Rationale for Endoscopic Ear Surgery

Cholesteatoma is usually a manifestation of advanced retraction of the tympanic membrane that occurs when the sac advances into the tympanic cavity proper and then into its extensions such as the sinus tympani, the facial recess, the hypotympanum, and the attic. Only in advanced cases, which now occur rarely, does a cholesteatoma progress further to reach the mastoid cavity proper. Most surgical failures associated with  a postauricular approach seem to occur within the tympanic cavity and its hard-to-reach extensions rather than in the mastoid. Therefore, the most logical approach to the excision of a cholesteatoma involves transcanal access to the tympanic membrane and tympanic cavity and the subsequent step-by-step pursuit of the sac as it passes through the middle ear. In the past, mainstream ear surgery has usually involved the mastoid and the postauricular approaches because operating with the microscope through the auditory canal is a very frustrating and almost impossible process, especially when the sac is excised from the mesotympanum. The view during microscopic surgery is defined and limited by the narrowest segment of the ear canal.

This basic limitation has forced surgeons to create a parallel port through the mastoid to gain keyhole access to the attic, the facial recess, and the hypotympanum.

In contrast, transcanal operative endoscopy bypasses the narrow segment of the ear canal and provides a wide view that enables surgeons to look “around the corner,” even when a zero-degree endoscope is used (Figure 2). Another anatomic observation that supports transcanal access to the attic, which is the most frequent auricular site of cholesteatoma, is the orientation of the ear canal in relation to the attic. The image below shows a coronal computed tomographic section through the temporal bone, which reveals that an axis line drawn through the ear canal ends in the attic rather than the mesotympanum. The only structure that is in the way is the scutum, and its removal allows wide and open access to the attic, which is the natural cul de sac of the external auditory canal. 

The use of the endoscope enables the surgeon to visualize past the shaft of larger surgical instruments, such as drills and curettes, and allows better visualization of structures that are parallel to the axis of the microscope. It is usually necessary to position structures such as the ear canal at a right angle to the axis of the microscope for adequate visualization. However, there are usually 2 issues of feasibility that raise the most questions about the use of the endoscope in ear surgery. 

The first consideration is the use of an endoscope  of 4 mm, which is large for the ear canal. During this author’s 10 years of experience in performing endoscopic surgery on patients as young as 3 years, that concern proved unfounded. In addition, it is almost impossible to operate through a smaller scope because the field of view that is essential for orientation is lost. The second concern has arisen because during microscopic transcanal surgery, many otologists use one hand to hold the speculum and the other hand to operate. This type of one-handed surgery, the lack of suction, and the possibility of excessive bleeding can be problematic. Also, prior experience in performing postauricular procedures (in which many layers of tissue are violated and a tremendous amount of healthy bone is removed during cortical mastoidectomy) cannot be applied to the transcanal endoscopic approach, in which surgically induced trauma is quite limited, there is less bleeding, and the dead-end structure of the canal and cavity allows for the interim packing of certain areas to control bleeding. The amount of bone removed is also limited to a relatively thin scutum that is easily excised with a curette instead of a drill. 

Some experts in the otologic community have stated that the transcanal approach to the removal of a cholesteatoma could be performed with the aid of a microscope. The limited view provided by the microscope is the main reason for which those making such an argument cannot recall excising a cholesteatoma via the transcanal approach over the last few years. However, this author uses primarily the transcanal approach for the removal of a cholesteatoma.
 

Safety Concerns:

Two major safety concerns are associated with endoscopic ear surgery: excessive heat dissipation and secondary direct trauma from the tip of the endoscope, which is caused by unintentional movement of the patient. To avoid excessive heat dissipation that is associated with the size of the cavity, adequate illumination of the middle ear space can be accomplished with the use of lower settings on a Xenon light source to reduce heat. The tip of the endoscope also requires continual cleaning with an antifog solution, which may cool the endoscope. Although secondary direct trauma from the tip of the endoscope remains a concern, the diameter (4 mm) of the endoscope used by this author and the anatomy of the ear canal and middle-ear space usually prevent the introduction of the endoscope beyond the tympanic ring. Even during endoscopic stapedectomy, there is less need for curettage of the posterior and superior aspects of the canal to enable exposure. This provides a protective rim that prevents the advancement of the endoscope beyond the tympanic ring.

IWGEES