Optimal Head Position for Intratympanic Dexamethasone Injection Relative to the Round Window.

Objective

Intratympanic dexamethasone injection (ITDI) is widely used for inner ear disorders. However, optimal head positioning to maximize drug absorption through the round window membrane (RWM) while minimizing Eustachian tube (ET) washout remains undefined. This study aimed to determine the ideal head position for ITDI using a multimodal approach and to compare it with the traditional 45-degree head rotation.

Methods

A multimodal analysis incorporating cadaveric dissection, 3-dimensional (3D) anatomic modeling, and clinical perilymph sampling from patients was performed. Twelve sagittal-sectioned human temporal bone cadavers were dissected to identify the transcanal angle required for direct RWM contact, and corresponding yaw, roll, and pitch head-position angles were measured. A 3D-printed anatomic model of the external auditory canal, RWM, and ET was constructed to confirm fluid flow toward the RW. Additional fresh-frozen cadavers were used to compare perilymph dexamethasone concentrations following ITDI administered in either the traditional or ideal head position. Clinically, 5 patients undergoing translabyrinthine vestibular schwannoma resection received ITDI after induction of anesthesia and surgical positioning, followed by perilymph sampling during surgery.

Results

The optimal head position relative to the RWM was identified as 58.9 degrees of yaw, 31.1 degrees of roll, and 22.5 degrees of pitch. Three-dimensional modeling demonstrated increased drug flow toward the RWM and reduced ET washout when roll and pitch were optimized together, while yaw alone had minimal effect. Cadaveric and clinical patient perilymph sampling showed a consistent trend toward higher perilymph dexamethasone concentrations in the ideal head position than in the traditional 45-degree position. When the cadaveric and clinical samples were pooled for exploratory comparison, the ideal head position showed a 2.94-fold higher dexamethasone concentration than the traditional position (0.0447% vs. 0.0152%), although this difference did not reach statistical significance.

Conclusion

Ideal intratympanic dexamethasone delivery requires adjustment of roll and pitch in addition to yaw. Implementing a 3-axis ideal head position is a simple, cost-effective strategy to improve intratympanic steroid absorption and therapeutic efficacy.