Purpose: To elucidate the frequency of false-positive results in imaging diagnoses of a functioning pituitary microadenoma, the authors studied various kinds of incidental lesions greater than 2 mm in diameter from a larger series of pituitary glands.
Materials and methods: One thousand pituitary glands were studied in a nonselected autopsy series. Most causes of death were acute diseases or accidents. Each gland was fixed in 10% formalin and was then cut horizontally into three or four pieces, which were prepared for usual light microscopy.
Results: Of 178 glands found to have incidental lesions, 61 (34%) lesions were larger than 2 mm. Included were adenomas and hyperplasias (n = 20), Rathke cysts (n = 37), infarctions (n = 2), and hemorrhages (n = 2). Seventeen (74%) of 23 laterally localized lesions were adenomas, and 33 (87%) of 38 medially situated lesions were Rathke cleft cysts. These lesions were found in 5.8%-8.3% of subjects in every generation aged 30 years or older.
Conclusion: Incidental lesions should be considered a cause of false-positive findings (6.1%) when an imaging diagnosis is made of a functioning pituitary microadenoma.