Age-related Qualitative Histological and Quantitative Stereological Changes in the Equine Pituitary

Summary The aim of this study was to characterize the age-related morphological changes in the equine pituitary and to identify features that allow distinction between pituitary pars intermedia dysfunction (PPID)-associated and non-functional/age-associated pars intermedia (PI) adenoma. Pituitary glands of all horses submitted for necropsy examination at the Institute of Veterinary Pathology, Ludwig Maximilians University Munich, between 2008 and 2012 were examined. The pituitary glands of 124 horses were weighed, cut into ∼2 mm slices and examined histologically. A slightly modified grading scheme (grades 1–5) was applied to evaluate histological alterations of the PI semiquantitatively. The volume fractions and total volumes of the three pituitary lobes, PI, pars distalis (PD) and pars nervosa (PN), as well as the total number and mean size of PI cells (PICs), were determined using state-of-the-art quantitative stereological methods. There were significant associations between histological grade, the appearance of PI adenomas, follicles and cysts in the PI, lipofuscin in the PN ( P