The new World Health Organization classification divides pituitary tumors simplistically into
Table 11.2. Simplified classification of pituitary adenomas
GH cell adenoma
PRL cell adenoma
Mixed GH cell / PRL cell adenoma
Mammosomatotroph cell adenoma
ACTH cell adenoma
FSH/LH cell adenoma
TSH cell adenoma
Null cell adenoma
Unclassified adenoma pituitary adenomas and carcinomas, and the traditional categorization of pituitary adenomas by their tinctorial properties has been abandoned. Ultrastructural appearance, in particular the size of the cytoplasmic granules, also aids in the diagnosis of these tumors. The latter system, however, requires pituitary adenomas to be extensively examined by multiple modalities in specialist centers .
The majority of adrenocorticotrophic hormone (ACTH)-producing tumors are microscopic. GH, prolactin (PRL) and ACTH-containing tumors correlate well with endo-crinological behavior, whereas the others do not. Pituitary adenomas are also subdivided by virtue of their size into those less than 1 cm in diameter (microadenomas) and those greater than 1 cm (macroadenomas). These divisions usually correlate with presentation - microadenomas presenting with endocrinological manifestations and macroadenomas with compres-sive effects - although GH-secreting tumors and prolactinomas in males, in particular, may reach substantial size before diagnosis.
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