Virtual exploration and comparison of linear mastoid drilling trajectories with true-color volume rendering and the visible ear dataset

Abstract

This paper provides instructions for a virtual exploration and self-study of surgical approaches within the temporal bone. Linear drilling trajectories in the sense of "keyhole" accesses are compared with true-color rendering techniques using freeware to introduce and evaluate new otologic approaches. On the basis of public-domain cyro-histology image data from a temporal bone six different drill trajectories are presented. This virtual method has the potential to be a first step in investigation of new surgical approaches before moving to cadaver testing.

Figure 1

Different keyhole accesses towards the scala tympani. The subfigures (a)–(c) show two almost perpendicular views plus a view through the outer ear canal. The first two images of each subfigure are cropped in that way that the channel is lying directly on or half inside the truncated surface. Additionally some landmarks are shown as spheres (color/electronic version only - purple: scala tympani, red: scala vestibular, green: spiral ligament). (a) and (b) illustrate MPTA (KA1, KA2) and (c) the Veria technique (KA3).

Figure 2

Further keyhole accesses towards the scala tympani as shown in Figure 1. (a) illustrates a SMA approach (KA4), (b) an extended SMA approach (KA5) and (c) an experimental approach tangential to the brain (KA6).

Figure 3

Six different keyhole accesses. Facial nerve and chorda tympani are shown and not touched by all six channels. The surface model of the ear is used from the files of the Visible Ear Simulator [5]. (a) Top view, (b) magnified top view without ear surface model and (c) view from occipital. The different channels can be identified counterclockwise in (a) and (b) as KA3, KA4, KA1, KA2, KA6 and KA5.