Minimally Invasive, Image-Guided, Facial-Recess Approach to the Middle Ear: Demonstration of the Concept of Percutaneous Cochlear Access In Vitro *Robert F. Labadie, *Pallavi Choudhury, †Ebru Cetinkaya, *Ramya Balachandran, *David S. Haynes, ‡Michael Fenlon, ‡Steven Juscyzk, and †J. Michael Fitzpatrick *Department of Otolaryngology–Head and Neck Surgery, Vanderbilt University Medical Center, Nashville, Tennessee, U.S.A.; †Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee, U.S.A.; ‡Department of Prosthodontics, King’s College, London, U.K. Hypothesis: Image-guided surgery will permit accurate access to the middle ear via the facial recess using a single drill hole from the lateral aspect of the mastoid cortex. Background: The widespread use of image-guided methods in otologic surgery has been limited by the need for a system that achieves the necessary level of accuracy with an easy-to-use, noninvasive fiducial marker system. We have developed and recently reported such a system (accuracy within the temporal bone = 0.76 6 0.23 mm; n = 234 measurements). With this system, image-guided otologic surgery is feasible. Methods: Skulls (n = 2) were fitted with a dental bite-block affixed fiducial frame and scanned by computed tomography using standard temporal-bone algorithms. The frame was removed and replaced with an infrared emitter used to track the skull during dissection. Tracking was accomplished using an infrared tracker and commercially available software. Using this system in conjunction with a tracked otologic drill, the middle ear was approached via the facial recess using a single drill hole from the lateral aspect of the mastoid cortex. The path of the drill was verified by subsequently performing a traditional temporal bone dissection, preserving the tunnel of bone through which the drill pass had been made. Results: An accurate approach to the middle ear via the facial recess was achieved without violating the canal of the facial nerve, the horizontal semicircular canal, or the external audi- tory canal. Conclusions: Image-guided otologic surgery provides access to the cochlea via the facial recess in a minimally invasive, percutaneous fashion. While the present study was confined to in vitro demonstration, these exciting results warrant in vivo testing, which may lead to clinically applicable access. Key Words: Image-guided surgery—Minimally invasive surgery— Otologic surgery—Fiducial markers—Target registration error— Cochlear implantation. Otol Neurotol 26:557–562, 2005. BACKGROUND Image-guided surgery technology has been clinically available since the mid-1980s (1). Analogous to global positioning systems (GPS), image-guided surgery facil- itates intraoperative surgical navigation by linking pre- operative radiographs to intraoperative anatomy. Central to the image-guided surgery process is registration: the linking of the radiographic images to the patient. To achieve high accuracy, the registration is based on fidu- cial markers that are identified both in the radiographs and on the patient. A mathematical transformation mat- rix is created to optimize the alignment of the fiducials. This same transformation matrix is then applied to all information in the radiograph, allowing an overlay of the radiograph onto the patient’s physical anatomy. This infor- mation is typically presented to the surgeon via a video monitor; a pointer placed within the surgical field is linked to a cursor on the monitor to show the corresponding radio- graphic position in axial, sagittal, and coronal sections. Image-guided surgery is widely used in neurosurgery, where the standard fiducial is a rigidly affixed N-frame. Screwed directly into the cranium, the N-frame is secured before imaging studies are obtained and remains in place throughout surgical intervention. Such stereotactic Address correspondence and reprint requests to Robert F. Labadie, M.D., Ph.D., 7209 Medical Center East, South Tower, Vanderbilt University Medical Center, Nashville, TN 37232-8605, U.S.A.; E-mail: robert.labadie@vanderbilt.edu Presented at the Annual Meeting of the American Otologic Society, May 1–2, 2004, Phoenix, AZ. This work was supported by Vanderbilt University Medical Center (Discovery Grant, PI-RFL) and the National Institute of Biomedical Imaging and Bioengineering (R21 EB02886-01, PI-RFL). Otology & Neurotology 26:557–562 Ó 2005, Otology & Neurotology, Inc. 557 JOBNAME: ajo 26#4 2005 PAGE: 1 OUTPUT: Fri July 1 9:30:04 2005 lww/ajo/99855/MAO200022 Prod. #MAO200022