Discussion
Residual cholesteatoma is the first cause of failure in cholesteatoma surgery, leading sometimes the surgeon to adopt expensive and invasive strategies such as the “second look” tympanoplasty. Among strategies to reduce the risk of residual cholesteatoma, EES has shown an improvement in the visualization of hidden areas of the middle ear and has consequently been accepted as a useful tool in cholesteatoma surgery. DIE endoscopic visualization may be a further advance in the intraoperative detection of residual cholesteatoma.
DIE systems such as SPIES have been developed to better identify and distinguish pathological from healthy tissue and thereby remove the disease while respecting normal mucosa. In contrast to the commonly used white light, DIE makes avascular structures (e.g. cholesteatoma) appear whiter than vascularized tissues: This allows the surgeon to define its extension precisely and to remove the disease completely.
In other surgical specialties such as ureteroscopy, endoscopic thyroidectomy and laparoscopy, SPIES was already used for early tumour detection by means of highlighting hyper-vascular structures13,14. Improved visualisation of differently vascularized tissue and thus clearer distinction between pathologies and normal anatomy are generally cited as the main advantages8,9.
To the best of authors’ knowledge, the retrospective case series by Lucidi et al. (2020) was the first paper to investigate the usefulness of the SPIES image enhancing system in ear surgery8. The challenge in cholesteatoma surgery is to completely remove the squamous epithelial, while sparing normal middle ear and mastoid mucosa. According to the previously mentioned study, spectra A and B filters in EES are deemed suitable to recognize cholesteatoma remnants8.
In our study, the comparison of the three DIE techniques (clara, spectra A, spectra B) makes clear that each of those modalities brings along its own advantages. When considering the surgeons’ point of view on the suitability of the three image-improving modalities, a general attitude in favour of the use of clara followed by spectra B and lastly spectra A was found. This is expected, as Clara is the “state-of-the-art” technique used to perform EES. The spectra A and B techniques have recently been introduced to depict residual cholesteatoma after complete removal of the disease.
We investigated and quantified separately the added value of clara, spectra A and spectra B for the first time. In all three imaging techniques, diseased images are detected more successfully than disease-free images. This difference becomes very apparent with Spectra B. With the highest sensitivity but the lowest specificity, a lot of tissue is misinterpreted as cholesteatoma but only few cholesteatomas are missed. In our opinion, this increase in sensitivity justifies its use at the end of every cholesteatoma surgery. Using the spectra B technique most cholesteatoma-remnants are detected and results regarding residual cholesteatoma may be improved. Moreover, a high intra-rater reliability was observed and was highest for spectra B. In our opinion, this further indicates an additional value regarding the performance of spectra B. Clara in contrast has the highest accuracy overall and its general image properties with high illumination makes it most suitable to perform the surgery itself. By having the smallest number of false positives, Clara is considered the most conservative restrained method. Spectra A lies between Clara and Spectra B in terms of sensitivity-specificity-difference, as well as in terms of detection, missing, identification and misidentification of cholesteatoma. Therefore, we don’t see any indication in the use of the Spectra A technique in cholesteatoma surgery.
Interestingly, some special situations require special considerations while using digital image enhancement in EES (figure 4). For example, the tendon of the tensor tympani muscle appears bright at its insertion in the malleus and may be mistaken for squamous epithelium. Similarly, upon thorough review of the image set represented in Figure 4 D-F and related histopathology, it appears that bone fragments produced during drilling may also be mistaken for cholesteatoma. In summary, Clara may be considered the most appropriate image modality for use during surgery. However, as the removal of small amounts of inflamed mucosa has few consequences for the patient, whereas cholesteatoma remnants can result in serious complications and require a second operation, we recommend the use of Spectra B as a final overview at the end of cholesteatoma surgery, in order to avoid missing any pathological finding. Indeed, the combined use of Clara and Spectra B, as proposed, permits to increase the overall accuracy of the endoscopic visualization up to 75.4% in our study.
The present study includes responses from ear surgeons with different surgical background (microscopic and endoscopic), different experience and from different countries. This is a strength of the study, as it explores the accuracy of the DIE technique in ear surgeons with variable experience in dealing with endoscopic images of the middle ear, eventually providing data which can be considered closer to real-life. In addition, this can also explain the difference of the observed sensitivity and specificity compared with previous studies8 and permits to hypothesize a learning curve-related outcome.
Since not all surgeons who were invited to fill out the questionnaires responded, we eventually obtained an uneven distribution of responses across the questionnaires. As a result, not all images were presented with each technique the same number of times overall. This is certainly a limitation of the current study, as some responses therefore influenced the overall result heavier than others. Nonetheless, due to the high number of responses received, the limited availability of ear surgeons overall and also limited time resources specifically, we decided to stop data collection with a slightly unbalanced distribution. Additionally, the images in the questionnaire were always presented in the same order, which could have influenced the intra-rater reliability measure. However, as the focus of the current study was on the results of the first time point, this limitation can be neglected.
Finally, another limitation can be the static nature of pictures, which is different from the dynamic visualization, which occurs during EES along with the manipulation of the suspicious tissue. Indeed, accuracy in the detection of cholesteatoma could be affected by the dynamic movements of the endoscope, changes in the point of view, light reflexion, direct suction and information about previous surgical steps.