Pituitary Adenoma - Classification

Classification

Pituitary adenomas are classified based on 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 ≥I0 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 is 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 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, nonsecretive adenomas may be either null cell adenomas or a more specific adenoma that, however, remains nonsecretive.