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→Pituitary Dependant Hyperadrenocorticism
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==
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[[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>]]
</gallery>
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.
Grossly the adrenals have an irregular surface with protruding nodules of cortical tissue; the hyperplased zona fasciculata cells.
Grossly the adrenals have an irregular surface with protruding nodules of cortical tissue; the hyperplased zona fasciculata cells.