In contrast to the binocular microscope, the endoscope allows for improved visualization of the middle ear because the light source is located at the distal tip of the instrument. With the introduction of three-chip camera systems and high-resolution monitors in the 1990s, endoscopes now provide ultra-high-resolution images of the middle ear never previously seen (see figure 1). Pioneers of endoscopic ear surgery (EES) espouse its high resolution and magnification, and the newfound ability to look around corners.
Transcanal endoscopic ear surgery allows the external auditory canal to become a minimally invasive surgical portal for complex middle ear surgery (see figure 2). Drawbacks of endoscopic ear surgery include a steep learning curve, the necessity of operating with only one hand (the other hand must hold the endoscope), the lack of true depth perception (the user must rely on parallax to assess depth), and the limited instrumentation.
Initially, endoscopes were used in the ear only for diagnostic purposes.1,2 Over the past decade, otologists have refined operative techniques and begun utilizing the endoscope as the sole instrument for visualization during dissection. Investigations have demonstrated the technique's utility3 and safety.4,5
Some cases previously requiring use of an operative microscope may now regularly be performed with an endoscope placed through the ear canal. As with all new technologies and surgical approaches, the application of an endoscope for visualization of the tympanic cavity is currently under debate, and indications are being refined.
FEASIBLE AND MINIMALLY INVASIVE
Studies have begun to examine patient outcomes following endoscopic ear surgery, as well as new surgical approaches. Two recently published articles by Daniele Marchioni, MD, and Livio Presutti, MD, pioneers of EES, highlight emerging research.
Endoscopic Exclusive Transcanal Approach to the Tympanic Cavity Cholesteatoma in Pediatric Patients: Our Experience
Marchioni D, Soloperto D, Rubini A, et al
Int J Pediatr Otorhinolaryngol
In the first study, Dr. Marchioni and colleagues examine outcomes of cholesteatoma resection in pediatric patients following an exclusive transcanal approach.6 The study is a retrospective chart review of 54 patients who had cholesteatoma surgery over a seven-year period.
The patients were divided into two study groups: those who underwent EES because of the absence of cholesteatoma extension into the mastoid, and those who had a traditional canal wall up (CWU) mastoidectomy because of the cholesteatoma's extension into the mastoid. Study outcomes included need for second look, audiometric measures, and presence of residual disease.
The EES and CWU study groups had 31 and 28 patients, respectively. The median patient age was 9.6 years. Single-stage surgery was carried out in 63 percent of EES cases versus 37 percent of CWU cases; however, this difference did not reach statistical significance. The ossicular chain could be preserved in a significantly greater proportion of patients undergoing EES compared with CWU (42% versus 10%, respectively).
Notably, very few patients underwent revision surgery for recurrence: two patients in each of the EES and CWU groups. Both groups had a drop in pure-tone average (PTA) postoperatively; however, the CWU group had a greater decrease. There was no mention of statistical significance for the PTA differences. Finally, the rate of residual disease was 19.3 percent in the EES group versus 34.4 percent in the CWU group, but this difference did not reach statistical significance.
Dr. Marchioni and colleagues provide an important review of their patients’ outcomes following EES or the more traditional CWU approach. The authors conclude that endoscopic ear surgery represents a feasible, minimally invasive, conservative technique for the management of pediatric middle ear cholesteatoma.
The study highlights a critical aspect of EES: the endoscope is not meant to replace the microscope in all patients but may serve a specialized purpose in select cases. In certain patients with extensive disease, transcanal endoscopic ear surgery is not tenable for complete extirpation. At this point in EES, only bony drilling via a mastoidectomy will enable eradication of disease if there is extension of the cholesteatoma into the antrum.
In the future, new instruments such as a curved drill may enable a transcanal approach for resection of extensive cholesteatoma. Today, it is important that surgeons continue to preoperatively delineate for which patients EES is indicated versus a traditional approach in order to ensure patient safety and reduce morbidity.
Endoscopic Transcanal Corridors to the Lateral Skull Base: Initial Experiences
Marchioni D, Alicandri-Ciufelli M, Rubini A, Presutti L
2015; DOI: 10.1002/lary.25203 http://onlinelibrary.wiley.com/doi/10.1002/lary.25203/abstract;jsessionid=22F5AF3FE0D74E26437CB5D719B81782.f03t01
In a second recent paper, Dr. Marchioni and colleagues outline novel transcanal endoscopic approaches to the lateral skull base and internal auditory canal.7 The numerous conditions that involve the lateral skull base include vestibular schwannoma (acoustic neuroma), facial nerve schwannoma, meningioma, and glomus tumors.
The authors reported on 12 patients who underwent surgery for a variety of reasons, noting three main corridors to the lateral skull base: transcanal suprageniculate (above the facial nerve in the skull base), transcanal transpromontorial (through the cochlea), and transcanal infracochlear (below the cochlea).
These approaches provide access to a host of clinically relevant areas, such as the fundus, internal auditory canal, cochlea, and geniculate ganglion/facial nerve, the authors concluded. Notably, Dr. Marchioni and colleagues were able to access these areas without external incision or craniotomy.
Although the lateral skull base approaches described by Drs. Marchioni and Presutti need to be refined and further measured, their importance cannot be emphasized enough. The use of endoscopy to access the lateral skull base opens the door to new surgical techniques.
Current approaches often require lengthy incisions, significant drilling, and craniotomy. Consequently, traditional approaches have extensive patient morbidity. The use of the ear canal as a minimally invasive portal may improve future outcomes and decrease morbidity for patients.
Indeed, at our own institution, we have begun to explore the benefit of using CT-guided lateral temporal bone surgical navigation with EES to demonstrate in real time a patient's surgical anatomy beyond surface landmarks.8
Surgical navigation may gain greater favor for endoscopic transcanal approaches to the inner ear, similar to contemporary endoscopic sinus surgery. Prospective outcome studies are needed to determine whether the endoscope is associated with equivalent or better outcomes than microscopic techniques for lateral skull base disease.
Ear endoscopy is gaining momentum in the otologic community worldwide, enabling exciting new developments in otologic surgery using minimally invasive approaches. With the increased development of EES-specific instruments, refinement of surgical approaches, availability of educational courses, and conduct of long-term prospective studies, endoscopic ear surgery will likely be incorporated into widespread practice. Studies by Drs. Marchioni and Presutti highlight both practical and theoretical advances in this technique.
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