Crooke's cell pituitary adenoma in a 7-month-old dog with Cushing's syndrome

A 7-month-old Boxer puppy was referred for growth retardation. Cushing's syndrome was diagnosed based on clinical signs, physical appearance, elevated urine cortisol/creatinine ratios and unsuppressed plasma cortisol after a low dose of dexamethasone. At the time, there was no evidence of pituitary or adrenal neoplasia on imaging studies. After 60 days of trilostane treatment, the clinical signs of Cushing's syndrome had disappeared. Thirty months later, the dog died of cardiac disease. Pathological examination revealed a pituitary macroadenoma with bilateral adrenocortical hyperplasia. Immunostaining for adrenocorticotropic hormone confirmed a corticotroph adenoma. High Ki-67 staining denoted the aggressiveness of the tumour. Haematoxylin-eosin, periodic acid-Schiff and cytokeratin 7 staining revealed a perinuclear hyaline ring in the neoplastic cells, compatible with a Crooke's cell adenoma. This is the first case of Crooke's cell pituitary adenoma causing Cushing's syndrome in a puppy with growth retardation.