Implant Surgery

Dr , Ibrahim habib barakat , M.D.

overview

Definition

Purpose History Hardware Description

Indications Surgical Procedure Normal results Risks

Definition

A cochlear implant is a small, complex electronic device used to treat severe to profound hearing loss.

It is surgically implanted underneath the skin behind the patient's ear.

purpose

A cochlear implant bypass nonfunctional parts of the ear and directly stimulating the auditory nerve.

It does not merely amplify sound.

It increases the amount of nervous response to sound.

It often improves sound detection and increases speech understanding.

history

Between 1965 and 1970, Dr. House teamed up with Jack Urban, an innovative engineer, to ultimately make cochlear implants a clinical reality

The new devices consisted of a single electrode and benefited from microcircuit fabrication derived from space exploration and computer development

history

Between 1965 and 1970, Dr. House teamed up with Jack Urban, an innovative engineer, to ultimately make cochlear implants a clinical reality

The new devices consisted of a single electrode and benefited from microcircuit fabrication derived from space exploration and computer development

In 1972, a speech processor was developed to interface with the single-electrode implant and it was the first to be commercially marketed as the House/ 3M cochlear implant

More than 1,000 of these devices were implanted between 1972 to the mid 1980s

In 1980, the age criteria for use of this device was lowered from 18 to 2 years and several hundred children were subsequently implanted

The House 3M Single-Electrode Implant

During the late 70s, work was also being done in Australia, where Clark and colleagues were developing a multi-channel cochlear implant later to be known as the Cochlear Nucleus Freedom

Multiple channel devices were introduced in 1984, and enhanced the spectral perception and speech recognition capabilities compared to House’s single-channel device

Multi-Channel Implants

Cochlear Nucleus Freedom

Cochlear Nucleus Freedom

Advanced Bionics Hi-Res 90K

Advanced Bionics Hi-Res 90K

Description Normal hearing , sound vibrates the eardrum.

The vibration is carried through the middle ear and the cochlea. Movement in the cochlear fluid is transferred to hair fibers within the cochlea. The movement of these hair cells stimulates ganglion cells that send an electrical current to the auditory nerve. The nerve carries the current to the brain, where the electrical stimulation is recognized as sound.

description

Damage to the hair cells within the cochlea (sensorineural deafness ), can often be treated with cochlear implants , if damage to the hair cells is not accompanied by damage to the auditory nerve itself.

description

Cochlear implants consist of internal and external parts.

The external parts include a microphone, a speech processor, and a transmitter.

The internal parts include a receiver-stimulator and an electrode..

The various components are :

1. The electrode array (which is placed in the inner ear).

2. The receiver for the electrode array.

3. The speech processor, a small electronics package that typically is placed in the wearer's pocket.

4. Transmitting coil and

5. Microphone, both of which are worn behind the ear.

description

Within the headpiece, the microphone picks up sound in the environment.

The speech processor converts these sounds into a digital signal.

The content of the generated digital signal is determined by the programming of the processor and is complex.

The transmitter converts the digital signals into FM radio signals and sends them through the skin to the internal parts of the implant.

description

The internal parts are those that are surgically implanted into the patient. The receiver-stimulator is disk-shaped and is about the size of a quarter.

It receives the digital signals from the transmitter and converts them into electrical signals..

description

A wire connects the receiver to a group of electrodes that are threaded into the cochlea when the implant is placed.

As many as 24 electrodes, depending on the type of the implant, stimulate the ganglion cells in the cochlea.

These cells transmit the signals to the brain through the auditory nerve. The brain then interprets the signals as sound.

description

The sounds heard through an implant artificial or robot-like.

This is because the implant's electrodes cannot match a person's 15,000 hair cells.

However, as more electrodes are added, and the software for the implant speech are moving closer to how speech and other sounds are naturally perceived.

indications

For children who can respond reliably,

standard pure-tone and speech audiometry tests are used to screen likely candidates.

Otherwise, ABR and OAEs can be used to detect very young children with severe-to-profound hearing loss

indications

For children aged 12-23 months, the pure-tone average (PTA) for both ears should equal or exceed 90 dB. For individuals older than 24 months, the PTA for both ears should equal or exceed 70 dB.

indications

Older children are then evaluated with speech-recognition tests with best-fit hearing aids in place in a sound field of 55-dB

One of the most common speech-recognition tests is the hearing in noise test (HINT), which tests speech recognition in the context of sentences (open set sentences)

Current guidelines permit implantation in children whose recognition is <60%

12 months is the current age limit the FDA has established for implantation

However, a child with deafness due to meningitis may develop labyrinthitis ossificans, filling the labyrinth with bone

In these cases, special techniques may be needed for implantation and suboptimal outcome may result

Meningitis and labyrinthitis ossificans

Meningitis and labyrinthitis ossificans

Using serial imaging, implant teams may monitor patients with new deafness due to meningitis and perform implantation at the first sign of replacement of the scala tympani with fibrous tissue or bone

Otherwise, implantation in patients with postmeningitic deafness is usually recommended after 6 months to allow for possible recovery of hearing

Meningitis and labyrinthitis ossificans

Preoperative CT scan should always be performed, to detect cochlear abnormalities or absence of CN VIII

Cochlear malformations, though, do not necessarily preclude implantation

In pediatric patients with progressive hearing loss, neurofibromatosis II and acoustic neuromas should be excluded by performing MRI

Cochlear Abnormalities

Cochlear Abnormalities

procedure

The future site of the implant reciever is marked with methylene blue in a hypodermic needle

This site at least 4 cm posterosuperior to the EAC, leaving room for a behind-the-ear controller

Next, a postauricular incision is made and carried down to the level of the temporalis fascia superiorly and to the level of the mastoid periosteum inferiorly

Anterior and posterior supraperiosteal flaps are then developed in this plane

procedure

Next, an anteriorly based periosteal flap, including temporalis fascia is raised, until the spine of Henle is identified.

Next, a superior subperiosteal pocket is undermined to accept the implant transducer

Using a mock-up of the transducer, the size of the subperiosteal superior pocket is checked

procedure

Next, using a 6 mm cutting burr, a cortical mastoidectomy is drilled

It is not necessary to completely blueline the sinodural angle, and doing so may interfere with proper placement of the implant transducer

procedure

Using a mock-up of the transducer for sizing, a well is drilled into the outer cortex of the parietal bone to accept the transducer magnet housing

Small holes are drilled at the periphery of the well to allow stay sutures to pass through.

These suture will be used to secure down the implant

Stay sutures are then passed through the holes

procedure

Using the incus as a depth level, the facial recess is then drilled out

Through the facial recess, the round window niche should be visualized

Using a 1 mm diamond burr, a cochleostomy is made just anterior to the round window niche

procedure

The transducer is then laid into the well and secured with the stay sutures

The electrode array is then inserted into the cochleostomy and the accompanying guidewire is removed

procedure

Small pieces of harvested periosteum are packed in the cochleostomy around the electrode array, sealing the hole

Fibrin glue is then used to help secure the electrode array in place

The wound is then closed in layered fashion and a standard mastoid dressing is applied

Aftercare

For a short period of time after the surgery, a special bandage is worn on the head during sleep. After about one month, the surgical wounds are healed and the patient returns to the implant clinic to be fitted with the external parts of the device and to have the device turned on and mapped. Mapping involves fine tuning the speech processor and setting levels of stimulation for each electrode, from soft to loud. The patient is then trained in how to interpret the sounds heard through the device. The length of the training varies from days to years, depending on how well the person can interpret the sounds heard through the device.

Normal results

Most profoundly deaf patients who receive an implant are able to discern medium and loud sounds, including speech, at comfortable listening levels.

Many use sound clues from the implant, together with speech reading and other facial cues, to achieve understanding.

Normal results

Almost all adults improve their communication skills when combining the implant with speech reading (lip reading), and some can understand spoken words without speech reading. More than half of adults who lost hearing after they learned to speak can understand some speech without speech reading. Especially with the use of accessory devices, the great majority can utilize the telephone with their implants.

Risks

As with all operations, there are risks with this surgery. These include: infection at the incision site bleeding complications related to anesthesia transient dizziness facial paralysis (rarely) temporary taste disturbances additional hearing loss device failure

Risks

However, it should be noted that serious surgical complications have been observed at only one in 10,000 procedures of this type.

Some long-term risks of the implant include the unknown effects of electrical stimulation on the nervous system.

It is also possible to damage the implant's internal components by a blow to the head, which will render the device unworkable.

Risks

magnetic A further consideration is that the use of(MRI) for patients with cochlear resonance imaging

implants is not recommended because of the magnets present in the devices. Several companies have developed implants that do not use magnets or have altered the receiver-stimulator make up to make it easier to remove the magnets before testing. One fact that reduces the concern about MRI testing is that for many medical indications, MRI can be replaced with a computer assisted tomography scan (CAT or CT scan), which is not a problem for persons with cochlear implants.

Risks

Additionally, in July 2002, the Food and Drug Administration (FDA) issued a warning about a possible connection between increased incidence of meningitis and the presence of a cochlear implant.

This warning included special vaccine recommendations for those with implants, as well as the voluntary removal from the market of certain devices. Specifically, those implants that included a positioner to hold the electrodes in place in the cochlea appear to be associated with an increased risk of the disease.