Nelson's syndrome is most likely seen after:

Answer is B (Adrenalectomy): Adrenalectomy predisposes to development of Nelson's syndrome. Nelson syndrome Nelson syndrome is a disorder characterized by rapid enlargement of a preexisting ACTH pituitary adenoma after adrenalectomy. This syndrome occurs because following adrenalectomy, the suppressive effect of coisol on ACTH secretion and tumor growth is removed resulting in increased ACTH secretion and tumor growth. Patients with Nelson's syndrome present with hyperpigmentation and with manifestation of an expanding intrasellar mass lesion (visual field defects, headache, cavernous sinus invasion etc.) These tumors represent one of the most aggressive and rapidly growing of all pituitary tumors. ACTH levels are markedly elevated. Preoperative Radiotherapy may be indicated to prevent development of Nelson's syndrome after adrenelectomy.