Classification of Pituitary Adenomas

Primary Classification Systems

Pituitary adenomas are classified based on multiple complementary systems, including hormonal functionality, size, histopathological characteristics, and molecular markers, such as Ki-67 proliferation index, as recommended by the European Pituitary Pathology Group 1, 2

The European Pituitary Pathology Group recommends a multilevel approach for histopathological assessment, including a basic immunostaining panel for pituitary hormones, cytokeratin, and Ki-67, with additional markers when indicated 1, 6
A basic immunostaining panel should include pituitary hormones, cytokeratin, and Ki-67, according to the European Pituitary Pathology Group 1, 6

Ki-67 staining should be accurately quantified to help predict clinical outcomes, with a Ki-67 ≥3% combined with local invasion on imaging predicting a 25% recurrence rate after surgery in pediatric patients 1, 6
The Ki-67 labeling index is an important adverse prognostic factor, with 55% of patients in pediatric series having Ki-67 ≥3% 1, 6

Genetic assessment should be offered to all children and young people with pituitary adenomas, particularly those with GH and prolactin excess, due to the high prevalence of genetic abnormalities, as recommended by the European Pituitary Pathology Group 1, 6
Genetic syndromes associated with pituitary adenomas include familial isolated pituitary adenoma, multiple endocrine neoplasia type 1 (MEN1), MEN1-like syndrome, phaeochromocytoma-paraganglioma-related pituitary disease, and AIP mutations 1, 3, 6

The current WHO 2022 classification emphasizes functional and molecular characteristics over outdated morphological categories, and should be used instead of the traditional classification into eosinophilic, basophilic, and chromophobe types 1, 2
Thyrotropinomas, a rare type of functioning adenoma, secrete TSH, causing hyperthyroidism, according to the European Society of Endocrinology 3, 4