Magnetic resonance imaging of the brain in dogs with recently diagnosed but untreated pituitary-dependent hyperadrenocorticism.

Magnetic resonance imaging was used to determine the prevalence of visible pituitary masses in 21 dogs with recently diagnosed and untreated pituitary-dependent hyperadrenocorticism. All dogs had clinical signs and routine database values (CBC, serum biochemical panel, and urinalysis) consistent with a diagnosis of hyperadrenocorticism, and none had clinical signs suggestive of an intracranial mass. Each dog had plasma cortisol concentrations after adrenocorticotropic hormone administration or low-dose dexamethasone administration consistent with hyperadrenocorticism. Pituitary-dependent hyperadrenocorticism was confirmed by the finding of 2 equal-size adrenal glands on abdominal ultrasonography and by results of plasma endogenous adrenocorticotropic hormone concentration and high-dose dexamethasone suppression testing. Sagittal and transverse T1-weighted magnetic resonance images of the brain were obtained before and after IV administration of gadopentenate dimeglumine. Eleven dogs had visible masses, ranging in size from 4 to 12 mm at greatest vertical height. Mean age and body weight of dogs with a visible pituitary mass was not significantly different from dogs without a visible mass. There was no significant difference in endocrine test results when comparing dogs with a visible pituitary mass to dogs without. The prevalence of visible pituitary masses in dogs with pituitary-dependent hyperadrenocorticism was greater than suggested by the prevalence of clinical neurologic signs.