Differences in secretion characteristics in Cushing's disease with and without radiologically evident pituitary tumors.

In a group of 22 unselected patients with Cushing's disease 3 had a moderately enlarged pituitary fossa, while 6 patients showed asymmetry of the sella turcica at lateral tomography. This group of 9 patients with radiologically evident pituitary adenomas had:i) a higher average basal urinary excretion of 17-hydroxycorticosteroids which showed a greater day to day variation;ii) a greater (although insufficient) decrease of plasma cortisol in response to a single oral dose of 1 mg dexamethasone and larger postdexamethasone rebound excretion of urinary 17-hydroxycorticosteroids after 8 mg dexamethasone daily for two days; and iii) a larger maximal increase of plasma cortisol after lysine vasopressin administration than the other 13 patients. The increase in the size of a pituitary (micro-) adenoma in patients with Cushing's disease is accompanied by a more severe hypercortisolism and an increased responsiveness of the pituitary-adrenal axis to the manipulations mentioned.