Nonfunctional pituitary tumors are uncommon in most species. Chromophobe adenomas appear to be endocrinologically inactive, but they may cause compression atrophy of adjacent portions of the pituitary gland and extend into the overlying brain. Clinical disturbances occur because of either a lack of secretion of pituitary trophic hormones and diminished target organ function (eg, adrenal cortex) or dysfunction of the CNS. Affected animals often are depressed, incoordinated, and weak and may collapse with exercise. (Also see adult-onset panhypopituitarism.)
Endocrinologically inactive pituitary adenomas often attain considerable size before they cause obvious signs (or death). The proliferating tumor cells incorporate the remaining structures of the adenohypophysis and infundibular stalk. The entire hypothalamus may become compressed and replaced by the tumor.