|Year : 2020 | Volume
| Issue : 4 | Page : 280-285
Experience with the use of the navigation system for ear surgeries: A cohort study
Mariam Al-Amro1, Manal Bin Manea2, Hassan Al Shehri3, Abdulrahman Hagr1
1 King Abdullah Ear Specialist Center, King Saud University, Riyadh, Saudi Arabia
2 Department of Otolaryngology, University Medical City, King Saud University, Riyadh, Saudi Arabia
3 Department of Otolaryngology, King Salman Hospital, Riyadh, Saudi Arabia
|Date of Submission||14-Feb-2020|
|Date of Decision||05-Apr-2020|
|Date of Acceptance||22-May-2020|
|Date of Web Publication||25-Aug-2020|
King Abdullah Ear Specialist Center, King Saud University, P O Box 245, Riyadh 11411
Source of Support: None, Conflict of Interest: None
Objectives: Image guidance has been well characterized in spinal, orthopedic, sinonasal, and skull base surgery, but there is limited information on the use of these systems in cochlear implant and ear surgery. The aim of this study was to evaluate the use of image guidance systems to facilitate cochlear and bone-anchored hearing aid (BAHA) implant surgery. Study Design: Cohort. Materials and Methods: Eleven patients, including 10 who underwent cochlear implantation and 1 who underwent BAHA implantation with the assistance of the navigation system, were included in the study. Patient's data (age, gender, type and cause of hearing loss, and type of surgery), preoperative computed tomography scan findings, accuracy of the navigation system, operating time, and postoperative complications were collected and analyzed. Results: All 11 patients underwent uneventful surgeries finding the desired sites for implantation with ease by using the navigation system. All surgeries were completed without any complications. Conclusion: Performing cochlear and BAHA implantation with the assistance of the navigation system is a safe way to treat patients with normal or abnormal anatomy. In particular, it is helpful for identifying the round window for electrode insertion in cochlear implantation and for choosing the site with the thickest bone for BAHA implantation.
Keywords: Bone-anchored hearing aid implantation, cochlear implantation, navigation
|How to cite this article:|
Al-Amro M, Manea MB, Shehri HA, Hagr A. Experience with the use of the navigation system for ear surgeries: A cohort study. J Nat Sci Med 2020;3:280-5
|How to cite this URL:|
Al-Amro M, Manea MB, Shehri HA, Hagr A. Experience with the use of the navigation system for ear surgeries: A cohort study. J Nat Sci Med [serial online] 2020 [cited 2021 Jan 21];3:280-5. Available from: https://www.jnsmonline.org/text.asp?2020/3/4/280/294055
| Introduction|| |
Improvements in diagnostic imaging led to the identification of subtle anatomic abnormalities of the inner ear in up to 20% of patients with profound sensorineural hearing loss at birth.
Radiographic imaging plays a major role in many types of ear surgery in terms of preoperative evaluation of candidacy, intraoperative monitoring, and postoperative evaluation, as well as in research and experimental techniques.
With the increasing sophistication of imaging methods, the scope of surgical practice is expanding. Integration of imaging with the surgical field allows the visualization of different types of images simultaneously and structures that are normally only visible intraoperatively as well as intraoperative navigation in the areas of anatomic sensitivity.
Surgical navigation involves a concept and set of methods that utilizes computer technology for presurgical planning and for guidance when performing surgical interventions. It is also known as computer-assisted surgery, computer-assisted intervention, image-guided surgery, or computer-aided surgery. Such systems have been used widely in sinus and skull base operations and been shown to be very helpful and accurate. It has been suggested that surgical navigation should be the gold standard in these types of surgery.,
Image guidance has potential applications across a wide range of surgical specialties and is likely to be particularly useful in the areas of complex anatomy where precision is required, such as the head and neck.
Use of image guidance for spinal, orthopedic, sinonasal, and skull base surgery has been well characterized, but there is limited information on the use of these systems in ear surgery.
The aim of this study was to evaluate the ability of an image guidance system to facilitate certain types of ear surgery.
| Materials and Methods|| |
This is a prospective study of 11 patients who underwent cochlear implantation (n = 10) or bone-anchored hearing aid (BAHA) implantation (n = 1) with the assistance of a navigation system in our department at King Abdul Aziz University Hospital, Riyadh, Saudi Arabia. We randomly collected the cases that were done in 1-month period as we want to assess if the use of the navigation system is of any benefit in implantable hearing devices, and if this will affect our practice in ear surgeries.
The Institutional Review Board at the College of Medicine, King Saud University approved the study.
All patients had been evaluated and accepted by the cochlear implant committee. In the admission clinic, surgery benefits, risks, and complication were discussed with the patients and/or guardians and informed consent was signed.
Data on preoperative computed tomography (CT) findings, accuracy of the navigation system, operating time, and postoperative complications, such as facial nerve paralysis, were collected and analyzed.
The patient age, set-up time, and intra-operative time are determined. The sex distribution and indications for surgery were also recorded.
We used the Karl Storz Navigation Panel Unit (KARL STORZ GmbH and Co. KG, Tuttlingen, Germany), which is small enough to be supported on a stand used for intravenous fluids [Figure 1]. This unit is also a mobile space-saving system that can be assembled easily and used in a flexible way in the operating room. A technician who was experienced in the use of this navigation system was present in the operating room for all procedures. For each case, a compact disc containing the preoperative CT scans was viewed on the navigation system and registration was completed. Automatic registration was performed at the time of surgery using four anatomic points (radix, lateral canthus, incisura terminalis, and maxillary crest) [Figure 2]. The accuracy of the device has been tested, and the error was 0.4 which was acceptable.
|Figure 1: Karl Storz navigation system. (Figure obtained from the Internet)|
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|Figure 2: Intraoperative picture of computed tomography displayed in the navigation system showing different planes (sagittal, coronal, and axial) of one of the reference points which is the lateral canthus|
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Computed tomography protocol
- The current and voltage settings are similar to those used for a normal sinus CT with bone window
- Patient positioning: Axial to the occlusion plane
- Transversal (axial) acquisition plane – helical CT followed by creation of an axial data set
- Matrix size: 512 × 512 pixels
- Interslice gap: 1 mm
- Slice thickness: >1 mm
- Section size: 150–180 mm
- Voxel size: 1 mm × 150 mm/512 mm × 150
mm/512 = 1 mm × 0.3 mm × 0.3 mm The scan must include the upper lip, entire nose, forehead, and at least the medial portion of ear it should exclude dental implants, which can interfere with the calculations made by the navigation system
- In the patient who underwent BAHA, the surgeon located the desired anatomic point by moving the instrument and correlating it with the CT images until the thickest area of the skull bone was identified using the navigation probe; we chose a point that was located posteriorly in order to allow enough space for future auricular reconstruction.
| Results|| |
As shown in [Table 1], five of the 11 patients in the study were male and 6 were female. Nine were pediatric cases and 2 were adults. The mean age at the time of surgery was 4.15 (range from 1.80 to 35.5) years.
The audiological assessment for all cochlear implant patients confirmed the presence of profound sensorineural hearing loss in the ear planned for surgery. Analysis of the preoperative CT images for the 10 patients who underwent cochlear implantation revealed a normal cochlea in 5 cases and inner ear abnormalities in the remaining 5 (2 cases of incomplete partition, 1 case of a Mondini deformity, 1 case of fibrosis of the basal turn of the cochlea, and 1 case with enlarged vestibular aqueduct).
After registration and testing the accuracy of the navigation system by the technician for all cases, we used it to identify the facial recess and facial nerve to locate the round window which was of much help, especially in cases of inner ear malformation, and to locate a site with appropriate bone thickness to create the bed for the implant [Figure 3].
|Figure 3: Intraoperative picture of computed tomography displayed in the navigation system showing the thickest point of the skull suitable for the implant|
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The audiological assessment for the patient who received BAHA implant showed right ear profound conductive hearing loss up to 500 Hz rising to severe hearing loss up to 8 KHz with air-bone gap of 60 dB. Left ear hearing assessment was normal. The patient's CT scan of the temporal bone revealed right-sided microtia associated with right external auditory canal bony atresia, a right middle ear cavity that was rudimentary with relatively small ossicles, right mastoid air cells that were atrophic and denser when compared with the left side, bilaterally preserved inner ear structures, a preserved left middle ear cavity, preserved left mastoid air cells, and a preserved left ossicular chain. The tympanic membrane was obliterated on the right side and normal on the left. The jugular fossae and tympanojugular plates were within the normal limits. With the help of the navigation probe, we easily located the site of the thickest skull bone as usually in children the bone mass is not enough. We chose a point which is located posteriorly to give enough place for future auricular reconstruction.
All implants were placed at the desired sites. The wounds were sutured and a dressing applied. For the BAHA patient, a healing cap and ribbon gauze with antibiotic ointment were placed around the implant.
The mean operating time in all patients was 161 (range 90–220) min.
No intraoperative or postoperative complications were reported.
All patients were doing well at the postoperative clinic visit.
| Discussion|| |
The value of a navigation system lies in its ability to allow the surgeon to accurately determine the boundaries of the surgical field and locate surrounding vital structures. This facilitates safer surgery, particularly in cases of malformation or atresia. The navigation system allows more precise and confident identification of specific anatomic sites during ear surgery. However, image guidance cannot serve as a substitute for detailed knowledge of surgical anatomy or experience performing ear surgery.
Our experience has been that a navigation system during cochlear implantation is useful for identifying the correct site for electrode insertion, especially if the cochlea is malformed, and when placing the BAHA abutment in a young child after locating the most appropriate site for the bed of the implant. Schipper et al. performed a cadaveric study to assess the value of navigation in cochlear implant surgery in which cochlear implantation was simulated using a Stryker-Leibinger navigation system and a Nucleus 24 contour implant. The procedure was evaluated for accuracy, reliability, reproducibility, and practicability, and the accuracy was found to be within 1.5 mm. They concluded that the development of newer and more sophisticated referencing systems would be helpful.
In a subsequent clinical study, Labadie et al. validated the efficacy of cochlear implant surgery in 5 ears. First, bone-implanted anchors were placed around each mastoid in the clinic under local anesthesia. They then obtained CT scans of the temporal bone which were used to plan the path from the lateral mastoid cortex through the facial recess to the basal turn of the cochlea both “manually” and “automatically” using computer software. Customized microstereotactic frames were rapidly prototyped to serve as drill guides while constraining the drill so that it followed the appropriate path. During the surgery, after drilling of the facial recess, the drill guides were mounted on the bone-implanted anchors and the accuracy of the paths was assessed by intraoperative photo documentation. They concluded that percutaneous cochlear implant access using customized drill guides based on preoperative CT scans and image-guided surgical technology can be safely accomplished.
In a study by Majdani et al., 4 human temporal bones were scanned and a drilling channel was planned preoperatively from the mastoid surface to the round window niche, providing a margin of safety for all functionally important structures, e.g., the facial nerve, chorda tympani, the incus. Postoperatively, CT images were obtained, and conventional surgical exploration of the drilled route to the cochlea was performed. A cochleostomy located at the scala tympani anterior and inferior to the round window was confirmed in all specimens.
The use of the navigation system in our patient with BAHA helped us locate the area with the most amount of bone for the placement of the implant., Precise determination of the optimal implant placement site intraoperatively may be difficult in children because the skull bone is typically thin and alternative sites for safe placement of the implant are limited. This made BAHA implantation in children <5 years not the first option. The surgical procedure described here is relatively straightforward. Our experience is consistent with that of Kohan and Jethanamest who reported that interactive image-guided surgical navigation during complex otologic surgery may improve the surgical outcome and decrease morbidity by providing an accurate real-time display of surgical instrumentation relative to patient anatomy and pathology [Table 2].
|Table 2: Different studies that used navigation system in ear surgery and their conclusion|
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The most important aspect of the navigation procedure is the development of an accurate model for the individual patient, which can be gleaned from preoperative CT, magnetic resonance, ultrasonographic, or radiographic images. These images are uploaded into the computer system of the navigation control panel. The final step is the creation of three-dimensional images as well as plain images in different planes that reproduce the exact site of the normal and pathologic tissues and structures in the region of interest. Precise location of any point requires patient registration, which correlates the reference position of the images with the reference position of the patient., The surgeon uses a navigation probe connected to the navigation system to identify the correct anatomic position on the patient. This position is simultaneously shown on the images obtained from that patient.
It is our impression that BAHA is rarely used in children younger than 5 years of age because of difficulties in abutment placement due to thin bone and the need to perform surgery as a two-stage procedure. We believe that our method, which makes a one-stage procedure possible, will change practices in BAHA implantation, thereby allowing the improvement of conductive hearing loss in very young children who do not benefit from conventional hearing aids.
Navigation has some disadvantages, including inaccuracy if soft tissue is used as a landmark because of its susceptibility to changes, additional radiation exposure from preoperative CT, a potentially longer operating time, the problem of overconfidence on the part of the surgical team, and the high cost of the machines. However, it can be of great assistance to the surgeon, trainee, and patient, and also has a cost benefits. For example, neuronavigation reduces complication rates and stays in the hospital and the intensive care unit, with their attendant cost implications.
Our study has some limitations as it is a cohort with few numbers of patients which are not having different diagnoses to test the applicability of the navigation system on other ear related diseases, but we believe that it will open a door for new horizons in the field of surgical navigation in ear surgery.
| Conclusion|| |
We have found that performing cochlear and BAHA implantation with the assistance of a navigation system is a safe way to treat the patients with normal or abnormal anatomy helping to find the exact and most suitable site for the implant.
More studies are needed in the larger groups of patients and in patients with other diagnoses to test the efficacy of the navigation system in different types of ear surgery.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]