After bilateral adrenalectomy, patient developed gradual loss of vision, with hyperpigmentation of skin, and headache. Likely cause is

In 10% of patients with Cushing's disease who undergo a bilateral adrenalectomy after failed pituitary surgery, the pituitary adenoma causes Nelson's syndrome due to continued ACTH secretion at high levels, causing hyperpigmentation as a result of chemical synergies between ACTH and melanocyte-stimulating hormoneRef: Bailey and Love 27e pg: 842