Endoscopy of the middle ear through the eustachian tube: anatomic possibilities and limitations.

HYPOTHESIS: This anatomic study was designed to provide otosurgeons with a detailed description of the technique of transtubal middle ear endoscopy and anatomic landmarks facilitating orientation. To establish the role of transtubal endoscopy, its anatomical potentials and limitations were studied.

BACKGROUND: Transtubal endoscopy has recently been described as an atraumatic tool for exploring the tympanic cavity. From the nasopharynx, a thin, flexible endoscope is advanced into the middle ear through the Eustachian tube. After the endoscope has been placed, it offers an anteroposterior view of the tympanic structures.

METHODS: Temporal bone blocks and whole skulls of recently deceased persons were examined to define the average range of view obtained by transtubal endoscopy. Key structures in each region of the tympanic cavity were chosen for inspection, and positive identifications were noted.

RESULTS: With a 0.8-mm, flexible, steerable scope, most mesotympanic structures (stapes suprastructure, incudostapedial joint, tympanic chord, and inner surface of the eardrum) were clearly defined. Areas of the posterior wall that were not accessible with the otomicroscope (lateral tympanic sinus, tympanic sinus, and facial recess) were also seen. Unlike with transtympanic endoscopy, the epitympanum (incudomalleal joint and malleus neck) was also evaluable. The stapes footplate was not seen well and the round window niche was unable to be inspected in the anteroposterior view inherent in the technique. Technical factors (poor illumination and small image size) and the unfamiliar anteroposterior view made orientation in the middle ear difficult.

CONCLUSION: Transtubal middle ear endoscopy is a suitable method for exploring the tympanic cavity without traumatizing the eardrum.