Computed Tomographic Findings in the Pituitary Gland and Brain of Horses with Pituitary Pars Intermedia Dysfunction

Background: Pituitary pars intermedia dysfunction ( PPID ) is the most common endocrinologic disorder of aged horses. Hypothesis/Objectives: Pituitary glands of PPID ‐affected horses are larger than those of aged horses without signs of PPID , and the size difference can be detected using computed tomography ( CT ) imaging. Animals: Eight horses with clinical signs of PPID and supportive endocrinologic test results and 3 aged control ( PPID ‐negative) horses. Methods: Computed tomography examination of the brain and pituitary gland was performed twice in 10 of the 11 horses, approximately 6 months apart. Six PPID ‐affected horses were treated with pergolide for 6 months between CT scans. The second CT scan was followed by euthanasia and pathologic examination of 6 PPID ‐affected horses (4 treated horses). Results: On initial examination, pituitary glands of PPID ‐affected horses were larger in height ( P  < .01) and width ( P  < .01) than controls, but the difference in length was not significant ( P  = .06). After 6 months of pergolide treatment of PPID ‐affected horses, pituitary gland length increased ( P  < .05), but height and width were not different from pretreatment values. There was no difference between pituitary gland measurements made at the terminal CT scans and necropsy. Furthermore, pituitary gland volume calculated from the measurements was highly correlated to pituitary gland weight. Additional CT findings were bilaterally symmetrical mineralization in the thalamus and cholesterol granulomas adjacent to the lateral and fourth ventricles. Conclusions and Clinical Importance: CT is a useful imaging modality to determine pituitary gland size of PPID ‐affected horses,and CT measurements are similar to gross pathologic measurements.