory adenomas cause distinctive clinical syndromes that include acromegaly/gigantism (growth hormone (GH) secreting adenomas), Forbes-Albright syndrome (prolactin (PRL) secreting adenomas), and Cushing's disease (corticotropin (ACTH) secreting adenomas). The non-functioning adenomas (NFAs) have no endocrine features other than hypopituitarism (decreased pituitary hormone production) and generally present either incidentally or secondary to mass effect.
Table 1. Classification Schemes of Pituitary Adenomas
|
Scheme |
Features |
|---|---|
|
Microadenoma Macroadenoma |
≤ 10 millimeters > 10 millimeters |
|
Non-Functioning adenoma Functioning adenoma |
Endocrinologically inactive, patient may present with pituitary deficiency Excess of hormonally active pituitary hormone GH adenoma PRL adenoma ACTH adenoma TSH adenoma GH and PRL adenoma Other plurihormonal adenomas |