PRE-OPERATIVE EVALUATION OF PETROUS BONE CHOLESTEATOMA BY THREE-DIMENSIONAL (3D) RECONSTRUCTION IMAGES FROM CT

Minoru Hara, Haruo Takahashi

Department of Otolaryngology, Nagasaki University Hospital, Nagasaki, Japan

Introduction

The approaches to petrous bone cholesteatomas (PBCs) are selected usually based on the information of pre-operative CT images, however, it is extremely difficult for surgeons to understand the three-dimensional (3D) relationship of the complicated temporal-bone structures. The aim of this study is to create the precise 3D images from CT easily, and to examine its usefulness in the surgical planning of PBCs.

Methods

First we manually colored pre-operative CT images using Photoshop CS Extended. The inner ear, auditory ossicles, facial nerve (+ internal auditory canal (IAC)) and PBC were shaded in blue, red, yellow and green, respectively (Fig. 1a). We then converted the colored CT images to 3D images (Fig. 1b) using ‘Delta Viewer’, a freeware for Macintosh available on the Internet (http://delta.math.sci.osaka-u.ac.jp/DeltaViewer/index.html). The 3D images can be rotated freely using the Delta Viewer application. Before surgery, we discussed any problems anticipated based on the 3D images, and planned for the surgery of a PBC within the surgery group.

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Fig. 1a. Colored CT image of normal left temporal-bone structures.

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Fig. 1b. Lateral view of the 3D image of normal left temporal-bone structures, converted by Delta Viewer. Co: cochlea; PSC: posterior semicircular canal; IAC: internal auditory canal; FN: facial nerve; M: malleus; I: incus; S: stapes; AT: annulus tympanicus; AV: aqueduct of vestibule.

Case 1: a 17-year-old female

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Fig. 2. Colored CT images of case 1; left ear. The cholesteatoma of petrous bone part is colored in green.

The CT findings of the left ear (Fig. 2) showed that the cholesteatoma had derived from epitympanum extending anteriorly up to anteromedial to the anterior semicircular canal (ASC). The 3D images (Figs. 3 and 4) indicated that a part of the PBC was hidden by the ASC when viewed from the direction of mastoid approach. Referring to the 3D images, we were able to find out the appropriate direction to approach the PBC from anterior to ASC, and successfully removed the PBC without any complication.

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Fig. 3. Superior view of the 3D image of case 1. Co: cochlea; V: vestibule; FN: facial nerve; M: malleus; I: incus; IAC: internal auditory canal; EAC: external auditory canal; LSC: lateral semicircular canal; ASC: anterior semicircular canal; PSC: posterior semicircular canal.

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Fig. 4. 3D image viewed from the direction as in the surgery with the transmastoid approach. A part of the PBC is hidden by the ASC (white circle). Co: cochlea; FN: facial nerve; M: malleus; I: incus; IAC: internal auditory canal; EAC: external auditory canal; LSC: lateral semicircular canal; PSC: posterior semicircular canal.

Case 2: a 45-year-old female

The CT findings of the right temporal bone (Fig. 5) indicated a very complicated and odd shape of a cho-lesteatoma that had derived from the epitympanum and extensively destroyed the floor of the middle cranial fossa, and had extended around the IAC with fistula. The 3D images (Figs. 6 and 7) showed that most of the PBC was hidden by the semicircular canal and it was impossible to reach the part of the PBC around the IAC with the mastoid approach without destroying the ASC even partially. Then we decided to use the translaby-rinthine approach and the middle-fossa approach for the part around the IAC. We were able to remove all of the PBC without any remnant of PBC and any complications except post-operative dizziness.

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Fig.5. The colored CT images of case2; right ear. The PBC, shaded in green, was complicated and odd shape.

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Fig.6. Inferior View of 3D image of case 2. Co, cochlea; RW, round window; IAC, internal auditory canal; LSC, lateral semicircular canal; PSC, posterior semicircular canal.

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Fig.7. 3D image viewed from the direction as in the surgery with transmasitoid approach. Most of the PBC is hidden by the inner ear labyrinth. Co, cochlea; RW, round window; IAC, internal auditory canal; LSC, lateral semicircular canal; PSC, posterior semicircular canal.

The other cases

The 3D images of 2 other cases are shown in Figures 8 and 9.

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Fig.8. 3D image viewed from the direction as in the surgery with transmasitoid approach; 6-year-old boy, left ear. We performed normal mastoidectomy approach referring this 3D image. Co, cochlea; M, malleus; ASC, anterior semicircular canal; LSC, lateral semicircular canal; PSC, posterior semicircular canal.

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Fig.9a. 3D image viewed from the direction as in the surgery with transmasitoid approach; 67-year-old male, right ear. We performed translabyrinthine approach and sacrificed anterior semicircular canal. Co, cochlea; RW, round window; ASC, anterior semicircular canal; LSC, lateral semicircular canal; PSC, posterior semicircular canal.

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Fig.9b. 3D image of temporal bone viewed from posterosuperior direction; the same case as fig 9a. Asterisk (*) shows the bony defect due to the PBC.

Conclusions

We were able to successfully depict the temporal-bone structures and PBC as 3D images. They were extremely useful to build a strategy of approaching the PBC during the surgeries and we were able to complete the surgeries without any complications in all the cases. This method to make 3D images by Delta Viewer has been reported before.1

References

1.Minoru H, Haruo T, Yukihiko K. The usefulness of reconstructed 3D images in surgical planning for cochlear implantation in a malformed ear with an abnormal course of the facial nerve. Clin Exp Otorhinolaryngol 5 (Suppl 1):S48–52, 2012

Address for correspondence: Minoru Hara, harami@nagasaki-u.ac.jp

Cholesteatoma and Ear Surgery – An Update, pp. 407–411

Edited by Haruo Takahashi

2013 © Kugler Publications, Amsterdam, The Netherlands