Objective: We aimed to assess the spectrum of hormone immunoreactivity in our pituitary adenoma cases and discuss the diagnostic parameters of atypical pituitary adenomas.

Material and Methods: A total of 166 pituitary adenoma cases diagnosed from 2005 to 2008 in our department were included in the present study. Hematoxylin-eosin stained and immunohistochemistry performed slides (ACTH, PRL, GH, TSH, FSH, LH, Ki-67, and p53) were evaluated. Cases having more than two mitoses on 10 high power fields besides more than 3% Ki-67 index were accepted in the atypical group.

Results: Histologically, 159 cases were typical pituitary adenoma and 7 were atypical pituitary adenoma. Of the atypical pituitary adenoma cases, one case was ACTH, one GH and one both GH and prolactin hormone immunoreactive pituitary adenomas. Four cases were hormone immunonegative adenomas. Of the typical pituitary adenoma cases, 39 cases were GH, 19 ACTH, 17 prolactin, 10 FSH, 8 LH and one TSH immunreactive pituitary adenomas. Fourty-seven cases were hormone immunonegative adenomas.Twenty-two of the all pitutary adenoma cases had recurrence. Of these cases, 18 were typical adenoma and four were atypical adenoma.

Conclusion: The ratio of prolactin immunoreactive pituitary adenoma cases in the surgical material of neuropathology is decreasing due to medical therapy. Atypical pituitary adenomas are not the sole factor affecting the recurrence mechanism but these tumors have higher recurrence rate compared with typical pituitary adenomas and we think the proliferation index might be the principal approach in the diagnosis of these lesions.