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 vis ible 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 urinal ysis) consistent with a diagnosis of hyperadrenocorticism, and none ha d clinical signs suggestive of an intracranial mass. Each dog had plas ma cortisol concentrations after adrenocorticotropic hormone administr ation or low-dose dexamethasone administration consistent with hyperad renocorticism. Pituitary-dependent hyperadrenocorticism was confirmed by the finding of 2 equal-size adrenal glands on abdominal ultrasonogr aphy and by results of plasma endogenous adrenocorticotropic hormone c oncentration and high-dose dexamethasone suppression testing. Sagittal and transverse T1-weighted magnetic resonance images of the brain wer e obtained before and after Iv administration of gadopentenate dimeglu mine. 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 v isible pituitary mass was not significantly different from dogs withou t a visible mass. There was no significant difference in endocrine tes t results when comparing dogs with a visible pituitary mass to dogs wi thout. The prevalence of visible pituitary masses in dogs with pituita ry-dependent hyperadrenocorticism was greater than suggested by the pr evalence of clinical neurologic signs.