Abstract
PurposeDuring cochlear implant (CI) surgery, visual detection of the stapedius reflex as movements of the stapes tendon, electrically elicited via the CI, is a standard measure to confirm the system's functionality. Direction visualization of the stapedius muscle (SM) movements might be more reliable, but a safe access to the small SM is not defined. A new surgical planning tool for pre-operative evaluation of the accessibility to the stapedius muscle (SM) during a cochlear implantation (CI) via a retrofacial approach was now evaluated.MethodsA surgical planning tool was developed in MATLAB using an image processing algorithm to evaluate drilling feasibility. A flat-panel computed tomography (CT) combining a rotational angiographic C-arm units with flat-panel detectors (Dyna-CT) was used. In total, 30 3D Dyna-CT-based temporal bone reconstructions were evaluated by automatized algorithms, generating a series of trajectories and comparing their feasibility and safety to reach the SM via a retrofacial approach. The predictability of the surgical planning tool results was tested in 5 patients.ResultsThe surgical planning tool showed that a retrofacial access to the SM would be feasible in 25/30 cases. Moreover, the evaluation of the predictability of the results obtained with the surgical planning tool conducted during 5 CI surgeries confirmed the results. Both the surgical planning tool and the results on SM accessibility via retrofacial approach during CI showed that this is safe and feasible only when the SM-exposed area was > 25% of its total, the distance between the SM and the facial nerve was > 0.8 mm, and the surgical corridor diameter was > 3 mm.ConclusionThe surgical planning tool seems to be useful for the pre-operative evaluation of the accessibility to the SM during a CI surgery via a retrofacial approach. Further prospective studies are needed to validate the results in larger cohorts.
Highlights
The temporal bone is a complex structure housing small and functionally very important structures like the middle-ear including the ossicles; the inner-ear including the cochlea, vestibule and semicircular canals; the bony canals for the facial and vestibulocochlear nerves; and the related vasculature
We showed that retrofacial access to the unbent distal part of the stapedius muscle (SM), planned in advance and based on the analysis of high-resolution computed tomography (CT) datasets of the temporal bone and 3D reconstructions complies with these requirements [3]
Pre-operative planning tools are of paramount importance for any minimal-invasive otosurgical approach, for minimal-invasive robotic middle-ear surgeries, in order to prevent the damage of functional structures of the ear [4,5,6], supporting the conclusion of previous works describing the use of newly developed software for automated segmentation and trajectory planning for temporal bone surgery [7]
Summary
The temporal bone is a complex structure housing small and functionally very important structures like the middle-ear including the ossicles; the inner-ear including the cochlea, vestibule and semicircular canals; the bony canals for the facial and vestibulocochlear nerves; and the related vasculature. An effective alternative to visual detection is given by electromyographic (EMG) recording of the SM contraction [2]. While this technique is very reliable, it requires the EMG electrodes to be effectively and safely placed on the SM. Pre-operative planning tools are of paramount importance for any minimal-invasive otosurgical approach, for minimal-invasive robotic middle-ear surgeries, in order to prevent the damage of functional structures of the ear [4,5,6], supporting the conclusion of previous works describing the use of newly developed software for automated segmentation and trajectory planning for temporal bone surgery [7]. The present study describes the implementation and use of a new surgical planning tool designed to evaluate and plan the access to the SM via drilling of the temporal bone in otosurgery in a safe and effective way
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