Tympanoplasty

Tympanoplasty is a surgical technique to repair a defect in the tympanic membrane with the placement of a graft, either medial or lateral to the tympanic membrane annulus. The goal of this surgical procedure is not only to close the perforation but also to improve hearing. The success of the operation depends on the ability to eradicate disease from the middle ear (eg, inflamed granulation tissue and cholesteatoma). Various techniques have been developed and refined, and a number of grafting materials are available. Both the lateral and medial grafting techniques are detailed below.

Tympanoplasty is a safe and effective outpatient procedure used to both eradicate disease from the middle ear and restore hearing and middle ear function. ^{[1, 2]} A number of surgical approaches and grafting techniques are available for use by the surgeon. Paramount to success are the preoperative assessment, good hemostasis intraoperatively, and thoughtful surgical planning with careful placement of the graft.

Perforations are most problematic when they cause both conductive hearing loss and chronic otorrhea. Although most perforations heal spontaneously, those that persist after dry ear precautions, ototopical drops, or myringoplasty should be considered for surgical repair. Tympanic membrane perforations can arise as sequelae of acute otitis media or chronic otitis media with or without cholesteatoma, as a complication of PE tube insertion, or as a result of barotrauma to the ear. Smaller perforations of the tympanic membrane can result in low-frequency hearing loss, while larger perforations can cause high-frequency and low-frequency hearing loss. Chronic infections and cholesteatoma can also result from perforations of the tympanic membrane. ^{[3, 4]} A perforation lead to a significant risk of developing otitis media when swimming in lakes, rivers, or oceans, but not in chlorinated pools. ^[5]

Cholesteatoma

Cholesteatoma is keratinizing squamous epithelium in the middle ear that can cause locoregional destruction. Chronic otitis media and tympanic membrane perforation can occur with or without cholesteatoma, and both varieties can present challenges to the clinician and barriers to the success of a tympanoplasty.

A complete discussion on the etiology and pathophysiology of cholesteatoma is beyond the scope of this article. Primary acquired cholesteatoma involves retraction of the pars flaccida from negative middle ear pressure, resulting in invagination of squamous epithelium into the middle ear and mastoid. Secondary acquired cholesteatoma arises from ingrowth of epithelium through a perforation of the tympanic membrane. Congenital cholesteatoma is not commonly associated with chronic otitis media or tympanic membrane perforation.

Complications of cholesteatoma are related to growth and bony erosion of nearby structures, including hearing loss (via erosion of ossicles and/or cochlea), labyrinthitis or labyrinthine fistula, facial nerve paresis, and intracranial complications.

Although most perforations heal spontaneously, those that persist after dry ear precautions, ototopical drops, or myringoplasty should be considered for surgical repair.

Operating on an actively infected ear is contraindicated. Caution should be taken when deciding to operate on an only-hearing ear.

Tympanic Membrane

An understanding of the tympanic membrane anatomy is critical to successful repair. Tympanoplasty technique mandates an understanding of the layers. The tympanic membrane typically consists of the following 3 layers:

• Lateral epithelial layer

• Middle fibrous layer

• Medial mucosal layer

The outer epithelial layer is composed of stratified squamous epithelium, which is continuous with the skin of the external auditory canal. This is significant because in-growth of this outer epithelial portion through the perforation can result in acquired cholesteatoma. Untreated, this cyst then releases destructive enzymes that can enlarge the size of the perforation and ultimately cause ossicular erosion and other complications. The lateral grafting technique that is discussed later in this text requires that this entire epithelial layer be stripped from the drum remnant prior to placement of the graft so as to avoid iatrogenic cholesteatoma formation.

The middle fibrous layer is composed of connective tissue consisting of outer radial fibers and inner circular fibers. It provides strength to the drum. A healed perforation is also commonly deficient of this middle fibrous layer. The epithelial and endothelial layers regenerate creating a “dimeric” membrane. This miscalculation can be corrected when carefully examined under binocular microscopy. Because this middle layer is absent in the pars flaccida superiorly, the posterior-superior aspect of the drum can be detracted medially toward the middle ear and can lead to primary acquired cholesteatoma.

The inner layer of the tympanic membrane consists of simple cuboidal and columnar epithelium cells. This layer is identical to the mucosal lining of the rest of the middle ear mucosal tissue and is considered to be critical to ensure healing of tympanic membrane perforations.

Annulus

The peripheral edge of the tympanic membrane is rimmed by a dense fibrous layer called the annulus, which is essentially a thickening of the pars tensa. Successful elevation of the annulus is critical for medial grafting technique. The annulus is deficient superiorly at the “12 o’clock” location. This area is referred to as the notch of Rivinus and can guide the surgeon to a natural plane to elevate the annulus.

Ear Canal

The ear canal has bone in the medial component (inner one-third). The lateral portion (outer two-thirds), which extends into the pinna, is composed of cartilage. Most incisions that are made to raise a tympanomeatal flap or perform either an endaural or transcanal approach tympanoplasty are made medial to the bony/cartilaginous junction. The posteriorly placed vascular strip is another critical area within the ear canal. This region is demarcated by the tympanosquamous suture line superiorly and the tympanomastoid junction line inferiorly. Canal incisions are often made along these junctions.

Middle Ear

The middle ear is an air-filled space bordered by the bony labyrinth of the inner ear medially, the tympanic membrane laterally, and the middle cranial fossa superiorly. The middle ear space contains the three ossicles, nerves (facial nerve, chorda tympani, Jacobson's nerve), small muscles (stapedius and tensor tympani), ligaments, and blood vessels. The petrous portion of the internal carotid artery and the internal jugular vein, which are both in proximity to the middle ear space, can be dehiscent and should be noted on any preoperative imaging. Rarely, middle ear pathology can involve these structures.

In order for successful grafting of the tympanic membrane to improve hearing, an intact ossicular chain must be present. The malleus transmits energy from the tympanic membrane to the incus, which itself is connected to the stapes superstructure resting on the oval window. Diarthrodial joints connect the 3 ossicles and allow the transmission of acoustic energy from the tympanic membrane to the inner ear. The incudostapedial joint is the most fragile and, hence, has the highest likelihood to require repair.

Mastoid

The middle ear communicates with the mastoid air cells via the mastoid antrum. The temporal bone air cells are usually pneumatized by 3 years of age. However, the air cells can remain underdeveloped and sclerotic in patients with persistent eustachian tube dysfunction. A poorly pneumatized or fluid-filled mastoid bone predisposes a patient to require a more extensive tympanomastoidectomy to improve the chances of successful graft placement.

Eustachian Tube

The eustachian tube connects the middle ear with the nasopharynx and allows pressure equilibration in the middle ear. Enlarged adenoids or biofilms within this lymphoid tissue are hypothesized to predispose a pediatric patient to persistent middle ear disease. This bony-cartilaginous tube is approximately 45° from the horizontal in adults but only 10° from horizontal in infants. In addition, the infant eustachian tube is about 50% of the adult length.

Inner Ear

The inner ear is composed of the cochlea, which is the end-organ for hearing, and the vestibular organs. The vestibular organs include the utricle, saccule, and the 3 semicircular canals and are involved in balance.

The indications and outcomes vary depending on the specific clinical problem. Success rates of tympanic membrane closure vary greatly in the literature (35–98%) but are usually greater than 80% and depend largely on the size and location of the perforation, surgical technique, and overall health of the middle ear. ^{[6, 7, 8]}  A meta-analysis of tympanoplasty reported an average success rate of 87%. ^[9]

Complications of the surgery include recurrence of the perforation, tympanic membrane retraction, otorrhea, cholesteatoma development, persistence or worsening of any conductive hearing loss, sensorineural hearing loss (rare), and taste disturbances. Post-auricular incisions are at risk for hematoma, and a mastoid pressure dressing is recommended for the first postoperative night. Outcomes can be optimized by a proper and detailed preoperative assessment and the careful construction of an effective surgical plan.

The graft can fail because of infection, failure to pack the graft securely in place, technical error, failure to clear mastoid and middle ear disease, and because of a concurrent undetected cholesteatoma. Excising all tympanosclerosis at the edge of the perforation so as to allow vascularized perimeters to incorporate the graft is critical.