Augmented Reality-Assisted Transcanal Endoscopic Ear Surgery for Middle Ear Cholesteatoma

Abstract

Background: The indications for transcanal endoscopic ear surgery (TEES) for middle ear cholesteatoma have expanded for cases involving mastoid extension. However, TEES is not indicated for all cases with mastoid extension. In addition, predicting the extent of external auditory canal (EAC) removal needed for cholesteatoma resection is not always easy. The purpose of this study was to use augmented reality (AR) to project the lesion onto an intraoperative endoscopic image to predict EAC removal requirements and select an appropriate surgical approach. Methods: In this study, patients showing mastoid extension were operated on using a navigation system with an AR function (Stryker). Results: The results showed that some cases with lesions slightly extending into the antrum required extensive resection of the EAC, while cases with lesions extending throughout the antrum required smaller resection of the EAC, indicating TEES. Conclusions: By predicting the extent of the needed EAC removal, it is possible to determine whether TEES (a retrograde approach) or canal wall-up mastoidectomy, which preserves as much of the EAC as possible, should be performed. We believe that our findings will contribute to the success of middle ear surgeries and the implementation of robotic surgery in the future.

Keywords: augmented reality; cholesteatoma; transcanal endoscopic ear surgery (TEES); tympanoplasty.

Figure 1

Navigation monitor after completion of tracing of lesion. The lesion was traced every 1.2 mm in three computed tomography (CT) directions and was ready for the augmented reality (AR) display after pre-planning was performed. The upper-left, upper-right, and lower-right images are sagittal, coronal, and axial slices, respectively. The tracing colors are freely selectable, and a variety of colors were used in this case.

Figure 2

Questionnaire results of the two cases (Cases 2 and 3) in which the planned approach changed based on the AR display. The surgical approach in Case 2 and Case 3 changed significantly due to the AR display (*: p < 0.05). In Case 2, the proportion of performing MES increased significantly, while in Case 3, the proportion of performing TEES increased significantly. AR: augmented reality; MES: microscopic ear surgery; TEES: transcanal endoscopic ear surgery.

Figure 3

Imaging findings and AR display in Case 2. The AR display shows that the area of EAC drilling to be performed is large, whereas the area of progress is not very large. (a) Axial CT slice of the temporal bone showing a slight extension into the antrum. (b) Axial CT slice of the temporal bone showing extension into the attic. (c) Axial CT slice of the temporal bone showing extension into the tympanic cavity. The lesion extended close to the stapes; however, the superstructure did not exhibit any erosive changes. (d) Typical endoscopic findings of cholesteatoma with debris in the pars flaccida. (e) Endoscopic image with AR display overlaid on image (d). Extensive EAC drilling was required to remove the lesions. AR: augmented reality; EAC: external auditory canal; CT: computed tomography.

Figure 4

Imaging findings and AR display in Case 3. The AR display shows that the area of the EAC drilling to be performed is not very large, whereas the area of progress was relatively large. (a) Axial CT slice of the temporal bone showing extension into the entire antrum. (b) Axial CT slice of the temporal bone showing extension from the attic to the entire antrum. (c) MRI (non-echoplanar imaging (EPI)-based diffusion-weighted imaging (DWI) fused with T2) showing extension from the attic to the entire antrum, as well as (b). (d) Endoscopic findings of cholesteatoma with debris in the pars flaccida. Multiple mild osteomas were also observed in the EAC. (e) Endoscopic image with AR display overlaid on image (d). Extensive EAC drilling was not required to remove the lesion. (f) Endoscopic image after lesion removal. The range of the EAC drilling was consistent with that on the AR image. (g) The defect is covered with a single piece of tragus cartilage. (h) Otological findings 1 year postoperatively do not show retraction pockets.

Figure 5

Correction of faulty registrations. (a) The lesion and augmented reality (AR) images (shapes in blue) do not match significantly. (b) Re-registration based on the lateral process of the malleolus. (c) After correction, the lesion and AR images match.

Figure 6

Augmented reality (AR) image of the facial nerve. (a) Marking the facial nerve with a pink line on the axial computed tomography (CT) slice of the temporal bone. (b) Marking the facial nerve with a pink line on the sagittal CT slice of the temporal bone. (c) An AR image of the facial nerve overlaid on the endoscopic image (yellow arrowhead tip). It is not a 3D display; therefore, its depth is not known, but its direction is indicated.