Middle Ear Endoscopic Surgery

Introduction

Endoscopes have been used for middle ear inspection for decades. However, recent improvements in camera and optical technologies have yielded endoscopes that provide extremely high-definition video with a wide-angle field of view. Moreover, the use of angled endoscopes allows surgeons to peek around corners to see the most hidden recesses of the middle ear. With these new tools, surgeons are increasingly using endoscopes not only for visual inspection, but also for dissection, and in many cases forgoing use of the microscope altogether.

The increased resolution and field of view of current endoscopes have provided surgeons with a fresh look at middle ear anatomy. Many microscopic anatomic studies were necessarily performed on sectioned, cadaveric temporal bone specimens, as the microscope is incapable of visualizing many areas of the middle ear because of line-of-sight limitations. The endoscope, however, can be used for detailed in vivo anatomic studies without disrupting the natural state of the ear. Surgeons can now clearly see the myriad ligaments and membranous folds emanating from the ossicles, thereby leading to an improved understanding of the ventilation pathways of the middle ear. Characterization and classification of the deepest recesses of the ear, such as the sinus tympani, can assist with surgical approach optimization, as well as inform the prognosis for cholesteatoma recurrence.

In this chapter, we provide an introduction to endoscopic ear surgery. We then focus on detailed anatomy of the middle ear spaces as visualized by straight and angled endoscopes. Knowledge of these middle ear structures is critical to understanding patterns of middle ear ventilation and intervening surgically to restore blocked pathways. The many landmarks of the middle ear are highlighted, as these structures serve as guides to help surgeons perform safe, effective procedures regardless of the method of visualization employed. Surgical techniques required to endoscopically navigate these spaces, as well as the intended surgical goals are referenced, whereas technical details are demonstrated in greater detail on accompanying videos (see under “Basic Endoscopic Technique” ).

Initial Considerations

In principle, the endoscope is optimally suited for addressing all diseases confined to the tympanic membrane and middle ear by providing optimal visualization. However, there are certain patient and disease characteristics that can increase the difficulty or reduce the efficacy of this approach. For example, cholesteatoma that extends into the mastoid posterior to the dome of the lateral canal cannot typically be addressed via an endoscopic approach alone and will usually necessitate mastoidectomy and microscopic visualization. A preoperative computed tomography scan is a valuable tool for assessing the extent of disease in order to determine the optimal surgical approach. In addition, a study by Abdul Aziz et al. identified other factors in computed tomography scans that suggest a postauricular approach may be required, including tegmen erosion, ossicular erosion, and mastoid opacification.

Common patient factors that can be favorable or unfavorable for a completely endoscopic approach are listed in Table 144.1 . Some characteristics are dependent on the experience of the surgeon with endoscopic techniques. For example, the lack of true depth perception can make ossiculoplasty or stapedotomy very difficult for surgeons just starting out in endoscopic ear surgery, yet surgeons well versed in the technique often prefer to perform these cases using the endoscope rather than the microscope. With the characteristics listed in Table 144.1 as general guidelines, surgeons can increasingly incorporate endoscopic ear surgery into their practice, as their comfort and proficiency with endoscopic dissection improve.

Equipment Considerations

Although a wide array of specialized equipment is commercially available, initial explorations in endoscopic ear surgery can readily be performed with a standard set of ear instruments and endoscopes typically used for sinus surgery. The majority of cases can be performed with 0- and 30-degree endoscopes, with the addition of 45- and 70-degree scopes for “looking around corners” in the middle ear. There is a balance between image quality and endoscope diameter, and most surgeons find that 3-mm-diameter endoscopes provide high-quality visualization and are sufficiently narrow to be accommodated in most adult and pediatric ear canals. Endoscope length is another important consideration, as very short endoscopes intended for office endoscopy do not provide adequate clearance for the surgeon's other hand and can increase the difficulty of dissection. For this reason, most ear surgeons use endoscopes ranging from 14 to 18 cm in length, realizing that longer endoscopes can easily be bent and damaged when introducing the rod in a tortuous ear canal. As surgeons become comfortable with the technique, more specialized instrument sets including angled instruments, angled suctions, and suction dissectors may become useful.

Perhaps the most important instrumentation consideration is the endoscope camera and viewing displays. In order to reap the benefits of optimal visualization, a 3-chip or 3CCD camera must be utilized. These cameras provide the high-resolution video necessary for performing precise, safe surgery and are commercially available from several manufacturers. High-definition monitors are also critical for displaying superior quality images. Fortunately, these systems are typically in place at centers where endoscopic sinus surgery is currently performed.