Abstract: Objective To explore the relationship between bone crest and crypt of the retrotympanum and hypotympanum and to provide anatomical data for clinical use. Methods Eighty sides of the middle ears were selected(20 adult patients with fresh frozen caddies and 40 cases of endoscopic surgery). The middle ears were accessed through the external auditory canal using 0° and 30° endoscopes, and the relevant areas of the retrotympanum and hypotympanum were dissected and observed. The morphology of bone crest and crypt in the retrotympanum and hypotympanum were recorded and made into charts. Results (1)The incidence of ponticulus was 62.50%(50/80; solid bone ridge, 52.50%; bridge-like bone ridge, 10.00%); (2)Subiculum was 52.50%(42/80; solid bone ridge, 41.25%; bridge-like bone ridge, 11.25%); (3)Funiculus was 52.50%(42/80; solid bone ridge, 46.25%; bridge-like bone ridge, 6.25%); (4) Based on structural variation, the position of posterior sinus and sinus tympanic was classified as classical shape(50%), confluent shape(47.50%), partitioned shape(1.25%), and restricted shape(1.25%); (5) The proportion of chordal, vertebral, and styloid crests was 67.50%(54/80), 75.00%(60/80), and 57.50%(46/80), respectively. Conclusion The endoscopic vision of the ear could provide a full range of visual field to observe these hidden anatomical regions, bone crests, and sinus of the retrotympanum and hypotympanum varied.

Key words: Retrotympanum and hypotympanum, Sinus tympani, Posterior sinus, Ponticulus, Subiculum