Spontaneous regression after standard transsphenoidal surgery in a huge pituitary adenoma with epidural extension

A 59-year-old female presented with a huge non-functioning pituitary adenoma which mainly extended from the intrasellar region to the epidural space of the anterior cranial base, manifesting as a 2-year history of disturbance of the visual field. Transsphenoidal surgery was performed to decompress the optic pathway as the first step of a two-staged operation. Postoperative magnetic resonance images unexpectedly showed spontaneous regression of the major portion of the epidural tumor which had not been manipulated during the first operation. The reason for the spontaneous regression remains unclear.