Usefulness of Cone-Beam Computed Tomography in Determining the Position of Ossicular Prostheses

Abstract

Cone-beam computed tomography (CT) is proving useful in various operative settings. We hypothesize that it has great potential as an intraoperative assessment tool for ossicular prosthesis positioning. Results from prosthetic ossiculoplasty are frequently disappointing. Undetected intraoperative displacement of the prosthesis may be caused, and obscured, by placement of an overlying cartilage graft. A cadaveric right temporal bone was prepared with a tympanomeatal flap, and an extended posterior tympanotomy through a cortical mastoidectomy. Each of 3 commercially available prostheses was positioned in 3 different locations: (1) optimal, (2) grossly displaced, and (3) marginally displaced. The intended prosthetic positions were confirmed by endoscopy before and after cone-beam CT image acquisition. The primary outcome measure was the position of the prosthesis in relation to the stapes and tympanic membrane, as assessed by 5 expert reviewers blinded to the study. Secondary outcome measures included optimal dosing for adequate image resolution and radiographic scatter associated with different prosthetic materials. Cone-beam CT accurately demonstrated the position of ossicular reconstruction prostheses with respect to the stapes and tympanic membrane. Prosthesis displacement, whether minimally or marked, was also accurately demonstrated. Interobserver agreement among the 5 reviewers, measured using a Fleiss κ statistic, ranged from 0.4 to 0.8 (fair to substantial agreement depending on type and position of the prosthesis). Cone-beam CT is a useful tool for determining the position of ossicular reconstruction prostheses in situ. We suggest it has potential for intraoperative assessment, to check positioning after the prosthesis has been covered with a cartilage graft and tympanomeatal flap.