Endogenous glucocorticoid excess (Cushing's syndrome [CS]) most commonly results from an ACTH-producing pituitary adenoma. The majority are small microadenomas, and are difficult to define on magnetic resonance imaging (MRI) imaging: the mean size of an ACTH-secreting pituitary adenoma is 6 mm. Adenomectomy is the treatment of choice to control Cushing's disease (CD), and it is recommended that surgery be performed by a specialist surgeon. In this setting, approx 90% of patients with CD will undergo successful cure, i.e., a lowering of cortisol production to within the normal range (18). However, this figure falls to 50-65% (in three recent British audits; Oxford, Newcastle, and the National Hospital, London) if cure implies removal of all tumor tissue such that the residual cortisol from the normal corticotrophs is suppressed to below the detectable range.
Removal of the ACTH-secreting adenoma results in an immediate reduction in circulating ACTH levels, with consequent lowering of serum cortisol concentrations. The remaining corticotrophs require a variable period of recovery before restoration to normal ACTH secretion and feedback control. A stricter definition of surgical cure is based on measurement of postoperative early morning serum cortisol concentration, with a value <50 nmol/L (1.8 ^g/dL) indicative of a successful outcome. Occasionally, low but detectable values decrease with time to normal or subnormal levels, but immediate postoperative values >100 nmol/L
(3.6 M-g/dL) in general indicate residual corticotroph adenoma. Management of patients after pituitary surgery for CD can be subdivided into patients with continuing glucocorticoid excess and those with successful cure.
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