Dynamic Cone-Beam CT of the Middle Ear for Determining Excursion of the Ossicles: Technical Proof of Concept.

Objective: Conductive hearing loss can be caused by fixation or discontinuity of the ossicles. Current noninvasive methods such as tympanometry and conventional clinical imaging might indicate mobility and/or pathology but cannot quantify the excursion. The objective of this study is to measure the excursion of the malleus and incus using timed pressurization during clinical cone-beam CT (CBCT) of the middle ear.

Patients: Five human cadaveric heads.

Intervention: CBCT imaging obtained at an isotropic resolution of 0.08 mm of five cadaveric heads (10 ears). A tympanometer was used to pressurize the ear drum and change pressure during the scan.

Main outcome measures: The excursion of the manubrium of malleus and the long process of incus was determined based on manual segmentation of the imaging series.

Results: It was technically feasible to change pressure midways during scan and use 180° virtual reconstructions of the negative and positive pressure phase to quantify the mobility of the malleus and incus. In ears with normal impedance of the tympanic membrane (type A tympanogram), we found an average excursion of the manubrium of malleus of 0.61 mm and the long process of incus of 0.27 mm.

Conclusion: Dynamic CBCT of the middle ear can be used to quantify the excursion of malleus and incus in ears with normal ear drum impedance. This might provide additional information compared with conventional static imaging at atmospheric pressure and other current in vivo methods such as wideband tympanometry. Further studies are needed to explore the clinical value of the method.