The following three chapters of this surgical roundtable discuss important techniques for the reconstruction of the tympanic membrane. This type of surgical intervention is generally called a Type I tympanoplasty, according to the classification of Wullstein, but it can also be referred to as a myringoplasty when the surgery is isolated to the drumhead and no attempt is made to open or manipulate the middle ear space through the development of a tympanomeatal flap. The nomenclature used for the different surgical techniques generally is based on one of several factors: the graft material used (e.g., cartilage tympanoplasty, fat graft myringopasty), the position of the graft relative to the remnant drum (e.g., underlay or overlay tympanoplasty), and/or the surgical approach utilized (e.g., postauricular, endaural, trans-speculum). Whereas each has its advantages and disadvantages, modern tympanoplasty techniques all have common ground in that they endeavor to reconstruct the deficient middle fibrous layer of a tympanic membrane perforation or retraction pocket with graft materials that then act as a scaffold for lateral epithelial growth. Although simplified myringoplasty techniques that utilize non-grafted temporary scaffold materials, such as a thin paper patch, can be used for small perforations, they are relatively limited in application and simple to learn. Thus, patch myringoplasty techniques are not a focus of Part 4.
22.2 Surgical Approach
The importance of assuring proper visualization and exposure to surgically manipulate the tympanic membrane and middle ear may seem obvious, but if taken for granted, surgical results can be compromised. Line-of-sight visualization in itself does not always signify adequate exposure. The surgeon must ensure that instruments are allowed to enter the microscopic field at a sufficiently open lateral angle so as not to impede binocular vision or require awkward manipulation. Although minimally invasive approaches can be desirable, these should only be utilized if they provide equally sufficient access and exposure to the surgical target. The morbidity associated with even the widest tympanoplasty access route (postauricular with canalplasty) is generally not high.
Although each chapter in this part includes some discussion of approach, a few general comments are in order. The surgical approach for tympanoplasty is dictated by the degree of pathology in combination with the anatomical makeup of the ear canal and eardrum of the individual. These are usually described as the postauricular approach, which involves a skin incision behind the ear, and the transcanal approach, which involves various types of techniques with minimal external incisions. The latter can be further divided into trans-speculum and endaural, which are similar in concept but with each having its advantages and disadvantages.
The trans-speculum approach is the least invasive in the sense that the only external incision required is that used to harvest the graft material, but it requires a fair degree of technical skill. First of all, it is necessary to learn to support the speculum with the nondominant hand that is usually also used to manipulate the middle ear suction. Some surgeons utilize a speculum holder that connects to the surgical table, but this is time-consuming to set up and cumbersome under local anesthesia cases where the patient may move slightly and take it out of adjustment. Likewise, the added length of the speculum above the concha makes it difficult for the surgeon to stabilize his/her hands against the patient’s head. Thus, trans-speculum tympanoplasty is typically reserved for very simple posterior perforations.
The endaural approach adds a lateral 12 o’clock radial incision to the tympanomeatal flap that extends into the terminal incisure area and allows placement of self-retaining retractors, which reduces the depth of the surgical field, affording more hand stability. A limited endaural incision, as would be utilized for tympanoplasty, only generates a small externally visible scar that is hidden in the natural skin crease of the helicotragal groove. Thus, if properly executed, cosmesis should not be an issue with endaural surgery unless the incision is extended superiorly around the pinna, as has been described for mastoidectomy. Endaural access can be used for most perforations, especially if combined with a canalplasty procedure. The disadvantages of endaural exposure center around the 12 o’clock incision because if this made too deeply, the temporalis muscle can be injured, leading to increased postoperative pain. An endaural incision also requires additional time for suturing during wound closure as well as postoperative packing to prevent webbing of the superior external auditory meatus.
The postauricular approach involves a C-shaped incision that is placed behind the pinna. It is cosmetically preferable to place this incision at least 1 cm behind the postauricular sulcus to prevent disruption of the natural concha-mastoid angle, which may result from subsequent scar contracture if it is too close to the pinna. At times, it is favorable to extend the incision further posterior to hide it in the hairline. Commonly, the ear canal is approached within a surgical plane that is immediately deep to the postauricular muscle fibers, and often this is combined with a layered T-shaped periosteal flap over the mastoid cortex. Various canal incisions have been described to allow concomitant anterior reflection of the pinna and creation of a tympanomeatal flap. The choice of a canal incision scheme is probably less important than the degree of care applied when elevating a tympanomeatal flap to prevent undue soft tissue trauma. Postauricular surgery affords wide circumferential exposure to the entire external auditory canal, as needed for canalplasty, tympanoplasty, mastoidectomy, and the harvest of temporalis fascia, all through a single incision.
All of the approaches for tympanoplasty can be performed under local anesthesia, and the decision for anesthesia type should not be a determinant of surgical approach in most cases. It should be noted that the surgical approach is not to be dictated by the pathology alone, nor by anatomical considerations in isolation, but, rather, by a combination of both. A subtotal perforation that is easily visualized in a large, straight canal can be repaired through a transcanal approach as long as the entire annulus and eardrum remnant can be easily seen from a single vantage point without moving the microscope. On the other hand, a small anterior perforation with an obstructing anterior canal bulge is best repaired through postauricular access, often with the addition of a canalplasty. A reasonable pearl of wisdom would be that “when in doubt, go postauricular.” The morbidity is minimal, it adds very little surgical time, and it is the most versatile of all the approaches.
22.3 Graft Material
The tympanic membrane is the major element of the middle ear transformer mechanism, acting as a barrier between the sound pressure of the ear canal and the middle ear. Its motion, which has been studied with laser vibrometry and stroboscopic holography, is both complex and variable depending on the frequency of stimulation.1,2 At frequencies up to 1000 Hz, the tympanic membrane tends to vibrate in one consolidated phase, but as frequency rises further, its vibration splits into a state of phase subdivision, with overall diminished efficiency.
Although it is intellectually satisfying to assert that reconstruction of the tympanic membrane must endeavor to exactly re-create these native vibratory patterns, in truth it is unknown if this is possible or even necessary. Numerous tympanic membrane graft materials have been used that are quite dissimilar to the native drumhead in rigidity and thickness, yet excellent acoustic outcomes have been attained. For example, reconstruction with large cartilage grafts has been reported to result in hearing outcomes equal to those with more pliable temporalis fascia,3,4,5,6 including occurrences of complete air-bone gap closure in the speech frequencies. Further complicating the situation is uncertainty regarding the interplay between an aphysiologic reconstructed tympanic membrane and the underlying aphysiologic reconstructed ossicular chain in collectively providing acoustic gain.7 Inconsistencies between observed clinical outcomes and predicted tympanoplasty outcomes based on tympanic membrane acoustic models highlight the fact that there is still much to be learned.