ONE-YEAR FOLLOW-UP EVALUATION OF MAGNETIC-RESONANCE-IMAGING OF THE BRAIN IN DOGS WITH PITUITARY-DEPENDENT HYPERADRENOCORTICISM

Objective-To evaluate magnetic resonance imaging (MRI) brain scans of dogs with pituitary-dependent hyperadrenocorticism (PDH) and no signs of CNS dysfunc tion 1 year after diagnosis and initial MRI. Design-Pro spective study of surviving dogs from a previous study. Animals-13 dog s underwent MRI of the brain at the lime that PDH was diagnosed and pr ior to treatment. At that time, none of the dogs had clinical signs su ggestive of an intracranial mass. Approximately 1 year after diagnosis and MRI, the brain was again evaluated by MRI. Results-On the initial MRI scan, 5 of the 13 dogs had normal findings, and 8 had evidence of a mass (tumor) in the area of the pituitary gland. Of the 5 dogs that had no visible pituitary mass on the initial MRI scan, 3 had a normal MRI brain Scan 1 year later. Of the 5 dogs that had no visible pituit ary mass on initial MRI scan, 2 had a visible pituitary mass at 1 year . The 8 dogs that had a visible mass on the initial MRI brain scan had easily identified pituitary masses on the second MRI scan. Of these 8 dogs, 4 had no apparent change in pituitary mass size, and 4 had obvi ous increase in vertical height of the pituitary mass. Of the 4 dogs, 2 developed signs of neurologic dysfunction within 1 year after diagno sis of PDH, presumably attributable to that mass. Of the 13 dogs, 12 w ere treated with mitotane soon after completion of the initial MRI sca n. Sensitivity to mitotane and initial pituitary mass size or growth w ere not correlated. Of the 13 dogs evaluated initially and 1 year afte r diagnosis, 10 had pituitary masses identified on MRI brain scans. Cl inical Implications-The incidence of visible pituitary masses among do gs with PDH at the time of or within a year of diagnosis was > 75%. In 2 dogs, signs of CNS dysfunction developed within 1 year of PDH diagn osis when pituitary masses were greater than or equal to 10 mm.