Exploratory Tympanotomy

Exploratory tympanotomy refers to the surgical approach to the middle ear and its structures for diagnosis. The steps of exploratory tympanotomy are the same as those that would precede transcanal middle ear surgery, such as stapedectomy or removal of a small glomus tympanicum tumor. The operation is performed under otomicroscopy across the external auditory canal (transcanal). Canal skin incisions are created that permit tympanic membrane elevation to gain the necessary exposure to the middle ear and the structures contained within.

Exploratory tympanotomy takes its origins from early fenestration surgeries performed by Sourdille[1] and Lempert[2] for otosclerosis. Rosen performed the same exploratory tympanotomy steps prior to stapes mobilization.[3] It was simply a means to access the middle ear and its structures.

The ear is composed of external, middle (tympanic) (malleus, incus, and stapes), and inner (labyrinth) (semicircular canals, vestibule, cochlea) portions.

The primary functionality of the middle ear (tympanic cavity) is that of bony conduction of sound via transference of sound waves in the air collected by the auricle to the fluid of the inner ear. The middle ear inhabits the petrous portion of the temporal bone and is filled with air secondary to communication with the nasopharynx via the auditory (eustachian) tube (see the image below).

The tympanic membrane is an oval, thin, semi-transparent membrane that separates the external and middle ear (tympanic cavity). The tympanic membrane is divided into 2 parts: the pars flaccida and the pars tensa. The manubrium of the malleus is firmly attached to the medial tympanic membrane; where the manubrium draws the tympanic membrane medially, a concavity is formed. The apex of this concavity is called the umbo. The area of the tympanic membrane superior to the umbo is termed the pars flaccida; the remainder of the tympanic membrane is the pars tensa (see the image below).

For more information about the relevant anatomy, see Ear Anatomy.

The decision to perform an exploratory tympanotomy is made when middle ear pathology is suspected that requires direct visual inspection and or middle ear manipulation. Diagnosis is not obvious based on either the patient’s clinical presentation or radiographic imaging. The otoscopic examination suggests an abnormal appearance of the tympanic membrane or, possibly, a middle ear mass present. A conductive hearing loss is present on audiometric evaluation and inspection of the ossicular chain’s integrity and mobility is planned. The conductive hearing loss may be post-traumatic, congenital, or acquired.

Indications for exploratory tympanotomy for sensorineural hearing loss are less common, usually for suspected perilymphatic fistula.[4, 5] Perilymphatic fistula is a disorder of an abnormal leakage of perilymph from either the round window or oval window, 2 areas readily accessible by exploratory tympanotomy if surgical repair is required. The symptoms of perilymphatic fistula include hearing loss and vertigo induced on physical exertion. A traumatic event leading to sudden intralabyrinthine fluid pressures usually precedes the onset of symptoms.

Even though the purpose of an exploratory tympanotomy may be to establish diagnosis, the otosurgeon must plan for treatment that will ensue after the exploration. This is the situation for patients with conductive hearing loss. Stapedectomy or ossicular chain reconstruction (re-establishing the continuity of the ossicular chain) may follow an exploratory tympanotomy once the cause is determined. If a middle ear mass exists, measures to biopsy or remove the mass will be undertaken. Middle ear masses include congenital cholesteatoma, glomus tympanicum, or middle ear adenoma, for example.

Exploratory tympanotomy should not be undertaken if the external auditory canal does not permit passage and manipulation of the otologic micro-instrumentation to the tympanic membrane and middle ear. It should also not be performed if the portion of the tympanic membrane annulus that will need to be elevated is poorly visualized. Office examination under otomicroscopy should be performed prior to surgery to determine if an alternative approach to the middle ear should be taken. The ear canal should permit passage of at least a size-5 aural speculum.

The anatomy of the bony external auditory canal may prevent or make exploratory tympanotomy difficult. A prominent anterior bony canal wall bulge may be present. This may limit the space available to raise an adequate tympanomeatal flap and limit exposure of the middle ear. A hypertrophic tympanic ring will create an elevated bony canal floor that will impair visualization of the posterior fibrous tympanic annulus. If the fibrous tympanic annulus is not clearly identified during tympanomeatal flap elevation, a tear in the flap may result and lead to a perforation of the tympanic membrane. Clearly identifying the tympanic annulus and elevating from under it is important.

Various congenital and acquired conditions of the external auditory canal may prevent exploratory tympanotomy. Patients may have varying degrees of congenital ear canal stenosis. This must be kept in mind when operating on patients with craniofacial anomalies or syndromic hearing loss.

Acquired conditions, such as exostoses or osteomas, may physically obstruct and prevent access to the tympanic membrane. In this case, these obtrusive bony canal growths need to be removed prior to exploratory tympanotomy.

Exploratory tympanotomy is performed under otomicroscopy, typically through an aural speculum. A speculum holder may be used depending on the otosurgeon’s preference.

If the external auditory meatus is constricted, an endaural incision through the auricular incisura terminalis may be required to help expand the aperture of the cartilaginous external auditory canal and accommodate the largest size speculum possible.

Prior to elevation of the tympanomeatal flap, the canal skin is infiltrated with a local anesthetic/vasoconstrictor, not only to provide local anesthesia but also for its vasoconstrictive effects to reduce blood loss. Poor hemostasis will result in poor visualization throughout the surgical procedure.

Surgical site preparation should include periauricular areas (tragus, postauricular) that serve as potential tissue graft donor sites. These include cartilage, perichondrium, and fascia.

The otosurgeon should decide, in advance, whether the procedure should be performed under IV sedation/monitored anesthesia care or general anesthesia. The former has advantages by providing the surgeon with immediate patient feedback regarding hearing status, dizziness, or facial nerve stimulation.

Chronic otitis externa and other dermatologic conditions affecting the skin of the external canal may need to be treated with ototopical medications (antibiotics and/or corticosteroids) weeks prior to exploratory tympanotomy. In this way, the condition and health of the canal skin are optimized for surgery. Exploratory tympanotomy may be complicated by external auditory canal skin that is friable, edematous, hypertrophic, or hyperemic.

The outcome for tympanotomy for exploratory purposes is generally good. Care must be taken not to disturb the anatomical relationships between the tympanic membrane and the ear canal, as well as the relationship between the tympanic membrane and the malleus. The tympanic membrane that has been elevated is returned to its original anatomical position and stabilized using ear canal packing. The attachment between the tympanic membrane and manubrium of the malleus should not be disrupted. Inadvertent TM perforations must be repaired at the same setting using standard tympanoplasty technique.

When exploratory tympanotomy is undertaken in the setting of conductive hearing loss without history of otitis media, studies looking at the results of surgical middle ear exploration reveal that the common causes are otosclerosis, ossicular fixation, and ossicular discontinuity.[6, 7]

When exploratory tympanotomy is undertaken in the setting of sudden sensorineural hearing loss, abnormalities in the round window (perilymphatic fistula, scarring, and poor round window reflex) were found in nearly two thirds of the cases.[8]

Exploratory tympanotomy performed for conductive hearing loss after head trauma reveals that the most common injury is incudostapedial joint disruption.[3]

Patient instructions

Postoperative instructions are given to the patient prior to surgery. This often assists patients in their preparation for surgery. Patients are instructed to keep dry ear precautions until healing inside the ear canal is complete. They should avoid forceful nose blowing, closed-mouth sneezing, or autoinflation of the ears to prevent inadvertent mobilization and displacement of the tympanomeatal flap that has been stabilized with ear canal packing.

Elements of informed consent

When exploratory tympanotomy is indicated, the otosurgeon should explain, in the simplest of terms, to the patient that the surgery will be performed through the ear canal so that the eardrum can be raised and the middle ear can be entered. The goals of the surgery, whether to identify/correct a conductive hearing loss, to obtain direct visualization of the middle ear and it structures, or to retrieve tissue from the middle ear for diagnosis, must be clearly delineated.

Potential risks and complications include bleeding, infection, tympanic membrane perforation, altered taste or dysgeusia, dizziness, hearing loss, and facial paralysis.

Options and alternatives to the surgery should be discussed in the preoperative counseling. This is usually case specific and individualized. Hearing alternatives may include a conventional hearing aid or bone-anchored hearing apparatus.

Anesthesia

Exploratory tympanotomy may be performed under intravenous sedation/monitored anesthesia care (MAC) or under general endotracheal tube anesthesia. The choice of which anesthetic to be administered depends on surgeon and patient preference. If the patient’s hearing is to be tested intraoperatively, IV sedation/MAC is undertaken. This is particularly useful for the surgeon to not only receive immediate verbal feedback from the patient with regards to hearing changes, but also if any dizziness or facial contractions occur with surgical manipulation of the vestibule or tympanic facial nerve, respectively.

Positioning

Patient positioning during exploratory tympanotomy is the same as for other otologic surgeries. After induction of general anesthesia, the operating table is turned 180°. The anesthesiologist is now situated at the foot of the bed. The surgeon is at the head of the bed.

If the operation is carried out under IV sedation/MAC, provisions are made to suspend the drapes off the patient’s face. A pillow is placed under the knees to prevent strain on the patient’s lower back lying supine.

Necessary surgical equipment required past the exploratory phase of middle ear surgery should be available. These include the gamut of ossicular and stapes prostheses, high-power drills for mastoidectomy, and stapes microdrill.

Equipment

Equipment required for exploratory tympanotomy includes operating microscope and standard middle ear surgical tray.

Rigid oto-endoscopes may be incorporated into an exploratory tympanotomy. These are particularly useful to visualize areas that are difficult to see through the straight line of sight obtained from the operating microscope. Difficult to visualize areas include the protympanum, sinus tympani, and aditus ad antrum. Oto-endoscopes come in a variety of thickness (2.7 mm or 4 mm) and view angles (0°, 30°, 70°).

Intraoperative facial nerve monitoring may be used during exploratory tympanotomy if middle ear anatomy is distorted or surgical manipulation in the vicinity of the tympanic facial nerve is anticipated. The monitoring unit is also able to deliver electrical current to stimulate and verify the position of the facial nerve.

Exploratory tympanotomy is typically performed in the outpatient setting. The postoperative patient should return to the office in one week to check that the canal packing is secure and not infected. Topical drops are used to moisten the packing that will be removed in 2-3 weeks. Hemotympanum should resolve in several weeks. The tympanomeatal flap is checked to make sure that it has healed in place and that no perforation exists.

If the ear canal is patent enough to accommodate at least a size-5 aural speculum, enough space should exist to create the tympanomeatal flap. If the external meatus is small, an endaural incision is created in the incisura terminalis to widen it. In this manner, the membranous external auditory canal is expanded. The patency of the bony external auditory canal is unaltered by an endaural incision.

Meticulous control of bleeding from the external auditory canal after skin incisions is vital to the success of the surgery. Injection of a topical anesthetic containing a vasoconstrictor and topical application of epinephrine is recommended for hemostasis.

See the list below:

• With the patient’s head turned away from the operated ear, the entire auricle is prepped and draped. Local anesthetic with vasoconstrictor (eg, 1% lidocaine with 1:100,000 epinephrine) is injected in advance into potential tissue graft donor sites in advance. These may include the tragal area for cartilage/perichondrium or postauricular area for temporalis fascia (see the image below).

  Injection points for local anesthetic/vasoconstrictor prior to exploratory tympanostomy.

• The operating microscope (250-mm objective lens) is used to visualize the ear canal and TM. The same local anesthetic-vasoconstrictor solution is injected into the posterior canal skin adjacent to the bony-cartilaginous junction of the canal. Blanching of the posterior canal skin should be visible from the injection point laterally and progressing medially toward the tympanic annulus. Injection is best placed in the subperiosteal plane using a TB syringe. Avoid subepithelial injections that create skin blisters. This obstructs visualization through the ear canal and increases friability and bleeding of the canal skin during canal skin elevation.

• If an endaural incision is required, the incisura region is infiltrated with the local anesthetic/vasoconstrictor solution. Incision is created with a number 15 blade down to bone. An endaural speculum is used to spread and retract the subcutaneous soft tissue away (see the image below).

  Endaural speculum used to assist in retraction of tissues as incision through the incisura terminalis is made.

• The incisura area is devoid of cartilage, therefore, no cartilage should be exposed or encountered during this exposure. Electrocautery is usually required in this area for hemostasis. If excellent hemostasis is not achieved, blood will trickle medially into the ear canal and impair visualization during the tympanotomy.

• With a sickle and round knife, canal skin incisions are created to form the tympanomeatal flap (see the image below).

  Endaural speculum used to assist in retraction of tissues as incision through the incisura terminalis is made.

• Tympanomeatal flaps may be cut rectangular or triangular with the apex directed laterally. The lateral extent of the flap should measure 8 mm from the tympanic annulus. A curvilinear or square flap typically spans from 12 o’clock to 6 o’clock position posteriorly. The incisions should just come short of and not into the tympanic annulus. A wider flap from 12 o’clock to 4 o’clock can be created for more anterior inferior access to the middle ear if needed.

• Round knife is used to elevate the tympanomeatal flap over a broad front. To best preserve the integrity of the flap, do not suction directly on it. Suctioning on the bone just behind the flap should be adequate to evacuate any bleeding that impairs visualization of the leading edge of the flap. Bleeding from the cut skin edges is controlled by applying cotton balls soaked in epinephrine (1:1000).

• Once canal skin elevation reaches the tympanic annulus, care must be taken to stay in the plane deep to the fibrous tympanic annulus. A Rosen needle may help the elevation of the fibrous annulus get started (see the image below).

  Outline of canal skin incisions to create tympanomeatal flap.

• The annulus elevator is used to raise the fibrous annulus from its bony groove. Elevation of the annulus begins inferiorly toward the hypotympanum and proceeds superiorly toward the oval window niche, thereby gradually increasing the exposure into the middle ear. The reason to begin inferiorly is that more space exists toward the hypotympanum. More critical structures are located in the posterior-superior mesotympanum, such as the ossicular chain.

• Care is taken not to mistake the chorda tympani for the fibrous annulus. Do not forcibly push the chorda tympani nerve out of its bony channel that could avulse the nerve. This is another reason to begin the elevation of the fibrous annulus inferiorly, below the origin of the chorda tympani nerve.

• The segment of the posterior tympanic membrane that has been elevated should be folded forward enough to achieve the desired middle ear exposure. The farthest point forward that the TM may be folded will be limited by the manubrium’s attachment to the undersurface of the TM.

• At this point, the exposure gained from this type of TM elevation will provide access to the promontory, hypotympanum, round window niche, incudostapedial joint. The bony canal can be curetted away to obtain more exposure if necessary (see the image below).

  Rosen needle used to facilitate elevation of tympanomeatal flap as entry is made into the middle ear.

• If additional posterior-superior exposure is desired, the chorda tympani nerve can be liberated from its bony canal by curetting the bone lateral to the nerve or using an otologic drill with a diamond bur. Once the nerve is freed, it can be transposed forward and the remainder of the bony scutum can be curetted or drilled away. This provides better exposure to the oval window niche, stapes crura, stapes footplate, tympanic facial nerve, stapedial tendon, and pyramidal process.

• Additional superior exposure is gained by further superior elevation of the fibrous annulus toward the notch of Rivinus. The fibrous annulus terminates in this area. The neck of the malleus and Prussak’s space (lateral epitympanic space) may be accessed through this exposure.

• Upon completion of the middle ear exploration, the chorda tympani nerve is returned to its original position and the tympanomeatal flap is laid back down onto the canal wall. Upon laying the flap down, if the middle ear becomes hyperinflated, instruct the anesthesiologist to turn off any nitrous oxide inhalant anesthetic being administered via endotracheal tube. A Baron suction is briefly placed into the middle ear to evacuate the gas and the tympanomeatal flap should lay down close to its native position.

• The lateral surface of the tympanic membrane and tympanomeatal flap is packed with gelatin sponge soaked in an ototopical antibiotic or ear canal packing of choice to prevent displacement. Make sure that the edges of the tympanomeatal flap are completely unfurled to prevent iatrogenic canal cholesteatoma or keratin pearls.