The Past, Present, and Future Statuses of Formerly Classified “Atypical Pituitary Adenomas”: A Clinicopathological Assessment of 101 Cases in a Cohort of More than 1,000 Pure Endoscopically Treated Patients in Single Center

Objective  This study was aimed to assess the clinical aggressiveness of pituitary neoplasms that were previously defined as atypical adenomas. Methods  A total of 1,042 pituitary adenomas were included in the study and 101 of them were diagnosed as atypical adenoma. Demographic characteristics, radiological evaluations, and clinical information were obtained from a computer-based patient database. Cases were categorized as atypical or typical using the criteria listed in 2004 Classification of Tumors of Endocrine Organs. Results  The cure and reoperation rates did not show any statistically significant difference between the typical and atypical adenomas. However, a higher K i -67 labeling index was found to be associated with a higher rate of reoperation ( p  = 0.008) in atypical adenomas. Of note, cavernous sinus invasion or parasellar extension was found to be associated with lower cure rates in patients with atypical pituitary adenomas ( p  < 0.001 and p  = 0.001, respectively). Conclusion  Although atypical pituitary adenomas are known to be more invasive, this study demonstrated that the reoperation and cure rates are the same for typical and atypical adenomas. Our findings advocate for omitting the use of atypical adenoma terminology based solely on pathological evaluation. As stated in the 4th edition of the World Health Organization (WHO) classification, accurate tumor subtyping, evaluation of proliferation by means of mitotic count and K i -67 labeling index, and radiological and intraoperative assessments of tumor invasion should be taken into consideration in the management of such neoplasms.