1889
The history of the endoscope in skull base surgery is de facto the history of pituitary surgery. The first pituitary operation was likely performed by Sir Victor Horsley in 1889 via a transfrontal approach though he did not publish his results 1).
1)
Pollock JR, Akinwunmi J, Scaravilli F, Powell MP. Transcranial surgery for pituitary tumors performed by Sir Victor Horsley. Neurosurgery. 2003 Apr;52(4):914–925