Epitympanum volume and tympanic isthmus area in temporal bones with retraction pockets

Objectives/Hypothesis: To compare the volume of the epitympanic space, as well as the area of the tympanic isthmus, in human temporal bones with retraction pockets to those with chronic otitis media without retraction pockets and to those with neither condition. Study Design: Comparative human temporal bone study. Methods: We generated a three-dimensional model of the bony epitympanum and measured the epitympanic space. We also compared the area of the tympanic isthmus. Results: The mean total volume of the epitympanum was 40.55 ± 7.14 mm³ in the retraction pocket group, 50.03 ± 8.49 mm³ in the chronic otitis media group, and 48.03 ± 9.16 mm³ in the neither condition group. The mean volume of the anterior, lateral, and medial compartments in temporal bones in the retraction pocket group was significantly smaller than in the two control groups (P < 0.05). Total epitympanic volume was also significantly smaller in the retraction pocket group than in both control groups (P < 0.05). The mean area of the tympanic isthmus was significantly smaller in the retraction pocket group (8.11 ± 2.44 mm²) than in the chronic otitis media group (9.82 ± 2.06 mm²) or the neither condition group (10.66 ± 1.78 mm²) (P < 0.05). Conclusion: Our data indicate that temporal bones with retraction pockets have a smaller volume bony epitympanum and a smaller tympanic isthmus area as compared with temporal bones from both control groups. The smaller volume tympanic isthmus in the retraction pocket group may suggest that a blockage in the aeration pathways to the epitympanum could create dysventilation, resulting in negative pressure and ultimately in retraction pockets and cholesteatomas. Level of Evidence: NA Laryngoscope, 126:E369–E374, 2016.