Freehand Stereotactic Image-Guidance Tailored to Neurotologic Surgery

Abstract

Hypothesis: The use of freehand stereotactic image-guidance with a target registration error (TRE) of μTRE + 3σTRE < 0.5 mm for navigating surgical instruments during neurotologic surgery is safe and useful. Background: Neurotologic microsurgery requires work at the limits of human visual and tactile capabilities. Anatomy localization comes at the expense of invasiveness caused by exposing structures and using them as orientation landmarks. In the absence of more-precise and less-invasive anatomy localization alternatives, surgery poses considerable risks of iatrogenic injury and sub-optimal treatment. There exists an unmet clinical need for an accurate, precise, and minimally-invasive means for anatomy localization and instrument navigation during neurotologic surgery. Freehand stereotactic image-guidance constitutes a solution to this. While the technology is routinely used in medical fields such as neurosurgery and rhinology, to date, it is not used for neurotologic surgery due to insufficient accuracy of clinically available systems. Materials and Methods: A freehand stereotactic image-guidance system tailored to the needs of neurotologic surgery-most importantly sub-half-millimeter accuracy-was developed. Its TRE was assessed preclinically using a task-specific phantom. A pilot clinical trial targeting N = 20 study participants was conducted (ClinicalTrials.gov ID: NCT03852329) to validate the accuracy and usefulness of the developed system. Clinically, objective assessment of the TRE is impossible because establishing a sufficiently accurate ground-truth is impossible. A method was used to validate accuracy and usefulness based on intersubjectivity assessment of surgeon ratings of corresponding image-pairs from the microscope/endoscope and the image-guidance system. Results: During the preclinical accuracy assessment the TRE was measured as 0.120 ± 0.05 mm (max: 0.27 mm, μTRE + 3σTRE = 0.27 mm, N = 310). Due to the COVID-19 pandemic, the study was terminated early after N = 3 participants. During an endoscopic cholesteatoma removal, a microscopic facial nerve schwannoma removal, and a microscopic revision cochlear implantation, N = 75 accuracy and usefulness ratings were collected from five surgeons each grading 15 image-pairs. On a scale from 1 (worst rating) to 5 (best rating), the median (interquartile range) accuracy and usefulness ratings were assessed as 5 (4-5) and 4 (4-5) respectively. Conclusion: Navigating surgery in the tympanomastoid compartment and potentially in the lateral skull base with sufficiently accurate freehand stereotactic image-guidance (μTRE + 3σTRE < 0.5 mm) is feasible, safe, and useful. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT03852329.

Keywords: accurate navigation in neurotology; clinical trial; image-guidance; lateral skull; lateral skull base; neurotology; surgical navigation; temporal bone.

Conflict of interest statement

SW is cofounder, shareholder, and chief executive officer of CASCINATION AG Bern, Switzerland. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2021 Schneider, Anschuetz, Mueller, Hermann, O'Toole Bom Braga, Wagner, Weder, Mantokoudis, Weber and Caversaccio.

Figures

Figure 1

Freehand stereotactic image-guidance system tailored to neurotologic surgery. It comprises a spatial tracking camera, a tracked handpiece providing the possibility to track a registration and pointer instrument, a bone-anchored tripod embedding four titanium registration fiducials and providing an interface to attach the patient tracker, and a navigation user interface.

Figure 2

Experimental setup to preclinically verify a TRE TRE+3σTRE). A task-specific phantom made of carbon fiber and measured using a coordinate measurement machine with a measurement error <0.015 mm was used. The user was guided by the software through the registration and measurement process.

Figure 3

Experimental setup during microscopic removal of a facial nerve schwannoma.

Figure 4

Flowchart for non-randomized clinical trial.

Figure 5

Summary of the accuracy and usefulness ratings (N = 75). Five surgeons each rated 15 anatomical landmarks from two study participants.

Figure 6

Example of corresponding images from the endoscope (top) and the stereotactic image-guidance system (bottom) depicting the pointer pose at the bony overhang of the round window niche. The image pair was rated in terms of accuracy (median: 4, interquartile range: 4–5, N = 5) and usefulness (median: 4, interquartile range: 4–5, N = 5). Inspection of and zooming into the individual MPR and 3D viewer panels were possible during rating. cht, chorda tympani; eac, external auditory canal; ma, malleus; p, promontory; rw, round window.

Figure 7

Example of corresponding images from the microscope (top) and the stereotactic image-guidance system (bottom) depicting the pointer pose on the bone of the mastoid tegmen covering the dura. The image pair was rated in terms of accuracy (median: 4, interquartile range: 3.5–4.5, N = 5) and usefulness (median: 4, interquartile range: 4–4.5, N = 5). Inspection of and zooming into the individual MPR and 3D viewer panels were possible during rating. eac, external auditory canal.

Figure 8

Time required for the intervention steps. *Surgery time includes the non–study-related time during which period, the surgeon manipulates the patient. Time measurement was started with the incision and ended with the finished suture. It includes image annotation time (as the surgery was simultaneously continued). It excludes time required for image acquisition and export, as, during this period, the surgery was interrupted.

Figure 9

Freehand stereotactic image-guidance during an endoscopic cholesteatoma removal.