Pituitary macroadenomas and macroadenocarcinomas in dogs treated with mitotane for pituitary-dependent hyperadrenocorticism: 13 cases (1981-1986)

Pituitary macroadenoma/macroadenocarcinoma (PMA; tumor size greater than or equal to 1 cm in diameter) was diagnosed in 13 dogs after 0.5 to 24 months of mitotane treatment for pituitary-dependent hyperadrenocorticism (PDH). The diagnosis of PDH was established on the basis of results of common tests of the pituitary-adrenocortical axis in conjunction with results of x-ray computed tomography or necropsy. Initial clinical findings and clinicopathologic test results were typical of PDH. Signs referable to the CNS developed in 7 of the 13 dogs. The most common neurologic sign was stupor. Pituitary macroadenoma/macroadenocarcinoma was an unexpected finding in the other 6 dogs, because none had clinical signs of disease referable to the CNS at the time that pituitary tumor was documented. In the 13 dogs, strong correlation existed between tumor volume, compression/invasion of the surrounding nervous tissue, and development of neurologic signs, ie, neurologic signs were most frequently associated with larger tumors. The size of the tumor, however, was not always an indication of whether neurologic signs would be observed. All 7 dogs with neurologic signs were euthanatized because of the deleterious effects of the PMA. Of the 6 dogs without neurologic signs, 2 died of unrelated cause. Alternative treatment (ie, hypophysectomy, 60Co-teletherapy) was used successfully in 2 other dogs. Alternative treatment would seem indicated if PMA is documented in a dog with PDH. However, identification of PMA is dependent on evaluation of x-ray computed tomographic images. Signalment, history, physical examination, and alterations in routine clinicopathologic findings in these 13 dogs of our study were similar to previously reported findings in dogs with PDH but apparently without large pituitary tumors.(ABSTRACT TRUNCATED AT 250 WORDS)