Diagnosis: Cochlear Ossification
Deafness after stapedectomy is a well-known complication with an incidence of 0.3 to one percent. While the exact etiology cannot be elucidated in every case, the most common causes of this unfortunate occurrence likely fall into four categories. The first is perilymph fistula, which is due to a break in the seal around the prosthesis in the oval window. This can occur when a patient strains, coughs, sneezes, blows his or her nose, lifts something heavy, or does any activity that increases the central venous pressure. Such an increase in pressure is transmitted to the perilymphatic component, likely via the cochlear aqueduct, which connects the subarachnoid space of the brain to the cochlea. The cochlear aqueduct in humans is usually closed and filled with tissue, but it can transmit pressure and bacteria from the brain that may invade the ear, and vice versa. This increased pressure can also be transmitted in the scala tympani via the cochlear aqueduct, which can cause a leak in the seal around the prosthesis in the oval window. Perilymphatic fistula causes dizziness and hearing loss. Treatment involves surgery or a blood patch, where blood is injected through the tympanic membrane.1
The second mechanism involves a virus or bacteria that go from the middle ear into the inner ear, causing infectious labyrinthitis that leads to deafness and dizziness. Treatment requires systemic antibiotic usage, but recovery of hearing is unlikely. Antibiotic is also prescribed to prevent meningitis. The third mechanism involves serous labyrinthitis wherein the invasion of inflammatory mediators or blood leads to an inflammatory response in the inner ear and causes subsequent deafness and dizziness. This is best treated with systemic corticosteroids. The fourth possibility is reparative granuloma, which is a large inflammatory reaction to the prosthesis, Gelfoam, or fibers from the surgical linen that were carried into the middle ear by the fascia, prosthesis, or surgical instruments. This foreign body reaction causes a significant inflammatory mediator invasion in the inner ear via the open oval window. Reparative granuloma appears as a red mass in the posterior superior quadrant. It has been associated with Gelfoam use in the oval window and tends to occur about a week after surgery. This is treated by excising the granuloma.
In the case of this patient, her CT of the temporal bones prior to cochlear implantation showed complete ossification of the cochlea (Figs. 2-3). When looking at the patient's coronal CT of the temporal bone at the level of the oval window (Fig. 3), one can see that the prosthesis is displaced and positioned slightly lateral and superior to the oval window. The cochlea was ossified, indicating that an intense inflammatory reaction had ensued after the stapedectomy and resulted in deafness and dizziness. Interestingly, the vestibule had not ossified. However, it is still difficult to identify which mechanism led to the patient's hearing loss and dizziness. Ossification occurs as a result of a significant inflammatory reaction within the cochlea. An inflammatory reaction initially develops within the cochlea, followed by the formation of fibrous tissue and endosteal reaction, which then leads to ossification. This phenomenon is associated with meningitis-induced labyrinthitis ossificans. Labyrinthitis after meningitis requires quick action; cochlear implantation must be done before full ossification of the cochlea so the implant electrode can be placed close to the neurons. Ossification will still likely occur, but performing the surgery and electrodeposition will be much easier before full ossification.
When this patient underwent cochlear implantation, the surgeon was already faced with a fully ossified cochlea, which made the surgery much more difficult to perform and required drilling out of the basal turn of the cochlea. Some cochlear implant manufacturers have developed dual-electrode array implants, which allow for one array to be placed in the basal turn and the second array to be placed in the second cochlear turn. This way, the surgeon has to drill two channels, one in the basal turn and another in the second turn. Occasionally, ossification of the cochlea from meningitis only occurs in the scala tympani because the bacteria and inflammatory mediators invade the cochlea through the cochlear aqueduct, which opens below the cochlea into the scala tympani. In such cases, scala vestibuli implant placement is performed by opening the cochlea anterosuperior to the round window.
Traditionally, the electrode is placed in the scala tympani, which has been found to improve clinical outcomes.2 This can be done by placing the electrode through the round window or via cochleostomy on the anterior, inferior to the round window. Placing the electrode in the second turn is a bit more challenging. Drilling approximately 2 mm anterior to the oval window has been found to get the electrode into the second (middle) turn.3 Some surgeons suggest placing the electrode through a middle cranial fossa when the basal turn has ossified, but this would require a craniotomy, which has its own inherent risks.
Evaluation of the patient's post-cochlear implant CT scan showed that the electrode started at the basal turn of the cochlea at the level of the round window; however, it ended up traversing below the cochlea (Fig. 4A-C).
BONUS ONLINE VIDEOS: VISUAL DIAGNOSIS
Read this month's Clinical Consultation case, then watch the accompanying videos from Hamid R. Djalilian, MD, to review the patient's imaging for yourself.
- Video 1. Axial (horizontal) CT of temporal bones showing prosthesis position.
- Video 2. Coronal (parallel to face) pre-cochlear implant CT showing the prosthesis position and cochlear ossification.
- Video 3. Sagittal (parallel to ear) CT of temporal bone prior to cochlear implantation showing anatomy in the sagittal direction.
- Video 4. Axial (horizontal) CT of temporal bone right after cochlear implantation showing electrodeposition.
- Video 5. Coronal (parallel to face) post-cochlear implant CT showing electrodeposition.
- Video 6. Axial (horizontal) CT of bilateral temporal bones showing normal left cochlea for comparison.
Watch the patient videos online at thehearingjournal.com https://journals.lww.com/thehearingjournal/Pages/collectiondetails.aspx?TopicalCollectionId=23.
1. Otolaryngol Head Neck Surg. 2009 Aug;141(2):294-5. Intratympanic injection of autologous blood for traumatic perilymphatic fistulas (Garg R, Djalilian HR.).
2. Role of electrode placement as a contributor to variability in cochlear implant outcomes. Finley CC, Holden TA, Holden LK, Whiting BR, Chole RA, Neely GJ, Hullar TE, Skinner MW. Otol Neurotol
. 2008 Oct;29(7):920-8.).
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3. Laryngoscope. 2008 Dec;118(12):2200-4. Anatomy of the middle-turn cochleostomy. Isaacson B, Roland PS, Wright CG).