Oskar Hirsch described the fully extracranial endonasal transethmoid transsphenoidal approach in 1909. He was the first to describe the surgical entrance to the sella using this exclusively unilateral endonasal route, which he demonstrated on a cadaver. He reports performing this procedure on a live patient in April, 1910, under local anesthesia in stages over 5 weeks. For better exposure, Hirsch consolidated his method with Killian's submucosal window resection of the posterior nasal septum allowing for bilateral access to the sphenoid sinus and sella, and completed a single-stage procedure on a patient in June 1910.

Oskar Hirsch was the first to describe and perform a stepwise surgical approach to the sella using an exclusively extracranial, endonasal, transethmoidal, and transsphenoidal approach. He built upon his mentor Markus Hajek's approaches to the posterior ethmoid cells and sphenoid sinus ¹⁾.