Objective: To determine the anatomical relationship between the facial recess and the round window membrane and to
measure the distance between the chorda tympani nerve and the facial nerve through the round window membrane.
Material and Method: A descriptive study of the embalmed Thai cadaveric temporal bones was conducted at the Department of Otorhinolaryngology, the Faculty of Medicine, Khon Kaen University.
Results: Thirty-seven Thai cadaveric temporal bones from 22 males and 15 females were included in the study. The length of
the facial nerve from the crotch of the facial nerve and the chorda tympani nerve (CFC) to the fossa incudis was 13.52 mm
(95% CI: 12.74-14.31), and the length from the CFC to the round window position was 10.28 mm (95% CI: 9.52-11.04). The length of the chorda tympani nerve from the CFC to the round window position was 9.34 mm (95% CI: 8.61-10.07). The width of the facial recess (the distance between the chorda tympani nerve to the facial nerve) through the round window was 2.89 mm (95% CI: 2.71-3.09). The round window was located at a ratio of 0.75 (95% CI: 0.72-0.79) of the facial nerve length from the CFC. The mean distance of the posterior crus of stapes footplate to the round window membrane was 2.24 mm (95% CI: 2.16-2.33). The diameter of the stapes footplate was 2.66 mm (95% CI: 2.58-2.76).
Conclusion: The round window could be identified at 3/4 the length of the facial nerve from the CFC to the fossa incudis or
from the posterior crus of stapes at approximately the length of the stapes footplate. The width of the facial recess at the round
window position was 2.89 mm.

Keywords: Facial recess, Facial nerve, Round window membrane, Posterior tympanostomy, Cochlear implantation