Current Trends in Endoscopic Ear Surgery

Endoscopes have found broad applications within the field of otolaryngology by allowing direct visualization of hidden anatomic areas. However, while the endoscope has been robustly incorporated into standard practice in rhinology and laryngol-ogy for anterior skull base, sinus, and laryngeal surgery, its use in otology is emerging. Currently, the operating microscope is the preferred surgical instrument used by most otologists. Over the past 4 decades, however, use of the endoscope for otologic procedures has incrementally grown. In the 1990s, Tarabichi, Thomassin, and Poe utilized the endoscope for performing middle ear surgeries rather than purely for inspection, beginning a revolution in the way the endoscope is used in ear surgery (1–4). Many studies have since demonstrated the improved visualization of the tympanic cavity with the endoscope compared to the operating microscope, and clinical studies have shown outcomes of endoscopic ear surgery (EES) to be comparable to those of the operating microscope (5–13). This article provides an overview of EES, including its history, current trends, advanced uses, integration into medical training, ergonomic and safety considerations, and utility of endoscopes in an office-based setting.

Endoscopes have found broad applications within the field of otolaryngology by allowing direct visualization of hidden anatomic areas.However, while the endoscope has been robustly incorporated into standard practice in rhinology and laryngology for anterior skull base, sinus, and laryngeal surgery, its use in otology is emerging.Currently, the operating microscope is the preferred surgical instrument used by most otologists.Over the past 4 decades, however, use of the endoscope for otologic procedures has incrementally grown.In the 1990s, Tarabichi, Thomassin, and Poe utilized the endoscope for performing middle ear surgeries rather than purely for inspection, beginning a revolution in the way the endoscope is used in ear surgery (1)(2)(3)(4).Many studies have since demonstrated the improved visualization of the tympanic cavity with the endoscope compared to the operating microscope, and clinical studies have shown outcomes of endoscopic ear surgery (EES) to be comparable to those of the operating microscope (5)(6)(7)(8)(9)(10)(11)(12)(13).
This article provides an overview of EES, including its history, current trends, advanced uses, integration into medical training, ergonomic and safety considerations, and utility of endoscopes in an office-based setting.

HISTORY
Initially, the endoscope in otologic surgery was primarily used as an adjunct to the microscope and limited to diagnostic purposes.In the late 1980s to early 1990s, Nomura and Takahashi first reported transtympanic middle ear endoscopy (14,15).Poe and Bottrill used the technique to confirm perilymphatic fistula and to identify other middle ear pathologic conditions (16).Nearly a decade later, Thomassin used endoscopes to visualize residual cholesteatoma in the tympanic sinus and the retrotympanum (17).McKennan reported a second-look endoscopic inspection of mastoid cavities using a postauricular approach (18).In 1997, Tarabichi described EES for cholesteatoma without using a microscope (19).He subsequently described other procedures including endoscopic tympanoplasty and stapedotomy (2).
The works of Poe, Thomassin, and Tarabichi were pivotal in shaping the landscape of EES today (1)(2)(3)(4).Technological advances in light sources and endoscopic cameras significantly improved the clarity of images.Endoscopic surgery, which previously required the surgeon to look through the endoscope with the naked eye, became more practical as video monitoring equipment improved, permitting quality visualization with preservation of the sterile field.In the 2000s, there was a growth in the use of transcanal endoscopic techniques to visualize hidden areas such as the posterior epitympanium (20).The International Working Group on Endoscopic Ear Surgery was created in 2007 to foster collaboration among otologists and to further the development of EES.Since then, EES has become increasingly used for all common otologic procedures (21)(22)(23)(24)(25). Clinical studies have shown outcomes following EES to be comparable to outcomes following microscopic ear surgery while allowing a less invasive approach (10)(11)(12)(13)26).

CURRENT TRENDS
A classification system introduced in 2018 defines EES and facilitates comparisons with traditional techniques (13).This classification ranges from class 0 (no endoscope) to class 3 (transcanal EES) and has helped resolve ambiguity in reporting outcomes with EES and enabled better communication among researchers (Table 1).A 2018 study found that the number of transcanal EES publications increased from 36 before 2010 to 283 between 2011 and 2018.This study also showed significant growth of Class 3 EES for cholesteatoma, from 14.9% in 2010 to 53.5% in 2018 among US surgeons.General endoscope use (regardless of EES class) for ear surgery also increased from 53.2% to 82.2%, highlighting the progressive movement towards incorporating the endoscope into mainstream practice in the United States (27).

LATERAL SKULL BASE AND INNER EAR SURGERY
Advances in EES have prompted neurotologists to explore EES as a technique to manage lateral skull base and inner ear pathologies.Current management of these lesions primarily includes translabyrinth, transpetrosal, retrosigmoid, and middle cranial fossa approaches (38).However, these open, line-of-sight approaches may require wide craniotomy and prolonged brain retraction.Minimally invasive approaches have been explored using an endoscopic-assisted or exclusive endoscopic approach (39,40).
Three main endoscopic corridors for entering the lateral skull base have been described: the transcanal suprageniculate, transcanal transpromontorial, and transcanal infracochlear routes (38).These corridors can provide direct access for managing pathologies such as petrous apex cholesterol granulomas, vestibular schwannomas, intracochlear or intralabyrinthine schwannomas, and perilymph fistulas (41).The disadvantages of transcanal endoscopic lateral skull base surgery are similar to that of transcanal endoscopic middle ear surgery, only the risks are magnified.Simultaneous suction and dissection is challenging unless specialized combination instruments are available.At the same time, the relatively wider corridors may allow for endoscope holders and 2-handed surgery.Given the diversity in size and location of lateral skull base pathology, only certain types of tumors may be approachable through a transcanal corridor.

MEDICAL EDUCATION
EES exposure varies significantly across training programs (42).The main challenge of EES is the difficulty of 1-handed dissection since the non-dominant hand must hold the endoscope.In 1 study of otolaryngologists and trainees, 44% reported single-handed surgery to be their main concern (30).Experienced surgeons who are accustomed to 2-handed dissection may find this transition particularly difficult (43).
One solution for overcoming these challenges is to increase early EES exposure by incorporating EES training into medical school and residency programs.In a study of resident perspectives of EES during surgical training, the majority of residents viewed EES favorably and expressed a desire to learn the technique (44).Medical students who were taught middle ear anatomy also perceived learning with endoscopes to be superior to microscopes (45,46).When surgical skill acquisition by students, residents, and attending physicians was compared using an endoscope or microscope, fewer injuries to the ossicular chain on cadavers were noted with endoscopes (47).A comparison of outcomes of endoscopic versus microscopic tympanoplasty during adoption of EES showed that similar outcomes in tympanic membrane closure, mean air-bone gap improvement, and mean duration of surgery can be maintained during the surgeon's learning period while simultaneously teaching residents (48).

ERGONOMICS
Operating for long periods of time in suboptimal postural positions can cause musculoskeletal disorders (MSDs) among surgeons.Otolaryngologists face an increased risk for MSDs (49,50).In surveys conducted in the United Kingdom, India, Canada, and Spain, 48%-97% of otolaryngologists reported work-related MSDs (49,(51)(52)(53).Another survey of 325 otolaryngologists revealed that otologists suffered the highest pain among ENT subspecialties due to prolonged sitting and microscopic work (54).These findings highlight the importance of ergonomics when performing EES.Studies have shown that healthy posture improves operative performance and efficacy (55).
A challenge for otologists when working with microscopes is prolonged neck flexion.EES permits improved ergonomic posture by allowing for "heads up" surgery (Fig. 1).A neutral neck position can be achieved by placing the video tower directly in front of the surgeon with the monitor at eye level of the surgeon (41).Sitting in an upright position with elbows upon the bed or arm rests and utilizing back support can further maintain neutral neck, back, and arm positions (56).

SAFETY
Numerous studies have documented the safety and efficacy of EES for treating common middle ear conditions such as cholesteatoma, otosclerosis, and tympanic membrane perforations (57,58).Nevertheless, there remain safety concerns when using endoscopes, primarily related to excessive heat (59).Studies have shown a positive correlation between endoscope diameter and heat, and elevated temperatures at the round window when  using a xenon or LED light source, with the latter producing less heat (60,61).Desiccation of the chorda tympani nerve may be a potential risk (62,63).It has also been reported that removing the endoscope from the ear can decrease the temperature within 20-88 seconds of turning off the light source and that application of suction or irrigation to the middle ear results in almost immediate temperature reduction (60,64).Thus, avoiding prolonged static positioning of the endoscope, decreasing the light intensity to the minimum effective level, and use of suction instrumentation or irrigation can improve EES safety (59,60,64,65).

OFFICE-BASED OTOENDOSCOPY
The improved visualization provided by the endoscope applies to office-based otology procedures.Endoscopes allow for increased visualization of the depth of retraction pockets which can be difficult to assess with otomicroscopy (66).Endoscopic inspection of tympanic perforations can visualization of the anterior tympanic annulus and the entire margin of the perforation, which can be helpful for surgical planning.Preoperative endoscopic images can also be helpful for surgeons to review before surgery and to aid in patient education.Postoperatively, endoscopy can allow photo-documentation of outcomes and enable visualization to confirm healing after tympanoplasty for an anterior perforation.Innovative uses for in-office endoscopy include myringoplasty to repair small anterior perforations otherwise challenging to repair under microscopy and endoscopic debridement of mastoid cavities poorly accessible under microscopy (66).

CONCLUSION
EES has seen gradual but increasingly significant developments over the past 4 decades.The rise in EES literature and changing attitudes have made it clear that EES is gaining interest among otologists around the world.Endoscopes are increasingly used for primary management of cholesteatoma and tympanic membrane perforations.Use of EES for treating other middle and inner ear conditions and lateral skull base disease has potential for continued growth.

FIG. 1 .
FIG. 1.Comparison of operating room setups for endoscopic versus microscopic ear surgery.Ninety-degree rotation of the table with a left patient ear is depicted.A, Endoscope in use.The video tower is positioned directly in front of the surgeon.The surgeon, assistant surgeon, and scrub technician are sitting next to each other and facing a single screen, allowing for heads-up surgery.B, Microscope in use.The video tower is moved slightly away to accommodate the swinging microscope arm.The video tower is connected to the microscope and allows the scrub technician to view the image on the screen.However, the surgeon and assistant surgeon are required to operate by looking through the microscope oculars.