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Hyperadrenocorticism is a common disease of adrenal hyperfunction that is seen most commonly in the dog. There are three known causes of the adrenal hyperfunction: dysfunction of the pituitary gland, dysfunction of the adrenal glands and iatrogenic administration of corticosteroids.
Hyperadrenocorticism is a common disease of adrenal hyperfunction that is seen most commonly in the dog. There are three known causes of the adrenal hyperfunction: dysfunction of the pituitary gland, dysfunction of the adrenal glands and iatrogenic administration of corticosteroids.
==Pituitary Dependant Hyperadrenocorticism==
==Pituitary Dependant Hyperadrenocorticism==
[[Image:Chromophobe adenoma.jpg|right|thumb|150px|<small><center>'''Chromophobe Adenoma'''. Courtesy of A. Jefferies</center></small>]]
[[Image:Chromophobe adenoma.jpg|right|thumb|150px|<small><center>'''Chromophobe Adenoma'''. Courtesy of A. Jefferies</center></small>]]
[[Image:Nodular hyperplasia.jpg|right|thumb|150px|<small><center>'''Adrenal Nodular Hyperplasia'''. Courtesy of A. Jefferies</center></small>]]
[[Image:Nodular hyperplasia.jpg|right|thumb|150px|<small><center>'''Adrenal Nodular Hyperplasia'''. Courtesy of A. Jefferies</center></small>]]
80-85% cases of Cushings disease show bilateral adrenal hyperplasia due to excess stimuation by ACTH. There is a failure of the negative feedback mechanism at the level of the pituitary and so ACTH is produced in an unregulated fashion. This is thought to occur due to a functional chromophobe cell (Produces ACTH and MSH) neoplasia, although visible macroadenomas are only found in 10-15% cases with this aetiology. Most cases are therefore thought to be microadenomas and may be visualised by histopathological staining of the pituitary.
80-85% cases of Cushings disease show bilateral adrenal hyperplasia due to excess stimuation by ACTH. There is a failure of the negative feedback mechanism at the level of the pituitary and so ACTH is produced in an unregulated fashion. This is thought to occur due to a functional chromophobe cell (Produces ACTH and MSH) neoplasia, although visible macroadenomas are only found in 10-15% cases with this aetiology. Most cases are therefore thought to be microadenomas and may be visualised by histopathological staining of the pituitary.