Nelson Syndrome [Disease/Finding] C4414 43019009 A syndrome characterized by HYPERPIGMENTATION, enlarging pituitary mass, visual defects secondary to compression of the OPTIC CHIASM, and elevated serum ACTH. It is caused by the expansion of an underlying ACTH-SECRETING PITUITARY ADENOMA that grows in the absence of feedback inhibition by adrenal CORTICOSTEROIDS, usually after ADRENALECTOMY. Nelson Syndrome N0000002118 C0027577 Nelson Syndrome 1025318 M0014557 D009347 ACTH-Secreting Pituitary Adenoma [Disease/Finding]