Intratympanic Microwick Placement

Anatomy and Physiology

The ear is traditionally divided into the outer, middle, and inner ear; each division plays a vital role in sound transduction. The outer ear comprises the auricle, external auditory canal, and tympanic membrane. The tympanic membrane separates the outer ear from the middle ear, which houses various structures, including the ossicles. Sound is transmitted from the outer ear to the tympanic membrane, articulating with the malleus. Sound waves are transmitted through the ossicular chain from the malleus to the incus to the stapes; the stapes articulates with the cochlea at the oval window. Movement of the oval window transmits vibrations into the perilymphatic fluid within the membranous labyrinth of the inner ear. The stimulated signal from the perilymph terminates at the round window, which aids in counteracting the initial stimulus propagated at the oval window to improve overall sound conduction.[6] 

The round window is caudal and medial to the oval window. The round window measures approximately 1.5 to 2.1 mm horizontally, 1.9 mm vertically, and is 0.7 mm thick.[7][8][9] The round window may appear ovoid, skewed, or nonplanar in shape.[7] The round window is located approximately 3.44 mm posterior to the umbo of the malleus and at an approximate angle of 113° from the long process of the malleus.[10] The round window membrane separates the scala tympani from the middle ear space.[7][11] 

The round window membrane comprises three layers: an epithelial outer ear layer, an epithelial inner ear layer, and a connective tissue layer in between.[9][11] The access to the round window membrane can be obscured by a thin, bony overhang from the promontory called the round window niche.[7] Anatomical variations of the niche and the degree of round window membrane occlusion can increase the complexity of gaining direct access to the perilymph.[12] A thin mucosal layer forming a pseudomembrane can also obstruct access to the round window membrane.[7][8]

The outer epithelial layer of the round window determines the overall permeability of the structure. This outer epithelial layer comprises cuboidal epithelial cells connected by gap junctions; cellular microvilli permit molecular transport. The structure of the round window membrane makes it semipermeable to solutes such as antibiotics, toxins, and topical anesthetics. Additionally, diffusion across the round window membrane is affected by its thickness and the concentration, size, and ionized state of diffusing molecules. Molecules are absorbed into the perilymphatic system after diffusing across the round window membrane. Round window membrane permeability can be diminished by local inflammation, as in the setting of otitis media.[11]

Indications

Disease processes that benefit from intratympanic drug delivery through either intratympanic injections or intratympanic MicroWick™ placement include, but are not limited to:

• Idiopathic sudden sensorineural hearing loss (ISSNHL) as primary or salvage therapy[2][5][13][14]
• Ménière disease (MD)[5][15][16]
• Autoimmune inner ear disease (AIED)[2][3][4]

Intratympanic MicroWick™ placement is also indicated for patients who may have difficulty traveling to the clinic for repeated intratympanic injections. Utilizing the MicroWick™ allows patients to manage their care from home with otic drops for a set duration.[16] Intratympanic delivery of medications also avoids the adverse effects associated with the systemic administration of pharmaceuticals.[17]

Contraindications

The contraindications to the insertion of an intratympanic MicroWick™ include:

• Any patient who is unable or unwilling to undergo an office-based procedure 
• The presence of middle ear masses such as glomus tumors or cholesteatomas
• Vascular abnormalities such as an aberrant internal carotid artery or high-riding jugular bulb
• Unresolved obstructed access to the round window membrane[7]
• Unresolved obscured view of the tympanic membrane and middle ear space.

Equipment

The equipment typically required to perform an intratympanic MicroWick™ placement includes:

• Binocular operating microscope
• 30-degree endoscope (optional)
• Operating ear speculum
• Otolaryngology examination chair
• Local anesthetics such as Phenol, 10% lidocaine topical, or 1% lidocaine with 1:100,000 epinephrine
• Loop curette
• Earpick
• Myringotomy knife or CO₂ laser
• Frasier suction instruments
• Alligator forceps
• Cup forceps
• Tympanostomy tube with a 1.42 mm inner diameter and 3.25 mm flange
• 1 x 9-mm polyvinyl acetate MicroWick™
• Otic medications such as:[5][16][13][14][5]
  • Dexamethasone solution, 4 mg/mL
  • Prednisone solution, 60 mg/mL
  • Methylprednisolone solution, 62.5 mg/mL
  • Gentamicin solution, 10 mg/mL

Personnel

Intratympanic MicroWick placement is typically performed by an otolaryngologist with the help of an assistant such as a nurse or medical assistant.

Preparation

Informed consent for the procedure should be obtained after a comprehensive discussion of the risks, benefits, alternative therapies, and the procedure between the performing physician and the patient.

Technique or Treatment

Intratympanic MicroWick insertion is performed using an operating microscope with the patient reclined in the otolaryngology exam and their head placed with the procedural ear facing up. Obstructing cerumen should be removed in the usual fashion to visualize the tympanic membrane and middle ear structures.

In the usual fashion, apply a local anesthetic to the inferoposterior quadrant of the tympanic membrane. Perform a myringotomy overlying the round window niche using either the myringotomy knife or laser; laser myringotomy may be preferable due to decreased bleeding at the operative site.[16] Excess blood within the field or a middle ear effusion can lead to premature swelling of the MicroWick and impair correct placement.

Visualize the middle ear structures using an operating microscope or 30-degree endoscope. Remove any pseudomembranes blocking access to the round window membrane with a small pick.[4][5][16] Place the previously described tympanostomy tube in the usual fashion using the malleus handle and umbo as landmarks to determine the position of the round window membrane.[10][18] Insert the MicroWick through the tympanostomy tube, ensuring contact with the round window membrane.[4][5][16][18]

After confirming the correct positioning of the MicroWick, place the pertinent otic medications in the ear or inject them directly into the MicroWick.[5] Expansion of the MicroWick via medication absorption will secure the MicroWick within the tympanostomy tube.

The patient should remain seated in the operating chair under observation so that any procedure-induced transient dizziness may resolve.[19] The MicroWick must be removed or replaced within 4 weeks of placement to prevent adherence to the round window niche. The MicroWick can be removed in the office with a small pick after therapy.[16]

Complications

While placing an intratympanic MicroWick is considered a safe procedure, it is not without risk of complications or adverse events. Concurrent use of antibiotic drops is recommended when administering intratympanic corticosteroids to decrease the risk of infection. Patients may report pain and pressure at the myringotomy site or transient dizziness.[19]

Other potential complications or adverse events of intratympanic MicroWick placement include:

• Otitis media and otitis externa[4][16]
• Cholesteatoma development[4]
• Hearing loss[18]
• Adherence of the MicroWick to the round window niche[16]
• Loss or breakage of the MicroWick into the middle ear space[16]
• Persistent tympanic membrane perforation[4][5][16][18]
• Spontaneous myringotomy tube extrusion[16]
• Vertigo, usually transient[19]
• Injury to surrounding structures such as the ossicles or facial nerve.

Clinical Significance

The intratympanic MicroWick provides otolaryngologists with another avenue to the inner ear, specifically, the round window membrane. Administering medication directly to the perilymph via the MicroWick promotes more effective treatment of inner ear pathologies. The intratympanic delivery of pharmaceuticals facilitates their diffusion into the inner ear, avoiding the systemic adverse effects of oral administration while achieving higher concentrations of medication within the inner ear.[11][18] 

Hill et al demonstrated control of vertiginous symptoms in 76.8% of patients MD treated with intratympanic delivery of gentamicin using the MicroWick system.[14] Delivering methylprednisolone via an intratympanic MicroWick restored hearing in 66% of patients requiring salvage therapy for ISSNHL.[5] 

Intratympanic MicroWick placement is a straightforward office-based procedure performed under local anesthesia that lowers healthcare costs and reduces morbidity from various neurotologic disease processes. Additional benefits of intratympanic MicroWick placement include decreased patient travel times, visit frequency, and overall discomfort compared to intratympanic injection protocols.[16] Inserting an intratympanic MicroWick for medication delivery is a viable therapeutic option for many patients with inner ear pathologies.

Enhancing Healthcare Team Outcomes

Patients with inner ear pathologies frequently present to primary care practitioners with complaints of hearing loss, vertigo, or tinnitus. Prompt identification of neurotologic disorders with timely referral to specialty care improves patient outcomes. The medical management of inner ear disorders has primarily focused on the systemic delivery of drugs, surgical intervention, device use, and behavioral therapy. However, these approaches vary in effectiveness; a significant unmet need for treating inner ear disorders exists.[1] 

After a comprehensive specialty patient evaluation, including an audiology evaluation, select patients may benefit from intratympanic MicroWick placement for medication delivery. Clinical nursing and medical assisting staff play a critical role in the success of this office-based procedure. Pharmacists may assist with the procurement of necessary otic medication preparations. Depending on the underlying diagnosis, repeat audiology evaluation may be required.